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Published online 7 June 2005
Published in J Environ Qual 34:1186-1193 (2005)
DOI: 10.2134/jeq2004.0361
© 2005 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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TECHNICAL REPORTS

Organic Compounds in the Environment

Residues of Endosulfan and Other Selected Organochlorine Pesticides in Farm Areas of the Lower Fraser Valley, British Columbia, Canada

Michael T. Wan*, Jen-ni Kuo and John Pasternak

Environmental Protection Branch, Environment Canada, Pacific and Yukon Region, 201-401 Burrard Street, Vancouver, BC, Canada

* Corresponding author (mike.wan{at}ec.gc.ca)

Received for publication September 22, 2004.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Crop soils, ditch sediments, and water flowing from several farm areas to salmon tributary streams of the Fraser River in the Lower Fraser Valley (LFV) of British Columbia, Canada, were sampled in 2002–2003 to quantify for residues of an organochlorine cyclodiene pesticide, endosulfan (END = {alpha}-endosulfan + ß-endosulfan + endosulfan sulfate). Residues from historical use of other selected organochlorine pesticides, namely, cyclodienes (aldrin, {alpha}-chlordane, {gamma}-chlordane, dieldrin, endrin, endrin aldehyde, heptachlor, and heptachlor epoxide), hexachlorocyclohexanes [{alpha}-benzene-hexachloride ({alpha}-BHC), ß-BHC, {delta}-BHC, and {gamma}-BHC (lindane)], and DDT-related compounds (p,p-DDT, p,p-DDD, p,p-DDE, and methoxychlor) were also determined. Reference and background levels of these pesticides in ditches leading to fish streams were obtained from pristine watershed areas. Varying amounts of END residues were detected in soils (<0.02–5.60 mg kg–1 dry wt.) and ditch sediments (<0.02–3.33 mg kg–1 dry wt.) in mainly three of five farm areas sampled. Likewise, residues (excluding END) of other selected organochlorine compounds such as aldrin, BHC, chlordane, endrin, p,p-DDT, methoxychlor, and their respective major transformation products (endosulfan sulfate, dieldrin, endrin aldehyde, heptachlor, heptachlor epoxide, p,p-DDD, and p,p-DDE) were found in crop soils (<0.02–16.2 mg kg–1 dry wt.) and sediments (<0.02–9.73 mg kg–1 dry wt.). Most of these pesticides (END: <0.01–1.86 µg L–1; other selected organochlorine pesticides: <0.0.1–1.50 µg L–1) were also found in ditch water leading to salmon streams in several farms. The END levels of crop soils from the same LFV study farms in 1994 and 2003 indicated an estimated decline of 22% to 1.35 mg kg–1 dry wt. during that period. This reduction was probably due to the increasing use of alternate pesticides (e.g., organophosphorus compounds). Some possible biological implications of these pesticide residues on nontarget organisms in the LFV are discussed.

Abbreviations: DT50, 50% degradation time • END, {alpha}-endosulfan + ß-endosulfan + endosulfan sulfate • LC50, 50% mortality in a test population • LFV, Lower Fraser Valley


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
HISTORICALLY, large quantities of organochlorine pesticides, notably aldrin, BHC, chlordane, dieldrin, endosulfan, endrin, heptachlor, methoxychlor, and p,p-DDT were used annually in the 1950s to early 1970s in the agricultural areas of British Columbia, notably in the LFV (Szeto and Price, 1991; Van Vliet et al., 2001). Szeto and Price (1991) found that the mean total concentration of END and other organochlorine pesticides (excluding END) in crop soils was 5.76 and 7.05 mg kg–1 dry wt., respectively. About five years later, Environment Canada monitored the same general areas for END residues and found an average of 1.72 mg kg–1 dry wt. in crop soils (Wan et al., 1995). While an accurate comparison of pesticide residue levels cannot be made unless the sampling sites and points were the same, these studies, nonetheless, provided an estimated bench mark for END and other organochlorine pesticides levels in farm soils and waterways about 20 yr after their use was discontinued in the LFV. The use of organochlorine pesticides (except END) was phased out or banned in Canada more than 30 yr ago. The use of END, however, continues to this day. In British Columbia, END was used for the control of boring, chewing, sucking insects and cyclamen mites in fruit trees, greenhouse plants, potatoes, and vegetables (BC Environment, 1995). In recent years, however, it has been used for the control of specific, hard-to-manage soil-dwelling pests, such as those in potatoes and vegetable crops.

The active ingredients of commercial END products consist of a mixture of two isomers, that is, about 67 and 32.5% technical-grade {alpha}-endosulfan and ß-endosulfan, respectively (National Research Council of Canada, 1975; Tomlin, 2002). In soils and water, the degradation time (DT50) for the breakdown of half the original amount of the {alpha}-endosulfan is about one to three months while the DT50 for ß-endosulfan and endosulfan sulfate (the transformation product of both isomers) in both media is more than two years (National Research Council of Canada, 1975). In the LFV, the 1991 survey indicates that the concentration of total END of crop soils adjacent to ditches, ditch sediments, and water averaged 1.72 mg kg–1 dry wt., 0.38 mg kg–1 dry wt., and 0.71 µg L–1, respectively, (Wan et al., 1995). Accordingly, the objectives of this study are to (i) determine the residue concentrations of END in the same LFV farms (as those sampled in 1991) after more than a decade of further use and (ii) audit the environmental levels of residues of selected organochlorine pesticides and their transformation products resulting from historical use in the same areas after these chemicals were phased out more than three decades ago.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Sampling Sites and Procedure
The 1991 sampling sites (Fig. 1) were revisited and resampled, although the crops grown on these sites since that time varied from year to year due to the practice of crop rotation (Wan et al., 1995). Similar criteria were used for selecting ditch characteristics for sampling, namely, ditch size averaged about 1.5 m in width, 0.5 m in depth, and less than 0.025 m3 s–1 flow rate. As well, these ditches must not receive industrial effluents or residential runoff or sewage. They must drain either singly or collectively into the Fraser, Nicomekl, or Sumas Rivers, with crop setbacks of at least 3 m (except for streams in the control sites). Based on these considerations, nine locations were chosen for the study (Fig. 1): four control sites [Coquitlam watershed (A), UBC forest watershed (B), Kanaka Creek head water (C), and Vedder Mt. watershed (D)] and five farm study sites [Sumas Prairie (F), Cloverdale (H), Delta (J), Westham Island (K), and Burnaby (M)]. In addition, five locations of large waterways were selected for sampling: Sumas Canal (E), Nicomekl River (G), Pump Stations (I), Fraser Estuary (L), and Fraser River (N).



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  		Fig. 1. Location of survey and sampling sites.

 
The technique of grab-sampling was applied, with each sample consisting of a composite of 10 subsamples for water and sediment samples (Wan, 1989; Wan et al., 1995). Crop soil samples (also a composite of 10-subsamples/sample) were collected from the same farms (as those sampled in 1995) at random from the top 10 cm with a steel trowel. The sample size for water sample was 1 L, while that for sediments and soils was 0.3 kg. Sampling was conducted four times over a period of one year from June–July 2002, September–October 2002, February–March 2003, and June–July 2003. All samples were stored at 4°C and shipped on the same day to Environment Canada's Pacific Environmental Science Center Organic Chemistry Laboratory (North Vancouver, BC, Canada).

Extraction and Cleanup
The procedure of extraction and cleanup processes for water, sediments, and soils was similar to the one outlined in Wan et al. (1994)( 1995). After volume measurement, each water sample (including suspended particulates) was transferred quantitatively without filtering to a 1-L separatory funnel. The measuring cylinder and the amber bottle storing the water sample were rinsed with 50 mL of pesticide-grade dichloromethane to remove any organochlorine pesticide residues adsorbed onto the glass walls. The water sample was extracted three times, each time with 80 mL of dichloromethane (DCM). The combined extracts were dried with heat-treated anhydrous Na2SO4 (treated at 320°C for 24 h). Sediment and soil samples (approximately 10 g) were extracted once with 60 mL of 2:1 DCM to methanol for 1 h and filtered. They were then partitioned with 60 mL of 2% NaCl solution in a separatory funnel after about one minute of vigorous agitation by hand. The crude extracts were reduced in volume to approximately 2 mL.

The crude extracts were cleaned up by florisil column chromatography. Glass columns (30 cm x 1.1-cm i.d.) with Teflon stopcocks were packed from the bottom with a glass wool plug, 1 cm anhydrous Na2SO4, 8 g of 2% deactivated florisil, and 1 cm anhydrous Na2SO4. The packed columns were prewashed with 50 mL of hexane. The crude extract of each sample was quantitatively transferred to the column, eluted with 150 mL petroleum ether followed by 100 mL 20% ethyl acetate in petroleum ether. The combined extracts were reduced to a volume of 1 mL for water and 2 mL for soil and sediment and used for gas chromatographic (GC) analysis.

A Hewlett-Packard (Palo Alto, CA) Model 5890 Series II GC instrument equipped with dual electron capture detectors (ECD) was used for the determination of all organochlorine compounds except {alpha}-chlordane and {gamma}-chlordane. A split/splitless inlet was used for sample introduction. Two capillary columns were used for analyte identification and confirmation in water and sediment and soil samples: a DB-5 dimethyl-diphenyl-siloxane capillary column (30 m x 0.25-mm i.d., 0.25 µm thick) and a DB-1701 cyanopropyl-phenyl-dimethyl-siloxane capillary column (30 m x 0.25-mm i.d., 0.25 µm thick). The DB-1701 column was used for confirmation only. For the ECD, the detector temperature was 330°C and the detector gas was 32 mL min–1 of 5% methane in argon. Helium at 105 kPa was the carrier gas, under constant pressure mode. Column temperature was programmed as follows: initial 90°C for 2 min; first program rate 10°C min–1 to 160°C, then 3°C min–1 to 280°C and hold for 10 min.

To avoid interference in the DB-5 column by other organochlorine compounds, notably END, residues of chlordanes were independently determined and quantified on a HP6890 gas chromatograph (GC) coupled to a 5973 mass spectrometer (MS). Column temperature was programmed as follows: initial 60°C for 1.5 min; first program rate 20°C min–1 to 180°C, then 3°C min–1 to 230°C, then at the rate of 30°C min–1 to 300°C and hold for 3.5 min, with a run time of 30 min. Helium was used as the carrier gas under constant flow at 1.2 mL min–1. The column was a Restek (Bellefonte, PA) 5MS (30 m x 0.025-mm i.d., 0.25-µm film) and the data were acquired in selected ion monitoring (SIM) mode. Using multiple point calibration, quantification was performed on ion mass 373, with 375 as the qualifier.

Evaluation of Analytical Method and Results
Control samples of water, sediments, and forest soils were collected from pristine tributary creeks of protected, unoccupied, and uninhabited watershed areas of Coquitlam (A), UBC Forest (B), Kanaka Creek (C), and Vedder Mountain (D) of the LFV (Fig. 1). Eight additional 300-g sediment and soil samples and 1-L water samples from the same pristine areas were collected at different times of the year for the quality assurance–quality control (QA–QC) program. These QA–QC samples were fortified with organochlorine pesticides by adding an appropriate volume of a standard stock solution mixture (purchased from Chem Service, West Chester, PA) in acetone. After fortification, samples were equilibrated (agitated or tumbled mechanically) at room temperature in the fume hood for at least an hour before extraction. Fortification levels were either 5 or 10 times the detection limits, that is, 0.05 or 0.10 µg L–1 in water, and 20 or 200 µg kg–1 in sediments and soils. All fortified samples of each substrate were submitted along with regular field samples and analyzed as "blind" QA–QC samples. Detection limits were defined as method detection limits (MDLs). These values were determined by analyzing spiked samples (n = 7). A statistical analysis was then performed to determine the mean ± 95% CI. The detection limits for all compounds with >95% confidence limits were 0.01 µg L–1 for water and 20 µg kg–1 for sediments and soils.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Efficiency of Analytical Methods
Based on the detection limits stated earlier, no interfering gas chromatographic response was detected in water, sediment, or soil samples obtained from the control sites. The recovery of organochlorine pesticide residues from "blind" fortified water, sediment, and soil samples from these sites are presented in Table 1. The average recovery ranged from 80.5 to 127.8%, with the exception in sediments for {alpha}-chlordane (131.9%) and {gamma}-chlordane (155.7%), and in water for endrin (159.4%) and methoxychlor (153%). The reason(s) for the higher recovery rates of {alpha}-chlordane, {gamma}-chlordane, endrin, and methoxychlor residues in these substrates are not known. The data reported in this paper were not corrected for the percentage of recovery and were in terms of dry weight for both sediments and soils.


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  		Table 1. Recovery from fortified{dagger} pristine water and sediment and soil samples.

 
It is feasible to detect residues of ultra-low concentrations of END and other organochlorine pesticide residues in water and/or in the atmosphere. That involves the collection and extraction of extraordinarily large volume samples (e.g., 20 to 300 L for water or even greater volumes for air samples). Using XAD resin column extraction, trace amounts of organochlorine pesticide residues, ranging from 0.05 to 3.5 ng L–1, were detected in the water samples of the LFV (Fluegel et al., 2004). Ultra-low levels (e.g., 1 ng L–1 or 1 pg L–1) of organochlorine pesticide residue recovery were not actively pursued in the current study because of the substantial added cost to determine their frequency of positive findings to a confidence limit of 95%. Beside that, recent studies indicate an inherent "uncertainty factor" in such data caused by both the field and laboratory sampling process and the possibility of systematic errors and artifacts during identification and quantification at trace levels (Oehme et al., 2002; Thompson et al., 1999). And unless ultra-low residues data are verifiable statistically, they are of only limited practical value for toxicological assessment.

Occurrence of Endosulfan and Selected Historical Organochlorine Pesticide Residues
Residues of END were detected in crop soils, ditch sediments, and water in the LFV (Fig. 2). The order of increasing frequency of positive detection was water, sediments, and crop soils (Fig. 2A). As expected, residues from historical use of other selected organochlorine pesticides such as cyclodiene, hexachlorocyclohexane, and DDT-related compounds were also found in the three substrates. They have a similar trend of positive occurrence. Apart from END, the other most commonly found cyclodiene pesticides were aldrin, {alpha}-chlordane, {gamma}-chlordane, and endrin. Some of their transformation products (e.g., dieldrin, endrin aldehyde, heptachlor, and heptachlor epoxide) were also detected. While residues of hexachlorocyclohexane {alpha}-BHC pesticides were not found in the three substrates, residues of other ß-BHC, {delta}-BHC, and {gamma}-BHC were detected, particularly in soils and sediments. Residues of selected DDT-related pesticides such as p,p-DDD, p,p-DDE, p,p-DDT, and methoxychlor were also detected in crop soils, ditch sediments, and water.



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  		Fig. 2. Frequency (%) of positive detection: (A) total number of samples per substrate (n = 36), (B) ditch water samples, (C) sediment samples, and (D) soil samples, n = 8 samples per site, except site J, where n = 4.

 
Residues of END and other selected organochlorine pesticides from historical use were consistently found in three of five farm sampling areas: Cloverdale (H), Westham Island (K), and south Burnaby (M) (Fig. 2B, 2C, and 2D). In contrast, these pesticide residues were inconsistently and less commonly found in the Sumas Prairie (F) and Delta (J) sampling sites. Farm sampling sites at south Burnaby, Cloverdale, and Westham Island contained muck and silt loam soils, while those in the Sumas Prairie and Delta were mostly sandy loam soils. Szeto and Price's study (1991) indicated that residues of organochlorine pesticides in the LFV were found less frequently in loamy sand farms than in muck farms. Also, it has been well established that soil types affect the persistence and retention of organochlorine pesticide residues (Edwards, 1966; Day et al., 1997; Rao and Hornsby, 2001).

Pesticide residues were generally the highest in crop soils, followed by ditch sediments and ditch water (Table 2). The estimated amount of mean total organochlorine pesticide residues (including END) in crop soils from all the sampling areas of the LFV was 4.99 mg kg–1 dry wt. Residues of END pesticides accounted for 1.35 mg kg–1 dry wt., while residues of all other cyclodiene, hexachlorocyclohexane, and DDT-related pesticides produced a mean total of 3.64 mg kg–1 dry wt. Likewise, the estimated mean amount of total organochlorine pesticide residues (including END) in sediments from ditches of all the sampling areas in the LFV was about 48% that of crop soils at 2.39 mg kg–1 dry wt. The estimated amount of residues of END pesticides was 0.63 mg kg–1 dry wt., while residues of all other organochlorine pesticides totaled 1.76 mg kg–1 dry wt.


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  		Table 2. Endosulfan and selected historical organochlorine pesticide residues (means, with ranges in parentheses) in the Lower Fraser Valley farm areas.{dagger}

 
Residues of END, but not all other selected organochlorine pesticides from historical use, were detected in the ditches from four of five farm areas where water samples were collected (Fig. 2B). As expected, the concentrations of organochlorine pesticide residues (including END) detected in ditch water were three orders of magnitude lower than those found in sediments and soils, with an estimated mean total of 0.73 µg L–1. The estimated amount of END pesticide residues was 0.20 µg L–1 while residues of other selected organochlorine pesticides totaled 0.53 µg L–1. Residues of endrin aldehyde, heptachlor, methoxychlor, and the cyclohexane compounds were not detected in ditch water.

Szeto and Price (1991) detected total organochlorine pesticides (excluding END) of 7.05 mg kg–1 dry wt. in crop soils 20 yr after they were phased out in Canada. The present study found a total organochlorine pesticide (excluding END) concentration of 3.54 mg kg–1 dry wt. in similar soils from the same general area after another 10 yr had passed. Using the concentrations of both studies as a rough gauge, there appears to be a decline in organochlorine pesticide level in crop soils of about 50%. The DT50 rates of organochlorine pesticides vary from 4 to 30 yr, depending on climatic and other environmental conditions (Edwards, 1966; Tomlin, 2002). The dissipation of organochlorine pesticide residues in the soils of the Pacific Northwest areas may likely fall on the high end of the DT50 range. This is because of the prevailing cool or cold environment, except for annual periods of brief warm summers. The main route of organochlorine pesticide degradation is through microbial activity, and this action is much less vigorous under cool or cold conditions (National Research Council of Canada, 1974, 1975).

Despite the continuing use of END, a decline of 22% of this pesticide to 1.35 mg kg–1 dry wt. was found in crop soils in the current study when compared with a total of 1.72 mg kg–1 dry wt. in 1991 (Wan et al., 1995). It is speculated that END normally used for the control of many agricultural pests is being replaced by alternative, newer organophosphate pesticides (Environment Canada and British Columbia Ministry of Water, Lands and Air Protection, 2001; Verrin et al., 2004). As indicated in the introductory paragraphs, END is now used only to control specific, hard to manage soil-dwelling pests, such as those in potatoes and vegetable crops.

The END concentrations detected in ditch water from the same general areas in 1995 and 2003, respectively, averaged 0.43 and 0.20 µg L–1. The continuing use of END in varying quantities appears to have decreased inputs to the ditch water of these farm areas. This may be attributed to the selected use of minimum quantities of END by farmers. It is also likely that inputs of this insecticide to water are a function of suspended particulate concentration, where the residues were absorbed and transported. These varied from season to season and from year to year, depending on the climatic conditions and rainfall events that control the activities of farm surface soil erosion and the amounts of suspended particulates during runoff.

Organochlorine Pesticide Residues in the Ambient Environment
As indicated earlier, no interference of pesticide residues above the detection limits (water, 0.01 µg L–1; sediments and soils, 0.02 mg kg–1) was detected in any of the control samples. These samples were obtained from the pristine watershed areas of Coquitlam (A), UBC Forest (B), Kanaka Creek (head water) (C), and Vedder Mountain (D). Likewise, during the one-year sampling period, no residues were detected in the samples (n = 36) from the ambient environment of Sumas Canal (E), Nicomekl River (G), Pump Stations of Delta Slough (I), the south Fraser estuary of Westham Island (L), and north arm of Fraser River of Burnaby (N). These water bodies are interconnected to the huge Lower Fraser River drainage system, and the dilution factor is probably very great. Although organochlorine pesticides were probably banned at about the same time as in Canada, residues are still found in the aquatic systems of many countries, notably, Australia, Brazil, and the United States (Baker and Richards, 2000; Leonard et al., 2001; Laabs et al., 2002). The amount of END residues resulting from its continuing use entering the tributary streams of the Fraser River in the LFV is minuscule when compared with the aquatic systems of these countries, where substantial residues of this pesticide continue to be detected in the river systems.

Implications for Nontarget Aquatic and Terrestrial Organisms
The potential acute and subacute toxicities of residues of END and of historical organochlorine pesticides to nontarget organisms inhabiting the aquatic and terrestrial environments of the LFV depends, to a great extent, on their presence and persistence in soils and sediments and solubility in water. These organochlorine properties determine their length of exposure time to, and subsequent uptake by, living creatures and the ensuing biological activity. The persistence (DT50) of organochlorine pesticides varies from 0.14 to 30 yr (Howard and Meylan, 1997; Lee, 2003; Tomlin, 2002; Yalkowski and Hee, 1990) and, with the exception of END, it is not surprising that detectable and varying amounts of organochlorine pesticide residues from historical use continue to be found in the LFV farm soils. Their occurrence in varying high concentrations in crop soils is possibly one of the major input sources to the aquatic environment of the Fraser River and its tributaries, especially the adjacent wetland areas, for now and likely for years to come.

Although most of the organochlorine pesticides are practically insoluble in water because of their hydrophobicity, they are, nonetheless, soluble to a very small extent, varying from 1 to 300 µg L–1 (Howard and Meylan, 1997; Tomlin, 2002; World Health Organization, 2004). Concentrations of END residues detected in the ditch water of the LFV ranged from <0.01 to 1.86 µg L–1, and that for total organochlorine pesticides varied from <0.01 to 3.36 µg L–1 (Table 2). Within such concentration ranges, it is conceivable that both aquatic invertebrates (e.g., Gammarus lacustris, Hyalella azteca, Pteronarcys californica) and fish (Onchorhynchus kisutch, O. mykiss) would likely be acutely impacted (Table 3). Both groups of nontarget indicator organisms are highly sensitive to both END and various organochlorine pesticides. Indeed, the maximum amount of END (i.e., 1.86 µg L–1) detected in ditch water approximates the 50% mortality in a test population (LC50) value (1.4 µg L–1) of Hyallela azteca for endosulfan sulfate. However, ({alpha} + ß)-endosulfan is about 2.7 times the LC50 value (0.7 µg L–1) for the same aquatic invertebrate. As well, the highest level of END (3330 µg kg–1 dry wt.) found in ditch sediments is about 9.3 times greater than the LC50 value (360 µg kg–1) for Hyallela azteca (Wan et al., 2005). The concentration range for END (<20 to 5600 µg kg–1 dry wt.) and total other selected organochlorine pesticides (<20 to 17500 µg kg–1 dry wt.) in crop soils of the LFV was even greater than those detected in ditch sediments. It is quite conceivable that at these levels, the well-being of nontarget indicator terrestrial organisms such as Bufo fowleri and Lumbricus terristris would be negatively impacted (Table 3).


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  		Table 3. Acute{dagger} toxicity of selected technical and formulated organochlorine pesticides to indicator organisms.

 
However, many researchers believe that the use of acute toxicity values of toxicants to assess environmental impact on nontarget organisms is inappropriate. Such data are derived under conditions representing the worse case scenario and do not necessarily reflect effects under prevailing ambient conditions. An alternate approach is mesocosm tests and field studies of population densities of macroinvertebrates (Leonard et al., 2000; Hose et al., 2003). Unless there is an adequate database of effects on nontarget organisms using alternate methods of toxicity determination, acute toxicity values must be relied on to gauge or extrapolate for possible impacts on nontarget indicator organisms. This is especially important when environmental concentrations detected are compatible to acute toxicity values of the biota. Because of their persistence, residues of END and organochlorine pesticides are dispersed by various routes, for example, biota via the food chain, transportation by air, water, and land through emission and atmospheric activities, and leaching and surface runoff (Forsyth et al., 1983; Hoffman et al., 1995; Barbash and Resek, 1996; O'Conner, 2003). Accordingly, these pesticide residues will continue to occur and would likely be bioaccumulated and/or bioconcentrated in biota. The LFV and its surrounding areas are no exception, even though organochlorine pesticides (except END) were banned more than three decades ago.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Residues of END and other selected organochlorine pesticides from historical use were detected in crop soils, ditch sediments, and water of several farm areas but not in similar substrates from pristine watershed areas. These pesticide residues were also not detected in sediments and water of the major tributaries of the Fraser River at detection limits deemed realistic and statistically practical for toxicological evaluations. This present study indicates that selected organochlorine pesticide (except END) residues from historical use, despite being banned for more than three decades, are prevalent in soils of several LFV farm areas in varying concentrations. They are most likely one of the major sources of continuing input to the LFV aquatic environment, possibly by way of transportation via emission and surface runoff and leaching from historical contaminated crop soils. Concentrations of END and other selected organochlorine pesticides from historical use detected in many farm ditches flowing to fish streams exceeded the LC50 values of benthic invertebrates and salmonids. They are also likely to occur at levels conducive for both bioaccumulation and bioconcentration in the food chain for years to come.


   ACKNOWLEDGMENTS
 
Funding for this study was provided by Environment Canada. We would like to thank L. Churchland and M. Isman for their constructive comments. The technical staff, notably B. McPherson, L. Chow, and J. Mazur of the Pacific Environmental Science Center, North Vancouver, BC, Canada, are gratefully acknowledged for the analyses of environmental samples. We are also grateful to the farmers from the study sites for their cooperation and the use of their farms for sampling and observations.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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