accumulation pattern of pesticides in tropical fresh waters

Accumulation Pattern of Pesticides in TropicalFresh Waters

Ravi Bhushan,1w Sangita Thapar1 and R. P. Mathur2

1 Department of Chemistry, University of Roorkee, Roorkee 247 667, India2 Department of Civil Engineering, University of Roorkee, Roorkee 247 667, India

High-performance liquid chromatography has been used to study the persistence of commonly usedorganophosphorus and carbamate pesticides — carbaryl, carbendazim, carbofuran, dimethoate, malathion andmethyl parathion in river water in the presence of bottom sediment in laboratory aquaria. The fate of pesticidesin water and sediment in pre- and post-monsoon water from three sources has been compared. It has beenestablished that rapid degradation occurs once the pesticide leaches into sediment from water. Degradation wasat a much faster rate in post-monsoon water and sediment. It was fould that pH and organic matter content affectrate of decay. © 1997 by John Wiley & Sons, Ltd.

Biomed. Chromatogr. 11, 143–150, 1997No. of Figures: 9. No. of Tables: 0. No. of Refs: 10.

Keywords: Pesticides, water, sediment, organophosphates, carbamates, pH, hardness, organic load, persistence, HPLC.

INTRODUCTION

Pesticides in water cause massive fish kills and contamina-tion of aquatic animals (Fullner and Weissner, 1976) whichwould ultimately be consumed on the table and enter humanbody tissues. Most of the information generated onpersistence in fresh water in temperate regions is of littlerelevance to tropic situations since the high temperatures inthe tropics encourages volatilization of pesticides and rich,humid organic matter fosters rapid biodegradation. Theresearch reported herein was carried out in the Western UPregion of the Indian sub-continent. India, with its tropicaland sub-tropical climate, has a distinct monsoon season.This influences the persistence pattern to a considerableextent. A number of authors have commented on thedifferences in pre- and post-monsoon water with respect toclimate response (Gupta, 1986; Waite, 1984).

This study was undertaken to determine the persistencepattern of selected pesticides in water in the presence ofbottom sediment. Laboratory-scale studies were undertakenin aquaria, to simulate mini-ponds. In spite of all attempts toemulate natural conditions, significant differences remain.Pesticides in a river would be rapidly removed by the flow,away from the point of introduction. Dilution factors wouldalso play a critical role. Environmental factors in the field,such as climate and ambient temperature, would beexpected to influence degradation. However, it is possible todraw certain conclusions about the general behaviour ofthese pesticides in an aquatic system and this has beenattempted in the present work.

EXPERIMENTAL

The Waters Associates (USA) liquid chromatographicsystem consisting of two high pressure pumps (M 501) with

a pressure and flow capability of 6000 p.s.i. and 9.9 mL/min, respectively, was used. A model 680 automatedgradient controller was used to programme the elutionsystem and to produce the gradient profiles. Eluents weremonitored using a Lambda-Max Model 481 variablewavelength spectrophotometer with a 5 mL cell andrecorded using a Waters 740 data module. HPLC equipmentfrom Merck-Hitachi (Darmstadt, Germany) was also used,consisting of an L-6200A intelligent pump, L-4250 UV-visvariable wavelength absorption detector and a D-2500chromato integrator. The column was an octadecyl bondedphase mBondapak C18, 30 cm33.9 mm.

Operating conditions. Column temperature, ambient; chartspeed, 5 cm/min; injection mode, 25 mL Hamilton syringe(Mode # 802 N) U6-K universal injector (Syringe-loopinjector); recorder range, 10 mV. Filtration assembly, Milli-pore (Milford, MA, USA) assembly with filters of pore size0.45 mm and 0.50 mm porosity, solvent compatible.

Reagents/Solvents. Acetone, methanol, acetonitrile anddichloromethane were all chromatography grade from E.Merck. Sodium sulphate, acenaphthene, and buffers wereanalytical grade from E. Merck. PCP, ethion, phorate and allstandard pesticides were from DARC and Union Carbide.All solvents were degassed by simultaneous warming(gently) and evacuation for 15 min. Double-distilled waterwas filtered through a 0.45 mm Millipore assembly anddegassed before use.

Selection of chromatographic variables. The chromatogramswere run at a flow-rate of 1.25 mL/min for malathion andmethyl parathion and at 1.00 mL/min for the rest. Acetoni-trile:water (70:30 v/v) was selected as the mobile phase and221 nm as the working wavelength for all pesticides exceptcarbendazim, for which methanol:water (70:30 v/v) at254 nm gave better resolution.

Extraction. An endeavour was made to evolve a generalextraction scheme which could be applied satisfactorily toboth classes of compounds in aqueous samples. Methylenew Correspondence to: R. Bhushan.

CCC 0269–3879/97/030143–08 Received 20 June 1996© 1997 by John Wiley & Sons, Ltd. Accepted 16 September 1996

BIOMEDICAL CHROMATOGRAPHY, VOL. 11, 143–150 (1997)

chloride, methylene chloride+sodium chloride (100:2.5),and methylene chloride+sulphuric acid (50% until the pHdropped to 4.0), were used as the extracting media; acomparison of the three methods is shown in Fig. 1. Thefinal scheme used for the persistence studies was as detailedin Fig. 2a, b. Partial cleanup was affected using Sep-Pakcartridges (C18).

Sampling. Integrated samples of water with sediment werecollected across three rivers — the Solani, the Yamuna andthe Hindon — to represent water bodies fed predominantlyby rural sources, urban run-off and industrial effluent. Thesampling sites are shown in Fig. 3. Table 1 records thephysico-chemical parameters of water (Greenberg et al.,1980; Mathur, 1985).

Studies in a static environment cannot fully compare witha dynamic system of a river. Dissolved oxygen DO depletesrapidly in aquaria while atmospheric oxygen continuouslydissolves in a flowing system. The aquaria were aerated atregular intervals. Losses due to evaporation were made upby adding unspiked water. Photodegradation would alsocontribute to a certain extent in the riverine system.Pesticides like carbaryl are especially sensitive to sunlight.The aquaria were exposed to sunlight for 6–8 h a day.

The samples were spiked with pesticides (5.0 p.p.m.) andaliquots were removed at regular intervals and extracted asper methods established. Sediment samples were extractedby the method for soils developed by Grou and Radulescu(1983) as detailed in Fig. 2b (after characterization usingmethods specified by Nikol’skii, 1963 and ISI 2720, 1976)except for the absence of any water in the extractingmedium. Sampling was done in triplicate. Blank watersamples run by HPLC showed no detectable residues of thesix pesticides. Water samples were arranged, as far aspossible, to imitate a field environment. Pentachlorophenol(PCP) was selected as the internal indicator for carbamateswhile standard ethion, another organophosphorus pesticide,was used for malathion, dimethoate and methyl parathion.The level of pesticides was measured at 0, 6 and 18 hfollowed by 2, 4, 6 to 16 days and then once every threedays. The pH of the water was noted frequently. Pesticidecontent was measured in water and after agitation ofsediment, in both pre- and post-monsoon samples.

RESULTS AND DISCUSSION

The six pesticides under investigation showed a favourabledistribution between methylene chloride and water. The

differences in several of the documented methods arise onlyfrom the pre-treatment of the sample and the amount ofsolvent used for extraction and clean-up. The effect of thesefactors on the resultant efficency was evaluated. Three grabsamples were initially screened for pesticide content. Sincethese six pesticides were not found in the samples at levelsabove the limit of detection, microlitre amounts of theformulations were diluted with the water samples toevaluate chromatographic behaviour of the extracts andrecoverability of the pesticides from the matrix. Animportant observation was that the presence of some notablepeaks did not coincide with the peaks of the six pesticides,further identification was not done. Their elution early in thechromatogram indicated their polar nature.

Figure 1 compares the three techniques. Organophos-phate extraction appeared to suffer little from lack of samplepreparation while carbamates clearly extracted better afterdigestion with sulphuric acid, as suggested by Grou andRadulescu (1983). This could be because acidic mediastablize most carbamates and alkaline media hydrolysethem. In addition, they assist in the formation of a well-defined interface when partitioning with an organic solvent.The improved stablity aids higher recovery. No singlemethod was superior for all six pesticides but methylenechloride:sulphuric acid showed consistently good recoveryand hence was selected as the method for further fieldstudies. The uitlity of Sep-Pak C-18 cartridges in pre-concentration and clean-up came out clearly during thestudies on water. Samples eluting out of the cartridge at the

Table 1. Physico-chemical characteristics of water

Total

Sampling Temp. D.O. BOD COD Cond. TDS hardness

station (°C) pH (mg/1) (mg/1) (mg/1) mho (mg/1) (mg/1)

(Pre-monsoon)

S1(S) 28.6 8.24 7.4 NIL 4.1 487.2 231 142

S2(Y) 33.2 8.00 5.7 0.5 6.1 312.7 160 130

S3(H) 30.1 7.70 5.3 1.4 9.2 272.1 133 136

(Post-monsoon)

S1(S) 28.9 8.5 7.8 NIL 4.4 581.0 311 181

S2(Y) 34.2 8.2 6.7 2.7 8.9 532.1 272 155

S3(H) 32.7 8.0 5.5 3.2 18.1 402.8 209 171

S, the Solani; Y, the Yamuna; H, the Hindon, as per Fig. 3

D.O.=Dissolved Oxygen; BOD=Biological Oxygen Demand;

COD=Chemical Oxygen Demand; Cond.=Conductance;

TDS=Total Dissolved Solids

Figure 1. Comparison of the three methods for total recoveryfrom water. DIM, dimethoate; MAL, malathion; METHPARA,methyl parathion; CAR, carbaryl; CBDZM, carbendazim; CFRN,carbofuran.

R. BHUSHAN ET AL.144

© 1997 by John Wiley & Sons, Ltd. BIOMEDICAL CHROMATOGRAPHY, VOL. 11, 143–150 (1997)

clean-up stage gave neater chromatograms and allowedmeasurements at lower concentrations.

Persistence

Salient features of the sampling sites are given below.

Sampling site S1. This site is situated in the foothills of theShiwaliks on the Solani river, a predominantly limestone

area. Being seasonal, the Solani gets some water only afterthe first few showers. After the substantial monsoons thatthis area experiences, it becomes a full-blown river whichslowly diminishes by the end of the year. This accounts forthe relatively high hardness and alkalinity of its water. Lowhuman and industrial activity account for the higher DO andnegligible biological oxygen demand BOD.

Sampling site S2. This site is situated on the Yamuna river,which has its source in the Himalayas and traverses through

Figure 2. Extraction of pesticides from water samples.

ACCUMULATION OF PESTICIDES IN TROPICAL FRESH WATERS 145


several highly populated and industrialized areas before itmeets the Ganga at Allahabad. It receives large quantities ofwastes during its flow from domestic and industrialdischarges and its several tributaries. In the upper stretch,large quantities of slate and limestone leach into itaccounting for its hardness and alkalinity.

Sampling sites. This site is located on the Hindon river, atributary of the Yamuna, originating north of Saharanpur(UP) in the lower Shivaliks. In its course, it passes throughdensely populated and highly industrialized areas. In thepre-monsoon season, industrial effluents predominantlyfeed the river. This area has good precipitation in themonsoon and this has a diluting effect on the pollutionload.

Figures 4a–9d portray the disappearance of the sixpesticides in pre- and post-monsoon season for all threewater samples, detailing water and water plus sediment(stirred) separately for the three sampling stations at Solani(S1), Yamuna (S2) and Hindon (S3).

A survey of results for water alone (Fig. 4a, b–9a, b)would imply that the pesticides deplete rapidly in theaqueous environment. Comparison with the results forwater plus sediment (Fig. 4c, d–9c, d), however, producedsome interesting observations. The curve for pesticidedepletion from day 0 to day 4 (taking the example ofcarbaryl, for instance) in water coincided with a distinctincrease in its concentration in the sediment fraction. Thiswould mean that there is a strong adsorption onto sedimentand most of the pesticide was transferred onto the sediment

surface. This was followed by degradation of the pesticide.The dissipation process appeared to be slower than in soils(Thapar et al., 1995) because of the static nature of theenvironment for these experiments, the greater microbialand organic load in soils as compared with sediment and themore congenial environment for decay. As indicated by thelater stages of the decay curves degradation was more rapidin sediment than in water (day 5 onwards). From the pointwhere there was build up of maximum concentration insediment its degradation appeared to follow a regularexponential pattern. This behaviour was seen to be commonfor all the pesticides except for carbendazim, which showedunusually high concentrations. Its behaviour could not beassigned any explanation at face value. Perhaps a study ofthe binding and speciation of pesticides on sedimentsurfaces would offer some rational argument. The composi-tion of sediment could not be assessed but pesticidesappeared to adsorb very strongly onto it. Equilibriumconcentrations of residues and their bio-availability areregulated by adsorption–desorption and precipitation–dis-solution mechanisms. These associations render theresidues less or more bio-available, as the case may be. Thisbecomes of greater significance especially for those sedi-ments contaminated heaviy by organic wastes as in the caseof Yamuna and Hindon. Bottom sediments then becomesmore reduced due to continuous release of electrons to theenvironment through the respiration processes of the micro-organisms. Further changing environmental parameters likepH affect remobilization of pesticides from sediment.

This became increasingly clear from the decay curves for

Figure 3. Sampling sites for water.



Figure 4. Persistence of carbaryl in water (a) and (b), persistence of carbaryl inwater and sediment (c) and (d). Y, Yamuna; H, Hindon; S, Solani.

Figure 5. Persistence of carbendazim in water (a) and (b), persistence ofcarbenduzim in water and sediment (c) and (d). Y, Yamuna; H. Hindon; S,Solani.



Figure 6. Persistence of carbofuran in water (a) and (b), persistence ofcarbofuran in water and sediment (c) and (d). Y, Yamuna; H, Hindon; S, Solani.

Figure 7. Persistence of dimethoate in water (a) and (b), persistence ofdimethoate in water and sediment (c) and (d). Y, Yamuna; H, Hindon; S, Solani.



Figure 8. Persistence of malathion in water (a) and (b), persistence of malathion inwater and sediment (c) and (d). Y, Yamuna; H, Hindon; S, Solani.

Figure 9. Persistence of methyl parathion in water (a) and (b), persistence of methylparathion in water and sediment (c) and (d). Y, Yamuna; H, Hindon; S, Solani.



carbaryl (Fig. 4a–d). The water fraction showed continuousdepletion, while in sediment there was first a build up andthen a rapid dissipation, folowed by a slower step whichcoincided with the stationary phase in water. Karinen et al.(1967) had noted an initial increase in carbaryl content as itslowly dissolved in the water sample. This step was notobserved in this study perhaps because of solubilitybehaviour of the formulation used.

Carbaryl dissipation is highly influenced by pH. This iswhy, in spite of the lower organic pollution load experi-enced in the Solani, degradation was almost at a par withthat observed in the Yamuna and the Hindon, which haveheavy organic pollution. Carbendazim degraded moreslowly, both in water and in water plus sediment, andfollowed similar patterns in all three samples, indicating thelesser influence of pH in this case. Carbofuran degradationwas comparable with carbaryl both in water and insediment.

Malathion dissipation indicated the stronger impact ofadsorption characteristics of sediment for organophos-phates. Its decay was more rapid in the Yamuna and theHindon samples which carry a heavier organic load.Organophosphates are also known to be strongly sorbedonto clay minerals. Influence of pH was not significantlyobserved. Methyl parathion dissipated rapidly after the first2 days and was found only in traces of sediments after 4days. Dimethoate appeared to associate strongly with thesediment as its concentration did not decrease significantlyafter 10 days.

Comparison of pre- and post-monsoon samples showsthat, although increase in organic load, as was the case inpost-monsoon samples, should typically decrease the degra-dation rate because of excessive adsorption sites,degradation, on the contrary, was increased. This would

suggest that pesticides are also closely associated withsediment compounds other than organic matter. Theincrease could be attirubted to (a) the increase in DO, whichencourages microbial proliferation and, therefore bio-degradation; (b) increase in pH which assistsdecomposition; and (c) increased hardness, which wouldmean increased calcium and magnesium content. Thesemay vie with the pesticides for adsorption sites on thesediment surface.

Some salient points that emerge are, first, that themajority of pesticides are adsorbed onto or are stronglyassociated with sediment, and are then released over aperiod of time. Only part of the total residue fraction isadsorbed onto sediment organics. Degradation is influencedby organic matter content but not to the extent expected.Therefore components like clay also contribute as adsor-bents to a significant degree. Second, that pH influencescarbamates to a larger extent than organophosphates.Especially for carbaryl, pH is a critical factor. Hardness ofwater is another salient feature. Degradation is more rapidas hardness increases. This relation requires more researchinput. Dissipation is more rapid under alkaline conditionsowing to the base–neutral nature of most of the pesticides.

Decay in Solani samples can be attributed mainly to thehigher alkalinity and hardness while in the Yamuna and theHindon, degradation due to the microbial load alsocontributes to the total dissipation rate.

Acknowledgements

The authors are thankful to CSIR, India, for financial support (to S.T.).Thanks are also due to Alexander Von Humboldt-Stiftung, Bonn, Germanyfor donating the Merck-Hitachi HPLC equipment (to R.B.).

REFERENCES

Fullner, R. and Weissner, H. (1976). Proc. of Conf. HazardousMaterials, Spills. Am. Inst. Chem. Eng. p. 345.

Greenberg, A. E., Connors, J. J. and Jenkins, D. (eds.) (1980).Standard Methods for the Examination of Water and WasteWater, 15th edn. Jointly prepared and published by: Amer-ican Public Health Association, American Water WorksAssociation and Water Environment Federation, Wash-ington DC.

Grou, E. and Radulescu, V. (1983). J. Chromatogr. 260, 502.Gupta, P. K. (1986). Pesticides in the Indian Environment, p. 34.

Inteprint, New Delhi.Indian Standards, 2720 (1976). Methods for Tests of Soils,

Bureau of Indian Standards, New Delhi, India.Karinen, J. F., Lamberton, J. G., Stewart, N. E., and Terriere, L. C.

(1967). J. Agric. Food Chem. 15, 148.Mathur, R. P. (1985). Manual for Methodology of Physico-

chemical Characteristics of Water, p. 2. Nem Chand & Bros,Roorkee, India.

Nikol’Skii, N. N. (1963). Practical Soil Science Israel Program forScientific translations, p. 105. Jerusalem.

Thapar, S., Bhushan, R., and Mathur, R. P. (1995). Biomed.Chromatogr. 9, 18.

Waite, T. D. (1984). Principles of Water Quality, p. 78. AcademicPress, NY.



accumulation pattern of pesticides in tropical fresh waters

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