Comparison of pesticide root zone model 3.12: leaching predictions with field data

As part of a process to improve confidence in the results of regulatory modeling, predictions of the pesticide root zone model (PRZM) 3.12 were compared with measured data collected in nine different field leaching studies. Reasonable estimates of leaching were obtained with PRZM 3.12 in homogeneous soils where preferential flow is not significant. The PRZM 3.12 usually did a good job of predicting movement of bromide in soil (soil and soil pore-water concentrations were generally within a factor of two of predicted values). For simulations based on the best choices for input parameters, predictions of soil pore-water concentrations for pesticides were usually within a factor of three and soil pore-water estimates within a factor of 11. When the model input parameters were calibrated to improve the simulation of hydrology, predicted pesticide concentrations in soil pore water were usually within a factor of two of measured concentrations. Because of the sensitivity of leaching to degradation rate, the most accurate predictions were obtained with pesticides with relatively slow degradation rates. When conservative assumptions were used to define input pesticide parameters, predictions of pesticide concentrations were usually a factor of two greater than when using the best estimate of input parameters without any built-in conservatism.     

Sensitivity analysis for validating expert opinion as to ideal data set criteria for transport modeling

Environmental fate modeling results are often used in risk assessment without adequately considering uncertainty in exposure predictions. Sensitivity analysis is fundamental to model validation and error prediction since sensitive model input parameters account for the largest variance in model prediction. Once identified, sensitive model input parameters can be used to propagate parametric uncertainty in numerical predictions. Output sensitivity to variation in input code sequences was investigated for the pesticide root zone model (PRZM 3) using Plackett-Burman analysis for six runoff and leaching data sets. The analysis utilized an incomplete block factorial design with even parameter weighting and uniform proportional input perturbation. Timing and duration of key period rainfall were assumed a priori to be dominant sensitive inputs. Thus, meteorological data were fixed, allowing identification of additional input components contributing to model sensitivity. Results validated expert modeler assumptions concerning parameters most critical for model validation. For leaching data sets, the application rate, soil bulk density (an indicator of available water-holding capacity), chemical partition coefficient, and pesticide degradation rates were commonly the most sensitive inputs. For runoff data sets, the in-crop runoff curve number was the most significant input governing pesticide loss in runoff and erosion flux. The chemical partition coefficient, soil and foliar decay rates, and soil bulk density were also common sensitive components for runoff predictions. These commonly observed sensitive components for runoff and leaching prediction need to be carefully considered in the design and conduct of relevant field studies, modeling assessment of such studies, and future improvements in algorithms for environmental transport modeling.     

Distribution of chlorinated hydrocarbons in overlying water,sediment, polychaete,and hornyhead turbot (Pleuronichthys verticalis) in the coastal ocean,Southern California,USA

1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its primary metabolites (DDTs) and polychlorinated biphenyls (PCBs) are a major source of concern in the Southern California Bight (SCB), USA. The fate of DDTs and PCBs is a key element in assessing the effects imposed by these potential carcinogens on the marine ecosystem. We found that DDTs and PCBs remained widely distributed in the overlying water, sediment, polychaetes, and liver and muscle tissues of the hornyhead turbot (Pleuronichthys verticalis) collected from three nearshore locations of the SCB with different levels of contamination. Student's t tests indicated that the measured partition coefficients between the nonaqueous phases (sediment, polychaete, and fish) and overlying water at a heavily contaminated location were significantly greater than those predicted by the equilibrium partitioning theory (EPT). Measured partition coefficients between the nonaqueous phases and overlying water for a few DDT components at two other stations (moderate and low contamination) were also generally greater than the EPT predictions. On the other hand, DDTs and PCBs in polychaetes and fish tissues may be taken up from sediments via equilibrium partitioning or from food sources. These findings are suggestive of the possibility that contaminated sediments may have become an important source of contamination.     

Pesticides in Water,Fish and Shellfish from Littoral Area of Lake Biwa

A survey of 29 pesticides was performed for water and sediment from two littoral areas of Lake Biwa in 2007. Two insecticides, 5 fungicides and 13 herbicides in the water and an insecticide, 4 fungicides and 7 herbicides in the sediment were detected from the present survey. Pesticide accumulation potential in the sediment was calculated as “Pesticide concentration ratio” from the results of the survey on water and sediment in Lake Biwa. Correlation was investigated for each of the detected pesticides between sediment ignition loss and pesticide concentration ratio or between sediment particle size and pesticide concentration ratio. The ignition loss correlated well with the pesticide concentration ratio for pyrokiron, simetryn, and isoprothiolane (p < 0.01 to p < 0.001) but did not for molinate, bromobutide and pretilachlor. Further, the <0.025 mm particle size ratio correlated well with the pesticide concentration ratio for pyrokiron, simetryn, flutolanil, isoprothiolane and mefenacet (p < 0.01 to p < 0.001) but did not for bromobutide and pretilachlor. The correlation between <0.025 mm particle size ratio and pesticide concentration ratio had almost the same tendency as that between ignition loss and pesticide concentration ratio, suggesting sediment with higher <0.025 mm particle size ratio had higher weight (%) of ignition loss.     

Fate and effects of the insecticide-miticide chlorfenapyr in outdoor aquatic microcosms

The concentrations of chlorfenapyr in water and sediment in a lentic pond following early and late applications in a Florida crop treatment program were predicted using PRZM and EXAMS modeling and incorporating 30 years of actual rainfall data. An outdoor microcosm study was also conducted to determine the fate of chlorfenapyr and its effects on zooplankton, macroinvertebrates, phytoplankton, and fish in a freshwater system under exposure conditions representing simulated surface runoff and/or spray drift. The microcosm design used a regression model with five treatments (i.e., 300 microg/L spray, 30 microg/L spray, 15 microg/L spray and 30 microg/L runoff, 1.2 microg/L spray and 2.5 microg/L runoff, 30 microg/L runoff) plus a control. Chlorfenapyr was applied as an aqueous suspension concentrate (36% a.i.) to six microcosm tanks (30.9 m3). The no-observed-effect-concentration (NOEC) for zooplankton was the water concentration produced from the combination 1.2 microg/L spray and 2.5 microg/L runoff treatment. The NOEC for bluegill sunfish was the water concentration produced from the 30 microg/L runoff, which was significantly higher than the exposure concentrations from the lowest combination treatment. Chlorfenapyr was more toxic via spray to the water than via an exposure simulating surface runoff. The 96-h time weighted average concentrations (TWAs) from the lowest joint treatment and the 30 microg/L runoff treatment in the microcosm study were similar to model-predicted water 96-h TWA concentrations from early and late applications. The toxicity data from laboratory and microcosm studies along with water exposure data indicate low hazard to zooplankton species in the water column. Although chlorfenapyr remained in sediment, TWAs concentrations from the microcosm study along with model-predicted concentrations indicate low hazard to benthic invertebrate species based on acute toxicity to amphipods in the laboratory. Results from this assessment indicate that with appropriate measures to mitigate spray drift to shallow water bodies, applications of chlorfenapyr do not present a hazard to aquatic organisms during labeled uses.     

Partitioning of current-use and legacy pesticides in salmon habitat in British Columbia, Canada

Current regulatory paradigms have favored a shift from persistent pesticides that amplify in aquatic food webs to pesticides with reduced persistence and bioaccumulative potential (low log K(OW)). Although these new generation pesticides preferentially partition away from food web-associated lipids, aquatic biota may nonetheless be exposed to them via other environmental compartments. To characterize pesticide patterns in coho salmon (Oncorhynchus kisutch) habitat, we studied two salmon-bearing watersheds (agricultural and urban) in British Columbia, Canada's Fraser River valley and one in a remote area of the province's central coast. The agricultural and remote sites exhibited pesticide patterns dominated by current-use pesticides, whereas the urban site was largely dominated by legacy organochlorine pesticides. When adjusted to trans-chlordane concentrations across environmental matrices, correlations were observed between water to sediment ratios for the pesticides and their octanol:water partitioning coefficients (log K(OW); r2=0.48, p < 0.0001); between air to water ratios and Henry's Law coefficients (r2=0.55, p<0.0001); and between fish to water ratios and log K(OW) (r2=0.74, p<0.0001). These relationships underscore the importance of physicochemical properties in determining the fate of pesticides in freshwater salmon habitat, and highlight the need for research on the nature of health risks associated with exposure where little or no accumulation occurs.     

Dynamic in-stream fate modeling of xenobiotic organic compounds: a case study of linear alkylbenzene sulfonates in the Lambro River, Italy

Using a conceptual hydraulic model, a one-dimensional dynamic river water quality model has been developed to assess the short-term fate of linear alkylbenzene sulfonates (LAS) in the river compartments water and benthic sediment. The model assumes local equilibrium sorption and that both dissolved and sorbed chemical are available for biodegradation. To investigate the interaction of nutrient dynamics and organic contaminant fate, the model is coupled with a basic water quality model. On the basis of the Lambro River (Italy) as a case study, the result shows that the model predictions agree well with the measured data set. The model output sensitivity to model parameters has been tested, and the results depict that the model is highly sensitive to the biodegrading parameters. Also, a comparison of a steady state with a dynamic simulation and the effect of nutrient dynamics on the LAS fate in the Lambro River as a scenario analysis are presented. The results indicate the usefulness of the proposed model for the short-term simulation of organic contaminant fate in unsteady environmental conditions.     

An evaluation of cause-effect relationships between polychlorinated biphenyl concentrations and sediment toxicity to benthic invertebrates

Cause-effect sediment-quality benchmarks for the protection of benthic invertebrates are needed for polychlorinated biphenyls (PCBs) to support predictive risk assessments and retrospective evaluations of the causes of observed sediment toxicity. An in-depth evaluation of PCB aquatic toxicity and organic carbon partitioning was conducted to predict sediment effect concentrations using the equilibrium partitioning (EqP) approach. This evaluation was limited to invertebrate toxicity data, because PCBs may exert toxicity to invertebrates and fish via different toxicological mechanisms. As a result of differences in organic carbon partitioning among PCBs of differing levels of chlorination, the estimated EqP benchmarks increase with increasing degree of chlorination for various commercial and environmental PCB mixtures. Studies of spiked sediment toxicity using PCBs were reviewed, and their results generally were consistent with EqP predictions. Additionally, toxicity and benthic community data were reviewed for eight PCB-contaminated sites; these data also showed agreement with EqP predictions. None of these lines of evidence supports previously proposed, empirical sediment-quality guidelines for PCBs. Reasons for the lack of agreement between cause-effect and association-based benchmarks are discussed, and areas of future research to further refine EqP predictions for PCBs are identified.     

Recommendations for the assessment of TNT toxicity in sediment

Previous investigations of the ecotoxicity of TNT in spiked sediments noted the rapid degradation and disappearance of the toxicant, yet little is understood regarding the effects of this process on toxicity and subsequent derivation of toxicity reference values. We conducted environmental fate studies and 28-d sediment toxicity tests with benthic oligochaete worms (Tubifex tubifex) with sediments spiked at three different TNT concentrations (440, 1,409, and 4,403 nmol/g dry wt) aged for 1, 8, and 29 d. Because of rapid degradation of TNT, disappearance of degradation products, and partitioning to overlying water, only 25 to 40% of the added nitroaromatic mass balance was associated with sediment immediately after spiking. Lethal toxicity decreased with aging time and was best described by measured sediment nitroaromatic concentrations (sum of TNT and degradation products) at the beginning of exposure, with a median lethal concentration of nitroaromatic compounds of 184 nmol/g dry weight. To accurately describe the ephemeral exposure doses of TNT and its degradation products during toxicity tests with spiked sediments, we suggest that sediments should be aged at least 8 to 14 d after spiking, exposure should be based on measured sediment concentrations or chemical measures of availability, exchange of overlying water should be avoided or minimized, and short-term toxicity tests should be considered.     

Impact of pretilachlor herbicide and pyridaphenthion insecticide on aquatic organisms in model streams

To detect the impact of pesticides on aquatic organisms, model streams (3m wide, 20 m long) were established in paddy field in Japan. More than 100 species of aquatic organisms were generated in the model streams. Field tests with pretilachlor herbicide and pyridaphenthion insecticide were carried out in the streams for 3 yr (2001-2003). Exposure of pretilachlor (max. 0.382 mg/L) showed little density changes in algae with a Bray-Curtis percent similarity in the range 81.6-93.3% for algae. Exposure to high concentrations (>0.1mg/L) of pyridaphenthion produced visible density reductions in Cladocera zooplankton species. Reduction of individual aquatic insects in the model streams by pyridaphenthion caused an increase of chlorophyll a greater than that of the control streams. The pesticides used showed no substantial differences in the ecosystems of model streams exposed to maximum environmental concentrations (e.g., 0.01 mg/L) detected in real rivers.     

Pesticides in Water and Sediment from Littoral Area of Lake Biwa

A survey of 29 pesticides was performed for water and sediment from two littoral areas of Lake Biwa in 2007. Two insecticides, 5 fungicides and 13 herbicides in the water and an insecticide, 4 fungicides and 7 herbicides in the sediment were detected from the present survey. Pesticide accumulation potential in the sediment was calculated as “Pesticide concentration ratio” from the results of the survey on water and sediment in Lake Biwa. Correlation was investigated for each of the detected pesticides between sediment ignition loss and pesticide concentration ratio or between sediment particle size and pesticide concentration ratio. The ignition loss correlated well with the pesticide concentration ratio for pyrokiron, simetryn, and isoprothiolane (p < 0.01 to p < 0.001) but did not for molinate, bromobutide and pretilachlor. Further, the <0.025 mm particle size ratio correlated well with the pesticide concentration ratio for pyrokiron, simetryn, flutolanil, isoprothiolane and mefenacet (p < 0.01 to p < 0.001) but did not for bromobutide and pretilachlor. The correlation between <0.025 mm particle size ratio and pesticide concentration ratio had almost the same tendency as that between ignition loss and pesticide concentration ratio, suggesting sediment with higher <0.025 mm particle size ratio had higher weight (%) of ignition loss.     

Comparison of pesticide root zone model 3.12: runoff predictions with field data

As part of a process to improve confidence in the results of regulatory modeling, predictions of pesticide root zone model (PRZM) 3.12 were compared with measured data collected in nine different runoff field studies. This comparison shows that PRZM 3.12 provides a reasonable estimate of chemical runoff at the edge of a field. Simulations based on the best choices for input parameters (no conservatism built into input parameters) are generally within an order of magnitude of measured data, with better agreement observed both for larger events and for cumulative values over the study period. When the model input parameters are calibrated to improve the hydrology, the fit between predicted and observed data improves (results are usually within a factor of three). When conservatism is deliberately introduced into the input pesticide parameters, substantial overprediction of runoff losses occur. Recommendations for future work to improve regulatory models include implementation of more sophisticated evapotranspiration routines, allowing for seasonal variation of various model parameters (such as curve numbers, crop cover, and Manning's surface roughness coefficients), better procedures for estimating site-specific degradation rates in surface and subsoils, and improved sorption routines.     

Vegetated agricultural drainage ditches for the mitigation of pyrethroid-associated runoff

Drainage ditches are indispensable components of the agricultural production landscape. A benefit of these ditches is contaminant mitigation of agricultural storm runoff. This study determined bifenthrin and lambda-cyhalothrin (two pyrethroid insecticides) partitioning and retention in ditch water, sediment, and plant material as well as estimated necessary ditch length required for effective mitigation. A controlled-release runoff simulation was conducted on a 650-m vegetated drainage ditch in the Mississippi Delta, USA. Bifenthrin and lambda-cyhalothrin were released into the ditch in a water-sediment slurry. Samples of water, sediment, and plants were collected and analyzed for pyrethroid concentrations. Three hours following runoff initiation, inlet bifenthrin and lambda-cyhalothrin water concentrations ranged from 666 and 374 microg/L, respectively, to 7.24 and 5.23 microg/L at 200 m downstream. No chemical residues were detected at the 400-m sampling site. A similar trend was observed throughout the first 7 d of the study where water concentrations were elevated at the front end of the ditch (0-25 m) and greatly reduced by the 400-m sampling site. Regression formulas predicted that bifenthrin and lambda-cyhalothrin concentrations in ditch water were reduced to 0.1% of the initial value within 280 m. Mass balance calculations determined that ditch plants were the major sink and/or sorption site responsible for the rapid aqueous pyrethroid dissipation. By incorporating vegetated drainage ditches into a watershed management program, agriculture can continue to decrease potential non-point source threats to downstream aquatic receiving systems. Overall results of this study illustrate that aquatic macrophytes play an important role in the retention and distribution of pyrethroids in vegetated agricultural drainage ditches.     

Uptake and loss of chlorpyrifos and atrazine by Juncus effusus l. in a mesocosm study with a mixture of pesticides

Abstract-Aquatic organisms in agricultural regions typically are exposed to mixtures of agrochemicals, and effects are not adequately predicted from results of single pesticide exposure studies. Thus, a mesocosm study was designed to examine the fate and effects of varying mixtures of three pesticides (chlorpyrifos, atrazine, and monosodium methanearsonate) and mercury-contaminated sediment to the common freshwater macrophyte Juncus effusus L. Exposure doses of pesticides added to mesocosms represented those that might be encountered in a typical runoff or direct spray application. This study reports the uptake and loss of chlorpyrifos and atrazine in the leaves of J. effusus after a single and a repeated dose of the chemical mixture over 94 d. The measured chlorpyrifos levels in leaves were highest on day 1, but levels in both leaves and water dropped rapidly and were at background levels by day 32. Atrazine remained near nominal concentrations in the water through day 16 and reached maximum accumulation in the leaves on day 16. The chemical mixture affected uptake of chlorpyrifos more strongly than atrazine as measured by differences in uptake variability. After the second dose, J. effusus showed a similar uptake pattern for both compounds, although somewhat faster, to that observed after the first dose, with no diminished capacity for uptake of either compound. The greater volatility of chlorpyrifos, the higher solubility of atrazine, and the more efficient transport of atrazine to the root zone are characteristics that are consistent with the differences observed in their uptake and loss behavior.     

A dynamic multimedia environmental and bioaccumulation model for brominated flame retardants in Lake Huron and Lake Erie, USA

Polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) may pose a worldwide pollution problem because of their persistence, long-range transport capability, and predisposition to bioaccumulate. The ubiquitous presence of PBBs and PBDEs has heightened interest in determination of their fate. We report results for a fugacity-based dynamic environmental and bioaccumulation model of the fate of hexabromobiphenyl (hexaBB) discharged into the Saginaw Bay region of Lake Huron, USA. We calculated transient fugacity profiles of hexaBB in Lake Huron and Lake Erie water and sediment during the 1970s, 1980s, and 1990s. The hexaBB concentrations in the environmental compartments were used as inputs for a dynamic bioaccumulation model of Lake Huron and Lake Erie aquatic biota. The model results indicate that the sediment compartments of Lakes Huron and Erie serve as reservoirs for the accumulation and slow transfer of hexaBB to the food web constituents of these lakes. We present bioaccumulation factors (BAFs) and compare the predicted hexaBB concentrations in lake trout from the bioaccumulation model with measurements during the period 1980 to 2000. An uncertainty analysis for this model suggests that errors associated with input parameter uncertainty can be reduced by refining estimates of the sediment degradation half-life of hexaBB. The corroborated PBB model has carryover application for modeling the fate of polybrominated diphenyl ether (PBDE) contaminants in the Great Lakes. By fitting model outputs to field measurement data using the transformed least square fit method, we report estimations of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) emission rates into the Lake Huron and Lake Erie watershed areas.     

The slow recovery of San Francisco Bay from the legacy of organochlorine pesticides

The use of organochlorine pesticides, including DDTs, chlordanes, and dieldrin, peaked in San Francisco Bay's watershed 30-40 years ago, yet residues of the pesticides remain high. Known as legacy pesticides for their persistence in the Bay decades after their uses ended, the compounds and their breakdown products occur at concentrations high enough to contribute to advisories against the consumption of sport fish from the Bay. Combined with other data sets, the long-term monitoring data collected by the San Francisco Estuary Regional Monitoring Program (RMP) for trace substances allow us to track recovery of the Bay from these inputs and predict its future improvement. Legacy pesticides enter the water and sediment of San Francisco Bay from a variety of sources, including runoff from California's Central Valley and local watersheds, municipal and industrial wastewater, atmospheric deposition, erosion of historically contaminated sediment deposits, and dredging and disposal of dredged material. Runoff from small-urbanized tributaries may contribute as much or more to the loads than runoff from the agricultural Central Valley, even though 90 percent of the freshwater flow comes from the Central Valley via the Sacramento and San Joaquin rivers. The fates of legacy pesticides in San Francisco Bay are controlled by their chemical properties, including their solubilities and partition coefficients. Degradation in the sediments, outflow through the Golden Gate, and volatilization-in that relative order-result in removal of pesticides from the Bay. A contaminant fate model was used to estimate recovery times of the Bay under various scenarios. For example, under a scenario in which no new legacy pesticides entered the Bay, model predictions suggested that concentrations of pesticides in the water and the active sediment layer would reach risk-reduction goals within one to three decades. Under scenarios of continued inputs to the Bay, recovery time would be considerably longer or not reached at all. Long-term tissue monitoring corroborates model predictions of slow declines in DDT and chlordane concentrations. Field-transplanted bivalve samples indicate declines since 1980, and lipid-weight concentrations of pesticides have declined in fishes, but the declines are slow. The critical management question for the Bay is whether there are feasible management actions that would decrease concentrations in sport fish significantly faster than the existing slow progress that has been observed.     

Use of vegetated agricultural drainage ditches to decrease pesticide transport from tomato and alfalfa fields in California, USA

Irrigation and storm water runoff from agricultural fields has the potential to cause impairment to downstream aquatic receiving systems. Over the last several years, scientists have discovered the benefit of using edge-of-field practices, such as vegetated agricultural drainage ditches, in the mitigation of pesticides and sediment. After demonstrating this practice's feasibility in California, field trials were initiated to document irrigation runoff pesticide mitigation in California alfalfa and tomato fields. In the alfalfa field, chlorpyrifos concentration was decreased by 20% from the inflow to the ditch outflow. Thirty-two percent of the measured chlorpyrifos mass was associated with ditch plant material. In the tomato field, permethrin concentration was decreased by 67% and there was a 35% reduction in suspended sediment concentration from inflow to the ditch outflow. When surface water was not present in the ditch systems, the sediment was a significant repository for pesticides. Based on the field trials, vegetated agricultural drainage ditches can be successfully used as part of a suite of management practices to reduce pesticide and sediment runoff into aquatic receiving systems.     

Endosulfan Application to a Stream Mesocosm: Studies on Fate,Uptake into Passive Samplers and Caged Toxicity Test with the Fish <Emphasis Type="Italic">M. ambigua</Emphasis>

A model mesocosm system was used to simulate the effect of endosulfan entering a waterway from episodic events such as accidental overspray or in runoff water containing contaminated sediment following storm events. The fate of technical endosulfan applied to a 24-stream mesocosm was compared in experiments where the pesticide was applied either directly as water contamination or after being pre-bound to sediment. The flow of water through the streams was discontinued for a 10–12 h period following the pesticide application. Following the water application, only approximately 3% of endosulfan remained in the streams after 4 days and then was not detectable after 7 days. In contrast, after application pre-bound to sediment, approximately 33% of the endosulfan remained in the streams after 4 days and 14% after 7 days. Additionally, with the sediment-bound application, the proportion of endosulfan was higher in the substrate (11%) after 7 days than in the overlying water (3%), and approximately 1% was oxidised to the sulphate form. The dissipation of endosulfan in the water column of both experiments followed a two-parameter exponential decay model characterised by a relatively fast first-order single-phase process. In sediment of both experiments and the gravel of the sediment-dosing experiment, the dissipation of endosulfan followed more closely a four-parameter bi-exponential decay model characterised by first-order kinetics of two fractions: the first fraction dissipates quickly, and in the longer term the second fraction dominates the overall dissipation with a slower rate. In the gravel section of the water-dosing experiment, endosulfan dissipation was characterised by relatively very slow two-parameter exponential decay. The overall dissipation rates of the α- and β-endosulfan isomers were significantly higher in the water-dosing than in the sediment-dosing experiment, except in the gravel section of the mesocosm. The uptake of the endosulfan into passive samplers constructed from polyethylene membrane bags containing trimethylpentane solvent (TRIMPS) placed in the overlying water was linear. In contrast, TRIMPS buried in sediment failed to uptake endosulfan from the sediment substrate, indicating that short-term deployment of passive samplers can only be used to determine time-weighted average concentrations of bioavailable chemicals in the water column. A 34-h LC50 of 2.8 μg/l [95% confidence interval (CI) 1.5–4.2 μg/l] for juveniles of the native fish Macquaria ambigua was obtained when exposed during the water-dosing experiment. This study demonstrated that the pulse entry of sediment contaminated with endosulfan into a receiving waterway was more persistent compared with direct aqueous contamination and the endosulfan would be bioavailable to pelagic organisms following a gradual partitioning to the water column.     

A pesticide surface water mobility index and its relationship with concentrations in agricultural drainage watersheds

An index to benchmark pesticide mobility relevant to surface water runoff and soil erosion (surface water mobility index, or SWMI) was derived based on two key environmental fate parameters: degradation half-life and organic carbon-normalized soil/water sorption coefficient (Koc). Values assigned with the index of each individual compound correlate well with the concentration trend of 13 pesticides monitored in six Lake Erie, USA, tributaries from 1983 to 1991. Regression using a power function of SWMI fits concentration data well at various percentiles in the database for each tributary and all six tributaries combined, with r2 ranging from 0.71 to 0.94 for the concentrations at the 95th percentile. Good agreement was also obtained between SWMI and the time-weighted annual mean concentrations (r2 = 0.67-0.87). Although concentrations at or near peaks tend to be driven by rare hydrological events (intense precipitation immediately after application), SWMI explains the peak concentration data generally well (r2 = 0.53-0.86). The SWMI-concentration relationship was further evaluated with two other pesticide monitoring databases: the U.S. Geological Survey National Water Quality Assessment Program White River Study Unit (1991-1996) at Hazelton, Indiana, USA, and the Syngenta (previously Novartis) Voluntary Monitoring Program with Community Water Systems at the Higginsville City Lake, Missouri, USA (1995-1997). The ability of the proposed SWMI to discriminate pesticide runoff mobility and its correlation with surface water monitoring data can be significant in the development of screening methodologies and data-based models for government agencies and/or practitioners in general facing increasing pressure to assess pesticide occurrence in aquatic environments.     

Development of an enzyme-linked immunosorbent assay for determination of pretilachlor in water and soil

An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) has been developed for detection of pretilachlor in water and soil. An immunogen was prepared from haptens of pretilachlor conjugated to bovine serum albumin(BSA). The specific polyclonal antibodies were obtained by immunizing New Zealand white rabbits. The influence of parameters including concentrations of methanol, ionic strength and pH values were optimized to improve the sensitivity of the assay. The optimized ELISA was shown to have a high sensitivity and specificity for pretilachlor. Under optimal conditions, the ELISA has demonstrated an 50% inhibitory concentration (IC₅₀) value of 0.0359 mg/L with a limit of detection (LOD, IC₁₀) of 6.9 ng/L. The cross-reactivities to some analogs of pretilachlor (acetochlor, butachlor, metazachlor and metalaxyl) were below 1.5%. The average recoveries of pretilachlor from distilled water, tap water, paddy water and soil were in the range of 77.0-115.2% between 0.005 and 5.0 mg/L. The results of ELISA for spiked samples were confirmed by GC-ECD with a high correlation coefficient of 0.9950(n=11). Thus, the ELISA proven to be a sensitive, specific, inexpensive and quantitative tool for detection of pretilachlor from four kinds of spiked samples.