i

UK National

Monitoring

Programme

Scottish Regional Report

ii

1. Introduction 1

2. Methods 2

3. Quality Control 43.1 Chemistry 43.1.1 Aqueous determinands 43.1.2 Sediments 43.1.3 Biota 4

4. Benthos 54.1 Introduction 54.2 Methods 54.3 Quality Control 54.3.1 Biology Data 54.4 Benthic Macrofauna4.4.1 Taxa and abundance 54.4.2 Community diversity and evenness 74.4.3 Biomass 74.5 Conclusions 8

5. Biological Effects 105.1 NMP Requirements 105.2 Oyster Embryo Bioassay 105.2.1 Collection of water samples 105.2.2 Results and Discussion 115.2.3 Cautionary Remark 115.3 EROD 115.3.1 Introduction 115.3.2 Hydrocarbons and EROD in fish larvae

in the northern North Sea 11

6. Bioaccumulation 136.1 Trace Metals 136.1.1 Metals in shellfish 136.1.2 Metals in fish 166.2 Trace Organic Contaminants 226.2.1 Shellfish 226.2.2 Fish liver 23

7. Water 287.1 Dissolved Oxygen 287.2 Nutrients 287.2.1 Spatial variations of nutrients 287.2.2 Estuarine behaviour of micronutrients 317.3 Chlorophyll 317.3.1 Conclusions and suggestions for

future monitoring 327.4 Metals in Sea Water 337.4.1 Introduction 337.4.2 Data processing 337.4.3 Results (Cd, Pb, Cr, Cu, Ni and Zn) 34

Contents

iii

7.4.4 Results (Hg) 367.4.5 Conclusions 367.5 Trace Organic Contaminants in Water 377.5.1 Estuaries 377.5.2 Offshore and intermediate sites 39

8. Sediments 418.1 Metals 418.1.1 Introduction 418.1.2 Particle size and organic carbon 418.1.3 Trace metal concentrations 418.1.4 Normalisation to Al and enrichment factors 418.1.5 Other normalisation procedures 458.1.6 Variability around the sampling grid 458.1.7 Suggestions for future monitoring 458.2 Sediment Trace Organics 458.2.1 Introduction 458.2.2 Results 458.2.3 Conclusions 488.3 Analysis of Polycyclic Aromatic

hydrocarbons (PAH) in NMP Sediments 498.3.1 Naphthalene and 3-ring compounds 498.3.2 4-ring compounds 508.3.3 5-ring and 6-ring compounds 518.3.4 General 51

9. Summary and Conclusions 52

References 55

Appendix 58

Contents

iv

The work contained in this report represents the combinedefforts of many individuals. These include the officers andcrews of survey vessels, scientists in the field and analysts inthe laboratory. In addition representatives of the twoparticipating organisations (SEPA and SOAEFD (FRSMarine Laboratory)) drafted and edited the individualsections of this report. For SEPA contributing authors wereMichael Coffey, Michael Coyle, Judy Dobson, AnneHenderson, Tom Leatherland, Brian Miller and JohnRedshaw. For FRS the contributing authors were PhilipBalls, Colin Megginson and Ron Stagg.

Foreword

1

1. Introduction

The National Monitoring Plan (NMP) is a product of theUK Marine Pollution Monitoring Management Group(MPMMG). It establishes a network of 87 monitoringstations around the UK, including estuarine, intermediateand offshore sites. Eighteen of these sites are aroundScotland.

The purpose of the NMP is to ensure the production of aconsistent, coordinated and reliable dataset of potentiallysignificant contaminants in estuarine and coastal waters. Itis to provide a framework for assessing the need for, and theeffects of, national and European pollution control measures,and to be a mechanism for improving methods and standardsfor all marine environmental monitoring.

One of the aims of this initial spatial survey is to enable theidentification of sites where more detailed subsequenttemporal trend monitoring should be focused. Somecomments on this are included in this report.

The NMP work reported here has been carried out by theClyde, Forth and Tay River Purification Boards (all nowincorporated into the Scottish Environment ProtectionAgency, SEPA) and the Marine Laboratory of the ScottishOffice Agriculture, Environment and Fisheries Department(SOAEFD). There was good collaboration between all theselaboratories to ensure that all samples were analysed by themost appropriate organisation, which was often differentfrom that responsible for sample collection, and to achieveas much as practicable of the NMP specified requirements.

2

2. Methods

Sampling and analyses were carried out as detailed in theNMP (HMIP, 1994). Station positions are listed in Table2.1 (and shown in Fig. 2.1).

It was not possible to obtain all of the biota samples specifiedin the NMP, largely owing to the absence of specific speciesat selected sites. Some shellfish cannot grow or survive atthe low salinities of many of the estuarine sites, and dabwere also not found at these low salinities. Where there aregaps in the data these are identified in the main text.

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

Figure 2.1Location of Scottish NMP sites.

3

Table 2.1 National monitoring plan sampling stations

Estuary/ Location Site Type Responsibility Latitude Longitude

Solway15 Solway I NRA/RPB 54°52.50'N 03°25.00'W25 Offshore Solway O SOAEFD 54°45.00'N 04°00.00'W

Clyde35 Clyde O SOAEFD 55°20.00'N 05°05.00'W45 Clyde Inner Firth (CMT 5) I RPB 55°49.30'N 04°58.70'W55 Clyde Cloch Point (CMT 7) E RPB 55°56.85'N 04°53.65'W65 Clyde Port Glasgow (18 miles) E RPB 55°56.28'N 04°40.46'W75 Clyde Erskine (10 miles) EWS RPB 55°55.40'N 04°27.95'W

Highland85 Minches Minches I SOAEFD 58°00.00'N 05°40.00'W95 Moray Firth MF Intermediate I SOAEFD 57°40.00'N 03°49.00'W105 Moray Firth MF Offshore O SOAEFD 58°00.00'N 03°00.00'W

Tay115 Tay Broughty Castle EWS RPB 56°27.70'N 02°53.07'W

Broughty Castle EF RPB 56°27.73'N 02°52.18'W125 Tay Tayport EF RPB 56°27.05'N 02°51.71'W135 Tay Flisk EW RPB 56°23.85'N 03°07.34'W

Kingoodie Flats ES RPB 56°26.56'N 03°02.70'W145 Tay Balmerino EW RPB 56°25.14'N 03°02.55'W

Dog Bank ES RPB 56°24.06'N 03°07.26'W155 Tay Tay Intermediate I SOAEFD 56°30.00'N 02°30.00'W

Forth165 Tay/Forth Forth/Tay O SOAEFD 56°30.00'N 01°30.00'W

Offshore175 Forth Kingston Hudds I RPB 56°03.00'N 03°06.00'W185 Forth Longreach EWS RPB 56°07.50'N 03°53.72'W195 Forth Alloa EWS RPB 56°06.45'N 03°48.17'W205 Forth Hen and Chickens ES RPB 56°03.55'N 03°38.92'W

Blackness EW RPB 56°01.52'N 03°30.32'WBlackness EF RPB 56°00.28'N 03°30.55'W

Type of station: E Estuarine W Water sampling O OffshoreI Intermediate S Sediment sampling F Fish/shellfish sampling

(where omitted all matrices are sampled)

4

3. Quality Control

3.1 Chemistry3.1.1 Aqueous determinands3.1.1.1 NutrientsNutrient analyses were carried out by the laboratoryresponsible for sampling. All laboratories achieved thestandards required by the NMAQC scheme.

3.1.1.2 Trace metalsClyde RPB (River Purification Board) carried out analyseson their own samples and samples collected by SOAEFD.All chromium analyses were done at the Forth RPBlaboratories. Forth and Tay laboratories carried out theanalyses on their own samples.

Many laboratories encountered problems achieving therequired detection limit for mercury. This has resulted in apaucity of data for this determinand. The performance fortrace metal analyses in the scheme in general was relativelypoor, but steps are being taken to improve this.

Owing to the number and variety of laboratories submittingdata to the NMP it was recognised at the outset that anassessment of the accuracy and precision of the data wasrequired if comparisons were to be drawn. To this end twoQuality Control Schemes were established to run in parallelwith the NMP, i.e. the National Marine Analytical QualityControl Scheme (NMAQC) for chemistry and the NationalMarine Biological Analytical Quality Control Scheme(NMBAQC) for biology. Participation in these schemes isa prerequisite to submitting data to NMP.

Both schemes involve routine proficiency tests andworkshops to assist laboratories with problem determinands.Both schemes are run by National Coordinating Com-mittees made up of participants in the scheme. Annualreports on laboratories’ performance are produced andsubmitted to MPMMG. As the initial phase of the NMPhas been completed Balls (1996) has summarised theperformance of all laboratories in the NMAQC scheme.AQC performance relevant to the Scottish Regional Reportis given below:

3.1.1.3 OrganicsOrganics analyses were undertaken by each individuallaboratory. Performance in the NMAQC scheme wasgenerally good.

3.1.2 Sediments3.1.2.1 Trace metalsAll trace metals analyses were carried out at SOAEFD whohave the capability to perform total digests.

3.1.2.2 OrganicsForth and Clyde RPBs carried out analyses on their ownsamples, SOAEFD analysed the remaining samples. Alllaboratories demonstrated that they were capable of achiev-ing the required limits.

3.1.3 BiotaBiota samples were analysed by the laboratory responsiblefor collecting the sample for both trace metals and traceorganic determinands.

5

4. Benthos

4.1 IntroductionData are presented for stations in the Solway, Clyde andTay estuaries, Moray Firth and Firth of Forth. With oneexception (the Inner Solway, which was sampled by theEnvironment Agency), sites were sampled by the relevantSEPA regions or the SOAEFD Marine Laboratory, Aber-deen. Faunal analysis was all completed in house.

4.2 MethodsBiological sampling guidance in the UK NationalMonitoring Plan (HMIP, 1994) was minimal but methodspublished by Rees et al. (1990) formed the framework. Inthis the first spatial survey, nine replicates were collectedwhere possible across a 500 m spatial grid, with the centrenominally at the tabulated position in the monitoring plan.At Broughty Castle (115) only five replicates were collectedowing to bad weather, and sampling difficulties wereexperienced at Port Glasgow (65), where mussel beds overlaythe softer sediments. Some flexibility in position ensued.In 1993 in the Solway (15) sampling preceded the placementof the spatial grid and so only three replicates were collected(five in subsequent years).

Samples were collected where possible with 0.1 m2 van Veenor Day grab. Where shallow water precluded access withlarge samplers, samples were collected by a 0.02 m2 hand-held van Veen grab (Alloa, 195; Longreach, 185).

Samples were sieved through a 0.5 mm mesh and or a 1mm mesh, depending on site location. Samples werepreserved using formol saline with or without stain to aidin identification.

Biomass was determined for each species and sample, byblotted wet weight technique.

4.3 Quality Control4.3.1 Biology dataParticipation in the National Marine Biological AQCScheme is a prerequisite to submitting NMP biological datato the national database. The scheme involves the regularcirculation of standard samples and the re-analysis of lab“own samples” to aid in training and test proficiency ofidentification and sediment analysis. The laboratoriesparticipating in the NMP sampling and submitting datahave been full participants in the AQC Scheme since 1993.Assessing the performance of individual laboratories provedparticularly difficult when all were provided with the samesamples, since expertise is closely linked with the type of

sample routinely monitored (for example, estuarine vscoastal, east coast vs west coast). These observations led thecommittee to set targets and standards relating to “ownsample” performance. Each participating laboratory will beassessed on its analysis of samples from its own NMP siteor sites. To date insufficient of these exercises have beencompleted to assess performance adequately.

4.4 Benthic MacrofaunaBenthic data are reported here for 1993–94. Sampling hascontinued in some subsequent years.

4.4.1 Taxa and abundanceTaxa were identified to species level where possible and thetotal taxa recorded at each site are indicated within the textbelow. The summary breakdown statistics showing the meanand ranges of taxa or species and of numbers of individualsper replicate are shown in Table 4.1.

4.4.1.1 Estuarine sitesSeveral stations exhibited a very impoverished fauna withmeans of fewer than five taxa per sample. These stationstended to be in brackish or upper estuarine situations,reflecting naturally stressed localities. Comparison ofabundance recorded by 0.5 and 1 mm meshes reinforcesthe requirement for the use of the fine mesh in truly estuarinesites. Recorded abundance at some estuarine sites wasdoubtless underestimated owing to the use of 1 mm mesh.

At the most impoverished estuarine sites, means of <5 taxa/station were recorded. These included Kingoodie Flats(135), Dog Bank (145), Alloa (195) and Longreach (185),where imbalanced communities dominated by a single orvery few species were common. At Kingoodie Flats, a totalof only 12 taxa were recorded, ranging from 1 to 8 perreplicate dominated by two species, Bathyporeia pilosa andMarenzellaria viridis, which together made up >90% of thetotal numbers of individuals. At Dog Bank, only 10 taxa intotal were recorded (ranging from 1 to 5 per replicate) withpopulations of the small polychaete M. viridis, accountingfor >87% of the abundance. The remainder of the faunahere indicated considerable salinity or other environmentalstress. Longreach, with only five taxa in total, was clearlybrackish in character, heavily dominated (>84%) byLimnodrilus hoffmeisteri, a brackish oligochaete. Alloa waseven more stressed, with very few individuals of M. viridisand T. tubifex being recorded.

Numbers of individuals per sample at these impoverishedestuarine sites showed a wide range from 1 to 198 per grab.The most estuarine site in the Clyde was Erskine (75), which

6

Table 4.1 Mean numbers of taxa and individuals per replicate

No of taxa No of individualsDesignation Mean Range Mean Range

SolwaySolway I 5 4–6 13.3 6–25Offshore Solway O 34.2 32–37 446.4 356–514

ClydeErskine E 12.5 8–16 7554 82–2 409Port Glasgow E 19.2 11–124 411 48–907CMT7 E 32.4 15–48 188 134–258CMT5 I 12.4 10–27 82 23–138Firth of Clyde O 12.4 9–14 47 36–68

HighlandMinches I 30.4 21–40 62.4 37–99Moray I 28.7 23–37 98.6 68–135Moray O 25 16–38 72.8 42–104

TayDog Bank E 3 1–5 56.4 11–96Kingoodie Flats E 3.67 1–8 79 8–198Broughty Castle E 8.8 4–13 28.3 9–64Tay Intermediate I 19.2 16–24 53.4 27–75

ForthLongreach E (1 mm) 2.44 1–4 46.7 1–115

(0.5 mm) 1–5 18–236Alloa E (1 mm) 0.78 0–2 1.33 1–3

(0.5 mm) 1–3 60–236Hen and Chickens E 12.89 7–28 57.44 17–125Kingston Hudds I 41.56 12–60 156.22 25–327Forth and Tay O 44 36–57 94.2 55–131

in contrast had 22 taxa ranging from 8 to 16 per replicate.The highest abundance of all estuarine sites was recordedhere, with up to 2␣ 409 individuals per replicate (dominatedby Streblospio shrubsolii (>76%)). Despite the higher speciesrichness recorded, the fauna here was still clearly stressedreflecting both some organic enrichment and salinity stress.

Data from these highly stressed sites cannot be compareddirectly with those from the very different intermediate andoffshore sites.

In contrast, some other “estuarine” sites showed a muchricher and diverse fauna. In the Forth at Hen and Chickens(205) a total of 44 taxa (ranging from 7 to 28 per replicate)was recorded per station. Polychaeta dominated the fauna,with Nephtys spp., Aricidea suecica and Scoloplos armigeraccounting for >85%. In the Clyde, sites at Port Glasgow(65) and CMT7 (55) had total taxa of 53 and 118 ( meantaxa of 19 and 32 taxa) per station, respectively. At PortGlasgow, the fauna was dominated by Tubificoides benedeni

and T. pseudogaster ( >51%) and large populations of Mytilusedulis. At CMT 7, the benthos was dominated bypolychaetes (22.1%) Spiophanes kroyeri and Caulleriellazetlandica. The nemertean Tubulanus sp. composed asignificant part of the population here. At Broughty Castle(115), taxa per sample ranged from 4 to 13, and fauna wasdominated by nemerteans and polychaetes, includingProtodriloides chaetifer and Ophryotrocha dubia. Togetherthese three taxa accounted for >60% of the population.

Abundance at the more stable estuarine sites of Hen andChickens, Port Glasgow, CMT 7 and Broughty Castle, weremore evenly distributed among the taxa

4.4.1.2 Intermediate sitesAt the Solway site (15) , of the total of eight taxa recordedacross the replicates samples, Nephtys cirrosa and Hydrobiaulvae accounted for 73% of the abundance. The Solwaysite was exceptional in its paucity of fauna for anintermediate site.

7

A rich fauna in both Clyde and Forth was recorded, withtotal taxa per station of 47 and 105 respectively and meansof 18 and 41 per replicate. In the Clyde, the fauna wasdominated by molluscs (51.7%), particularly Abra alba andNuculoma tenuis. Nemerteans were found to be an importantcomponent of the Clyde intermediate fauna. Thecommonest polychaetes included Chaetozone setosa,Spiophanes kroyeri, Prionospio multibranchiata, Mediomastusfragilis and Nephtys incisa. The top 10 most abundant speciesmade up >84% of the population and were consistent withfine sediments and some organic enrichment.

The Forth site of Kingston Hudds (175) had a very variedfauna, with polychaetes (64.62%) and mollusca (20.2%)dominating. Rhodine gracilior, Prionospio fallax, Lumbrinerisgracilis, Heteromastus filiformis, Nephtys incisa andScalibregma inflatum co-dominated the polychaetes whileTuritella communis and Mysella bidentata were commonestof the mollusca. The top 10 most abundant species madeup >50% of the fauna.

Minches (85) had a total of 88 taxa per site (21–40 perreplicate) and a mean of 30. Samples were dominated bythe bivalve mollusc Abra alba (10.5%) and the polychaetesMyriochele sp. (5%) and Nephtys hombergii (>4%). The top10 ranked species composed 44% of the fauna.

In the Moray Firth ( 95) similar statistics were recorded,total taxa 64 and a range of 23–37 per replicate. The faunawas dominated notably by polychaetes (>57%) includingDiplocirrus glaucus . The echinoderm Amphiura chiajei wasalso common. The top 10 species made up 67% of thebenthos.

Mean numbers of individuals per station at intermediatesites ranged from 53.4 (Tay) to 156 (Kingston Hudds). Highnumbers of individuals at Kingston Hudds reflected thegreater species variety here compared with other inter-mediate sites.

4.4.1.3 Offshore sitesOffshore samples were notable by their high species variety,low abundance per species and dominance spread amongmany species. Dominance tended to shift into the molluscanand echinoderm groups.

Of all the Scottish sites, Forth/Tay (165) yielded the highesttotal taxa (118), though replicates ranged only from 36 to57. The samples were dominated by the echinodermEchinocyamus pusillus plus a range of polychaetes, includingSpiophanes bombyx and Ophelia limacina. The top 10 speciescomposed <50% of the population, indicating a diverse andheterogeneous fauna.

Other offshore sites ranged in total taxa from 27 in the Clyde(35) to 76 in the Moray Firth (105). Clyde populationswere dominated by Nucula nitidosa and Nephtys incisa,

together making up >55% of the population, while Moraywas dominated by Myriochele sp. (18%) and the molluscCircomphalus casina (>9%). Mollusca clearly dominated theSolway site (25), where faunal abundance per replicate wasgreatest, with Mysella bidentata clearly dominating the fauna,contributing >36% to the total of individuals recorded.

Fauna in the Solway and the Clyde were less well balancedwith dominance held among fewer species. The top 10rankers contributed between 80 and 90% to totals. Thismay be a result of higher organic content or physicalattributes of these systems.

4.4.2 Community diversity and even-ness

The derived statistics of evenness (the spread of abundanceacross species) along with community diversity (therelationship of abundance to faunal richness) measures arefrequently used to express a measure of invertebratecommunity “health”.

Table 4.2 shows mean and ranges per replicate of Peilouevenness and Shannon Weiner diversity values for theScottish stations.

Evenness and Shannon Wiener tended to be low, in responseto any increase in unequal spread of individuals across speciesvariety and imbalance in the community, i.e. highdominance by a single or a few species or reduction in speciesrichness. This can be the result of stress (organic, physico-chemical or toxic). Indices are open to misinterpretationand not reliable in areas of natural stress like estuaries wherepopulations are patchy or more homogeneous than furtheroffshore.

Indices were not calculated at some estuarine sites wherehighly stressed fauna were known to occur or where speciesrichness was very poor. Considerable stress was evidencedat other sites where mean evenness or diversity were relativelylow, Erskine, Port Glasgow and Hen and Chickens, probablyreflecting organic inputs to estuarine systems. However, inthe outer Firth of Clyde, in contrast, dominance of N.nitidosa reduced mean H' at this offshore site. Most stablesites occurred in intermediate and offshore stations wherehigh evenness (>0.8) and higher mean diversity wererecorded for example at Minches, Kingston Hudds andForth/Tay where mean diversity was high (4.29–4.98),reflecting a wide range of species and equal spread of speciesamong individuals. Most other sites showed moderateevenness (0.6–0.8) and diversity (3–4).

4.4.3 BiomassThe data have been bulked to show the range and meanvalues per station plus the contribution of numericallydominant phyla to the community. Mean and ranges of

8

Table 4.2 Mean and ranges of Peilou evenness and Shannon Weiner diversity (H')

Peilou evenness S-W diversityDesignation Mean Range Mean H' range

SolwaySolway I 0.62 - 3.15 -Offshore Solway O 0.62 0.58–0.64 3.15 2.92–3.31

ClydeErskine E 0.42 0.27–0.71 1.49 0.9–2.13Port Glasgow E 0.62 0.42–0.81 2.59 1.75–3.18CMT7 E 0.75 0.67–0.82 3.75 2.79–4.59CMT5 I 0.8 0.72–0.92 3.29 2.75–3.77Firth of Clyde O 0.78 0.72–0.83 2.75 2.55–3.17

HighlandMinches I 0.93 0.90–0.95 4.5 4.13–4.82Moray I 0.83 0.79–0.88 3.95 3.6–4.08Moray O 0.85 0.79–0.91 3.87 3.39–4.67

TayDog Bank E - - - -Kingoodie Flats E - - - -Broughty Castle E - - - -Tay Intermediate I 0.88 0.83–0.93 3.74 3.60–3.91

ForthLongreach E - - - -Alloa E - - - -Hen and Chickens E 0.8 0.67–0.91 2.84 2.24–3.81Kingston Hudds I 0.83 0.74–0.89 4.29 2.85–5.07Forth and Tay O 0.92 0.89–0.94 4.98 4.75–5.51

data are shown in Table 4.3. Values were very wide-rangingin different systems, variable among replicates and alsobetween similarly designated sites. Aberrantly high valueswere recorded at Port Glasgow owing to high abundance ofMytilus edulis which accounted for 99% of the recordedbiomass at this site. Highest mean biomass was recorded atSolway offshore, CMT 7 and Kingston Hudds due to heavybodied mollusc and echinoderm species.

4.5. ConclusionsThere was no evidence to suggest that pollution impactswere identifiable at many sites. Natural variation betweeneast and west coast fauna, site sediment characteristics,salinity gradients and stresses and natural variation in organicenrichment are likely to be responsible for much of themeasured variation in biomass and community structure.

9

Table 4.3 Biomass mean and range and dominant phyla: %abundance: %biomass per station

Biomass g/Station Dominant phylaLocation Designation Mean Range % abund % biomass

SolwaySolway I 0.0677 0.0352–0.0414 P 53.6 64.40Offshore Solway O 34.38 30.85–39.53 M 70.6 13.89

E 15.8 83.945

ClydeErskine E 0.908 0.026–2.236 P 81.2 76.50Port Glasgow E 595.25 0.034–5328.60 O 54.7 0.037

M 34.7 99.50CMT7 E 24.98 2.753–85.815 P 49.6 12.11

M 23.4 60.00CMT5 I 5.744 1.282–12.649 M 51.7 71.90

P 29.9 18.00Firth of Clyde O 2.090 1.336—2.375 M 58.38 65.75

P 36.19 16.72

HighlandMinches I 1.277 0.360–1.905 P 58.95 58.507Moray I 6.400 2.83–13.25 P 57.78 41.80Moray O 0.900 0.13–2.11 M 53.72 23.03

P 48.84 23.22

TayDog Bank E 0.290 0.007–0.767 P 87.06 25.39 #Kingoodie Flats E 0.232 0.016–1.010 C 83.97 74.59 #

P 15.47 98.00 #Broughty Castle E 2.406 0.097–7.856 P 43.62 9.86 #

Oth 40.43 89.97 #Tay Intermediate I 0.950 0.30–1.830 M 52.76 19.01

E 13.1 59.52

ForthLongreach E 0.141 0.003–0.367 O 98.8 99.60Alloa E 0.005 0.00001–0.287 P 75.0 93.40Hen and Chickens E 0.735 0.167–2.648 P 85.69 54.00Kingston Hudds I 18.718 1.031–54.070 P 64.62 42.00

M 20.2 39.00Forth and Tay O 3.290 2.44–4.270 P 44.91 17.53

M 15.69 66.82

#samples were analysed after longterm storage in alcohol

Taxa : P - Polychaeta; C - Crustacea; M -Mollusca; O - Oligochaeta; Oth - Others; Designation: E - Estuarine; I - Intermediate; O - Offshore

10

5.1 NMP RequirementsThe National Monitoring Programme (NMP) for UK tidalwater was initiated in 1993. The biological effectscomponent includes the following (HMIP, 1994):

(1) benthic macrofauna,

(2) oyster embryo bioassay (waters and sedimentelutriates),

(3) whole sediment bioassay (when suitable methodavailable),

(4) fish disease studies,

(5) dogwhelk imposex bioassay,

(6) mixed function oxidase test (EROD).

The biological effects monitoring in Scotland has beenlimited to benthic macrofauna, oyster bioassay on watersand MFO/EROD measurement in fish.

5.2 Oyster Embryo Bioassay5.2.1 Collection of water samplesWater samples were collected from three Scottish estuaries(see Table 5.1). Samples were collected from a depth of onemetre and were tested in accordance with the MPMMGguidelines (HMIP, 1994).

The NMP guidelines (HMIP, 1994) required that watersamples be collected from estuarine sites at a minimumfrequency of twice per year (winter and summer) and fromintermediate/offshore sites at a minimum frequency of onceper year. In practice, monitoring was carried out a lowerfrequency, partly owing to the encouraging results of initialtests (i.e. no evidence of toxicity).

No consideration was given to tidal state in collecting thewater samples. Although the guidelines (HMIP, 1994)recommended that estuary water samples be collected at ornear high water this proved to be impracticable in someestuaries. Water samples of low salinity were artificiallyadjusted to the approximate salinity of the controls (referencesea water) before being tested.

5. Biological Effects

Table 5.1 MPMMG NMP Scottish Regional Report: oyster embryo bioassay results for water samples collected fromScottish estuaries 1993–1996

Percentage net response (PNR) for oyster embryo bioassayLocation NMP site 19–21/04/93 14/03/95 11/07/95 26/03/96

ClydeInner Firth (CMT5) 45 0.1 8.8 -6.0 10.3Cloch Point (CMT7) 55 -25.4 4.2 -3.0 0Port Glasgow (18 miles) 65 -22.9 -9.3 28.4 5.1Erskine (10 miles) 75 -4.7 -5.8 -10.4 12.8

TayBroughty Castle 115 -18.1 N/A N/A N/AFlisk 135 -7.7 N/A N/A N/ABalmerino 145 -31.2 N/A N/A N/A

ForthKingston Hudds 175 -17.1 N/A N/A N/ALongreach 185 -18.8 51.1** N/A N/AAlloa 195 -22.0 7.6 N/A N/AHen and Chickens 205 -23.6 -0.1 N/A N/A

N/A = not analysed*Collection of water samples: Clyde - 19/04/93, Forth - 20/04/93, Tay - 21/04/93.

**Mean D-larval counts were significantly different from the controls (John Thain, MAFF, pers. comm.).

The analyses were conducted by Clyde RPB with the exception of the March 1995 samples which were tested by the MAFF Fisheries Laboratory,Burnham-on-Crouch, Essex.

11

5.2.2 Results and DiscussionData are presented as Percentage Net Response (PNR) values(Table 5.1) in accordance with the NMP requirements. LowPNR values, indicating good water quality, were found forthe majority of water samples. Two exceptions were thesamples taken from Port Glasgow (Clyde) in July 1995 andthat taken from Longreach (Forth) in March 1995. Thispattern is consistent with that for most UK estuaries wherewater samples have generally been found to be of low-to-negligible toxicity to oyster embryos (John Thain, MAFF,pers. comm.).

5.2.3 Cautionary RemarkIt should be emphasised that these results provide nothingmore than a “snapshot” of the biological water quality inthese estuaries. Furthermore, the requirement for samplesto be taken from a depth of 1 metre only is of limited valuein describing the water quality in highly stratified estuariessuch as the Clyde.

These limitations are widely recognised and are beingaddressed by MPMMG in their consideration of futuremonitoring requirements (see for example Thain andMatthiessen, 1996).

Furthermore, SNIFFER (Scotland and Northern IrelandForum for Freshwater and Environmental Research) isjointly funding a major Environment Agency researchinitiative into the development and application of toxicitybased standards for the receiving water environment. Thisproject should provide (inter alia) output useful for thedevelopment of the NMP biological effects monitoringprogramme.

It should also be recognised that suitable sediment bioassayprotocols (e.g. Corophium, Arenicola) are now available foruse in the NMP and that SEPA West Region has someexperience in the use of these methods.

5.3 EROD5.3.1 IntroductionThe majority of organic contaminants of concern arelipophilic which enables them to penetrate biologicalmembranes and to be transported around the body bylipoproteins. Cytochrome P450 dependent monooxygenases

are a group of enzymes which catalyse the insertion of anoxygen atom into a xenobiotic (foreign) molecule to facilitateconjugation to an endogenous substrate. The conjugationreactions are carried out by a second group of enzymes (PhaseII) such as UDPglucuronyl transferase (UDP-GT) andglutathione-s-transferase (GST). These reactions have theeffect of making a neutral, lipid soluble compound morewater soluble thus facilitating its elimination from the body.Although this sequence of events is generally a detoxicationmechanism it can result in the activation of relatively inertchemicals to highly reactive and damaging intermediates.

Specific forms of cytochrome-P450-dependent mono-oxygenases that catalyse aryl hydrocarbon hydroxylase(AHH) and ethoxyresorufin-o-deethylase (EROD) areenzymes that are induced by environmental exposure to adiverse range of planar molecules, such as polyaromatichydrocarbons (PAH), polychlorinated biphenyls (PCB),dioxins and dibenzofurans. The induction of these enzymescan therefore be used to monitor exposure to bioavailableplanar contaminants and are of value, for example, indetermining exposure to PAHs such as are found indischarges associated with the oil industry. EROD has alsobeen proposed to be a measure of a deleterious biologicaleffect in the sense that compounds such as PAHs can beactivated to compounds that cause DNA damage. Inductionof EROD activity can therefore be seen as an essential processinvolved in the aetiology of tumour initiation andcarcinogenesis by the activation compounds such as PAHsinto pre-carcinogens. The balance of induction of Phase Ienzymes such as EROD and Phase II enzymes such as UDP-GT and GST is also important in that the latter conjugatethe active intermediates from Phase I metabolism and renderthem innocuous.

5.3.2 Hydrocarbons and EROD in fishlarvae in the northern North Sea

In 1993 and 1994 field work was undertaken in the NorthSea to investigate the wider field effects of hydrocarbondischarges from the offshore oil industry in the water column(Stagg and McIntosh, 1996). A pronounced gradient ofputative aromatic hydrocarbon concentration was discoveredin the North Sea (Fig. 5.1(a)). EROD activity was measuredin fish larvae caught at each of the sampling stations andshowed a significant correlation with the fluorescencemeasurements made (Fig. 5.1(b)).

12

0

1

2

3

4

5

56 57 58 59 60 61 6200

Latitude °N

µg/l

pmol

/min

/mg/

l

01° 30' E (1994)00° 00' E (1994)Stations <1km from oil platforms01° 30' E (1993)

40

30

20

10

0

Depth averaged hydrocarbon fluorescence µg/l

Gadoid 1994

Sandeel 1994

Sandeel 1993

0.1 1 10

b)

a)

Figure 5.1

(a) Depth averaged concentrations of putative PAH determined by a towedhydrocarbon fluorimeter deployed on double oblique hauls on north-southtransects in the northern North Sea in 1993 and 1994.

(b) 7-ethoxyresorufin O-deethylase in pooled samples of three species of fishlarvae, caught on the same hauls using a METHOT net, in relation to thedepth averaged hydrocarbon concentration at each location.

13

6.1 Trace Metals6.1.1 Metals in shellfish6.1.1.1 IntroductionData for metals in shellfish were submitted for mussels fromonly seven of the 20 NMP sites. These seven sites werelocated in the Clyde, Forth and Tay estuaries, with the datasupplied by the former River Purification Boards. Data werenot submitted at the other sites because suitable shellfishwere not found, either at the inner sites in the aboveestuaries, or at the intermediate and offshore sites.

Data were available for cadmium, mercury, lead and zincfor mussels collected at all seven sites, but no results weresubmitted for TBT (tri-butyl tin). All metals data reportedwere for mussels collected in spring. This is in agreementwith JMP (Joint Monitoring Programme) guidelines, whichrecommend that mussels are collected in late winter priorto spawning (MAFF, 1990). Data for the Clyde have beenpooled for surveys in 1994 and 1995, as have data for theTay for surveys in 1993, 1994 and 1995, while the Forthdata are for mussels collected in 1993.

There are differences in batch size analysed. Forth RPBcollected 50 mussels from each of two sites and analysedthese as five batches of 10 mussels, as recommended by theNMP guidelines. Clyde RPB collected batches of 25 musselsand analysed these as such, to ensure that results obtainedwere consistent with historical data. Tay RPB used a batchsize of 20–22 mussels. In addition, the Clyde RPB collectedseveral batches of 25 mussels from different shore sites inorder to produce the most accurate result for these shore-based animals in comparison with the waters results for eachNMP site. For example, the median results for batches ofmussels from Dunoon East, Dunoon West, Gourock andLunderston Bay were used to represent site 55 in the Firthof Clyde. This was shown to be a valid approach by thenarrow spread of results for zinc and mercury in mussels atthe Clyde Estuary sites, compared with those in the Forthand Tay.

6.1.1.2 ResultsThe median metals concentrations for mussels collectedfrom the NMP sites in each of the Forth, Clyde and Tayestuaries are summarised in Table 6.1. For ease ofinterpretation the data are also shown in Fig. 6.1.

CadmiumConcentration gradients were observed in each estuary, withthe highest levels at the more landward sites (Fig. 6.2). Thehighest concentrations of 2.56 mg/kg dry weight wererecorded at site 65 in the Clyde Estuary. These were similarto historical results for the Clyde estuary (Miller, 1990) and

lower than many sites in the North Sea QSR of 1993 (NorthSea Task Force, 1993). The cadmium concentrations at eachof the other NMP sites fell into the “lower” JMP categoryaccording to the guidelines issued by the Oslo and ParisCommissions (MAFF, 1990), and were consistent withhistorical data for the Firth of Clyde and Solway Firth(Miller, 1986).

LeadConcentration gradients from landward to seaward wereevident for lead in mussels in the Forth and Clyde estuaries(Fig. 6.3). This may be a reflection of the sediment leadconcentration patterns for these estuaries. However, it wassurprising that the mussels’ body burdens were similarbetween the two estuaries (see Table 6.1), since the Clydesediments have markedly higher concentrations than thosein the Forth. It is proposed that the much higher suspendedsolids levels in the Forth Estuary, coupled with the filterfeeding by the mussels, may account for the similar bodyburdens for lead.

Lead concentrations in mussels from the site on the northernshore of the Tay estuary at Broughty Castle were surprisinglyhigh, similar to the levels at the Forth and Clyde estuarysites, although this may also reflect high sediment leadconcentrations.

Lead concentrations in mussels collected on the southernshore of the Tay estuary were similar to those in musselsfrom the inner Firth of Clyde site off Dunoon, and slightlylower than the level of 5 mg/kg dry weight used by ADRIS(the former Association of Directors and River Inspectorsin Scotland) as representing the “background” level (Miller,1986). Slightly lower concentrations were reported for theouter Firth of Clyde site (3.01 mg/kg).

6. Bioaccumulation

Table 6.1 Median metals levels in mussels (results asmg/kg dry weight)

Site Estuary Site Cd Pb Zn Hg n,bno name

115 Tay Broughty 1.85 13.5 144 0.300 75,3Castle

125 Tay Tayport 1.20 4.45 97 0.150 75,3175 Forth Ferny Ness 1.20 6.70 146 0.270 50,5205 Forth Blackness 1.75 14.5 205 0.530 50,545 Clyde CMT 5 1.33 3.01 97 0.143 75,355 Clyde CMT 7 1.40 4.89 110 0.114 175,765 Clyde 18 miles 2.56 12.7 172 0.232 225,9

Note that n,b = number of individual mussels analysed in bbatches

14

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

Cadmium in mussels

1.5 0.6 0.3 15 7.5 3.0 1.5

250 125 2550 0.6 0.3 0.060.12

Lead in mussels

Zinc in mussels Mercury in mussels

3.0

ZincZinc concentrations showed a similar gradient to those forlead (Fig. 6.4), although mussels from the inner Forthestuary site 205 were slightly more contaminated by zincthan mussels from the Clyde estuary site 65, with 205 mg/kg compared with 172 mg/kg dry weight. These concen-trations are typical of historical values for Clyde Estuary

mussels (Miller, 1986) and similar to levels found inEuropean mussels (North Sea Task Force, 1993). Zincconcentrations in mussels from the Broughty Castle site onthe northern shore of the Tay estuary contained 144␣ mg/kgzinc, perhaps indicating some degree of sewage pollution,since the mussels from the south shore at Tayport containedonly 97 mg/kg. This was similar to concentrations in mussels

Figure 6.1Median concentrations (mg/kg dry weight) of cadmium, lead, zinc and mercury in mussels from NMP sites. Concentrations are presented as area proportional symbols, scalesymbols are shown in the top left hand corner.

15

max/minm

g/kg

dry

wei

ght

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

115 125 205 175 65 55 45

mean median

max/min

mg/

kg d

ry w

eigh

t

0

5

10

15

20

25

115 125 205 175 65 55 45

mean median

max/min

mg/

kg d

ry w

eigh

t

50

100

150

200

250

115 125 205 175 65 55 45

mean median

300

350

0Broughty Castle Tayport Blackness Ferny Ness 18 miles CMT7 CMT5

SiteFigure 6.4Minimum, maximum, mean and median concentrations (mg/kg dry weight) of zinc in mussels from NMP sites.

Figure 6.2Minimum, maximum, mean and median concentrations (mg/kg dry weight) of cadmium in mussels from NMP sites.

Figure 6.3Minimum, maximum, mean and median concentrations (mg/kg dry weight) of lead in mussels from NMP sites.

16

Broughty Castle on the north shore of the Tay estuary,suggesting that this site is subject to sewage pollution or alocal industrial discharge. The high mercury concentrationsreported for Broughty Ferry mussels deserve furtherinvestigation.

6.1.2 Metals in fish6.1.2.1 IntroductionData for metals in fish liver and muscle were submitted for12 of the 20 NMP sites in Scottish waters. Availability offish in general, and of the NMP target species of dab andflounder in particular, was a problem at several sites. Datafor dab and flounder were reported at only five and foursites respectively. This is a potential problem if Section 7.4of the report on monitoring guidelines produced by theMonitoring Coordination Subgroup (HMIP, 1994) wereadhered to, since this requires data to be limited only todab and flounder. However, since the NMP survey was

designed to gather information on a spatial basis, it wasdecided to include all available data submitted for metals infish in this report (i.e. data for plaice, witch and megrim inaddition to those for dab and flounder). The available dataset is shown in Table␣ 6.2.

As outlined above, data were not submitted for several NMPsites. There are two main reasons for this. Firstly there wasa lack of fish during trawling: this was the case for sites 35and 45 in the Firth of Clyde. The second reason is linked tothe dangers of trawling in estuaries and to the movement ofa fish population within an estuary. This applies to site 75in the Clyde estuary, where obstacles on the estuary bedprevent safe trawling. However, studies have shown thatflounder in the Clyde estuary move over a wide area, coveringboth NMP sites 65 and 75. Hence Clyde RPB has reporteddata for fish collected at site 65 as representative of the fishpopulation in the whole estuary.

from the Firth of Clyde sites (97–110 mg/kg) andapproached the lower levels of 66–102␣ mg/kg found inSolway Firth mussels and the ADRIS “background” levelof 90 mg/kg dry weight (Miller, 1986).

MercuryMercury concentrations showed similar trends to thosereported above for lead and zinc (see Fig. 6.5). The highestmedian mercury concentrations of 0.530 mg/kg dry weightwere found in the Forth estuary. This is not surprising,considering that there are effluents discharged to the estuarywhich were known to contain mercury, which has a highaffinity for suspended particulate matter. However, it wassurprising that mussels from the Broughty Castle site onthe northern shore of the Tay estuary were reported ascontaining 0.300 mg/kg mercury, higher than the median

levels found at Ferny Ness in the Forth estuary (0.270 mg/kg) and higher than all the median concentrations in theClyde estuary. Bearing in mind that there are no knownmercury discharges to the Tay estuary, these high levelsdeserve further investigation.

6.1.1.3 SummaryMussel body burden concentrations of the metals cadmiumand lead, and perhaps of mercury to a lesser extent, appearto be strongly influenced by sediment concentrations ofthese metals, confirming that their mode of feeding byfiltration of particulate material plays a major role in theuptake of metals. Metals concentrations were generallyhigher in the inner Forth and Clyde estuaries, with aconcentration gradient to seaward. Relatively high metalsconcentrations were also observed in mussels collected at

Figure 6.5Minimum, maximum, mean and median concentrations (mg/kg dry weight) of mercury in mussels from NMP sites.

max/min

0Broughty Castle Tayport Blackness Ferny Ness 18 miles

0.2

0.4

0.6

CMT7 CMT5

115 125 205 175 65

55

45

mean median

Site

0.8

mg/

kg d

ry w

eigh

t

17

Table 6.2 Data set for metals in fish for NMP sites in Scottish waters

Site name Site no Site type Fish species Number of Number of Data for allbatches of fish fish per batch metals?

SolwaySolway 15 I n/aOffshore Solway 25 O Plaice 5 5 Yes

ClydeFirth of Clyde 35 O Plaice 1 5 Yes

Witch 2 5 NoInner Firth 45 I n/aCloch Point 55 E n/aPort Glasgow 65 E Flounder 15 5 YesErskine 75 E n/a

HighlandMinches 85 I Megrim 5 5 Yes

Plaice NoMoray Firth 95 I Dab 3 5 Yes

Plaice 6 1 YesMoray Firth 105 O Dab 4 5 Yes

Plaice 25 1 Yes

TayBroughty Castle 115 E n/aTayport 125 E n/aFlisk 135 E Flounder 5 5 YesBalmerino 145 E Flounder 4 5 YesIntermediate 155 I Dab 5 5 Yes

Plaice 9 1 No

ForthForth/Tay 165 O Dab 5 5 YesIntermediate Plaice 10 1 NoKingston Hudds 175 I Dab 5 5 YesLongreach 185 E n/aAlloa 195 E n/aBlackness 205 E Flounder 5 5 Yes

The required metals were cadmium and lead in fish liver,and mercury and arsenic in fish muscle. Coverage was verygood, with data for all four metals supplied for most fish.Exceptions were mercury and arsenic for plaice from theForth/Tay offshore sites and Firth of Tay intermediate site,and cadmium and lead for plaice from the Minchesintermediate site. The Scottish Office Marine Laboratoryin Aberdeen was responsible for monitoring these sites. Thelack of data has resulted from a decision by this laboratorythat since metals data were available for these sites for dab,one of the primary target species, then there was no need toanalyse the plaice collected.

The NMP guidelines were that five batches each consistingof five individual fish should be analysed. Table 6.2 indicatesthat this guideline was not always followed, especially for

plaice, of which differing numbers of single fish wereanalysed by the Scottish Office Marine Laboratory inAberdeen. This has been taken into account by mergingthe single fish data into batches of five fish, then takingmedian metals concentrations for all batches, to make thedata more comparable.

6.1.2.2 Cadmium and lead in fish liverMedian metals concentrations for each batch of fish analysedare presented in Table 6.3. Median cadmium concentrationsranged from 0.030 mg/kg wet weight (ww) in dab from theKingston Hudds site in the Forth Estuary to 0.804 mg/kgww, also in dab, from the intermediate site in the Firth ofTay. Concentrations of between 0.02 and 0.66 mg/kg wwwere reported in fish liver (dab, whiting and cod) in theNorth Sea Quality Status Report, 1993 (North Sea Task

18

Force, 1993), and concentrations of 0.09 to 0.14 mg/kgww in plaice and flounder respectively in Danish marinewaters (Jørgensen and Pedersen, 1994).

Median lead concentrations ranged from 0.011 mg/kg wwin plaice from the Moray Firth offshore site to 0.620 mg/kgww in plaice from the intermediate site in the Tay. Thesecan be compared to levels of between <0.2 and <0.8 mg/kgreported in the North Sea QSR report for dab, whiting andcod liver (North Sea Task Force, 1993) and to concentrationsof 0.052 and 0.074 mg/kg ww reported for plaice andflounder respectively in Danish marine waters (Jørgensenand Pedersen, 1994).

Figures 6.6 and 6.7 show the distributions of mediancadmium and lead concentrations in each batch of five fishby species. Cadmium concentrations were generally higherin dab than in plaice (0.162–1.028 compared with 0.130–0.347 mg/kg wet weight), which in turn were considerablyhigher than in flounder (0.021–0.110 mg/kg wet weight).This was contrary to expectations, since the dab and plaicewere mainly collected from offshore and intermediate sitesin unpolluted firths, whereas the flounder were collectedfrom sites in relatively more contaminated estuaries. Analysisof variance (ANOVA) showed that the results werestatistically different between dab and flounder, and betweenplaice and flounder, for cadmium in liver. This is clearly animportant observation, since the dab and flounder are thetwo NMP target species, yet this data set suggests that resultsfor these fish are statistically different for cadmium in liver.The data sets can be taken as reliable, for two reasons. Firstly,each laboratory submitting data passed the NMP AQCcriteria, and secondly their results for CRMs (Certified

Reference Materials) analysed showed good agreement withtarget values.

It is assumed that the differences in cadmium concentrationsreported above were not due to differences in the ages, sizesand sex of fish analysed. Variations in concentrations dueto these factors should have been eliminated or reduced bythe collection of fish according to the JMP guidelines.

Three other possible explanations are proposed which mayaccount for the differences reported above: (1) the dab andplaice may have been living in areas with soft, fine mudswith high cadmium concentrations, which were transportedto these areas and deposited; (2) that binding sites forcadmium uptake by flounder are blocked by othercontaminants in estuaries; or (3) that dab and plaice on theone hand, and flounder on the other, have different preypreferences, with dab and plaice having a diet of speciescontaining higher cadmium levels.

The Collins Guide to The Sea Fishes of Britain and North-Western Europe (Barrett and Yonge, 1973) confirms thatthe diets of the fish are different, with dab and plaice feedingmainly on filter-feeding bivalves while flounder feed onbrittle stars and worms. However, dab have been found tocontain more mercury in both stomach contents and musclethan plaice, for fish caught off the north-east coast ofEngland (Dixon and Jones, 1994), so the trend reportedhere for cadmium should be investigated further.

The low concentrations reported for cadmium in flounderin the Forth, Tay and Clyde Estuaries are not in doubt,since the data were supplied by three different laboratories

Table 6.3 Median concentrations of cadmium and lead in fish livers and mercury and arsenic in fish flesh(as mg/kg wet weight)

Site name Site no Site type Fish Cd Pb Hg As

Offshore Solway 25 O Plaice 0.160 0.165 0.062 10.6Firth of Clyde 35 O Plaice 0.187 0.100 0.072 16.5

Witch 0.104 0.024Port Glasgow 65 E Flounder 0.052 0.126 0.035 1.48Minches 85 I Megrim 0.117 0.015 0.121 24.8Moray Firth 95 I Dab 0.208 0.026 0.041 18.3

Plaice 0.210 0.096 0.063 17.4Moray Firth 105 O Dab 0.474 0.047 0.068 16.8

Plaice 0.213 0.011 0.024 10.4Flisk 135 E Flounder 0.081 0.033 <0.001 3.13Balmerino 145 E Flounder 0.062 0.036 <0.001 2.50Tay Intermediate 155 I Dab 0.804 0.082 0.081 18.1

Plaice 0.368 0.620Forth/Tay 165 O Dab 0.582 0.077 0.092 20.9Intermediate Plaice 0.182 0.286Kingston Hudds 175 I Dab 0.030 0.130 0.035 5.96Blackness 205 E Flounder 0.044 0.095 0.054 3.14

19

and are supported by literature values. Stronkhorst (1992)reported 0.07 and 0.06 mg/kg wet weight cadmium in theliver of flounder from the Ems and Scheldt Estuaries,respectively.

Fig. 6.7 indicates that lead levels were similar for most fishspecies except plaice, the data for which showed much morescatter and higher overall concentrations. The analysis ofplaice as individual fish rather than as batches of five fishwas a contributing factor to this observation. The lowestlead concentrations were found in megrim collected in theMinches.

The highest cadmium concentrations were found in dabfrom the offshore Moray Firth, the intermediate Tay andthe offshore Tay/Forth sites. The highest lead concentrationswere for plaice collected at the Tay intermediate and Tay/Forth offshore sites.

Lead concentrations for plaice were reported for single fish

for several sites. These data were pooled as batches of fivefish, for comparison with other data reported in this way.However, 10 plaice from the Moray Firth offshore site werereported as having lead concentrations of less than 0.005mg/kg wet weight, while the other 15 individuals from thissite had lead concentrations in the range 0.006–4.47 mg/kg wet weight. The “less than” results may be flagged asunusual, since all other plaice from other sites also hadquantifiable concentrations of lead.

The highest cadmium and lead concentrations weregenerally found in dab and plaice respectively from sites offthe east and north-east coasts of Scotland. Flounder fromthe Forth, Clyde and Tay estuaries were found to havesurprisingly low liver concentrations of both metals.

6.1.2.3 Results for mercury and arsenic in fish muscleTable 6.3 shows the median metals concentrations for eachbatch of fish analysed. Median mercury concentrationsranged from <0.001 mg/kg wet weight in flounder from

max/min

mg/

kg w

et w

eigh

t

0

0.2

0.4

0.6

mean median

Dab

1.0

1.2

1.4

Plaice Witch Megrim FlounderFish Species

0.8

max/min

mg/

kg w

et w

eigh

t

0

0.2

0.4

0.6

mean median

Dab

0.8

1.0

1.2

Plaice Witch Megrim FlounderFish Species

Figure 6.7Minimum, maximum, mean and median concentrations (mg/kg wet weight) of lead in fish liver from NMP sites as a function of species.

Figure 6.6Minimum, maximum, mean and median concentrations (mg/kg wet weight) of cadmium in fish liver from NMP sites as a function of species.

20

the Tay estuary to 0.121 mg/kg wet weight in megrim fromthe Minches. The low Tay estuary results were confirmedon the basis of results for a CRM analysed with the samebatch. The mercury concentrations at the NMP sitescompare with levels of between 0.03 and 0.22 mg/kg wetweight for dab, whiting and cod collected from the NorthSea and reported in the 1993 Quality Status Report (NorthSea Task Force, 1993). For descriptive purposes, guidelineshave been adopted by the Joint Monitoring Programme ofthe Oslo and Paris Commissions. These allow fish to becategorised as having low mercury concentrations if levelsare below 0.1 mg/kg wet weight, medium between 0.1 and0.3, and upper if the concentrations are above 0.3 mg/kgwet weight. The data reported here for the Scottish NMPsites show that mercury levels in most fish fall into the “low”category.

6.1.2.4 Differences in metal concentration by speciesFigures 6.8 and 6.9 show the distribution of median mercuryand arsenic concentrations in batches of five fish, by species.While the median mercury concentrations were similar for

dab and plaice, the pattern of concentrations varied greatlyfrom species to species, with the highest levels in the fewmegrim analysed and the lowest levels in flounder. A one-way analysis of variance (ANOVA) showed that mercurylevels in flounder were significantly lower than for the otherfish types.

Median arsenic concentrations followed a similar patternto that for mercury for each fish species, with the highestlevels in the few megrim analysed , then dab slightly higherthan plaice, both significantly higher than flounder (see Fig.6.9).

This analysis again highlights the fact that the two NMPtarget species, dab and flounder, do not produce comparabledata either for cadmium in liver, or for mercury and arsenicin fish muscle. It is important that results for these metalsshould be compared only for fish of the same species. Theresults presented here for Scottish NMP sites indicate thatcomparisons between species are not valid, and thaterroneous conclusions could be drawn.

max/min

mg/

kg w

et w

eigh

t

0

5

mean median

Dab

15

25

30

Plaice Witch Megrim FlounderFish Species

10

20

max/min

mg/

kg w

et w

eigh

t

0

0.05

mean median

Dab

0.15

0.20

0.25

Plaice Witch Megrim FlounderFish Species

0.10

Figure 6.8Minimum, maximum, mean and median concentrations (mg/kg wet weight) of mercury in fish muscle from NMP sites as a function of species.

Figure 6.9Minimum, maximum, mean and median concentrations (mg/kg wet weight) of arsenic in fish muscle from NMP sites as a function of species.

21

6.1.2.5 Spatial differencesMercury levels in flounder collected at the NMP sites inScottish estuaries were slightly lower than for fish trawledin Danish waters east of Jutland (Jørgensen and Pedersen,1994), and considerably lower than fish from the Ems and

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

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8°W 6°W 4°W 2°W 0°

Hg in fish muscle

0.05 0.02 0.01 25 12.5 5.0 2.5

As in fish muscle

0.10

59°N

58°N

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8°W 6°W 4°W 2°W 0°

59°N

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56°N

55°N

8°W 6°W 4°W 2°W 0°

0.8 0.4 0.080.16 0.6 0.3 0.060.12

Cd in fish liver Pb in fish liver

Figure 6.10Summary of spatial distribution (mg/kg wet weight) of mercury and arsenic in fish muscle and cadmium and lead in fishliver for NMP sites. Concentrations are presented as area proportional symbols; scale symbols are shown in the top lefthand corner of each plot. Key to circle shading, open - dab, black - plaice, light stippled - flounder, dark stippled - megrim.

Scheldt estuaries (Stronkhorst, 1992). Mercury concen-trations in dab and plaice from the Firth of Clyde(Mathieson and McLusky, 1995) and in dab from the ForthEstuary were much lower than in fish from the intermediateand offshore Scottish NMP sites, which was anomalous at

22

first, but comparison with data for the Tyne (Leah et al.,1993) and for Liverpool Bay (Leah et al., 1992) showedsimilar results.

The median metals concentrations of cadmium and lead infish liver and of mercury and arsenic in fish muscle aresummarised in Fig. 6.10, which shows the spatial and inter-species distributions throughout Scotland.

6.2 Trace Organic Contami-nants

6.2.1 Shellfish6.2.1.1 IntroductionNMP details 15 sites for the analysis of shellfish. Sampleswere to be analysed for PCBs, α−HCH, γ-HCH (lindane),dieldrin, endrin, aldrin, pp-DDT, pp-TDE, pp-DDE,HCB, HCBD, and lipid content. Partial data were availablefrom four of these sites from the Forth (two) and Clyde(two) estuaries, containing only some of the abovedeterminands. Reasons for the limited nature of the datasetare detailed in Section 6.1.

NMP required 50 individuals to be sampled and dividedinto five pools for analysis. The required shellfish wereMytilus edulis, preferably size 2–6 cm (mean 4–6 cm) or atoffshore stations Modiolus modiolus (range 7–9 cm) may beused. Other species were not acceptable to the NMP.

6.2.1.2 Sampling protocolsThere were differences in the sampling approach betweenlaboratories, also referred to above (Section 6.1.1.1). TheForth RPB collected batches of 50 mussels from specificNMP sites and analysed these as one batch. Results wereavailable from 1994 surveys. The Clyde RPB collectedbatches of 25 mussels from a series of sites to represent aspecific NMP station. The reason behind this approach wasthat mussels collected on a single shore site could be subjectto localised effects and may not be truly representative of alarger area. A selection of shore sites in close proximity wouldreflect the larger area more accurately. PCB (as Arochlor1254 Equivalent) results only, were available from 1994surveys. No lipid data were available from Clyde estuarymussels.

6.2.1.3 Organics concentrationsThe data for ∑PCB (Arochlor 1254 Eq), ∑DDT, dieldrin,aldrin, endrin, lindane, and HCB are summarised in Table6.4.

The only dataset for which information was available fromall sites was for ∑PCB (Arochlor 1254 Eq). Mussels collectedfrom sites on the Clyde estuary contained the highest levelsof PCBs and fall into the “medium” contamination category,as defined by the Joint Monitoring Group guidelines (JMG,1992). Mussels collected from the Forth Estuary lie in the

“lower” level of PCB contamination. Comparison ofnormalised PCB data was not possible since lipid data werenot available for mussels collected from the Clyde estuary.

In a national context, PCB results reported for Clyde estuarymussels are comparable to other industrial estuaries inBritain. MAFF found concentrations of PCBs in musselsfrom the Humber and Thames Estuaries to be 35 and 95µg/kg respectively (MAFF, 1993). PCB contamination inmussels at various sites throughout the North Sea wasreported between 3.8 and 195 µg/kg.

Mussels collected from the Forth estuary and Forthintermediate sites contained similar background levels ofPCBs and organochlorines. The only notable differencebetween the two sites is the presence of HCB at the estuarinesite of Blackness. This distribution of HCB is consistentwith other data compiled for the NMP, e.g. elevated levelsof HCB in fish liver (Section 6.2.2) and sediment (Section8.2) collected from the Forth estuary. This distribution ofHCB reflects the considerable industrial discharge of HCBinto the Forth estuary.

6.2.1.4 Conclusions and suggestions for furthermonitoring

(1) Mussels collected from the Clyde Estuary containedhigher levels of total PCBs than those musselscollected from the Forth Estuary. Clyde mussels fellinto the “medium” level of contamination whilstForth mussels lay in the “lower” level, in relation toJMG guidelines.

(2) Consideration should be given to the inclusion ofthese data in the national database since NMPguidelines were not adhered to for any station.

(3) The assessment of spatial trends and identificationof “hot-spots” of organic contamination in musselsfrom Scottish waters proved difficult as there wereinsufficient data to fulfil the aims of the NMP. Futuremonitoring plans should address the problems thatare responsible for this lack of data, e.g. musselavailability and analytical protocols.

(4) The former Clyde RPB approach to the NMP, i.e.collection of mussels from a number of selected sitesto represent the larger area, should be considered interms of future NMP guidelines. This approach hasthe following advantages over the present guidelines:(i) it minimises the possibility of localised effects.(ii) it may tackle the problems associated with

availability of mussels.(iii) it is more representative of a given area of shore.

This approach would also not incur an increased workloadas most of the institutes submitting NMP data have alreadyundertaken an annual “Mussel-watch” survey.

23

6.2.2 Fish liver6.2.2.1 IntroductionThe NMP details 13 sites for the analysis of fish liver.Samples were to be analysed for PCB, dieldrin, endrin,aldrin, pp-DDT, pp-TDE, pp-DDE, and lipid content.Data were available for nine of these sites, and includedmost of the required determinands.

Where possible, a minimum of 25 individuals was sampledand divided into five pools at sites as near as possible to thecorresponding sediment sampling grid. Five replicate resultswere reported for six of the nine stations.

The required fish were dab (Limanda limanda) or flounder(Platichthys flesus); other species were not acceptable to theNMP. These fish were sampled at five of the nine stations.The results are summarised in Table 6.5a. Normalised resultsare summarised in Table 6.5b. Spatial patterns are showngraphically using proportional symbols in Fig. 6.11.

6.2.2.2 Organics concentrationsThe data for ∑PCB

ICES7, ∑DDT, dieldrin and endrin are

summarised in Table 6.5a. Data for HCB is also included.Although HCB is not a required NMP determinand, therehas been a significant discharge of this substance to the ForthEstuary, and it is monitored in sediments as part of the NMP.

Highest concentrations of ∑PCB were found in fish fromthe Forth intermediate and Forth estuary stations. Thesesites contained concentrations which fell into the “medium”contamination band with regard to guidelines issued by theJoint Monitoring Program of the Oslo and Paris Com-missions (JMG, 1992). Dieldrin and endrin levels werehighest at the offshore Outer Moray Firth station. This sitecontained the only measurable levels of endrin from thedataset available. The results reported here are similar topreviously published data (North Sea Task Force, 1993; Kellyand Campbell, 1994). Normalised data are looked at in moredetail below.

Normalisation to lipidOrganic contaminants accumulate in the lipid fraction ofthe liver. Lipid concentrations are used as a co-factor in thenormalisation of organic contamination. Normalisation tolipid concentrations should (1) reduce the variability of data

Table 6.4 NMP organics in shellfish (all results in µg/kg wet weight unless stated)

NMP site Lipid ∑PCB ∑ pp HCB Lindane Dieldrin Aldrin Endrinmg/g (Arochlor 1254) DDTs

205 Blackness 7.9 16.1 1.47 0.31 0.44 0.26 <0.15 <0.15(Forth Estuary)

175 Fernyness 9.8 15.8 1.65 <0.15 0.53 0.21 <0.15 <0.15(Forth Intermediate)

65 Port Glasgow 80(Clyde Estuary)Ardmore 29Cardross 32Woodhall 40Port Glasgow 36Median ND ND ND ND ND ND

55 Cloch Point 25(Clyde Estuary)Dunoon East 32Lunderston Bay 61Gourock 32Median ND ND ND ND ND ND

JMG GuidelinesLower <20Medium 20–100Upper >100

Total PCB quoted in terms of Arochlor equivalents. An Arochlor equivalent was calculated by multiplying ∑PCB ICES 7

by 2.5(Kelly and Campbell, 1994). ND = no data available

24

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

PCB (ICES 7) (fish liver) (normalised)

1000 400 200 700 350 140 70

500 250 50100 200 100 2040

DDT (fish liver) (normalised)

DIELDRIN (fish liver) (normalised) HCB (fish liver) (normalised)

2000

Figure 6.11Summary of spatial distribution of organic contaminants (∑PCBICES 7, ∑DDT, Dieldrin and HCB) in fish liver for NMP sites. Concentrations are normalised to lipid contents(µg/kg lipid) and presented as area proportional symbols; scale symbols are shown in the top left hand corner of each plot. Key to circle shading, open - dab, black - plaice, darkstippled - megrim.

25

Table 6.5a NMP organics in fish livers (all results in µg/kg wet weight unless stated)

Station (No of pools analysed) % Lipid ∑PCB ICES 7

∑DDT Dieldrin Endrin HCB

Minches (5) Median 20.6 49.4 12.5 6.5 1.5* 1.7RSD % 23.3 21.3 31.6 90 71Range 14–22 37–60 8–17 0.1–11 1–4

Solway Firth (5) Median 11.5 28 10.9 3.6 0.8* 0.8RSD % 17.7 31 33.6 24.6 24.1Range 8–13 20–41 6–15 2–5 0.7–1

Forth/Tay offshore (5) Median 11.2 77.9 13.3 4.9 0.8* 0.8RSD % 34.3 15.5 16.1 18.9 31.1Range 10–20 69–102 10–16 4–5 0.7–1.4

Tay int (5) Median 19.3 108 27.4 8.7 1.3* 1.3RSD % 19 35.7 32.8 17.3 20.3Range 13–23 74–183 15–38 8–12 0.9–1.7

Clyde offshore (3) Median 15.7 74.4 22 9.8 1.1* 1.1RSD % 44.5 68.3 54.9 17.3 28.6Range 6–16 26–130 13–39 5–12 0.6–1.2

Inner Moray Firth (3) Median 21.6 144 20.6 13.2 1.5* 1.9RSD % 8.5 62.5 55.2 36.8 14.8Range 19–22 57–242 12–34 6–17 1.5–2

Outer Moray Firth (4) Median 14.9 53.6 39.7 72 4.1 3.6RSD % 38.9 51.6 41 73.5 78.2 36Range 11–26 26–122 16–50 22–156 2–9 2–5

Forth int (5) Median 17.9 355 28.9 15.9 2.0* 2.5RSD % 6.6 46.8 27.7 67.8 34.6Range 17–19 214–675 24–45 13–52 2–4

Forth estuary(5) Median 10.4 211 66.1 23.3 1.5* 21.8RSD % 31.3 40.1 47 50.4 70.4Range 5.7–11.6 95–278 29–94 7–27 7–417–11.6

UK guidelines Lower <201 1500 E 200–300E 100 E(JMG, 1992. Medium 200–40017/3/10–E) Upper >400

*denotes < LOD used; E – The “expected” values1Guidelines for flounder liver as representative of flatfish. Total PCBs values expressed as “Arochlor equivalents”. Made comparable

to the above data by dividing by 2.5 (Kelly and Campbell, 1994).

within stations, (2) allow more accurate comparisonsbetween stations, and (3) allow comparison betweendifferent species. Normalised results based on µg/kg lipidare summarised in Table 6.5b and Fig. 6.11.

Normalisation to lipid does not change the pattern ofcontamination described above but provides a bettercomparison between stations.

Offshore: Livers sampled from the Outer Moray Firthcontained the highest levels of organic contaminationcompared with other offshore stations. Dieldrin, endrinand DDT were all present.

Intermediate: Forth intermediate fish livers containedthe highest concentrations of organics. ∑PCB levelswere comparable to those found in estuarine fish liver.

26

Table 6.5b NMP organics in fish livers (normalised results in µg/kg lipid)

Station (No of pools analysed) ∑PCB ICES 7 ∑DDT Dieldrin HCB

Minches (5) Median 254 58.4 39.5 7.3RSD % 4.9 15.8 86 62.6Range 240–273 56–80 1–47 7–21

Solway Firth (5) Median 294 107 37.5 7.4RSD % 22.1 28.2 25.6 9.4Range 170–315 55–133 23–44 7–9

Forth/Tay offshore (5) Median 695 108 36 7.2RSD % 30.1 29.8 28.2 11.2Range 366–905 68–150 25–55 7–9

Tay int (5) Median 582 133 50.2 6.9RSD % 39 31.3 25.4 2.5Range 393–949 79–196 36–66 6.5–7.5

Clyde (3) Median 468 206 74.5 7.5RSD % 37.5 27.1 17.2 25.2Range 428–817 139–245 63–89 7–11

Inner Moray Firth (3) Median 668 95.6 61.1 9.3RSD % 58 50.1 41.2 19Range 309–1192 67–175 31–76 7–10

Outer Moray Firth (4) Median 395 193 425 22.5RSD % 15.2 36.3 77 38.3Range 348–468 152–321 182–992 13–34

Forth int (5) Median 1787 174 95.7 13.4RSD % 53.2 26.5 67 38.4Range 1193–4066 131–244 74–285 11–25

Forth estuary (5) Median 2117 630 211 203RSD % 12.8 19.5 26.9 53.3Range 1673–2396 503–809 128–260 118–393

27

Estuary: Results were available only from the Forthestuary, hence comparisons with other estuaries werenot possible. Normalisation of the results indicatedgreater relative contamination of organics due to thesmaller lipid content. HCB, though not a requiredNMP determinand, was found to be substantiallyelevated at this station.

Variability within stationsFor six out of nine stations, results from the five individualpools were reported; at one station three results and at twostations four results were reported. Data from the Clydeoffshore site (35) contained results from three pools of whichtwo were of witch liver and one of plaice liver.

The Relative Standard Deviations (RSD) of the individualdeterminands for each station are summarised in Tables 6.5aand 6.5b for wet weight and lipid normalised datarespectively. RSD ranged from 8.7% to 90% for wet weightand from 4.7% to 86% for normalised data. The normalisedRSD were generally lower, demonstrating the value of thenormalising process. This was most evident with the datafrom the Forth Estuary where the normalisation processreduced the RSD for ∑PCB from 40% to 13%.

The different types of fish taken from the various stationsmeant that comparison of normalised data was morebeneficial, e.g. data from the Clyde offshore site includedanalysis of both witch and plaice liver. Witch liver contained30.6 µg ∑DDT/kg and plaice liver contained 12.6␣ µg∑DDT/kg. Normalised results were 204 and 210 µg∑DDT/kg lipid respectively.

There was no correlation between station type, i.e. offshore,inshore etc and variability of data. There was also littledifference between RSD of individual determinands.

6.2.2.3 Conclusions and suggestions for furthermonitoring

(1) Fish liver collected from the Forth estuary and Forth

intermediate stations contained the highest levels ofPCBs reported. Concentrations fell within the“medium” contamination band, with regard toguidelines issued by the JMG (JMG, 1992). PCBconcentrations at all other sites reported fell betweenthe “lower” and “medium” bands. Organochlorinecompounds reported at all sites were below“expected” values (JMG, 1992).

(2) NMP requirements mean that data from only fiveout of the nine stations should be included in thisreport (based on species sampled, and number ofpools reported). Consideration should be given toinclusion of the remaining data based oncomparisons with the normalised data.

(3) As the organochlorine contaminants analysed do notoccur naturally, fish liver sampled from remote sitesunaffected by contamination contained low levelsof organics. Intensive sampling of these sites in thefuture would add little value to the dataset.Infrequent (five year) monitoring would be adequate.

(4) Maximum concentrations of individualdeterminands are present at various sites. These areall source related. Future monitoring should befocused on these sites.

(5) Data are available from only one estuarine site.Comparison of organic levels in Scottish estuariesis therefore not possible. Problems were encounteredwith obtaining numbers of fish of the requiredspecies. This problem should be looked at in moredetail before future surveys.

(6) The NMP-required fish are all bottom feeders andorganic contaminants in the liver are related to thecontent of underlying sediment. HCB should beincluded as a required NMP determinand as it ismonitored in the sediment, and there is significantbioaccumulation of HCB in livers of fish from somestations.

28

Dissolved oxygen, nutrients (nitrate, nitrite, ammonium,phosphate and silicate), and chlorophyll data are reportedfor each of four sites in the Forth, Clyde and Tay estuaries,and from seven coastal sites around Scotland.

The NMP required that sampling be conducted four timesper year at estuarine sites, and once annually at intermediateand offshore sites throughout the period 1993 to 1995(MPMMG, 1994). Sampling was fully completed in theClyde and Forth estuaries, and at two sites in the Tay (115,145). At intermediate and offshore sites, data were submittedfor Winter 1994 and 1995 (sites 155 and 165, Winter 1995only). For Tay Estuary site 135, data were submitted foronly two samples, whilst no data were reported for site 125.

Subsequent sections discuss spatial variations in thesedeterminands, and the estuarine behaviour of micro-nutrients.

7.1 Dissolved OxygenDissolved oxygen (DO) data are reported here as percentagesaturations to enable a direct comparison to be maderegardless of differences in salinity and water temperature.Saturations measured in Scottish estuarine and coastal watersare summarised in Table␣ 7.1.

7.2 NutrientsNutrient concentrations vary seasonally as well as withinthe estuarine salinity gradient (e.g. Balls, 1994). Accordingly,nutrient data have been operationally divided into “summer”(April –September) and “winter” (October–March) datasetsto reduce the seasonal signal for the purpose of datacomparison and interpretation.

7.2.1 Spatial variations of nutrientsSpatial variations in nutrient concentrations in the Clyde,Tay and Forth estuaries are summarised in Fig. 7.1. Mediannutrient concentrations are highest in the Clyde and lowestin the Tay; this pattern is observed in both summer andwinter. For offshore sites, differences in nutrientconcentrations can be largely explained by differences insalinity (Fig. 7.2).

Nutrient concentrations decrease along the salinity gradientseawards in the three estuaries, with concentrations atoffshore samples being low relative to estuaries (Table␣ 7.2).The concentrations of nutrients reported here lie in the samerange as those reported previously. For example, for the Forthand Tay see Balls (1992) and Balls (1994); for the Clyde seeMuller et al. (1994).

One aim of this study is to establish winter maximumnutrient concentrations, assuming that concentrations ofthese nutrients will peak at this time when biological uptakeis at a minimum. Only silicate shows a consistent trend ofhigher winter concentrations at all salinities in the estuaries.Higher winter nitrate concentrations, relative to summer,occur at higher salinity, whilst summer concentrations arehigher in fresher waters. Median ammonium, nitrite andphosphate concentrations in the estuaries are generallyhigher in summer than in winter for the respective salinitybands.

The salinity dependence of nutrient concentrations extendsto the offshore sites; these sites provide representative valuesfor winter maxima concentrations in the coastal watersaround Scotland (6–10 µM nitrate; 0.6–1.2 µM phosphate;3.5–10 µM silicate; exact concentrations depend uponsalinity). The winter maxima indicate N/P ratios ofapproximately 10; this is similar to the ratio reported forthese waters in 1988 (North Sea Task Force, 1993).

7.2.2 Estuarine behaviour ofmicronutrients

Interpretation of estuarine behaviour can be made with theaid of property: salinity plots (Liss, 1976). Conservativebehaviour, indicated by a linear relationship between

Generally, lowest DO saturations occur at low to midsalinities in the Forth and Clyde estuaries. Suppressed oxygenlevels are a feature of many estuaries, especially during thesummer; low DO saturations are well documented in theForth (e.g. Griffiths, 1987). In both the Forth and Clydeestuaries, low DO saturations are due to discharges ofoxygen-demanding wastes rather than to excessive algalgrowth and degradation. These oxygen-demandingdischarges have been significantly reduced, but have left alegacy of organically enriched sediments with a high oxygendemand which continue to exert an influence on estuarineDO saturations.

Coastal surface waters are, as anticipated, near saturated withrespect to oxygen. Supersaturation of DO tends to occur inthe outer estuary sites.

Table 7.1 Dissolved oxygen saturation (%) summarystatistics for Scottish coastal and estuarine waters

Clyde Forth Coastal

Minimum 39 32 92.5Median 87 87 98.5Maximum 146 154 112.8No of Data 58 20 12

7. Water

29

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°

8°W 6°W 4°W 2°W 0°

Nitrite - summer

5 2.5 110

8°W 6°W 4°W 2°W 0°

7.5 3.0 1.515

Nitrate - summer

50 20 10100

Ammonia - summer

60 24 12120

Phosphate - summer

Silicate - summer

50 25 10100

Figure 7.1aSummary of spatial distribution of dissolved nutrient concentrations (µM) for nitrate, nitrite, ammonia, phosphate and silicate, in summer. Mean concentrations are presentedas area proportional symbols; scale symbols are shown in the top left hand corner of each plot. For the three estuarine sites the data have been grouped into salinity bands, 0–10,10–20 and 20–30. The innermost estuarine site represents data in the lowest salinity band and the outermost that in the highest.

Table 7.2 Salinity and nutrient concentration ranges (µM) at NMP sites in the Clyde, Forth and Tay estuaries(1993–1996)

Site Salinity TOxN1 Nitrite Ammonia Phosphate SilicateClyde

75 0.4–17.1 37–132 0.64–19.8 25–239 6.4–24 8.5–10465 6.4–29.12 13.1–61 0.79–7.2 13.1–107 1.76–12.1 2–5655 18.77–31.58 0.64–26 0.12–1.11 <0.08–11.7 0.17–7.33 0.5–3945 25.04–32.3 0.41–23 <0.05–0.94 <0.08–8.7 0.1–6.99 0.1–33

Forth185 0.04–1.82 27.4–93.7 0.25–4.94 1.9–40.1 0.39–2.84 16–83.3195 1.55–24.26 13.6–82.4 0.3–2.89 5.4–18.7 0.97–2.78 14.3–60.1205 26.14–33.99 0.5–29.6 0.14–1.38 0.1–8.9 0.68–1.61 3–26175 32.46–34.42 0.2–16.3 0.04–1.01 0.1–7.9 0.05–1.11 0.8–10.4

Tay145 6.4–23.3 <0.1–63.6 0.18–0.64 0.1–14.0 0.19–1.05 no data115 13.9–29.8 4.3–50.5 0.16–0.89 <0.1–8.9 0.21–1.32 no data

1Total oxidised nitrogen – sum of the nitrate and nitrite concentrations. Nitrite concentrations normally constitute only a small fraction of the TOxN

concentrations. In discussion TOxN will therefore be taken as representing the nitrate concentrations.

30

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°

8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

Nitrate - winter

50 20 10100

Nitrite - winter

5 2.5 110

Ammonia - winter

60 24 12120

Phosphate - winter

Silicate - winter

50 25 10100

8°W 6°W 4°W 2°W 0°

7.5 3.0 1.515

concentration and salinity, implies that simple physicalmixing of river and sea water controls chemical concen-trations along the estuary. In contrast, deviation from thissimple mixing line (non-conservative behaviour) implies thatchemical, biological and/or physical estuarine processes alsoaffect these concentrations.

Previous investigations of processes in the three estuariesconsidered here are published elsewhere (Balls, 1992, 1994;Muller et al., 1994). The reader is referred to this literaturefor a detailed description of nutrient behaviour in Scottishestuaries, where more intensive sampling has allowed closeridentification of the processes involved.

Where nutrient data are shown for this study, all NMPsamples for that estuary are included (i.e. data from differentyears), split into summer and winter datasets.

7.2.2.1 Nitrogen species (nitrate, nitrite, ammonia)Nitrate behaves near-conservatively in both the Clyde andTay (Fig. 7.3). However, in the Clyde particularly, somedata depart from the pattern, indicating a degree of inter-annual variability. In the Forth nitrate behaves non-conservatively (Fig. 7.3), with internal estuarine generationat low salinity by nitrification of particulate organic nitrogenand ammonia (Balls, 1992).

Nitrite and ammonia are non-conservative in both the Forthand Clyde (examples shown in Fig.␣ 7.4). Non-conservativebehaviour of both ammonia and nitrite has previously beenreported for the Forth (Balls, 1992; Balls, 1994). Ammoniainputs to low salinity waters of the Forth from waste watersare known to be significant, whilst internal conversion ofnitrogen species may be an important source of bothammonia and nitrite to this estuary, especially duringsummer (Balls, 1992). The data reported here imply thatsimilar processes may also be important in the Clyde.

Figure 7.1bSummary of spatial distribution of dissolved nutrient concentrations (µM) for nitrate, nitrite, ammonia, phosphate and silicate, in winter. Mean concentrations are presented asarea proportional symbols; scale symbols are shown in the top left hand corner of each plot. For the three estuarine sites the data have been grouped into salinity bands, 0–10,10–20 and 20–30. The innermost estuarine site represents data in the lowest salinity band and the outermost that in the highest.

31

32.5

5

10

32.0 33.0 33.5 34.0 34.5 35.0

8

10

6

4

2

0

1.2

1.4

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0.6

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a) NitratePh

osph

ate

(µM

)

c) Silicate

Nit

rate

(µM

)Si

licat

e (µ

M)

b) Phosphate

Salinity

In the Tay, both nitrite and ammonia are non-conservative,although the pattern of behaviour is less clear, possiblybecause of significant inter-annual variations.

7.2.2.2 PhosphatePhosphate behaves non-conservatively in the Clyde, Forthand Tay (Fig.␣ 7.5). The large amount of scatter in the datais consistent with the greater flow dependent variability ofphosphate concentrations in river inputs (relative to nitrate)and the significant particle reactivity of phosphate (Froelich,1988). Thus, dissolved phosphate concentrations are moredependent on suspended matter load and partitioningdynamics, wastewater inputs, and biological activity thansimply on salinity.

7.2.2.3 SilicateThe near-conservative behaviour of silicate observed in boththe Forth and Clyde (Fig. 7.6) is indicative of the restrictedimpact of any planktonic (diatomaceous) blooms within

these estuaries during the sampling period. Althoughconservative behaviour of silicate has been observedpreviously in the Forth (Balls, 1994) and Clyde (Mackayand Leatherland, 1976), nonconservative behaviour has alsobeen reported (Balls, 1994).

7.3 ChlorophyllThe available chlorophyll data (measured as chlorophyll-a)indicate that concentrations are highly variable (Fig. 7.7).This variability is presumably caused by the dependence ofobservations on sampling dates and the timing of blooms.

Generally, higher concentrations are more consistentlyobserved in the Clyde than in the Forth. Highestconcentrations (25 µg/l) occur in the inner Clyde, apparentlyduring a bloom period throughout the length of the estuary(May 1995). This is consistent with the higher winternutrient concentrations of the Clyde.

Nit

rate

(µM

)

50 10 15 20 30 35

c) Tay

Nit

rate

(µM

)

Salinity

140

25

SummerWinter

120

100

80

60

40

20

0

0

a) Clyde

Nit

rate

(µM

)

SummerWinter

140

120

100

80

60

40

20

b) ForthSummerWinter

0N

itra

te (

µM)

140

120

100

80

60

40

20

Figure 7.2Nutrient concentrations in offshore waters (winter) as a function of salinity,(a)␣ nitrate, (b) phosphate and (c) silicate.

Figure 7.3Nitrate concentrations in Scottish estuaries as a function of salinity, (a) Clyde,(b)␣ Forth and (c) Tay.

32

200

250

150

0

100

50

a) ClydeSummerWinter

Am

mon

ia (

µM)

50 10 15 20 30 350

b) Forth

Nit

rite

(µM

)

Salinity

4.0

5.0

3.0

2.0

1.0

25

SummerWinter

2.0

2.5

1.5

1.0

0.5

3.0

b) ForthSummerWinter

c) TaySummerWinter

0

a) Clyde

50 10 15 20 30 350

Phos

phat

e (µ

M)

Salinity

1.0

1.2

0.8

0.6

0.4

25

SummerWinter

25

20

15

10

5

0

1.4

Phos

phat

e (µ

M)

Phos

phat

e (µ

M)

0.2

Higher chlorophyll concentrations are sometimes, but notnecessarily, coincident with depleted nutrient concentrations(e.g. Clyde estuary (site 75) silicate concentrations aredepleted during the above mentioned bloom, but phosphateand nitrate are not).

7.3.1 Conclusions and suggestions forfuture monitoring

(1) The spatial distribution of nutrients in Scottishwaters shows highest concentrations in the Clydeestuary, notably of phosphate, nitrite andammonia; the Forth is next highest, whilst the Tayhas the lowest estuarine nutrient concentrations.Mean nutrient concentrations show a salinitydependence, being higher in fresher waters.

(2) Nutrient concentrations exhibit a strong seasonaldependence additional to that on salinity. Temporalvariability is greatest for chlorophyll, as expected.

(3) Analytical capabilities are sufficient to monitorestuarine and coastal nutrient concentrations, withfew values reported as less than the limit of detection.

(4) Several gaps exist in the current dataset. Somedeterminands (notably chlorophyll and silicate) wereconsistently not reported, whilst some reported DOdata were incomparable due to the absence ofsupporting salinity and temperature data used tocalculate saturations.

(5) Estuarine salinity coverage was sufficient onlybecause inter-annual variability was generally smallenough to allow the combination of data into two(seasonal) datasets. However, most notably in theTay, data for the freshest salinity band are sparse.Future monitoring programmes might consider theneed for more intensive sampling of the salinitygradient, although the logistical problems potentiallyinvolved would need to be considered in detail.

(6) The important seasonal dependence of nutrientsmeans that consistent sampling times are requiredat the various NMP sites for a better “snapshot”comparison. Synchronisation of offshore andestuarine site monitoring would help interpretation.The current monitoring frequency is inadequate tocharacterise episodic bloom events.

Figure 7.4Examples of non-conservative behaviour in the Forth and Clyde estuaries(a)␣ ammonia and (b) nitrite.

Figure 7.5Non-conservative behaviour of phosphate in the (a) Clyde, (b) Forth and (c) Tayestuaries.

33

100

120

80

0

60

20

a) ClydeSummerWinter

Silic

ate

(µM

)

50 10 15 20 30 350

b) Forth

Salinity

20

25

SummerWinter

40

Silic

ate

(µM

)

40

60

80

100

7.4 Metals in Sea Water7.4.1 IntroductionThe NMP specified that for aqueous determinands(including trace metals) three sampling locations wererequired in each of the three major Scottish estuaries (Clyde,Tay and Forth). Trace metal concentrations in estuaries area function of many factors, one of the most important ofwhich is salinity. The NMP further specified therefore thatthe individual sites should ideally cover the salinity ranges,0–10, 10–20 and 20–30. The salinity at a particular site isdependent primarily on fresh water input and tidal state. Inan effort to minimise the variation in salinity at individualsites the NMP recommended sampling at the same state oftide and at the same point in the neap/spring cycle.

Table 7.3 summarises the number of times each of theScottish NMP sites was sampled between 1992 and 1995.The table also provides information on the range and meansalinity at each of these sites. The table indicates thatalthough the salinity ranges at some of the estuarine siteswere greater than 10, mean values generally fell into thetarget ranges.

7.4.2 Data processingIn order to make sensible comparisons between individualestuaries, and between sites within the same estuary, the

effect of salinity must be taken into account. Therefore ratherthan simply taking the information from individual sitesall data have been grouped into the following salinity bands,0–10, 10–20 and >20. This approach acknowledges the factthat, as a consequence of varying hydrographic conditionson different sampling occasions, water of the same salinitymay not always be associated with the same geographicallocation. Taking this effect into account should reduce thevariability associated with sampling at a fixed geographicallocation and facilitate drawing meaningful conclusionsregarding comparative trace metal concentrations.

Data from estuarine sites in the Clyde, Tay and Forth havebeen included in Fig. 7.8, which provides a single sheetsummary of all information. In producing this figure the“less than” values have been included as actual concen-trations. The data for mercury have not been included inthis treatment; they are discussed separately in Section 7.4.4.Some important general conclusions emerge from Fig. 7.8.For elements such as copper and zinc the box and whiskerplots are rather symmetrical, i.e. the median concentrationgenerally lies close to the middle of the range. In contrastthe median concentrations for cadmium and lead (especiallyin the Clyde and Tay) lie at or close to the bottom of therange. This effect is a direct result of a high proportion ofthe cadmium and lead concentrations being at or close tothe analytical limit of detection.

A simple map based summary of the trace metals in seawater data, including the intermediate and offshore data,requires simplification of the information presented in Fig.

0 5 10 15 20 25Chlorophyll a (µg/l)

Su-94

Au-94

Wi-95

Sp-95

Su-95

Au-95

Wi-96

Sp-96b) Forth

Wi-93Sp-93Su-93

Au-93

Su-94

Au-94

Wi-95

Sp-95

Su-95

Au-95a) Clyde

Sp-94

Figure 7.7Chlorophyll-a concentrations (µg/l) in (a) Clyde estuary and (b) Forth estuary (springsummer, autumn and winter sampling times).

Figure 7.6Near conservative behaviour of silicate in (a) Clyde estuary and (b) Forth estuary.

34

7.8. One of the specific difficulties associated with theinterpretation of trace metal in sea water data is thepossibility of contamination. The data may not thereforebe normally distributed. The averaging of data may nottherefore be appropriate since the inclusion of contaminatedsamples would give the mean a positive bias. A more usefulapproach to summarising the results as a single number isto use the median values obtained from the box and whiskerplots in Fig. 7.8. This has been done in Fig.␣ 7.9.

7.4.3 Results (Cd, Pb, Cr, Cu, Ni andZn)7.4.3.1 CadmiumOther than the sites in the Tay estuary, median concen-trations were all less than 0.05 µg/l. In the Tay the detectionlimit of the method resulted in all values being quoted as<0.07␣ µg/l. Cadmium concentrations at intermediate andoffshore sites were <0.02 µg/l.

7.4.3.2 LeadThe median lead concentration at all sites was <0.5 µg/land at most sites <0.2 µg/l. Only in the Forth estuary wasthe analytical method sensitive enough to quantify dissolvedlead concentrations; here they ranged from 0.024 to 0.046µg/l.

7.4.3.3 ChromiumThe data reported here for dissolved chromium represent

the results of the first reliable survey for this element inScottish estuarine and coastal waters. Chromium concent-rations at intermediate and offshore sites were generally lessthan 0.5 µg/l. Concentrations in estuaries were higher butonly in the upper Clyde did median levels exceed 2 µg/l.

7.4.3.4 CopperCopper concentrations at intermediate and offshore siteswere generally less than 0.5 µg/l. Within estuaries medianconcentrations were lowest in the Tay (0.8–1.7 µg/l) andslightly higher in the Forth (1.2–2.4 µg/l) and Clyde (1.0–2.4 µg/l).

7.4.3.5 NickelThe highest dissolved nickel concentrations were observedin the Clyde estuary where median values ranged from 0.7to 2.0 µg/l. The lowest estuarine concentrations were in theTay (0.4–0.5␣ µg/l), and those in the Forth were intermediate(0.7–1.3 µg/l). At intermediate and offshore sitesconcentrations were generally <0.5 µg/l.

7.4.3.6 ZincZinc concentrations at intermediate and offshore sites weretypically 1–2 µg/l; in estuaries however they were higher.Median concentrations were highest in the Clyde estuary(3.0–8.9␣ µg/l) and lower in the Forth (2.2–4.3 µg/l) andTay (2.9–5.3 µg/l).

Table 7.3 Summary of salinity data from Scottish NMP sites (O - offshore, I - intermediate, E - estuarine). The rangeand mean salinity for each site are given, also the number of times each site was sampled

NMP site (type) No times sampled Salinity Mean salinity SPM (mg/l) Mean SPM (mg/l)Solway

25 (O) 2 32.19–32.81 32.5 20.2 20.2Clyde

35 (O) 2 32.45–32.71 32.58 5.9 5.945 (I) 7 25.03–32.46 30.77 7.7–62.2 39.755 (E) 7 22.87–32.23 28.36 9.1–67.7 34.365 (E) 9 10.00–24.48 19.14 15.0–41.9 25.575 (E) 9 1.08–14.00 6.40 9.9–40.6 24.9

Highland85 (I) 2 34.33–34.38 34.35 4.6 4.695 (I) 2 31.14–32.84 31.99 4.2 4.2

105 (O) 2 34.60–34.81 34.70 4.3 4.3Tay

115 (E) 12 13.9–29.8 23.2 <2–14.2 6.6135 (E) 3 – – – –145 (E) 12 2.0–23.3 15.4 <2–43.2 16.5155 (I) 1 34.50 34.5 - -

Forth165 (O) 1 34.59 34.59 - -175 (I) 16 32.89–34.39 33.77 <0.1–3.8 2.5185 (E) 16 0–1.82 0.28 4.5–97 72.3195 (E) 16 1.55–24.26 14.73 4.5–107 29.1205 (E) 16 26.14–33.99 30.96 3.4–22.2 6.9

35

5.00

3.75

2.50

1.25

0.00

0.20

0.15

0.10

0.05

0.000 10 20 30 40

Cd

diss

(µg

/l)

Cadmium21

57

7

10

8

11

12

18

0.20

0.15

0.10

0.05

0.000 10 20 30 40

Pb d

iss

(µg/

l)

Lead21

5

7

710

8

11

12

18

5.00

3.75

2.50

1.25

0.000 10 20 30 40

Cr

diss

(µg

/l)

Chromium

18

5

6 510

6

9

12

18

0 10 20 30 40

Cu

diss

(µg

/l)

Copper

21

5

7

7

10

9

11

12

17

Salinity bandSalinity band

6.0

4.5

3.0

1.5

0.00 10 20 30 40

Ni d

iss

(µg/

l)

Nickel

21

5

7

7

10

9

1112

18

12

9

6

3

00 10 20 30 40

Zn

diss

(µg

/l)

Zinc

19

5

7

7

9 8

11

8

18

5.00

3.75

2.50

1.25

0.00

Figure 7.8Box and whisker summary of all data from estuarine sites in the Clyde, Tay and Forth. The data for each estuary have been split into salinity bands, 0–10, 10–20 and >20. Themiddle of the box gives the median concentration; the edges of the box include half the values between this and the range (indicated by the whiskers). The number of data pointsincluded in each band is given at the top of each box and whisker plot.

36

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°

Copper (µg/l)

1.25 0.5 0.25 2.0 1.0 0.20.4

2.5 1.25 0.250.5

Zinc (µg/l) Nickel (µg/l)

Chromium (µg/l)

2.5

Lead (µg/l)

0.25 0.10 0.05 0.10 0.05 0.02 0.01

Cadmium (µg/l)

0.5

10 5 2.5 1.0

7.4.4 Results (mercury)There were major difficulties associated with theinterpretation of the mercury in sea water data. For examplewith the exception of one data point all data from the Taywere reported as less than the detection limit of 60 ng/l. Amuch improved detection limit of ca 4 ng/l was availablefor the Forth and Clyde data, but even here the majority ofthe reported data was reported as less than this figure.

A limited amount of Hg data is available from the Forthestuary. This derives from analysis during the special exerciseon mercury and trace metals in sea water. For this exercisethe results of the analytical laboratory were very good and adetection limit of 0.5 ng/l was achieved. These data cantherefore be considered as the most reliable available. Therange of concentrations observed at the three NMP stationswas:

NMP Site No Salinity Dissolved Hg (ng/l)

185 0–3.5 2.4–7.8195 14.5–19.3 0.7–4.6205 23.8–30 0.8–2.6

7.4.5 ConclusionsThe NMP results presented here are generally consistentboth with more detailed studies of the three estuaries (Ballset al., 1997a) and also wider surveys of the North Sea(e.g.␣ Kremling, 1985). For example Cd concentrations inthe Tay estuary (Balls et al., 1997a) were typically 0.02–0.04␣ µg/l. The relatively high concentrations of dissolvedZn reported for the Tay estuary are not consistent withpreviously published data (Balls et al., 1997a). The high Znconcentrations may be indicative of a contaminationproblem for this element.

Figure 7.9Area proportional symbols representing the concentrations of Cd, Pb, Cr, Cu, Ni and Zn in seawater. The data plotted for the estuarine sites are the median values obtained fromthe box and whisker plots in Fig. 7.8. The innermost station is the 0–10 salinity band, the middle one 10–20 and the outer the >20. Where the concentrations represent “lessthan” values open circles have been plotted; these should be interpreted as maximum concentrations.

37

Analytical methodology was generally adequate for Cr, Cu,Ni, and Zn. However if more realistic data are to beproduced for Cd and Pb some improvements will benecessary. Current analytical methodology for Hg also needsto be improved if realistic data are to be obtained, especiallyfor offshore water where concentrations are likely to be <1ng/l.

The highest concentrations of Cr, Ni and Zn were observedin the Clyde estuary. These observations are likely to berelated to relatively high inputs from the large populationand associated industry of the Glasgow conurbation.

7.5 Trace Organic Contami-nants in Water

Available data are summarised in Table 7.4 and shown inmap form in Fig.7.10

7.5.1 Estuaries7.5.1.1 IntroductionThe NMP monitoring requirements for trace organics inwater are detailed elsewhere (HMIP, 1994). In a Scottishcontext this involved sampling at nine estuarine sites. Thefollowing data are available:

(1) Forth: Samples were collected quarterly over theperiod 1992–95 at the three estuarine sites and oneintermediate site.

(2) Clyde: Quarterly data are available for the periodNovember 1994 to November 1995 for the threeestuarine and one intermediate sites.

(3) Tay: Quarterly data are available for two of theestuarine sites over the period 1993 to 1995inclusive.

Additional data are available from a range of sites aroundScotland sampled by SOAEFD in 1990. These data havebeen included for information as the analytical techniqueemployed allowed detection of compounds at lowerconcentrations than are routinely attainable.

7.5.1.2 ResultsData for suspended solids are included as an aid tointerpretation of results. The ability of an organic compoundto be adsorbed onto particulate matter is determined by itshydrophobicity. The HCH group are the most water solubleof the organic compounds determined and are thereforemost likely to be found in solution. Other organiccompounds are more likely to be adsorbed onto suspendedsolids. As the samples analysed were unfiltered, thosecontaining high concentrations of suspended solids may beexpected to contain higher concentrations of the morehydrophobic compounds.

In Fig. 7.10 average concentrations at a site are representedas areal proportional circles. For many of the determinandsconcentrations were below the limit of detection of theanalysis; only data for γ-HCH in the Forth and Clyde

Table 7.4 Average concentrations of aqueous organic compounds at NMP sites

Site Salinity γ-HCH ng/l HCB ng/l Suspended solids mg/lForth

185 (E) mean 0.28 1.63 2.45 72.4cv 161 74 99 143

195 (E) mean 14.7 1.43 3.86 29.0cv 46 59 81 88

205 (E) mean 30.9 1.33 1.76 6.9cv 7 40 84 7.7

Tay115 (E) mean 26.5 11.1 <1 6.67

cv 21 129 70145 (E) mean 14.1 7.0 <1 16.5

cv 52 96 87Clyde

75 (E) mean 9.47 12.2 <1 22.2cv 74 43 42

65 (E) mean 21.39 3.81 <1 25.9cv 22 155 32

55 (E) mean 29.03 4.62 <1 32.3cv 17 126 51

45 (I) mean 32.26 4.68 <1 36.1cv 2 147 49

EQS 20 30

38

estuaries and γ-HCH on the Tay gave sufficient data abovethe limit of detection for comparisons to be carried out.

Data for suspended solids showed that the Tay had the lowestconcentrations of the three estuaries; the highest con-centrations occurred at the low salinity site in the Forthand there was little variation in suspended solidsconcentrations along the length of the Clyde.

HCBMeasurable concentrations (8.9–<2 ng/l) of HCB werefound in the Forth estuary. The presence of HCB in theForth estuary has previously been recorded (Harper et al.,1992) and is a result of a known industrial discharge. Thisstudy also found concentrations of TCBs in the Forthestuary in the range 77–<2 ng/l. Comparison of NMP datawith these data show that significant reductions of bothTCBs and HCB have been achieved over the past five yearsin the Forth estuary. This is compatible with the reducedeffluent discharges. However the sediments of the Forthestuary provide a source of HCB which may result inelevated concentrations in aqueous samples in addition tothe point source discharge. This may explain the relativelyhigh concentrations recorded at site 185, which is upstreamof the discharge but contains higher concentrations ofsuspended solids than site 205, which is downstream of thedischarge.

No measurable concentrations of HCB were found in theTay or Clyde estuaries.

HCHThe highest concentrations of γ-HCH were found in theTay and the lowest concentrations of γ-HCH in the Forth(see Fig. 7.10).

Concentrations of γ-HCH have been plotted against salin-ity in Fig. 7.11. These plots show that the distributions donot arise from simple conservative mixing with river waters.In all the estuaries the distribution of γ-HCH could berelated to anthropogenic sources, e.g. a large urban con-urbation at the mouth of the Tay, and combined sewageand industrial discharges in the Forth and Clyde estuaries.

The UK has set Environmental Quality Standards (EQS)for the protection of aquatic life and these have beenincluded in Table 7.4 for comparison. In all cases the concen-trations of determinands are substantially below these EQS.

The extra data provided by the SOAEFD are given in Table7.5.

These data give additional information on γ-HCH and HCBand further data for PCBs and dieldrin in Scottish waters.For the Forth and Tay estuarine sites the mean result of six(Tay and Forth Eastern) or seven determinands are given.

The data confirm the distribution of HCB shown in theNMP data, i.e. highest concentrations in the Forth andbackground concentrations elsewhere of <0.5 ng/l.

59°N

58°N

57°N

56°N

55°N

γ-HCH in water

5 2 1

HCB in water

10

8°W 6°W 4°W 2°W 0°

4 2 0.8 0.4

8°W 6°W 4°W 2°W 0°Figure 7.10Mean concentrations (ng/l) of γ-HCH and HCB in unfiltered water from NMP sites. Concentrations are presented as area proportional symbols; scale symbols are shown in thetop left hand corner of each plot. “Less than” concentrations are indicated by open circles, the size of the circle indicating the detection limit.

39

PCBs are not included in NMP in the aqueous phase.However, these data show relatively high concentrations inthe Clyde and the lowest concentrations in the Tay.

Concentrations of dieldrin are all <0.4 ng/l, with highestconcentrations occurring in the industrialised regions of theForth and Clyde.

Data for γ-HCH show relatively high concentrations in theClyde (>1 ng/l) and low concentrations in the Tay (<0.4ng/l). This contrasts with the NMP data which showedrelatively high concentrations in the Tay.

7.5.1.3 ConclusionsOf the organochlorine compounds specified in the NMPonly γ-HCH is detected at concentrations above the limitof detection of routine analytical methods at all Scottishestuarine sites. HCB was measurable in the Forth estuary.Concentrations of γ-HCH and HCB were below therelevant EQS at all sites.

In the Forth, Clyde and Tay estuaries, the distribution of γ-HCH and HCB is consistent with known anthropogenicsources.

Future monitoring programmes should consider thepossibility of lowering the limit of detection for organic

determinands in order to provide a more comprehensivedataset.

Recent studies carried out as part of the National MarineAnalytical Quality Control Scheme (Jessep and Dobson,1996) have shown: that not all laboratories are able to recoverfully the more hydrophobic compounds (i.e. compoundswith a log K

ow greater than 6) from a sample spiked with

particulate matter; recoveries for these compounds were inthe range 50–70%. Further work may be required on thisaspect of the analyses in future monitoring.

It is important that all participating laboratories report thesame suite of determinands and provide comparable datasetsto enable comparisons between sites to be drawn.

7.5.2 Offshore and intermediate sites7.5.2.1 IntroductionOffshore and intermediate sites were required to be sampledannually over the period 1993–95. There are nine such sitesin Scotland. The Forth and Clyde River Purification Boardswere responsible for sampling the intermediate sites in theirareas. These tended to be sampled quarterly along with theestuarine sites. SOAEFD were responsible for sampling allother sites. No samples were collected at offshore sites as itwas considered that concentrations of organic compoundsin these samples were unlikely to be above the limit ofdetection of available analytical methods. SOAEFD haveprovided data from a survey carried out in 1990–91, when30–40 litres of sample were extracted to give lower detectionlimits than are normally achieved.

Table 7.5 SOAEFD data from 1990 survey(sites not coincident with NMP)

Site PCBs HCB γ-HCH Dieldrinng/l ng/l ng/l ng/l

Gourock 1.08 0 1.54 0.24

Forth mean 0.31 5.2 0.64 0.09Grangemouth sd 0.11 2.22 0.15 0.17

Forth mean 0.23 0.79 0.46 0.17Granton sd 0.18 0.20 0.15 0.04

Tay mean 0.10 0.04* 0.23 0.05Eastern sd 0.08 0.11 0.02

Tay mean 0.08 nd 0.36 0.087Bridges sd 0.02 0.04 0.018

Forth mean 0.51 0.08 0.55 0.096Eastern sd 0.15 0.05 0.15 0.015

nd = no data *only two data

sd = standard deviation

4

5

3

0

2

1

40

30

20

10

0

γ-H

CH

ng/

l50

γ-H

CH

ng/

l

50 10 15 20 30 350

Salinity

20

25

15

10

5

25

γ-H

CH

ng/

la) Tay

b) Forth

c) Clyde

Figure 7.11Concentrations of γ-HCH as a function of salinity in the Clyde, Forth and Tayestuaries.

40

7.5.2.2 ResultsThe compounds of interest were all below the limit ofdetection of the analytical method in the Forth. The Clyde(site No 45) data have been included in the discussion ofestuarine sites (see Section 7.5.1) as the data were morecomparable with these data.

The extra data provided by SOAEFD are given in Table7.6.

Table 7.6 Scottish offshore trace organic concentrations1990–91

Site PCBs HCB γ-HCH Dieldrinng/l ng/l ng/l ng/l

Inner Moray Firth 1.39 0.06 0.63 0.1SW Skye 0.52 0.04 0.75 0.07North Channel 0.74 0.03 0.44 0.04Upper Clyde 0.8 0.03 1.33 0.13Holy Island 0.48 0.03 1.38 0.14

These data confirm the low concentrations of thesedeterminands in coastal waters. PCBs and γ-HCH arepresent at higher concentrations than HCB or dieldrin.Concentrations of all compounds are much lower than therelevant EQS.

Low concentrations of γ-HCH (0.2 ng/l) are found in NorthAtlantic waters and are attributed to atmospheric inputs(North Sea Task Force, 1993). The concentrations reportedhere for the Scottish coastal waters are comparable to datafor the north western North Sea.

7.5.2.3 ConclusionsIt is recommended that the requirement for samplingoffshore and intermediate sites for organic determinands isdeleted from any further programme unless routinedetection limits are lowered.

41

8.1 Metals8.1.1 IntroductionAt each of the 18 Scottish NMP sites nine sediment sampleswere obtained. For offshore and intermediate sites these werefrom the corners, centre and mid points of the sides of a500 m square grid. For estuarine sites, unless local conditionsdictated otherwise, a rectangular grid (longer axis at least200 m) was used. The results are summarised in Table 8.1,which also contains data for the supporting parametersspecified in the NMP (Al, organic carbon and particle size).The data presented here are described in more detailelsewhere (Balls et al., 1997b).

8.1.2 Particle size and organic carbonThe highest percentages of sediment in the <63 mm fractionwere observed in the fine muds from the Firth of Clyde(>90); the values decreased to less than 20 in the Clydeestuary. A high percentage of fine sediment was also presentin the samples from station 95 in the inner Moray Firth.Sediments from the Forth estuary typically contained 50–70% of fine material; the coarsest sediments were observedin the Tay estuary where less than 5% of material was in thefine fraction. Within specific estuarine systems theconcentrations of organic carbon (OC) tended to show apositive relationship with particle size, i.e. high OCconcentration with a high proportion of fine material.Maximum OC concentrations were observed in the Forthestuary (3.1–4.2%) and the minimum in the Tay (0.1–0.3%).

8.1.3 Trace metal concentrationsThe data for Cu, Zn, Pb, Cd, Hg, Cr, Ni and As aresummarised in Table 8.1 and presented in map form in Fig.8.1. In these plots area proportional symbols have been usedto provide a simple visual representation of the data. Fornickel several results fell below the analytical detection limitof 1 mg/kg. A general conclusion from Fig. 8.1 is that tracemetal concentrations in sediments from the Clyde and Forthestuaries are consistently higher than those from offshorelocations. The contrast in concentrations between estuarineand offshore sites is greatest for Hg and As, least for Cd andCu. Trace metal concentrations in sediments from the Tayestuary were generally much lower than those in the Forthand Clyde. The exception was site 115, located close toDundee.

8.1.4 Normalisation to Al and enrich-ment factors

It is well established that trace metal contaminants arepreferentially associated with the fine fractions of sediments.Aluminosilicate minerals are dominant within these fractionsand the concentration of Al is often used as a measure of

8. Sediments

their abundance. Relative to trace metals Al is abundant insediments and consequently its concentration is not greatlyaffected by geochemical processes. To assess to what extentthe variations in trace metal concentrations between siteswere a consequence of those in grain size, a normalisationprocedure to Al was adopted. Metal aluminium ratios (mg/kg:%) for uncontaminated sediments were taken fromKersten et al. (1994). The values used for Cu, Zn, Pb, Cd,Hg, Cr, Ni and As were 3.87, 17.8, 4.47, 0.021, 0.0105,13.9, 6.73 and 2.33 respectively. An enrichment factor (EF)was calculated using the expression:

where [M/Al]obs

and [M/Al]ref

are respectively the observedand reference (Kersten et al., 1994) values of the metal (mg/kg) to aluminium (%) ratio. EFs facilitate the identificationand quantification of metal enrichment; absolute EF valuesare dependent on the choice of metal/Al ratios used as thereference. The principal value in the approach is that itenables the relative degree of contamination between areasto be established. The results of the EF calculations arepresented as area proportional symbols in Fig. 8.2. In orderto facilitate the identification of those metals which showthe greatest enrichment the same scale has been usedthroughout.

Enrichment of metals was evident in the outer part of theTay estuary and in all samples from the Clyde and Forthestuaries. From Fig. 8.2 it is apparent that EFs for anindividual metal show a similar pattern between the sites,i.e. high in the Clyde and Forth estuaries, low at offshoresites. There were, however, some notable differences in thedegree of enrichment for individual metals. EF values forCr, Ni, Cu, Zn and Cd were generally <5, those for Pb andAs were greater and those for Hg were highest of all (>10 inthe Forth and Clyde estuaries). With the exception of HgEF values tended to be greatest in the Clyde. The Forthestuary has a history of Hg contamination. Industrial inputshave now been eliminated, but the turbid nature of theestuary has resulted in considerable retention of Hg withinthe system (Elliott and Griffiths, 1986).

There are some subtle differences between the pattern ofcontamination in the Clyde and Forth estuaries. EF valuestend to decrease with increasing distance up the Clydeestuary; the reverse tends to be the case in the Forth. Thisdifference may be associated with the contrasting nature ofthe two estuaries. The maintenance of a navigable channelto Glasgow involves dredging, and consequently there islittle or no long term accumulation of fine material in theestuary. Supporting evidence for this suggestion comes fromthe decreasing fraction of fine material and metal

EF =[M / Al]

obs

[M / Al]ref

42

Table 8.1 Summary of Al, organic carbon, particle size and trace metal (mg/kg) data from Scottish NMP sites(O - offshore, I - intermediate, E - estuarine). The mean concentration for each metal at each site is given, and the

coefficients of variation (CV) around the grid of sampling points are also presented. Nine results were used in calculat-ing the CV; in a few cases where fewer data were available the number of results used is given in brackets after the mean

Site No Al (%) OC (%) <63 µm (%) Cu Zn Pb Cd Hg Cr Ni AsSolway

25 (O)Mean 2.7 0.46 59 7.1 63 28 0.046 0.058 46 5.8 7.5CV(%) 22 22 21 11 7.4 6.7 8 19 20 67 11

Clyde35 (O)Mean 5.8 1.1 92 17 130 49 0.13 0.1 94 24 9.5CV(%) 15 4.7 1.0 3.0 3.1 4.3 19 10 7.4 8.4 14

45 (I)Mean 4.6 3.5 95 47 250 160 0.14 0.6 240 72 50CV(%) 14 17 2.8 5.3 5.2 6.7 31 9.1 5 35 9.3

55 (E)Mean 4.1 2.0 80 47 290 180 0.19 0.48 190 41 74CV(%) 23 36 12 31 12 24 40 29 24 31 30

65 (E)Mean 3.6 1.4 24 32 170 100 0.18 0.2 110 10 25CV(%) 36 50 110 69 50 100 30 110 59 120 42

75 (E)Mean 2.9 1.1 17 14 93 48 0.087 0.17 75 5.5 41CV(%) 28 93 95 91 40 61 110 110 49 130 30

Highland85 (I)Mean 3.5 0.43 45 7.3 45 24 0.018 0.05 57 6.4 4.3CV(%) 11 21 14 16 17 11 39 28 15 44 10

95 (I)Mean 4.6 1.9 79 9.9 70 34 0.09 0.076 53 9.5 4.6CV(%) 20 9.9 1.8 23 15 16 20 25 22 38 16

105 (O)Mean 3.1 0.27 10 3.3 18 20 0.06 0.05 18 <1 1.5CV(%) 13 24 44 16 15 12 18 26 37 - 42

Tay115 (E)Mean 5.8 0.3 1.5(1) 32 110 93 0.082 0.016 47 <1 13CV(%) 7.7 220 - 95 77 220 140 25 49 - 12

135 (E)Mean 4.8 0.1 2.3 5.4 52 21 0.049 0.032 46 1.9 5.5CV(%) 21 27 46 22 15 14 41 59 16 120 43

145 (E)Mean 4.4 0.13 1.7(1) 4.4 41 20 0.053 0.056 28 <1 5.7CV(%) 15 110 - 30 21 15 47 25 33 - 24

155 (I)Mean 4.8 0.28 6.3(8) 4.5 38 24 0.26 0.052 45 <1 6.9CV(%) 12 21 13 5.9 7.3 6.7 18 18 9.2 - 11

Forth165 (O)Mean 3.3 0.41 4.8(2) 2.5 16 20 0.007 0.069 16 <1 8.3CV(%) 8.5 15 - 14 6.5 5.6 66 27 33 - 35

175 (I)Mean 3.9 1.8 62 11 77 41 0.11 0.21 63 6.7 11CV(%) 19 37 19 31 26 26 46 31 30 87 12

185 (E)Mean 7 3.9 67 39 150 66 0.18 0.94 110 20 69CV(%) 16 34 34 30 19 12 30 34 26 35 20

195 (E)Mean 9.6 4.2 72 48 160 72 0.18 1.2 140 25 13CV(%) 21 38 35 34 25 22 32 39 26 42 34

205 (E)Mean 4.7 3.1 48 29 120 56 0.094 0.71 86 11 21CV(%) 17 59 37 34 13 16 44 39 26 48 39

43

Mercury

Nickel Arsenic

Copper Zinc Lead

Cadmium Chromium

8°W 6°W 4°W 2°W 0°

80 40 816

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0°

80 40 816 NO DATA

59°N

58°N

57°N

56°N

55°N

0.250 0.125 0.0250.050 0.60 0.24 0.121.20

8°W 6°W 4°W 2°W 0°

250 125 50 25

200 100 2040300 150 60 30

59°N

58°N

57°N

56°N

55°N

25 10 550

Figure 8.1Mean concentrations (mg/kg) of copper, zinc, lead, cadmium, mercury, chromium, nickel and arsenic in sediments from NMP sites. Concentrations are presented as areaproportional symbols; scale symbols are shown in the top left hand corner of each plot. Open circles are used where concentrations were below the detection limit.

44

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°

Copper Zinc Lead

Cadmium Mercury Chromium

Nickel Arsenic

NO DATA15 7.5 3 1.5 15 7.5 3 1.5

59°N

58°N

57°N

56°N

55°N

7.5 3 1.515 15 7.5 3 1.5 15 7.5 1.53

59°N

58°N

57°N

56°N

55°N

15 7.5 1.53 7.5 3 1.515 15 7.5 3 1.5

8°W 6°W 4°W 2°W 0°

Figure 8.2Enrichment factors above “background concentrations” for copper, zinc, lead, cadmium, mercury, chromium, nickel and arsenic in sediments from NMP sites. Enrichmentfactors are presented as area proportional symbols; scale symbols are shown in the top left hand corner of each plot. Open circles are used where concentrations were below thedetection limit and enrichment factors could not be calculated.

45

concentrations in the sediments with increasing distanceup the estuary (see Table 8.1). In contrast the upper reachesof the Forth estuary are not dredged. In this respect theForth estuary represents a more natural situation and thepattern of EFs probably reflects historic inputs to the lowerestuary.

8.1.5 Other normalisation proceduresA summary of the relationship between trace metalconcentrations and all the common normalising factors (Al,OC and particle size) is given in Table 8.2. This analysis hasbeen restricted to the data from the Clyde and Forth estuarieswhere trace metal concentrations were highest. Table 8.2summarises the coefficients of determination obtained fromlinear regression analysis. The results indicate that generallymore of the variability in trace metal concentration can beexplained on the basis of variations in the Al content andthe <63 µm size fraction than those in organic carbon. Theseresults demonstrate the value of including Al determinationsas a supporting parameter in the NMP.

8.1.6 Variability around the samplinggrid

The variability in concentration of an individualdeterminand between the nine samples obtained from eachof the 18 sites is of direct relevance to any revision of theNMP. For example trend monitoring at a particular sitewould not be logical if there were a high degree of localvariability around it. The present data are therefore anessential step in screening the current NMP sites with theobjective of identifying those which might be candidatesfor a subsequent trend monitoring programme. Table 8.1contains the coefficients of variation for each parameteraround each site.

It is evident from Table 8.1 that coefficients of variationtended to be greatest at estuarine sites where they oftenexceeded 25%. Organic carbon was particularly variable and

exceeded 200% at site 12 in the outer Tay estuary. At theintermediate and offshore sites the coefficients of variationwere generally lower and for many parameters <20%.

8.1.7 Suggestions for future mon-itoring

On the basis of the present data there would appear to belittle purpose in continuing monitoring at sites such as 65and 115 where sampling variability was extremely high. Siteswhich are remote from inputs and exhibit backgroundconcentrations of metals (e.g.35,85,95,105) are useful forbaseline purposes. There seems little to gain however fromincluding more than a few of these in a monitoring scheme.Effort would be more effectively concentrated on those siteswhere sampling variability is small, enrichment factors arehigh and where input reductions are either in place or arescheduled. An assessment of interannual variability at thesesites would be required before a full trend monitoringprogramme could be initiated. Potential sites in this categoryinclude 45, 55, 175, 185.

8.2 Sediment Trace Organics8.2.1 IntroductionThere are 18 NMP sediment sites around the coast ofScotland: organics data are available for all of these sites.For offshore and intermediate sites nine replicate sampleswere collected from the corners, centre and mid points ofthe sides of a 500 m square grid. For estuarine sites sampleswere collected from the same points of a rectangular grid(longer axis at least 200 m) unless local conditions dictatedotherwise. Replicate samples were collected to give anindication of sample variability at a site.

8.2.2 Results8.2.2.1 Determinands analysedNMP specified the determination of a range of PCBcongeners, DDT (ppTDE, ppDDE, ppDDT), HCB,dieldrin, aldrin and endrin. Data are presented for the sumof the ICES 7 PCB congeners (i.e. 28, 52, 101, 118, 138,153, 180), total DDTs (ppTDE, ppDDE, ppDDT), HCB,dieldrin and endrin. Data reported for aldrin were all lessthan 0.01 µg/kg and therefore these data have not beenpresented. The results are summarised in Table 8.3, whichalso contains data for organic carbon. The mean of the ninereplicate samples is presented together with the coefficientof variation to give an estimate of variability at a site; themedian value is also presented as this gives a better estimateof the concentration at a site where the data are skewed.The data given in Table 8.3 are also summarised in mapform in Fig. 8.3. In these plots area proportional symbolshave been used to provide a visual representation of thedata; results below the limit of detection are presented asopen circles.

8.2.2.2 Organic carbonThe sediments of the Clyde and Forth estuaries were found

Table 8.2 Coefficients of determination (r2) for linearrelations of trace metals from the Clyde and Forth

estuaries with Al, organic carbon (OC) and particle size(%<63 µm)

Clyde ForthAl OC %<63 n Al OC %<63 n

Cu *65 33 45 36 *72 *65 43 36Zn 45 34 *59 36 *70 *64 43 36Pb 32 22 44 36 *69 *50 31 36Cd 19 9 8 36 42 41 *50 36Hg *51 44 *54 36 *66 *56 41 36Cr *63 *63 *67 36 *76 *55 *50 36Ni 9 47 *59 29 *73 *57 *59 36As 5 4 26 36 2 3 1 36

*indicates that the coefficient of determination is greater than50%, i.e. >50% of the variability in the data can be explained

on the basis of this relationship.

46

Table 8.3 Concentrations of organic contaminants in sediments from NMP sites

Site % carbon PCBs µg/kg DDTs µg/kg HCB µg/kg Dieldrin µg/kg Endrin µg/kgSolway

25 (O) median 0.46 0.85 0.20 0.035 0.03 0.04mean 0.46 0.97 0.25 0.040 0.04cv% 23 21 47 28 23

Clyde35 (O) median 1.05 2.05 1.44 0.078 0.25 0.15

mean 1.07 2.09 1.43 0.079 0.24 0.14cv% 5 20 14 27

45(I) median 3.47 19.9 11.6 0.32 1.3 <0.29mean 3.36 20.1 9.0 0.31 1.8 2.0cv% 6.5 15 53 13 39 133

55(E) median 2.40 19.1 6.12 0.39 0.98 ndmean 2.59 19.5 7.00 0.46 1.04cv% 32.3 22.6 39.0 16.0 33.0

75(E) median 0.70 13.1 1.54 <0.1 0.86 <0.5mean 0.96 12.0 4.95 0.25 2.03 <0.5cv% 76 118 103 40 101

65(E) median 0.77 3.08 <0.5 <0.1 0.85 <0.47mean 0.91 7.2 1.02 0.16 0.28 <0.47cv% 74 83 115 106 25

Highland85 (I) median 0.42 0.91 0.16 0.017 0.02 <0.01

mean 0.43 0.94 0.16 0.016 0.02 <0.01cv% 22 27 41 21

95(I) median 1.89 1.98 0.73 0.055 0.068 0.09mean 1.92 1.87 0.75 0.054 0.065 0.09cv% 10 17 16 24 31 18

105(O) median 0.23 0.63 0.08 <0.01 0.017 <0.01mean 0.26 0.63 0.09 <0.01 0.024 <0.01cv% 25 16 20 83

Tay115 (E) median <0.2 0.63 0.04 <0.01 0.01 <0.01

mean <0.2 0.75 0.05 0.01 0.013 0.09cv% 18 45 59 119

135(E) median <0.2 0.50 0.06 <0.01 <0.01 <0.01mean <0.2 0.70 0.17 <0.01 0.019 0.015cv% 28 80 117 130 76

145(E) median <0.2 0.39 0.03 0.012 <0.01 <0.01mean <0.2 0.48 0.21 0.011 <0.01cv% 116 51 246 2

155(I) median 0.26 0.44 0.09 <0.01 <0.01 <0.01mean 0.28 0.81 0.15 0.01 0.015cv% 22 61 33 2

Forth165 (O) median 0.39 0.58 0.02 <0.01 <0.01 <0.01

mean 0.41 0.55 0.02 <0.01 <0.01 -cv% 16 16 36 - -

175 (I) median 1.90 3.06 3.33 2.57 <0.01 <0.01mean 1.78 4.39 3.73 3.23 0.79 <0.01cv% 39 62 29 48 42

185 (E) median 37.6 10.2 9.26 62.8 2.76 <0.01mean 3.01 11.3 11.1 110 2.54 <0.01cv% 47 54 39 46

195 (E) median 4.50 9.50 10.9 82.2 2.50 <0.01mean 4.20 10.3 11.1 77.7 2.65 <0.01cv% 42 45 27 27 43

205 (E) median 2.79 6.69 3.9 83.9 2.20 <0.01mean 3.62 6.79 4.7 132 2.30 0.56cv% 48 46 47 64 54 23

47

to have the highest organic carbon content and the Tay thelowest. Much of the data for the Tay samples is below thelimit of detection of 0.2% for organic carbon and thereforecannot be reliably used to normalise the contaminant data(see below). The organic carbon content of offshore siteswas intermediate between these two extremes.

Normalisation of data to organic carbon contentMany trace organic compounds are preferentially adsorbedonto the organic fraction of sediment. The affinity ofhazardous organic compounds for sediments depends ontheir solubility in the overlying waters, the octanol waterpartition coefficient (K

ow) is used as a measure of this (see

section 7.5.1). The octanol water partition coefficient canbe used to derive Koc, which is a sediment partitioncoefficient normalised to organic carbon. K

oc can also be

derived empirically through experimentation. Koc

forcompounds in NMP are given below together with sedimentaction levels in Table 8.4. Sediment action levels are derivedfrom the relevant EQS for the overlying waters assumingequilibrium partitioning between solid and aqueous phases(GCSDM, 1994; Webster and Ridgway, 1994).

These data show that γ-HCH has a low affinity for sedimentswhereas PCB (7 ICES congeners) have a high affinity.

The NMP data have been normalised to the organic carboncontent to assess to what extent the variations incontaminant concentrations between sites are a consequenceof the variations in organic carbon. Data normalised in thisway are presented in Table 8.5 (overleaf ) and in map formin Fig. 8.4(below): results below the limit of detection arerepresented as open circles.

Table 8.4 Partition coefficients and proposed sedimentaction levels for organic contaminants

Compound Koc

Sediment actionlevel µg/g-oc

γ-HCH 1 950 0.04∑PCBs 314 0001 2.312

HCB 37 150 1.11ppDDT 7 205 0.16ppDDE 29 673 0.297Dieldrin 7 205–22 810 0.07–0.23Endrin 7 205 0.036

Notes:1mean K

oc value for a mixture of Arochlors commonly found

in UK waters.2sum total for 7

ICES congeners (28, 52, 101, 118, 138, 153,

180).

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°8°W 6°W 4°W 2°W 0°

PCB (ICES 7)

10 4 2

Total DDT

20 2 1 0.20.4

HCB DIELDRIN

100 50 102010 5 2 1

Figure 8.3Summary of spatial distribution of organic contaminants (∑ICES 7 PCBs, ∑DDT, HCB and Dieldrin) in sediments from NMP sites. Concentrations (µg/kg) are presented asarea proportional symbols; scale symbols are shown in the top left hand corner of each plot. Open circles are used where the concentrations is below the detection limit.

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0° 8°W 6°W 4°W 2°W 0°8°W 6°W 4°W 2°W 0°

4 2 0.8 0.4

Total DDT (normalised)

8°W 6°W 4°W 2°W 0°

PCB (ICES 7) (normalised)

10 4 220 40 20 48 4 2 0.40.8

HCB (normalised) DIELDRIN (normalised)

Figure 8.4Organic contaminant (∑ICES 7 PCBs, ∑DDT, HCB and Dieldrin) concentrations normalised to the organic carbon content of sediments at NMP sites. Concentrations(µg/g

oc) are presented as area proportional symbols, scale symbols are shown in the top left hand corner of each plot. Open circles are used where the concentrations were below

the detection limit and normalisation was therefore not possible.

48

8.2.2.3 PCBIn this spatial survey the highest concentrations of PCBwere found in the Forth and Clyde estuaries, which are bothindustrialised estuaries and contain the most organic richsediments. When the data are normalised to organic carbonthe contrast in concentrations between sites is much reduced,i.e. a dominant factor controlling PCB content is the organiccarbon content of the sediment. The concentration of PCBat site 75 in the Clyde is close to the sediment action level.This site is the furthest upstream site and close to a knownhistorical source.

8.2.2.4 HCBThe highest concentrations of HCB are found in the Forthand this is still the case when the data are normalised toorganic carbon. Concentrations in the Forth are two ordersof magnitude greater than elsewhere in Scotland, reflectingknown historic inputs (Harper et al., 1992). Theconcentrations at sites 185, 195 and 205 were close to thesediment action level. These are sites adjacent to andupstream of the discharge. This illustrates the ability ofsediment-bound contaminants to become distributed bothupstream and downstream of a discharge in response to theseasonal movement of sediments in the system.

8.2.2.5 DDTThe highest concentrations of DDT are found at theintermediate site in the Clyde and estuarine sites in theForth. Normalising the data to organic carbon decreasesthe difference in concentrations between sites. The sedimentsin the Forth and Clyde estuaries are still shown to containrelatively high concentrations of DDT although concen-trations are below the sediment action levels.

8.2.2.6 DieldrinAbsolute concentrations of dieldrin are generally low, andagain the highest concentrations are found in the Forthestuary. Normalised data show the highest concentrationsoccurring in the Clyde at the intermediate site. Concen-trations at this site were close to the sediment action level.

8.2.3 ConclusionsOrganic compounds are associated with organic carbon inthe sediments. A partition coefficient (K

oc) describes this

affinity for organic carbon. Values for Koc

show the followingorder of propensity to absorb onto sediments: PCB > DDT> HCB > Dieldrin, Endrin > γ-HCH.

The sediments of the Forth and Clyde estuaries have arelatively high percentage of organic carbon, and thereforethey also contain relatively high concentrations of traceorganic contaminants. The data have been normalised toorganic carbon content to remove this source of variabilitybetween sites. Normalised data reveal contamination of theClyde estuary with PCBs, and the Forth and Clyde withDDTs. The survey did reflect the known significantcontamination of sediments in the Forth estuary with HCB.

Table 8.5 Concentrations of organic contaminants insediments from NMP sites, normalised to organic

carbon (µg/goc

)

Site ∑PCBs ∑DDTs HCB Dieldrin

Sediment 2.31 1.11 0.07–0.23action level

Solway25 (O) mean 0.212 0.068 0.006 0.0046

cv 25 55 85 98

Clyde35 (O) mean 0.189 0.132 0.007 nq

cv 20 171 2645 (I) mean 0.579 0.329 0.010 0.058

cv 15 130 28 11955 (E) mean 0.777 0.272 0.017 0.040

cv 19.3 31.0 21.9 14.465 (E) mean 0.670 0.100 0.011 0.139

cv 60 39 42 23675 (E) mean 2.43 0.372 0.012 0.275

cv 55 140 70 119

Highland85 (I) mean 0.227 0.037 0.003 0.005

cv 36 30 50 3595 (I) mean 0.097 0.040 0.0028 0.0033

cv 14 200 17 31105 (O) mean 0.249 0.035 nq 0.010

cv 26 30 74

Tay115 (E)mean nq nq nq nq135 (E)mean nq nq nq nq145 (E)mean nq nq nq nq155 (I) mean 0.323 0.024 0.002 0.005

cv 71 85 117 68

Forth165 (O) mean 0.14 0.008 nq nq

cv 25 107175 (I) mean 0.284 0.221 0.187 0.044

cv 41 20 38 27185 (E)mean 0.284 0.263 2.45 0.061

cv 49 32 50 24.5195 (E)mean 0.218 0.246 1.83 0.062

cv 36 23 51 16205 (E)mean 0.218 0.134 3.90 0.069

cv 44 25 49 33

nq = not quantifiable

49

Little information was gained from the analyses of aldrinand endrin and it is recommended that these determinandsare not included in future surveys.

Replicate analyses reveal relatively high variability betweensamples, especially in the sandy sediments of the Tay. Theability to detect spatial and temporal trends requiresminimisation of this variability. This can be achieved eitherby analysing replicate samples or by replicate analyses ofpools of samples. A critique of these different approaches isgiven by Kelly et al. (1994) and consideration of theseoptions should be used for the future sampling programme.The sampling programme should also concentrate on theForth and Clyde estuaries, with sampling at a lesserfrequency at other sites.

General conclusions are that organics concentrations in theestuaries are greater than those from offshore locations. TheForth contains significantly higher concentrations of HCBthan any other location. The contrast in concentrationsbetween estuarine and offshore sites is greater for PCB, DDTand HCB than for dieldrin, endrin and aldrin. This reflectsthe degree to which these compounds adsorb ontosediments; those compounds with the greatest K

oc rapidly

adsorb onto sediments and are retained within the estuary.

8.3 Analysis of PolycyclicAromatic hydrocarbons(PAH) in NMP Sediments

Among the most well-known chemical carcinogens are thepolycyclic aromatic hydrocarbons (PAHs), many of whichare also potent toxins, mutagens and teratogens. Because oftheir potential health effects they are monitored andinvestigated extensively.

There are several ways by which PAHs may enter theenvironment naturally; by high temperature pyrolysis oforganic materials and incomplete combustion such as in

forest fires, by low to moderate temperature diagenesis ofsedimentary organic material to form fossil fuels, or directbiosynthesis by microbes and plants.

In addition to natural sources, PAH may be introducedanthropogenically from various industrial activities such as;pyrolysis of kerosene to form organic solvents, cokeproduction, drilling activities (i.e. drill cuttings), gasproduction from petroleum, and oil refinery operations.Single compounds are also produced from various industrialactivities. These PAH reach aquatic environments via sewageeffluents, surface run-off, deposition of airborne particlesand spillages. PAH dominated by unsubstituted species aremainly anthropogenically generated by combustion andvarious industrial processes, whereas most naturally-derivedPAHs show alkyl substitution.

PAHs were not mandatory determinands in the NMP andthe following results derive from just nine of the 18 ScottishNMP sites. Sixteen individual unalkylated PAHs (recognisedby the US EPA as priority pollutants) were determined.

PAHs were not included in the NMAQC scheme, andconsequently QA is provided by a Certified ReferenceMaterial (CRM, HS-5), the results of which are includedin Table 8.6 and recorded as individual, ring groups, andtotal PAH concentrations (µg/kg dry weight). NMP PAHconcentrations are also graphically displayed as areaproportional symbols in a series of maps showing total 2-,3-, 4-, and 5/6-ring PAH concentrations (Fig. 8.5).

8.3.1 Naphthalene and 3-ringcompounds

Concentrations of naphthalene ranged from 18 to 56 µg/kg, with all sites having detectable levels (exceptions are sites135a and 145a with 0.02 µg/kg). Comparable concen-trations of naphthalene have been found in the central andnorthern North Sea, the Skagerrak and Kattegat (1–55 µg/kg (1)), and lower levels in Sullom Voe (3–13 µg/kg (2)).At NMP 135a (Tay estuary, Flisk Point/Dog Bank) and 145a

59°N

58°N

57°N

56°N

55°N

8°W 6°W 4°W 2°W 0° 6°W 4°W 2°W 0° 6°W 4°W 2°W 0°

Total 2-ring PAH

30 12 6 250 125 2550 600 300 6012060

Total 5/6-ring PAHTotal 4-ring PAH

6°W 4°W 2°W 0°

50 25 10 5

Total 3-ring PAH

Figure 8.5Total concentrations of 2-, 3-, 4- and 5-ring PAH compounds in sediments from NMP sites. Concentrations (µg/kg) are presented as area proportional symbols; scale symbolsare shown in the top left hand corner of each plot.

50

(Tay estuary, Balmerino/Kingoodie) the levels of naph-thalene are quoted as 0.02 µg/kg. From the chromatogramsproduced it was evident that naphthalene was present, butat concentrations too low to integrate from the set ofstandards run. However, this may be a procedural problemand not a true result (i.e. loss of naphthalene from sample).

Acenaphthylene, acenaphthene, fluorene, and to a lesserextent anthracene, are present only in trace amounts at allnine sites. This may be an effect of the extraction process,as the CRM also shows lower than expected levels for thesePAHs. Phenanthrene makes up the bulk of total 3-ring PAHat all sites, which ranges from 3 to 40 µg/kg (phenanthrenecontributing 83% and above of the total 3-ring PAH

Table 8.6 Concentrations (µg/kg dry weight) of individual and grouped PAH in NMP samples

Location NMP % NAP ACNLE ACNE FLE PA ANT FLU PYR BAA CHRcarbon

Hebrides 85 0.420 27.6 <0.01 <0.01 <0.01 6.76 0.53 9.18 6.68 6.36 9.13Solway (O) 25 0.299 40.7 <0.01 <0.01 <0.01 23.2 3.36 36.9 30.2 26.3 29.4Clyde 35 1.038 56.1 <0.01 <0.01 1.41 34.7 4.14 60.1 51.0 47.9 48.0Moray Firth (O) 105 0.283 21.7 <0.01 <0.01 <0.01 4.26 <0.01 3.28 2.48 1.58 2.93Forth (O) 165 0.323 20.9 <0.01 <0.01 <0.01 5.63 <0.01 1.81 1.76 1.29 <0.01Tay (I) 155 0.322 20.8 <0.01 <0.01 <0.01 8.49 1.25 9.83 11.3 6.34 76.5Tay (E) 135a 0.092 0.02 <0.01 <0.01 <0.01 18.9 0.84 7.0 10.9 11.1 37.0Tay (E) 135b 0.095 28.4 <0.01 <0.01 <0.01 7.47 0.48 3.97 3.42 0.88 1.46Tay (E) 115a 0.075 17.8 <0.01 <0.01 <0.01 2.7 <0.01 1.07 1.25 0.63 1.16Tay (E) 115b 0.078 19.0 <0.01 <0.01 <0.01 3 <0.01 1.02 1.05 1.11 <0.01Tay (E) 145a 0.114 0.02 <0.01 <0.01 <0.01 8.1 <0.01 8.27 6.84 3.36 4.73Tay (E) 145b 0.107 19.7 <0.01 <0.01 <0.01 22.7 4.68 23.5 25.0 17.1 17.5

CRM HS-5 - - 1 38.9 2.41 4.74 28.7 2 173 85.6 7 179 3 155 1 184 1 784Expected values 250 150 230 400 5 200 380 8 400 5 800 2 900 2 800Range ±70 ±100 ±100 ±1 000 ±150 ±2 600 ±1 800 ±1 200 ±900

Table 8.6 (continued)

Location NMP BBF BKF BAP ICDP DBAHA Total Total Total Total Total2-ring 3-ring 4-ring 5/6 ring PAH

Hebrides 85 37.4 32.9 10.6 <0.01 <0.01 27.6 7.29 31.4 80.9 147Solway (O) 25 63.8 60.7 33.2 19.1 <0.01 40.7 26.5 123 206 396Clyde 35 134.2 126.5 75.9 102.1 1.62 56.1 40.3 207 551 854Moray Firth (O) 105 12.3 9.18 5.83 4.09 <0.01 21.7 4.26 10.3 39.1 75.4Forth (O) 165 2.34 <0.01 3.36 <0.01 <0.01 20.9 5.63 4.86 6.44 37.8Tay (I) 155 19.6 17.2 10.7 3.3 <0.01 20.8 9.74 104 62.0 196Tay (E) 135a 16.5 2.54 65.2 <0.01 <0.01 0.02 19.7 66.0 86.5 172Tay (E) 135b 2.48 <0.01 1.27 <0.01 <0.01 28.4 7.95 9.73 5.10 51.2Tay (E) 115a 1.11 <0.01 2.48 <0.01 <0.01 17.8 2.72 4.11 3.59 28.2Tay (E) 115b 1.06 <0.01 3.22 <0.01 <0.01 19.0 2.99 3.18 4.28 29.5Tay (E) 145a 13.5 11.9 5.73 3.88 <0.01 0.02 8.12 23.2 41.0 72.3Tay (E) 145b 20.2 20.8 20 1.34 <0.01 19.7 27.3 83.1 69.2 199

CRM HS-5 1 014 1 403 758 1.22 319Expected values 2 000 1 000 1 700 200 1 300Range ±1 000 ±400 ±800 ±100 ±700

concentration). Concentrations of phenanthrene in thecentral and northern North Sea, the Skagerrak and Kattegatrange from 1 to 150 µg/kg (1), and phenanthrene/anthracene concentrations in Sullom Voe range from 11 to300 µg/kg (2).

8.3.2 4-ring compoundsWith the exceptions of chrysene at NMP 165 (OffshoreForth) and NMP 115b (Tay estuary, Broughty Castle),fluoranthene, pyrene, benz[a]anthracene and chrysene werepresent at all nine sites. Total 4-ring PAH concentrationwas generally <50 µg/kg with roughly the same concen-trations of the four 4-ring compounds. Exceptions includeNMP 155 (Tay intermediate) and NMP 135a (Tay estuary,

51

Flisk Point/Dog Bank), which have larger concentrationsof chrysene. NMP 25 (Solway Firth) and NMP 35 (Firthof Clyde) have higher concentrations of all four 4-ringcompounds with total 4-ring concentrations of 123µg/kgand 207 µg/kg respectively. Concentrations of fluor-anthene/pyrene in Sullom Voe range from 14 to 183 µg/kg(2).

8.3.3 5-ring and 6-ring compoundsWith the exception of di-benz[a,h]anthracene, all5-ring (benzo[b]fluoranthene, benzo[k]fluoranthene,benzo[a]pyrene, and 6-ring compounds (indeno[1,2,3-cd]pyrene, and benzo[g,h,i]perylene) were present insignificant concentrations at NMP sites 25 (Solway Firth),35 (Firth of Clyde), 105 (Moray Firth), and 155 (Tay inter-mediate). Total 5- and 6-ring PAH concentrations rangedfrom 4 to 551 µg/kg.

Concentrations of benzo[a]pyrene ranged from 1 to 76 µg/kg. In the central and northern North Sea, the Skagerrakand Kattegat benzo[a]pyrene ranges from 0.6 to 240 µg/kg(1), and benzofluoranthenes/benzo[a]pyrene/perylene con-centrations in Sullom Voe range from 36 to 317 µg/kg (2).

8.3.4 GeneralTotal PAH concentrations ranged from 28 to 854 µg/kg.Since PAHs have a low solubility and hydrophobic naturethey tend to be adsorbed by inorganic and organicparticulate matter in the water column and gradually settleinto the sediment, where they are less susceptible tophotochemical and biological oxidation. The relatively highpercentage of carbon at NMP 35 (Firth of Clyde), coupledto its close proximity to highly populated/industrialised

areas, may be the reason for consistently higher PAHconcentrations.

In general, NMP sites closest to shore show the greatestconcentration of total PAH with the exception of NMP115 (Tay estuary, Broughty Castle), which also had thelowest percentage carbon value. NMP sites 85 (Hebrides,Minches), 105 (Moray Firth), and 165 (Offshore Forth/Tay) all had lower concentrations of individual and totalPAH. In the Tay estuary concentrations of PAH tended toincrease with increasing percentage carbon levels, with thehigher concentrations occurring at NMP 135 (Flisk Point/Dog Bank) and 145 (Balmerino/Kingoodie), which lie closerto shore.

Lower molecular weight compounds such as naphthaleneand phenanthrene are produced from combustion and oilsources, and therefore high levels of 2- and 3-ringcompounds would suggest some recent input of oil to thesediment, as PAHs, like aliphatic hydrocarbons, weather,with naphthalene and 3-ring PAHs going first.

NMP 115a/b with low percentage carbon values had lowerconcentrations of 3-, 4-, 5-, and 6-ring PAHs, and wererelatively higher in 2-ring PAHs

As 4-, 5-, and 6-ring PAHs are less volatile, less bio-degradable, and more readily adsorbed to particulate matter,these groups make up the bulk of total PAH at sites withhigher percentage carbon levels. High levels of 5-, and 6-ring compounds in areas unlikely to be contaminated byoils probably derive from the deposition of windbornecombustion products.

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The lack of coordination and comparability betweenmonitoring data from different organisations was a drivingforce in the creation of the NMP. The programme initiatedin the early 1990s set about correcting this unsatisfactorysituation. This report summarises the regional results fromthe implementation of the NMP in Scotland.

Close collaboration between participating organisationswithin Scotland has ensured that the survey and analyticalwork associated with the requirements of the NMP havelargely been met, and that high quality data have beengenerated. Coverage was particularly good for the benthicsurvey and also for contaminants in water and sediments.There were, however, notable gaps in the bioaccumulationwork; these were principally associated with the non-availablity of target species. Survey completeness was alsoless satisfactory for the biological effects component of thework.

The results from the benthic survey indicated that therewas no evidence to suggest that pollution impacts wereidentifiable at many sites. Natural variation between eastand west coast faunas, site sediment characteristics, salinitygradients and stresses and natural variation in organicenrichment are likely to be responsible for much of themeasured variation in biomass and community structure.The application and interpretation of the more specialisedbiological effects tests (e.g. oyster embryo bioassay andEROD) were less complete. In some cases the requiredtechniques were either not available to all participants orthey have been applied only in limited geographical areas.

In shellfish (mussels) concentrations of the metals cadmiumand lead, and perhaps of mercury to a lesser extent, appearto be strongly influenced by sediment concentrations ofthese metals, confirming that their mode of feeding byfiltration of particulate material plays a major role in theuptake of metals. Metal concentrations were generally higherin the inner Forth and Clyde estuaries, with a concentrationgradient to seaward. Relatively high metals concentrationswere also observed in mussels collected at Broughty Castleon the north shore of the Tay estuary, suggesting that thissite is subject to sewage pollution and/or a local industrialiseddischarge. The high mercury concentrations reported inBroughty Ferry mussels deserve further investigation.

In fish liver the highest cadmium concentrations were foundin dab from the offshore Moray Firth, the intermediate Tayand the offshore Tay/Forth sites. The highest leadconcentrations were for plaice collected at the Tayintermediate and Tay/Forth offshore sites. The results havehighlighted the fact that the two NMP target species, daband flounder, do not produce comparable data either for

9. Summary & Conclusions

cadmium in liver, or for mercury and arsenic in fish muscle.It is important that results for these metals should becompared only for fish of the same species.

Although less complete than some other parts of the surveythe organics in shellfish work indicated that mussels fromthe Clyde estuary contained higher levels of total PCBs thanthose collected from the Forth Estuary. Clyde mussels fellinto the “medium” level of contamination whilst Forthmussels lay in the “lower” level, in relation to JMGguidelines. The assessment of spatial trends and identi-fication of “hot-spots” of organic contamination in musselsfrom Scottish waters proved difficult as there wereinsufficient data to fulfil the aims of the NMP. Futuremonitoring plans should address the problems that areresponsible for this lack of data, e.g. mussel availability andanalytical protocols.

Fish liver collected from the Forth estuary and Forthintermediate stations contained the highest levels of PCBsreported. Concentrations fell within the “medium”contamination band, with regard to guidelines issued bythe JMG. PCB concentrations at all other sites reported fellbetween the “lower” and “medium” bands. Organochlorinecompounds reported at all sites were below “expected”values. As the organochlorine contaminants analysed do notoccur naturally, fish liver sampled from remote sitesunaffected by contamination contained low levels oforganics. Data are available from only one estuarine site.Comparison of organic levels in Scottish estuaries is thereforenot possible. Problems were encountered with obtainingnumbers of fish of the required species. The NMP requiredfish are all bottom feeders and organic contaminants in theliver are related to the content of the underlying sediment.

The spatial distribution of nutrients in Scottish waters showshighest concentrations in the Clyde estuary, notably ofphosphate, nitrite and ammonium: the Forth is next highest,whilst the Tay has the lowest estuarine nutrient concen-trations. Mean nutrient concentrations show a salinitydependence, being higher in fresh waters. Nutrientconcentrations exhibit a strong seasonal dependenceadditional to that on salinity. Temporal variability is greatestin chlorophyll, as expected. Analytical capabilities aresufficient to monitor estuarine and coastal nutrientconcentrations, with few values reported as less than thelimit of detection. The current monitoring frequency isinadequate to characterise episodic bloom events.

The NMP results of metals in sea water presented here aregenerally consistent both with more detailed studies of thethree estuaries and also with wider surveys of the NorthSea. For example Cd concentrations in the Tay estuary were

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typically 0.02-0.04 µg/l. The relatively high concentrationsof dissolved Zn reported for the Tay estuary are notconsistent with previously published data. The high Znconcentrations may be indicative of a contaminationproblem from this element. The highest concentrations ofCr, Ni and Zn were observed in the Clyde estuary.

Analytical methodology was generally adequate for Cr, Cu,Ni and Zn. However, if more realistic data are to be producedfor Cd and Pb some improvements will be necessary. Currentanalytical methodology for Hg also needs to be improved ifrealistic data are to be obtained, especially from offshorewater where concentrations are likely to be <1 ng/l.

Of the organochlorine compounds specified in the NMPto be determined in water, only γ-HCH was detected atconcentrations above the limit of detection of routineanalytical methods at all Scottish estuarine sites. HCB wasmeasurable in the Forth estuary. Concentrations of γ-HCHand HCB were below the relevant EQS at all sites. In theForth, Clyde and Tay estuaries the distribution of γ-HCHand HCB is consistent with known anthropogenic sources.

Trace metal concentrations in sediments from the Tayestuary were generally much lower than those in the Forthand Clyde. In part at least this is attributable to the higherproportion of fine-grained material in the Forth and Clydeestuaries. Normalisation of the data to aluminium, however,indicates that the higher concentrations in the Forth andClyde cannot entirely be accounted for on the basis of thepresence of this fine-grained material. Enrichment factorsof all metals were highest in the Clyde, indicating the greatercontamination of this estuary. The only exception to this

generality was mercury, the highest values of which occurredin the Forth, an estuary with a history of mercurycontamination.

Organic compounds are associated with organic carbon inthe sediments. The sediments of the Forth and Clydeestuaries have a relatively high percentage of organic carbon,and therefore contain relatively high concentrations of traceorganic contaminants. The data have been normalised toorganic carbon content to remove this source of variabilitybetween sites. Normalised data reveal contamination of theClyde estuary with PCBs and the Forth and Clyde withDDTs. The survey did reflect the known significantcontamination in the Forth estuary with HCB. Replicateanalyses reveal relatively high variability between samples,especially in the sandy sediments of the Tay. Generalconclusions are that organic concentrations are greater thanthose from offshore locations. The Forth containssignificantly higher concentrations of HCB than any otherlocation. The contrasts in concentrations between estuarineand offshore sites are greater in PCB, DDT and HCB thanin dieldrin, endrin and aldrin. This reflects the degree towhich these compounds adsorb onto sediments.

The results contained in this report have been entered ontoa National database and used to contribute to a larger reportdetailing the outcome of the NMP throughout the wholeUnited Kingdom. The conclusions and recommendationscontained within the individual sections of this report havecontributed to discussions at a Workshop which wasorganised specifically to debate the future shape of the NMP.The recommendations arising from this Workshop will formthe basis of a redesign of the NMP, which will then beimplemented in all parts of the United Kingdom.

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