Maximum Pesticide Concentration Research Articles

Pesticide dynamics in three small agricultural creeks in Hesse, Germany.

Due to their high biodiversity, small water bodies play an important role for freshwater ecosystems. Nonetheless, systematic pesticide monitoring in small creeks with a catchment <30 km2 is rarely conducted. In this study, event-driven water samples were taken from May until November 2017 and March until July 2018 after 20 rain events at three sampling sites with catchment areas of <27 km2 in the Wetterau, a region with intensive agriculture in Southern Hesse, Germany. Additionally, enriched extracts of the native water samples from the campaign in 2018 were used for the Microtox assay to determine baseline toxicity to invertebrates over time and sum of toxic units (STU) were calculated to compare the potential toxicity of the samples. Overall, 37 pesticides and 17 transformation products were found, whereby the herbicide metamitron (79 µg/L) showed the highest concentration. Regularly, pesticide concentrations peaked at the time of the highest water level within each sampling event. Within each sampling event maximum pesticide concentration was mostly reached in water samples taken during the first two hours. The sum of the time-weighted mean concentration values of all pesticides was between 2.0 µg/L and 7.2 µg/L, whereby the measured concentrations exceeded their regulatory acceptable concentration (RAC) at 55% of all sampling events for at least one pesticide. The mean EC50 values varied between 28.6 ± 13.1 to 41.3 ± 12.1 REF (relative enrichment factor). The results indicated that several samples caused baseline toxicity, whereby the highest activity was measured at the time of highest water levels and pesticides concentrations, and then steadily decreased in parallel with the water level. Median STUs of invertebrates ranged from -2.10 to -3.91, of algae/aquatic plants from -0.79 to -1.84 and of fish from -2.47 to -4.24. For one of the three sampling sites, a significant linear correlation between baseline toxicity and STUinvertebratewas found (r2=0.48). The results of the present study suggest that (1) current pesticide monitoring programs underestimate risks posed by the exposure to pesticides for aquatic organisms and (2) pre-authorization regulatory risk assessment schemes are insufficient to protect aquatic environments.

Typical Pesticide Residues and Their Risk Assessment in Farmland Environment of Different Plant Types in Shaya County, Xinjiang

In order to investigate the characteristics of typical pesticide residues in farmland soil of different plant types in Shaya County and to evaluate the level of human health risk and ecological risk caused by pesticide residues, a total of 55 samples of plants, soil, and water from nine areas of Shaya county were collected on September 29, 2020. The occurrence levels of 47 typical pesticides in the samples were analyzed using gas chromatography-mass spectrometry (GC-MS). The results showed that a total of 23 pesticides were detected in three environmental media, and the maximum concentrations of pesticides in soil, plants, and water were 70.58 μg·kg-1, 1832.18 μg·kg-1, and 188.53 μg·L-1, respectively. The levels of pesticide residues in the three environmental media in Shaya county were characterized as plants>water>soil. From the detection of pesticides in different plant types, P1, P2, P6, and P8 in the center of the county were the most seriously polluted. The plants with a high pesticide load level in the corresponding areas were cotton, walnut, red jujube, and poplar, and the pesticides with a high concentration contribution were hexachlorocyclohexanes, chlorpyrifos, cyhalothrin, fluvalinate, metalaxyl, difenoconazole, and procymidone. The human health risks of adults and children caused by oral intake, skin contact, and respiratory inhalation were evaluated. The results showed that oral intake was the main exposure route, and the risk level of children was significantly higher than that of adults but was within the acceptable range. The ecological risk level of earthworms in soil was subsequently evaluated. The results showed that the potential ecological risk level of a single pesticide was low, and the potential ecological risk level of bifenthrin was the largest. The calculation of the total ecological risk of mixed pesticides showed that areas P1, P4, P7, and P9 were at moderate risk, whereas other areas were at low risk. Therefore, the use of some pesticides in Shaya County should be restricted.

Features of Pesticide-Contaminated Surface Water

This work aims to investigate the concentration indices of 14 pesticides in the major water bodies of the Southern Federal District of the Russian Federation. The study was conducted in 2019 using samples of bottom sediments and surface waters collected from three reservoirs (Krasnodar, Proletarian, and Veselovsky) and two rivers (Don and Sal). Concentrations of active pesticide substances were studied, and the results were benchmarked against 2018. In 2019, 14 active pesticide substances were detected in water and sediment samples from the three reservoirs under study. Maximum pesticide concentrations were observed in the spring of 2019 and autumn 2018. Total concentration indices in these time frames were similar, but autumn 2019 is 20 times lower than 2018 (0.7 versus 6.5, p ≤ 0.001). Total pesticide concentrations for rivers and reservoirs averaged about the same (0.15-0.80, p ≥ 0.05). There are different levels of pesticides in rivers and reservoirs. The detected pesticide concentrations did not exceed the maximum allowable concentrations, but the cumulative effect can have a harmful impact on hydrobionts in the future.

PWC-based evaluation of groundwater pesticide pollution in the Júcar River Basin

Predicting pesticides' behavior in the environment is necessary to anticipate and minimize their adverse effects. Despite the use of pesticides in Spain is increasing, the implementation and use of predictive mathematical models is seldomly done in practice due to the lack of available data. In this original work, the Pesticide Root Zone Model version 5 (PRZM 5) mathematical model under the Pesticide in Water Concentration 1.52 (PWC) interface has been applied to model pesticide behavior in nine groundwater bodies located inside the Júcar River Basin (JRB) in Spain. Mathematical modeling allowed calculating the maximum concentration of pesticides after completing the calibration process. Bromacil, terbuthylazine, atrazine, desethyl-terbuthylazine, and terbumeton concentrations in groundwater were simulated between 2006 and 2019.Results show that the maximum pesticide concentration value on every well exceeds the current Spanish Maximum Concentration Limit (0.1 μg/L). PRZM 5 was able to reproduce pesticide concentration observations over time despite the limited amount of available data.This study contributes to assessing environmental risks caused by the use of pesticides inside the JRB and can potentially be applied in other areas of interest.

Is there an urban pesticide signature? Urban streams in five U.S. regions share common dissolved-phase pesticides but differ in predicted aquatic toxicity

Pesticides occur in urban streams globally, but the relation of occurrence to urbanization can be obscured by regional differences. In studies of five regions of the United States, we investigated the effect of region and urbanization on the occurrence and potential toxicity of dissolved pesticide mixtures. We analyzed 225 pesticide compounds in weekly discrete water samples collected during 6–12 weeks from 271 wadable streams; development in these basins ranged from undeveloped to highly urbanized. Sixteen pesticides were consistently detected in 16 urban centers across the five regions—we propose that these pesticides comprise a suite of urban signature pesticides (USP) that are all common in small U.S. urban streams. These USPs accounted for the majority of summed maximum pesticide concentrations at urban sites within each urban center. USP concentrations, mixture complexity, and potential toxicity increased with the degree of urbanization in the basin. Basin urbanization explained the most variability in multivariate distance-based models of pesticide profiles, with region always secondary in importance. The USPs accounted for 83% of pesticides in the 20 most frequently occurring 2-compound unique mixtures at urban sites, with carbendazim+prometon the most common. Although USPs were consistently detected in all regions, detection frequencies and concentrations varied by region, conferring differences in potential aquatic toxicity. Potential toxicity was highest for invertebrates (benchmarks exceeded in 51% of urban streams), due most often to the neonicotinoid insecticide imidacloprid and secondarily to organophosphate insecticides and fipronil. Benchmarks were rarely exceeded in urban streams for plants (at 3% of sites) or fish (<1%). We propose that the USPs identified here would make logical core (nonexclusive) constituents for monitoring dissolved pesticides in U.S. urban streams, and that unique mixtures containing imidacloprid, fipronil, and carbendazim are priority candidates for mixtures toxicity testing.

Occurrence and risk evaluation of organophosphorus pesticides in typical water bodies of Beijing, China.

AbstractHuman activities, particularly in large cities, can lead to pollution caused by micropollutants such as pesticides in water bodies, which have been recognized as serious threats to the environment and human health. The pollution level of six organophosphorus pesticides, three herbicides, and one bactericide in groundwater and the Wenyu River, and their fates in three sewage treatment plants (STPs) and a hospital were investigated in this study. The concentrations of the ten detected pesticides ranged from not detected (ND) to 323.44ngL-1 in different water samples from Beijing; metalaxyl was detected to have the highest concentration (89.58ngL-1), and the detection frequencies of atrazine and metalaxyl were 100%. The maximum concentrations of pesticides in the Wenyu River, STPs, and the hospital were 1-2 orders of magnitude higher than those in the groundwater. Good removal efficiencies by the treatment processes were observed for ametryn (100%), while the removal efficiencies for atrazine and omethoate were the lowest in the three STPs (- 9.6% and 12.67%, respectively). Finally, risk quotient (RQ) values of each contaminant were estimated from the maximum values determined for typical urban to assess the ecology and health effects. In the case of environmental toxicity, the highest RQ values (> 1) were obtained for dichlorvos and omethoate. In the case of health toxicity, the RQ values show that the pesticides found in groundwater pose no potential health risks to humans at current concentrations.

Determination of neonicotinoids and butenolide residues in avian and insect pollinators and their ambient environment in Western Canada (2017, 2018)

To examine the spatial, and temporal variation and potential sources of pesticide concentrations, primarily neonicotinoid insecticides, in hummingbirds in western Canada, we sampled their cloacal fluid from sites in British Columbia and Saskatchewan, Canada in 2017–2018. At a sub-sample of those sites, we also measured pesticides in honey bee (Apis mellifera) nectar, water, and sediment. We collected cloacal fluid from 5 species of hummingbirds (n = 26 sites) in British Columbia (BC) and Saskatchewan, Canada, and nectar from honey bee hives (n = 4 sites), water and sediment (n = 18 sites) in the Fraser Valley, BC. Among those, multiple types of samples were collected at 6 sites. We report the first measurement of flupyradifurone, a relatively new butenolide insecticide, in wildlife which was detected at 4.58 ng/mL in hummingbird cloacal fluid and 2.18 ng/g in honey bee nectar. We also detected three other neonicotinoids (imidacloprid, clothianidin, acetamiprid) and one metabolite desnitro-imidacloprid, and MGK264, a pesticide synergist, in our samples. Among 49 samples of cloacal fluid from rufous (Selasphorus rufus), Anna's (Calypte anna), calliope (Selasphorus calliope) black-chinned (Archilocus alexandri) and ruby-throated hummingbirds (Archilocus colubris), 26.5% (n = 13) contained neonicotinoids. Maximum pesticide concentrations in hummingbirds, water and sediment were found in samples collected in the Fraser Valley, BC within 0.5 km of conventionally sprayed blueberry fields (CSBF) but highest levels in honey bee nectar were detected at a site 1.5 km from a CSBF. Imidacloprid in honey bee nectar at one site exceeded concentrations (>1 ng/g) that can sublethally affect worker bee foraging efficiency. In water, imidacloprid concentrations at another site exceeded Canadian guidelines (230 ng/mL) for the protection of aquatic invertebrates.

Soil and Water Assessment Tool model predictions of annual maximum pesticide concentrations in high vulnerability watersheds.

Recent national regulatory assessments of potential pesticide exposure of threatened and endangered species in aquatic habitats have led to increased need for watershed-scale predictions of pesticide concentrations in flowing water bodies. This study was conducted to assess the ability of the uncalibrated Soil and Water Assessment Tool (SWAT) to predict annual maximum pesticide concentrations in the flowing water bodies of highly vulnerable small- to medium-sized watersheds. The SWAT was applied to 27 watersheds, largely within the midwest corn belt of the United States, ranging from 20 to 386 km2 , and evaluated using consistent input data sets and an uncalibrated parameterization approach. The watersheds were selected from the Atrazine Ecological Exposure Monitoring Program and the Heidelberg Tributary Loading Program, both of which contain high temporal resolution atrazine sampling data from watersheds with exceptionally high vulnerability to atrazine exposure. The model performance was assessed based upon predictions of annual maximum atrazine concentrations in 1-d and 60-d durations, predictions critical in pesticide-threatened and endangered species risk assessments when evaluating potential acute and chronic exposure to aquatic organisms. The simulation results showed that for nearly half of the watersheds simulated, the uncalibrated SWAT model was able to predict annual maximum pesticide concentrations within a narrow range of uncertainty resulting from atrazine application timing patterns. An uncalibrated model's predictive performance is essential for the assessment of pesticide exposure in flowing water bodies, the majority of which have insufficient monitoring data for direct calibration, even in data-rich countries. In situations in which SWAT over- or underpredicted the annual maximum concentrations, the magnitude of the over- or underprediction was commonly less than a factor of 2, indicating that the model and uncalibrated parameterization approach provide a capable method for predicting the aquatic exposure required to support pesticide regulatory decision making. Integr Environ Assess Manag 2018;14:358-368. © 2017 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

High frequency monitoring of pesticides in runoff water to improve understanding of their transport and environmental impacts

Rainfall-induced peaks in pesticide concentrations can occur rapidly. Low frequency sampling may therefore largely underestimate maximum pesticide concentrations and fluxes. Detailed storm-based sampling of pesticide concentrations in runoff water to better predict pesticide sources, transport pathways and toxicity within the headwater catchments is lacking. High frequency monitoring (2min) of seven pesticides (Dimetomorph, Fluopicolide, Glyphosate, Iprovalicarb, Tebuconazole, Tetraconazole and Triadimenol) and one degradation product (AMPA) were assessed for 20 runoff events from 2009 to 2012 at the outlet of a vineyard catchment in the Layon catchment in France. The maximum pesticide concentrations were 387μgL−1. Samples from all of the runoff events exceeded the legal limit of 0.1μgL−1 for at least one pesticide (European directive 2013/39/EC). High resolution sampling used to detect the peak pesticide levels revealed that Toxic Units (TU) for algae, invertebrates and fish often exceeded the European Uniform principles (25%). The point and average (time or discharge-weighted) concentrations indicated up to a 30- or 4-fold underestimation of the TU obtained when measuring the maximum concentrations, respectively. This highlights the important role of sampling methods for assessing peak exposure. High resolution sampling combined with concentration-discharge hysteresis analyses revealed that clockwise responses were predominant (52%), indicating that Hortonian runoff is the prevailing surface runoff trigger mechanism in the study catchment. The hysteresis patterns for suspended solids and pesticides were highly dynamic and storm- and chemical-dependent. Intense rainfall events induced stronger C-Q hysteresis (magnitude). This study provides new insights into the complexity of pesticide dynamics in runoff water and highlights the ability of hysteresis analysis to improve understanding of pesticide supply and transport.

Diuron, Irgarol 1051 and Fenitrothion contamination for a river passing through an agricultural and urban area in Higashi Hiroshima City, Japan

A study was conducted on the pesticides Diuron, Irgarol 1051 and Fenitrothion in Kurose River water, Higashi Hiroshima, Japan for a period of one year to assess the contribution of agriculture and urban activities on pesticide pollution of the river. Samples were analysed by a reverse phase HPLC system. The maximum pesticide concentrations were; 4620ng/L, 50ng/L and 370ng/L for Diuron, Irgarol 1051 and Fenitrothion, respectively. While Diuron and Fenitrothion were detected at all sites, Irgarol 1051 was only present at Izumi, a high density urban and industrial area which also registered the highest concentrations of the pesticides. The pattern showed by Diuron and Fenitrothion was linked to farming activities. Also, Diuron and Fenitrothion concentration correlated with pesticide utilization data for Hiroshima Prefecture. Irgarol 1051 showed a different pattern to that of Diuron and Fenitrothion and its source was attributed to paint. It was noted that 78% and 42% of water samples at Izumi sampling site exceeded the European Union (EU) guidelines for Diuron and Fenitrothion, respectively.

Wash off of imidacloprid and fipronil from turf and concrete surfaces using simulated rainfall

The surface runoff of imidacloprid granular product (GR) from turf surfaces, and imidacloprid emulsifiable concentrate (EC), fipronil suspension concentrate (SC) products and fipronil byproducts from concrete surfaces was investigated during 1h rainfall simulations at 50mm/h or 25mm/h with product incubation times of 1.5h, 1d, 7d, and 14d. About 57.3% of the applied mass of imidacloprid, corresponding to an event mean concentration of 392.0μg/L, was washed off from the concrete surfaces after 1.5h of incubation. After 1d, 7d, and 14d of incubation on either turf or concrete surfaces, up to 5.9% of the applied mass of pesticide was removed in each of the run-off events. The maximum concentrations of pesticides were observed in the initial fraction of the runoff collected in the first rainfall event. They were 157.8, 3267.8 and 143.3μg/L for imidacloprid GR, imidacloprid EC and fipronil SC, respectively. Imidacloprid was not persistent on concrete surfaces, with run-off concentrations below detection limits in 7d incubation experiments. The cumulative mass losses of imidacloprid from turf and fipronil from concrete had a linear relation with cumulative surface run-off depth, while cumulative mass losses of imidacloprid from concrete surfaces were better fit by a power function of the cumulative surface run-off depth. The concentrations of fipronil in the runoff from the third rainfall event at 14d incubation time were still relatively high and ranged from 12.0 to 31.0μg/L. A toxicity unit approach was also employed to evaluate the potential acute toxicity of fipronil and its byproducts to aquatic organisms.

Study of the presence of priority pesticides in surface water of river basins located in two areas of intensive dairy farming in the NW Spain (Galicia)

This study provides data about the monitoring over two years of 54 target pesticides in surface water of two river catchments located in two areas of the most intensive dairy farms of Galicia (NW Spain). Solid phase extraction of water samples followed by multi-residue analysis on a triple quadrupole mass spectrometer instrument coupled to liquid chromatography (LC-MS/MS) enabled to acquire the results. The most frequently detected pesticides were acetochlor, alachlor, atrazine and terbuthylazine, as well as some of their metabolites. The concentration profiles of these four substances show a seasonal variation, the highest concentrations corresponding to the period of maize sowing and the application of herbicides. Of the seven priority pesticides evaluated, only alachlor and atrazine were detected. Their follow-up revealed that the concentration thresholds laid down by the EQS for these substances were never exceeded. The sum of the concentrations of the most detected compounds reached a maximum slightly higher than 1 µg L−1. The sum of the AAC of these compounds was well below the allowed average values. Some comparisons made with studies carried out in other basins in Europe reveal that the compounds detected in the present study are usually present in rivers near intensive agricultural areas. However, the maximum concentrations of pesticides found in our survey were generally lower than those registered in these European river basins.

Implications of precipitation patterns and antecedent soil water content for leaching of pesticides from arable land

An improved understanding of how precipitation patterns control pesticide leaching from structured soils prone to macropore flow could lead to practical mitigation strategies that would help farmers minimize losses by optimizing application timings. A sensitivity analysis of the macropore flow model MACRO was therefore carried out to examine the influence of antecedent soil water content and precipitation patterns on pesticide leaching to drainage systems and groundwater. One thousand model runs were executed (20 four-year weather data series, 50 application dates per season) for both autumn and spring applications of a hypothetical moderately sorbed and quickly degraded herbicide for one of three national scenarios for pesticide risk assessment in Sweden (Näsbygård, a loamy moraine soil in Scania, southern Sweden). Rapid and direct transport of pesticides in macropores to drainage systems and shallow groundwater was predicted to occur rather infrequently in spring (in 4 of the 20 years) and even more rarely in autumn. For autumn applications, the soil water deficit at application ( SWD tot ) and medium-term precipitation (30–90 days after application) were the two most sensitive variables controlling pesticide leaching. For spring applications, total leaching was most closely linked to rainfall the following winter, while short-term precipitation (5 days after application) and the antecedent soil water deficit were the two most important predictors for maximum pesticide concentrations in drainflow. The potential for reducing leaching by restricting applications to periods of low risk was investigated. The results showed that avoiding applications on wet soil in autumn could potentially reduce total pesticide losses by a factor of two to three. Similarly, the risk of acute toxicological effects in surface waters following pesticide applications in spring could be reduced by a factor of 2–3 by avoiding application when 5-day weather forecasts predict precipitation >10 mm.

Pesticide bioconcentration modelling for fruit trees

The model presented allows simulating the pesticide concentration evolution in fruit trees and estimating the pesticide bioconcentration factor in fruits. Pesticides are non-ionic organic compounds that are degraded in soils cropped with woody species, fruit trees and other perennials. The model allows estimating the pesticide uptake by plants through the water transpiration stream and also the time in which maximum pesticide concentration occur in the fruits. The equation proposed presents the relationships between bioconcentration factor (BCF) and the following variables: plant water transpiration volume ( Q), pesticide transpiration stream concentration factor (TSCF), pesticide stem-water partition coefficient ( K Wood,W), stem dry biomass (M) and pesticide dissipation rate in the soil–plant system ( k EGS). The modeling started and was developed from a previous model “ Fruit Tree Model” (FTM), reported by Trapp and collaborators in 2003, to which was added the hypothesis that the pesticide degradation in the soil follows a first order kinetic equation. The FTM model for pesticides (FTM-p) was applied to a hypothetic mango plant cropping ( Mangifera indica) treated with paclobutrazol (growth regulator) added to the soil. The model fitness was evaluated through the sensitivity analysis of the pesticide BCF values in fruits with respect to the model entry data variability.

Distribution of pesticides, PAHs and heavy metals in prawn ponds near Kolleru lake wetland, India

This paper discussed the distribution of pesticides, polycyclic aromatic hydrocarbons (PAHs) and heavy metals in water, sediment and prawn from intensive prawn ponds ( n = 8) near the Kolleru lake wetland, India and assessed the quality of prawn for human consumption and also discussed the possible effects of these pollutants on pond environment and aquatic environment. The chemicals and other products used in prawn ponds near the Kolleru lake wetland were documented. The sediment, prawn and water samples were collected six times from selected prawn ponds during the production period of 3 months. Water samples were analyzed for selected physico-chemical parameters. The levels of pesticides, PAHs and heavy metals were found to decrease in the order sediment followed by prawn and water. The maximum concentrations of pesticides in sediment, prawn and water were α-BHC (174.2 μg g − 1), γ-BHC (234 μg g − 1), malathion (256 μg g − 1), chloripyrifos (198.5 μg g − 1), endosulfan (238 μg g − 1), dieldrin (19.6 μg g − 1) and p, p′-DDT (128.6 μg g − 1). Isodrin was found below detectable limit. The maximum concentrations of PAHs in sediment, prawn and water are anthracene (0.901 μg kg − 1), fluranthene (0.601 μg kg − 1), pyrene (0.786 μg kg − 1), chrysene (0.192 μg kg − 1), benzo( a)pyrene (0.181 μg kg − 1) and benzo( ghi)perylene (227 μg kg − 1). Benzo( e)pyrene, perylene, isomers of dibenzoanthracene and coronene were found below detectable limits. The maximum concentrations of heavy metals in sediment, prawn and water and also in prawn feed are Cu (791 μg g − 1), Pb (270 μg g − 1), Cd (1.07 μg g − 1), Mn (4417 μg g − 1), Ni (8.1 μg g − 1), Co (5.8 μg g − 1), Zn (1076 μg g − 1), Cr (36.4 μg g − 1), As (2.9 μg g − 1), Se (6.3 μg g − 1), Th (2.1 μg g − 1) and Mo (0.762 μg g − 1).

Spatial distribution and seasonal changes of pesticides in Lake Biwa, Japan

The spatial distribution and seasonal variation in the concentrations in Lake Biwa of pesticides used in paddy fields were studied. Lake Biwa is the largest lake in Japan and is a recognized water resource for 14 million people in the Kinki district. Samples were collected nine times from April to December 2001 at ten sites within the lake and at the mouths of six influent rivers. Weekly sampling was also carried out at a single site on an effluent river. Among the 20 pesticides analyzed, the detection frequencies in surface water were almost 100% for simetryn, bromobutide, and isoprothiolane; around 75% for molinate and pyroquilon; around 30% for three herbicides and one fungicide; and almost zero for the remaining substances. The maximum concentrations of pesticides detected frequently in the lake were in the range 0.1–0.4 µg l−1. The occurrence of a few pesticides below the thermocline may be explained by thermal stratification and vertical circulation. Although the thermocline suppressed vertical diffusion in spring and summer during pesticide application periods, a few pesticides remaining at the surface of the lake in winter were transported to the hypolimnion by vertical circulation and remained there even after the reestablishment of the thermocline. The half-lives of pesticides in the lake were estimated to be more than a year for simetryn, half a year for bromobutide, 1.5 months for molinate, and 1 month for dimepiperate. The main cause of elimination for molinate and dimepiperate was estimated to be degradation, that for simetryn was outflow, and for bromobutide both degradation and outflow were significant.

Prediction of pesticide concentrations found in rivers in the UK.

SWATCATCH is a distributed model combined with databases within a GIS as the POPPIE system to predict pesticide concentrations in rivers at the catchment outlet. The model was evaluated against a dataset of pesticide concentrations in rivers of England and Wales. More than 2000 individual analyses in each of the years 1995 and 1997 covered approximately 150 catchment-pesticide combinations drawn from 29 catchments and 16 pesticides, themselves selected to represent a range of characteristics and properties. SWATCATCH was better able to simulate maximum pesticide concentrations at any time during the year than the proportion of samples containing residues of a particular pesticide above the limit of quantification. The model simulated maximum pesticide concentrations in surface waters which were within a factor of 10 of those observed for 66-74% of catchment-pesticide-year combinations. Simulated and observed frequency of detection could not be differentiated using a Chi 2 test for 54-67% of simulations. Time series analysis for seven of the 29 catchment-pesticide combinations indicated that measured and detected series of concentrations generally followed similar patterns. The evaluation supports the intended use of the model in assisting the construction of pesticide monitoring programmes.

Simulation and model comparison of unsaturated movement of pesticides from a large clay lysimeter

A long-term (>10 months) leaching experiment was conducted with a large clay soil column and a rain simulator to study unsaturated transport of the nematicide aldicarb and the herbicide simazine in a cracked clay soil. Water retention and soil conductivity were derived from experimental outflow data and deterministic parameter estimation techniques. Under conventional application rates and realistic rain events, aldicarb's aerobic metabolites were found in very high concentrations, and did not meet the normal EC levels for water during the entire measuring period. A mass balance for aldicarb showed that 0.35% of the initial dose was leached. However, when the two isosteric metabolites aldicarb-sulfoxide and aldicarb-sulfone were included in the mass balance, this percentage increased dramatically to 19.7%. Simazine was found in relatively low concentrations of 0.05–0.6 μg/l, and only 0.11% of the initial dose was leached over 280 days. The absence of a `breakthrough behaviour' (peak exposure) implies long term delivery (chronic exposure) of the compound from the soil. The predictive performances of the widely used pesticide leaching models VARLEACH, LEACHP, MACRO, PESTLA and SIMULAT, which differ in their basic concepts for calculating water and solute transport and pesticide behaviour, were compared. This ring test revealed that none of the models were able to describe both water percolation and pesticide leaching to a completely satisfying degree. Moreover, there is little agreement on maximum pesticide concentrations and the time period in which these occur. This conclusion seriously limits the possibilities of model application and conducting reliable risk assessments for pesticides which are applied on the studied, or similar type of clay soils.

Movement of pesticides to surface waters from a heavy clay soil

AbstractA field experiment at Cockle Park, Northumberland on a clay loam soil (Dunkeswick series) cropped with winter wheat investigated the effects of drainage and season of application on pesticide movement. Isoproturon, mecoprop, fonofos and trifluralin were applied in two consecutive seasons at normal agricultural rates to three hydrologically isolated plots each of 0.25 ha. Two of the plots were mole‐drained and the third was an undrained control. Surfacelayer flow and drainflow from each plot were monitored at 10‐min intervals. Samples of flow were analysed for pesticides to evaluate transport of applied chemicals from the site. Despite widely differing properties (Koc 20–8000 ml g−1, t1/2 10–60 days), all four pesticides were found in surface‐layer flow and mole drainflow from the site. Maximum concentrations of pesticides in flow ranged from 0.1 to 121 μg litre−1 (aqueous phase) and &lt; 0.2 to 48 μg litre−1 (particulate phase). Over two contrasting seasons, total losses of pesticides in flow followed total amounts of flow and were approximately four and five times larger, respectively, in 1990/91 than in 1989/90. The maximum loss occurred from the undrained plot and was 2.8 g isoproturon (0.45% of that applied). Total losses of autumn‐applied pesticides from an undrained plot were up to four times greater than losses from a mole‐drained plot. Mole drainage decreased movement of pesticides from this slowly permeable soil by reducing the amount of surfacelayer flow. Maximum concentrations of mecoprop and isoproturon in drainflow were 10–20 times larger following spring application than after application in autumn. Bypass flow down soil cracks was an important process by which pesticide was lost from the site, with transport to the drainage system via mole channels (55 cm depth) after less than 0.5 and 6.7 mm net drainage in the two winters.