geochemistry and the environment division institute of ......mercury and lead concentrations in soil...

Geochemistry and the Environment Division

Institute of Chemistry

Jan Kochanowski University in Kielce

Current issues in establishing geochemical background of trace elements Agnieszka Gałuszka & Zdzisław M. Migaszewski

Outline of the talk

Defining geochemical background

Importance of the knowledge of geochemical

background of trace elements

Methods of establishing geochemical background

– the pros and cons

Tasks for the future


Historical use of the term ”geochemical background”

in exploratory geochemistry and geochemical

prospecting

Hawkes, Webb (1962): ”the normal abundance of an

element in barren earth material” – a lack of anomaly

GEOCHEMICAL PROSPECTING IS A SEARCH FOR

POSITIVE ANOMALIES

Ele

me

nt

con

cen

trat

ion

Positive anomaly

Negative anomaly

Distance

Geochemical background


Environmental approach:

”Geochemical background (…) is a relative

measure to distinguish between natural

element or compound concentrations

and anthropogenically-influenced

concentrations in real sample collectives” – a lack

of man-made pollution (Matschullat et al., 2000)

Ele

me

nt

con

cen

trat

ion

Positive anomaly

Negative anomaly Distance


Pollution source

Geochemical background types in environmental approach


Natural background

Pre-industrial

background

Taken from: Reimann, Garret, 2005; Gałuszka, 2007

Ambient background

Anthropogenic background

Area background

Related terms

Threshold value – the concentration above which all values are considered anomalous = the upper

limit of geochemical background range

Baseline – the present concentration of a given

substance in a given environmental sample,

measured to find any possible changes of

concentrations in the future

Environmental issues What is pollution?

”Pollutant is a substance present in greater than natural concentrations as a result of human activity and having a net detrimental effect on its environment” (Spellman, 1999)

NATURAL CONCENTRATIONS = GEOCHEMICAL BACKGROUND

Anthropocene – “the current interval of time, dominated by human activity” (Crutzen, 2002)

The begining:

Early agricultural practice (8,000 years ago)

Industrial Revolution (about 1760)

1800 (human population hits 1 billion and started to grow at an alarming rate)

Postwar “Great Acceleration” (marked by radionuclides derived from atomic detonations)

Industrial Revolution (about 1760)

How do humans change the environment?

How do humans change the environment?

Trace elements in the environment

Natural sources of trace

elements

Anthropogenic sources of

trace elements

Concentrations of trace

elements measured in

environmental samples

+

Anthropogenic trace element input

The main anthropogenic sources of trace elements:

Industry (mining, metallurgic, chemical etc.) – As, Cd, Cr, Cu, Hg, Ni, Mn, Pb, Zn

Power generation – As, Cd, Hg, Pb

Traffic – Cd, Mo, Ni, Os, Pb, Pt, Sb, V, Zn

Agriculture – As, Cd, Mn, V, Zn

Waste management – Cd, Cu, Hg, Mn, Ni, Pb, V, Zn

Geochemical calculations

Anthropogenic influence assessment

Enrichment factor (EF) = Ae – element concentration in environmental sample Be – reference element concentration in environmental sample Ac – Clarke value or average shale value of the element Bc – Clarke value or average shale value of reference element

EFs close to unity point indicate crustal origin whereas those greater than 10 are considered to be non-crustal source

Ae ∙ Bc

Be ∙ Ac

Reference (conservative) elements


Si – indicator of amount and distribution of element-poor quartz

Al – indicator of Al silicates, used to account for granular variations of element-rich fine silt and clay size Al-silicates

Fe – indicator of element-rich Fe-bearing clay minerals, Fe-rich heavy minerals and hydrous Fe oxides

Sc – indicator of Sc structurally combined in clay minerals Cs – indicator of Cs structurally combined in clay minerals

and feldspars Li – indicator of Li structurally combined in clay minerals

and micas

Example of the use

Shazili et al. (2007): Interpretation of anthropogenic input of metals in the South China Sea bottom sediments of Terengganu (Malaysia) coastline using Al as a reference element. Aquatic Ecosystem Health & Management 10/1: 47-56

”Enrichment factor (EF) values using Al as a reference element were determined and showed that sampling sites of the major rivers of Terengganu were anthropogenically influenced by Pb and Cd. Sources of pollution are probably sewage, agricultural wastes and atmospheric deposition of Pb from the use of leaded petrol”



Contamination Factor (CF) = Ci – mean content of element in samples taken from

at least 5 sampling sites (μg ∙ g-1 dw) Cn – pre-industrial concentration of element CFs values below 1 indicate low contamination, in the range of 1-3 – moderate contamination, 3-6 – considerable contamination, >6 very high contamination

Ci

Cn

Example of the use

Hoda et al. (2009): Heavy Metals Contamination in Sediments of the Western Part of Egyptian Mediterranean Sea. Australian Journal of Basic and Applied Sciences 3(4): 3330-3336

According to the values of contamination factors (CFs), sediment samples of the western part of Egyptian Mediterranean Sea were classified to be low contaminated by Cr, Cu, Mn, Ni, Zn and moderately polluted by Pb



Pollution load index (PLI) (Tomlinson, 1980)

The PLI is obtained as a concentration factor (ConcF) of each element with respect to the background value:

PLI = n√(ConcF1 ConcF2 … ConcFn) where: Concentration of the element in the sample Background concentration

The PLI represents the number of times by which the element content in the sample exceeds the background concentration

ConcF =

Example of the use

Galán et al. (2002): Residual pollution load of soils impacted by the Aznalcóllar (Spain) mining spill after clean-up operations.

The Science of the Total Environment 286 (1-3):167-179 The soils affected by the Aznalcóllar mining spill contained a significant residual contamination, especially in the vicinity of the river bed (pollution load indices = 3-9). Within profiles the PLI values of the samples decreased with depth, as the source of pollution was deposited on the soil surface during the flood



Geoaccumulation index (Igeo)

Ce

1.5 GB

Ce – concentration of the examined element in the sample

GB – geochemical background concentration According to Igeo values, there are 7 classes of the sample pollution, varying from 0 (unpolluted) to 6 (extremely polluted)

Igeo = log2

Example of the use

Loska et al. (2004): Metal contamination of farming soils affected by industry. Environment International 30(2): 159-165

The index of geoaccumulation was applied in the study of trace element concentrations in soils from Suszec commune (southern Poland). The results showed contamination of soils with Cd, Pb, As, Hg and Sb

SEM image of technogenic particles on pine needle surface, southern part of Magurski National Park

10 μm


Isotopic fingerprint


34S in precipitation

4.0–4.5‰

Soil 1994-1996

Pine needles 1993-1996

Industrial particles 1994-1996

Geochemical tracers


Geochemical tracers are used to assess anthropogenic influence, mainly on waters

Examples of geochemical tracers:

Boron and its isotopes

Strontium isotopes

Lead isotopes

Rare earth elements (REEs) (e.g. gadolinium, cerium)

Boron and its isotopes

gadolinium

Factors influencing concentrations of substances – geochemical variability

So

il h

orizo

n/s

ub

ho

rizo

n

µg ∙ kg-1

Concentrations of Σ17 PAHs in soil profile at Psarska Mt.

(Holy Cross Mts) in 2001

Concentrations of Σ17 PAHs in soil profile in Wymysłów

(Holy Cross Mts) in 2001

Mercury and lead concentrations in soil profile at Psarska Mt.

Soil horizon/ subhorizon

Year Hg (μg ∙ kg-1) Pb (mg ∙ kg-1)

Ol 1998 131 28

2000 123 62

Ofh 1998 253 95

2000 193 77

ABC 1998 73 24

2000 49 23

BC 1998 39 10

2000 35 15

R 1998 - -

2000 4 <5

Natural geochemical variability

Trace element concentrations in various environmental samples

As in water: 60 g ∙ L-1

As in soil: 171 mg ∙ kg-1

As in sediment: 1138 mg ∙ kg-1

As in pyrite: 9666 mg ∙ kg-1

Why is the knowledge of geochemical background so important?

In exploratory geochemistry and geochemical prospecting: it enables to indicate anomallies which are crucial in searching for new mineral deposits

In environmental sciences: it defines concentration above which substances are regarded pollutants; it is used to establish quality criteria for soils, waters and sediments

In other areas: health sciences, forensic sciences, land use management etc.

Methods of establishing geochemical background

Direct

(geochemical)

Indirect

(statistical)

Integrated

Direct methods

Historical approach – archival samples collected before Industrial Revolution or samples dated as representing pre-industrial period

Contemporary approach – samples collected in relatively pristine areas, not heavily influenced by anthropogenic activity

MEASURED GEOCHEMICAL

CONCENTRATIONS BACKGROUND

=

Advantages and disadvantages of direct methods

+ The values of geochemical background are easy to establish (means or medians of the results are commonly used)

+ The original results do not require any data processing

– Subjective sample/study area selection criteria

– High costs

– Heavy laboratory workload

– The neccessity of expert knowledge

Indirect methods

Are based on statistical techniques (computational and graphical), which aims at eliminating the outliers from statistical population distribution

Background is represented by non-anomalous concentrations

Traditional formula:

Range of Mean 2

geochemical background standard deviations

=

Example of indirect methods: Pb in the O soil horizon from the Holy Cross Mts

4-σ outlier test

0

50

100

150

200

250

300

0 10 20 30 40

Pb

in

O h

ori

zo

n

(mg

∙ k

g-1

)

Sample #

Mean = 60 mg ∙ kg-1 4 = 244

Geochemical background: Mean 2 = 5-182 mg ∙ kg-1

Iterative 2-σ technique

0

50

100

150

200

250

300

0 10 20 30 40

Pb

in

O h

ori

zo

n

(mg

∙ k

g-1

)

Sample #

1. Mean = 60 mg ∙ kg-1 2 = 122 - 3 values

2. Mean = 44 mg ∙ kg-1 2 = 74 - 1 value

3. Mean = 41 mg ∙ kg-1 2 = 66 -2 values

4. Mean = 35 mg ∙ kg-1

2 = 54 - 1 value

5. Mean = 33 mg ∙ kg-1 2 = 48 Geochemical background: 5-81 mg ∙ kg-1

Calculated distribution function

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40

Pb

in

O h

ori

zo

n

(mg

∙ k

g-1

)

Sample #

0

50

100

150

200

250

300

0 10 20 30 40

Pb

in

O h

ori

zo

n

(mg

∙ k

g-1

)

Sample #

Geochemical background: 5-79 mg ∙ kg-1

Tukey boxplots

Reimann et al. (2005): Background and threshold: critical comparison of methods of determination. Science of the Total Environment 346: 1-16

Cumulative Distribution Function

The histogram and cumulative distribution function curve for arsenic in topsoils (Geochemical Atlas of Europe© 2005, the Association

of the Geological Surveys of the European Union)

Advantages of indirect methods

+ Precision, accuracy and well established techniques of background evaluation

+ Wide selection of different statistical tests, graphical methods, which can be applied in calculating geochemical background

+ The possibility of using the easy available computer programs for data processing

Disadvantages of indirect methods

– Neglecting the significance of natural processes that influence distribution of elements or chemical compounds in environmental materials

– Not considering uncertainty of sample treatment stages, including sampling, sample preparation and chemical analysis

– Background concentrations are understood as non-anomalous (traditional approach in exploratory geochemistry)

Integrated method

It combines both the prerequisite to collect samples in relatively pristine areas, and subjecting the results obtained to statistical calculations

In the first use of integrated method for geochemical background evaluation in the Holy Cross Mts, the samples were collected in forest ecosystems within protected areas and iterative 2-σ technique was applied

Pros and cons of integrated method

+ Samples represent natural geochemical variability and due to low anthropogenic influence, the distributions of results are usually normal, which allows to restrict the data processing

– Subjectivity of selection of the study area

– High costs and heavy laboratory workload

– The neccessity of expert knowledge

Terminology relating to geochemical background in environmental and exploration geochemistry should be systematized

Reliable and plausible methodology of establishing geochemical background concentrations should be worked out

Geochemical background should be taken into account when considering environmental quality criteria

Tasks for the future

Soil screening values for unacceptable risk in selected European countries

mg/kg

Au

str

ia

Cze

ch

R

ep

ub

lic

Fin

lan

d

Ita

ly

Lit

hu

an

ia

Ne

the

r-la

nd

s

Po

lan

d

Slo

va

kia

UK

De

nm

ark

As 50 70 50 20 10 55 22.5 50 20 20

Cd 10 20 10 2 3 12 5.5 20 2 5

Cr 250 500 200 150 100 380 170 800 130 1000

Cu 600 600 150 120 100 190 100 500 - 100

Hg 10 10 2 1 1.5 10 4 10 8 3

Pb 500 300 200 100 100 530 150 600 450 400

Ni 140 250 100 120 75 210 75 500 - 30

Sn - 300 - 1 10 900 40 300 - -

Zn - 2500 250 150 300 720 325 3000 - 1000

”Derivation methods of soil screening values in Europe. A review

and evaluation of national procedures towards harmonization”

Wishing you great backgrounds!

1 hour break for LUNCH

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