A web-based pesticide risk assessment tool for drinking water protection zones in Sweden.

To protect human health, wildlife and the aquatic environment, "safe uses" of pesticides are determined at the EU level while product authorization and terms of use are established at the national level. In Sweden, extra precaution is taken to protect drinking water, and permits are therefore required for pesticide use within abstraction zones. This paper presents MACRO-DB, a tool for assessing pesticide contamination risks of groundwater and surface water, used by authorities to support their decision-making for issuing such permits. MACRO-DB is a meta-model based on 583,200 simulations of the physically-based MACRO model used for assessing pesticide leaching risks at EU and national level. MACRO-DB is simple to use and runs on widely available input data. In a qualitative comparative assessment for two counties in Sweden, MACRO-DB outputs were in general agreement with groundwater monitoring data and matched or were more protective than the national risk assessment procedure for groundwater.

Identification of Pesticide Transformation Products in Surface Water Using Suspect Screening Combined with National Monitoring Data.

Pesticides are widespread anthropogenic chemicals and well-known environmental contaminants of concern. Much less is known about transformation products (TPs) of pesticides and their presence in the environment. We developed a novel suspect screening approach for not well-explored pesticides (n = 16) and pesticide TPs (n = 242) by integrating knowledge from national monitoring with high-resolution mass spectrometry data. Weekly time-integrated samples were collected in two Swedish agricultural streams using the novel Time-Integrating, MicroFlow, In-line Extraction (TIMFIE) sampler. The integration of national monitoring data in the screening approach increased the number of prioritized compounds approximately twofold (from 23 to 42). Ultimately, 11 pesticide TPs were confirmed by reference standards and 12 TPs were considered tentatively identified with varying levels of confidence. Semiquantification of the newly confirmed TPs indicated higher concentrations than their corresponding parent pesticides in some cases, which highlights concerns related to (unknown) pesticide TPs in the environment. Some TPs were present in the environment without co-occurrence of their corresponding parent compounds, indicating higher persistency or mobility of the identified TPs. This study showcased the benefits of integrating monitoring knowledge in this type of studies, with advantages for suspect screening performance and the possibility to increase relevance of future monitoring programs.

Pesticide mixture toxicity to algae in agricultural streams - Field observations and laboratory studies with in situ samples and reconstituted water.

Long-term pesticide water concentrations were investigated in four agricultural streams and their mixture toxicity on algae was assessed, based on realistic (i.e. observed) concentrations in laboratory tests using (i) natural weekly water samples and (ii) reconstituted pesticide-spiked water samples representing mixtures with predicted high mixture. This approach both covered the full complexity of natural water samples and the controlled approach of reconstituted water samples. Long-term monitoring data (time-integrated, weekly samples) revealed more than 11 pesticides (range 11.0 ± 0.25-24.0 ± 0.44) in 75% or more of the almost 1600 samples collected between 2002 and 2018. ∑TUalgae exceeded 0.1 for 29 observations (or 1.8%). Despite the multitude of pesticides in a sample, ∑TUalgae was frequently set by one or a few dominating pesticides that contribute to more than 90% of the mixture's toxicity. Algal growth inhibition tests with in situ stream water showed a high frequency of inhibition, despite the low ∑TU for most of these samples (range 0.000014-0.3858). These "false positive" results were attributed to confounding effects of turbidity, the complexation of nutrients, and toxic effects of metals and/or other unknown contaminants. Algal inhibition tests with spiked reconstituted water showed significant inhibitory effects in the range of 1-10x the ∑TUalgae observed in worst-case field samples. Although these tests disregard the chemical complexity of natural water, they show that inhibitory effects of pesticides on algae may occur at the ∑TUalgae observed in monitoring. Furthermore, considering that the ∑TUalgae of stream water are based on weekly average concentrations and likely underestimate short-term peak concentrations of pesticides, these results strongly suggest that inhibitory effects on algae may occur in the agricultural streams of southern Sweden. We conjecture, however, that the rapid recovery of algae contributes to ameliorate these short-term effects and that pesticide contamination should be seen as one of many stressors in the streams that drain agricultural landscapes.

TIMFIE Sampler-A New Time-Integrating, Active, Low-Tech Sampling Device for Quantitative Monitoring of Pesticides in Whole Water.

The need for inexpensive, time-averaged, quantitative determination of pesticides and other organic pollutants in whole water is not matched by the field sampling procedures available. Our new Time-Integrating, MicroFlow, In-line Extraction (TIMFIE) sampler comprises a low-tech syringe pump driven by a rubber band and connected to a flow restrictor enabling low microliter per minute water flow through a solid phase extraction (SPE) cartridge. This allows target compounds to be continuously extracted in the field over 1 week. The extracted water ends up in the syringe, where sample volume is accurately determined. TIMFIE followed by online SPE-LC-MS/MS determination was validated for 72 selected pesticides, and, except for three compounds, detection limit was 0.1-1 ng/L. In a field study, concentrations in TIMFIE samples and in grab samples were compared. Following TIMFIE sampling, on average 19 pesticides per sample were quantified, compared with nine pesticides per sample with grab sampling, as a result of the extra in-field concentration step. Duplicate TIMFIE sampling showed Pearson's correlation coefficient r = 0.998. Comparing concentrations from TIMFIE sampling to grab sampling resulted in ratios between 0.05 and 16.5 (mean 1.7; r = 0.532), demonstrating a discrepancy between the two sampling strategies and possible underestimation of chronic exposure by grab sampling.

Surface Runoff of Pesticides from a Clay Loam Field in Sweden.

Pesticides stored at or close to the soil surface after field application can be mobilized and transported off the field when surface runoff occurs. The objective of our study was to quantify the potential pesticide losses in surface runoff from a conventionally managed agricultural field in a Swedish climate. This was achieved by measuring surface runoff volumes and concentrations in runoff of six spring-applied pesticides and autumn-applied glyphosate and its metabolite aminomethylphosphonic acid (AMPA). Measurements were performed for 3 yr both during the growing seasons and during intervening winter snowmelt periods on a clay loam field close to Uppsala. During growing seasons, surface runoff was generated on only five occasions during one 25-d period in 2012 when the infiltration capacity of the soil may have been reduced by structural degradation due to large cumulative rainfall amounts after harrowing. Concentrations in surface runoff exceeded Swedish water quality standards in all samples during this growing season for diflufenican and pirimicarb. Surface runoff was generated during three snowmelt periods during the winter of 2012-2013. All of the applied pesticides were found in snowmelt samples despite incorporation of residues by autumn plowing, degradation, and leaching into the soil profile during the period between spraying and sampling. Concentrations of glyphosate ranged from 0.12 to 7.4 µg L, and concentrations of AMPA ranged from 0 to 2.7 µg L. Our results indicate that temporal changes in hydraulic properties during the growing season and when the soil freezes during winter affect pesticide losses through surface runoff.

Greenhouse production contributes to pesticide occurrences in Swedish streams.

Greenhouse and other covered cultivation systems have increased globally over the past several decades, leading to considerably improved product quality and productivity per land area unit. However, there is a paucity in information regarding the environmental impacts of covered production systems, especially regarding pesticides entering the surrounding environment. Aiming to address this knowledge gap, we collected grab samples downstream of greenhouses from seven Swedish streams every 14 days during a 12 month period. In three of the streams, samples were also taken upstream of the greenhouses and in four of the streams time-integrated samples were collected by TIMFIE samplers in the period between grab sampling occasions. The samples were analyzed for 28 substances (27 that were permitted for use in greenhouse production systems in Sweden and one degradation product to a permitted substance). Pesticide use journals were collected from the greenhouse producers for the 12 month period. The results were examined for indications of greenhouse contributions to detection frequencies, maximum and average concentrations, and potential ecotoxicicity in several ways: (1) comparing locations downstream of greenhouses with registered use of a substance with those without registered use, (2) comparing results from this study with those from the Swedish environmental monitoring program of pesticides in surface water from catchments with no greenhouses from the same period and region, (3) comparing concentration trends with registered pesticide application times in the greenhouses, and (4) comparing up- and downstream concentrations. The results strongly suggest that greenhouse applications do contribute to pesticide occurrences, maximum and median concentrations for most of the pesticides included in this study, and to potential toxicity to aquatic organisms for several of them, most notably imidacloprid, acetamiprid, carbendazim, and pirimicarb.

Multiresidue analysis of 95 pesticides at low nanogram/liter levels in surface waters using online preconcentration and high performance liquid chromatography/tandem mass spectrometry.

A new multiresidue method for the analysis of 95 pesticides and breakdown products with a wide range of physiochemical properties in surface and ground water using online solid-phase extraction coupled with HPLC/MS/MS is presented. Using an injection volume of only 500 microL filtered water, an LOD in the 1-10 ng/L range was achieved for all but one substance, and recoveries were, with a few exceptions, in the 70-120% range. Large differences were found in the adsorption of pesticides on nine filter materials tested for filtration of the water samples. Filters of regenerated cellulose were chosen due to good recoveries and easy handling. Results from the proposed method were compared with results from previously used methods for 31 pesticides in 99 surface water samples, collected in 2008, with good agreement.

Concentrations, fluxes and field calibration of passive water samplers for pesticides and hazard-based risk assessment.

Three passive sampler types including Chemcatcher® C18, polar organic chemical integrative sampler-hydrophilic-lipophilic balance (POCIS-HLB) and silicone rubber (SR) based on polydimethylsiloxane (PDMS) were evaluated for 124 legacy and current used pesticides at two sampling locations in southern Sweden over a period of 6 weeks and compared to time-proportional composite active sampling. In addition, an in situ calibration was performed resulting in median in situ sampling rates (RS, L day-1) of 0.01 for Chemcatcher® C18, 0.03 for POCIS-HLB, and 0.18 for SR, and median in situ passive sampler-water partition coefficients (log KPW, L kg-1) of 2.76 for Chemcatcher® C18, 3.87 for POCIS-HLB, and 2.64 for SR. Deisopropylatrazine D5 showed to be suitable as a performance reference compound (PRC) for SR. There was a good agreement between the pesticide concentrations using passive and active sampling. However, the three passive samplers detected 38 pesticides (including 9 priority substances from the EU Water Framework Directive (WFD) and 2 pyrethriods) which were not detected by the active sampler. The most frequently detected pesticides with a detection frequency of >90% for both sites were atrazine, 2,6-dichlorobenzamide, bentazone, chloridazon, isoproturon, and propiconazole. The annual average environmental quality standard (AA-EQS) for inland surface waters of the EU WFD and the risk quotient (RQ) of 1 was exceeded on a number of occasions indicating potential risk for the aquatic environment.

Spatial and temporal patterns of pesticide concentrations in streamflow, drainage and runoff in a small Swedish agricultural catchment.

A better understanding of the dominant source areas and transport pathways of pesticide losses to surface water is needed for targeting mitigation efforts in a more cost-effective way. To this end, we monitored pesticides in surface water in an agricultural catchment typical of one of the main crop production regions in Sweden. Three small sub-catchments (88-242ha) were selected for water sampling based on a high-resolution digital soil map developed from proximal sensing methods and soil sampling; one sub-catchment had a high proportion of clay soils, another was dominated by coarse sandy soils while the third comprised a mix of soil types. Samples were collected from the stream, from field drains discharging into the stream and from within-field surface runoff during spring and early summer in three consecutive years. These samples were analyzed by LC-MS/MS for 99 compounds, including most of the polar and semi-polar pesticides frequently used in Swedish agriculture. Information on pesticide applications (products, doses and timing) was obtained from annual interviews with the farmers. There were clear and consistent differences in pesticide occurrence in the stream between the three sub-catchments, with both the numbers of detected compounds and concentrations being the largest in the area with a high proportion of clay soils and with very few detections in the sandy sub-catchment. Macropore flow to drains was most likely the dominant loss pathway in the studied area. Many of the compounds that were detected in drainage and stream water samples had not been applied for several years. This suggests that despite the predominant role of fast flow pathways in determining losses to the stream, long-term storage along the transport pathways also occurs, presumably in subsoil horizons where degradation is slow.

Pesticide mixtures in the Swedish streams: Environmental risks, contributions of individual compounds and consequences of single-substance oriented risk mitigation.

This paper presents the ecotoxicological assessment and environmental risk evaluation of complex pesticide mixtures occurring in freshwater ecosystems in southern Sweden. The evaluation is based on exposure data collected between 2002 and 2013 by the Swedish pesticide monitoring program and includes 1308 individual samples, detecting mixtures of up to 53 pesticides (modal=8). Pesticide mixture risks were evaluated using three different scenarios for non-detects (best-case, worst-case and using the Kaplan-Meier method). The risk of each scenario was analyzed using Swedish Water Quality Objectives (WQO) and trophic-level specific environmental thresholds. Using the Kaplan-Meier method the environmental risk of 73% of the samples exceeded acceptable levels, based on an assessment using Concentration-Addition and WQOs for the individual pesticides. Algae were the most sensitive organism group. However, analytical detection limits, especially for insecticides, were insufficient to analyze concentrations at or near their WQO's. Thus, the risk of the analyzed pesticide mixtures to crustaceans and fish is systematically underestimated. Treating non-detects as being present at their individual limit of detection increased the estimated risk by a factor 100 or more, compared to the best-case or the Kaplan-Meier scenario. Pesticide mixture risks are often driven by only 1-3 compounds. However, the risk-drivers (i.e., individual pesticides explaining the largest share of potential effects) differ substantially between sites and samples, and 83 of the 141 monitored pesticides need to be included in the assessment to account for 95% of the risk at all sites and years. Single-substance oriented risk mitigation measures that would ensure that each individual pesticide is present at a maximum of 95% of its individual WQO, would also reduce the mixture risk, but only from a median risk quotient of 2.1 to a median risk quotient of 1.8. Also, acceptable total risk levels would still be exceeded in more than 70% of the samples.

Pesticides from wastewater treatment plant effluents affect invertebrate communities.

We quantified pesticide contamination and its ecological impact up- and downstream of seven wastewater treatment plants (WWTPs) in rural and suburban areas of central Germany. During two sampling campaigns, time-weighted average pesticide concentrations (cTWA) were obtained using Chemcatcher® passive samplers; pesticide peak concentrations were quantified with event-driven samplers. At downstream sites, receiving waters were additionally grab sampled for five selected pharmaceuticals. Ecological effects on macroinvertebrate structure and ecosystem function were assessed using the biological indicator system SPEARpesticides (SPEcies At Risk) and leaf litter breakdown rates, respectively. WWTP effluents substantially increased insecticide and fungicide concentrations in receiving waters; in many cases, treated wastewater was the exclusive source for the neonicotinoid insecticides acetamiprid and imidacloprid in the investigated streams. During the ten weeks of the investigation, five out of the seven WWTPs increased in-stream pesticide toxicity by a factor of three. As a consequence, at downstream sites, SPEAR values and leaf litter degradation rates were reduced by 40% and 53%, respectively. The reduced leaf litter breakdown was related to changes in the macroinvertebrate communities described by SPEARpesticides and not to altered microbial activity. Neonicotinoids showed the highest ecological relevance for the composition of invertebrate communities, occasionally exceeding the Regulatory Acceptable Concentrations (RACs). In general, considerable ecological effects of insecticides were observed above and below regulatory thresholds. Fungicides, herbicides and pharmaceuticals contributed only marginally to acute toxicity. We conclude that pesticide retention of WWTPs needs to be improved.

Characterization and Application of Passive Samplers for Monitoring of Pesticides in Water.

Five different water passive samplers were calibrated under laboratory conditions for measurement of 124 legacy and current used pesticides. This study provides a protocol for the passive sampler preparation, calibration, extraction method and instrumental analysis. Sampling rates (RS) and passive sampler-water partition coefficients (KPW) were calculated for silicone rubber, polar organic chemical integrative sampler POCIS-A, POCIS-B, SDB-RPS and C18 disk. The uptake of the selected compounds depended on their physicochemical properties, i.e., silicone rubber showed a better uptake for more hydrophobic compounds (log octanol-water partition coefficient (KOW) > 5.3), whereas POCIS-A, POCIS-B and SDB-RPS disk were more suitable for hydrophilic compounds (log KOW < 0.70).

Environmental monitoring of pesticide exposure and effects on mangrove aquatic organisms of Mozambique.

The use of pesticides in Mozambique is increasing along with the development of agriculture in the country. Mangroves along the coastlines are ecologically important areas and vital nursing grounds for many aquatic species, several of which are of high economic value in Mozambique. Barred mudskipper (Periophthalmus argentilineatus), Jarbua fish (Terapon jarbua), Indian white prawn (Penaeus indicus) and the clam Meretrix meretrix were collected at three mangrove sites in the Maputo Bay area. This was complemented with samplings of the freshwater fish Mozambique tilapia (Oreochromis mossambicus), which was collected from three sampling sites along rivers in the surroundings of Maputo and from three sites along the Olifants and Limpopo River. Acetylcholinesterase (AChE) activity, which is an established biomarker for organophosphates and carbamate pesticides, was measured in brain and liver tissue in fish, and hepatopancreas tissue in prawn and clam. Butyrylcholinesterase (BChE) activity was also analyzed. Freshwater samples for pesticide analyses were collected in order to get an initial understanding of the classes and levels of pesticides present in aquatic systems in Mozambique. In addition to field samplings two 48-h exposure experiments were also conducted where the Indian white prawn and Barred mudskipper were exposed to malathion, and Mozambique tilapia exposed to malathion and diazinon. Field results show a significant decrease in AChE activity in fish from four of the sampling sites suggesting that pesticides present in water could be one stressor potentially affecting aquatic organisms negatively. The 48 h exposure experiment results showed a clear dose-response relationship of AChE activity in mudskipper and tilapia suggesting these species as suitable as sentinel species in environmental studies.

Stochastic modeling of diffuse pesticide losses from a small agricultural catchment.

The objective of this study was to identify the main sources of variation in pesticide losses at field and catchment scales using the dual permeability model MACRO. Stochastic simulations of the leaching of the herbicide MCPA (4-chloro-2-methylphenoxyacetic acid) were compared with seven years of measured concentrations in a stream draining a small agricultural catchment and one year of measured concentrations at the outlet of a field located within the catchment. MACRO was parameterized from measured probability distributions accounting for spatial variability of soil properties and local pedotransfer functions derived from information gathered in field- and catchment-scale soil surveys. At the field scale, a single deterministic simulation using the means of the input distributions was also performed. The deterministic run failed to reproduce the summer outflows when most leaching occurred, and greatly underestimated pesticide leaching. In contrast, the stochastic simulations successfully predicted the hydrologic response of the field and catchment and there was a good resemblance between the simulations and measured MCPA concentrations at the field outlet. At the catchment scale, the stochastic approach underestimated the concentrations of MCPA in the stream, probably mostly due to point sources, but perhaps also because the distributions used for the input variables did not accurately reflect conditions in the catchment. Sensitivity analyses showed that the most important factors affecting MACRO modeled diffuse MCPA losses from this catchment were soil properties controlling macropore flow, precipitation following application, and organic carbon content.

Characterization of five passive sampling devices for monitoring of pesticides in water.

Five different passive sampler devices were characterized under laboratory conditions for measurement of 124 legacy and current used pesticides in water. In addition, passive sampler derived time-weighted average (TWA) concentrations were compared to time-integrated active sampling in the field. Sampling rates (RS) and passive sampler-water partition coefficients (KPW) were calculated for individual pesticides using silicone rubber (SR), polar organic chemical integrative sampler (POCIS)-A, POCIS-B, Chemcatcher(®) SDB-RPS and Chemcatcher(®) C18. The median RS (Lday(-1)) decreased as follows: SR (0.86)>POCIS-B (0.22)>POCIS-A (0.18)>Chemcatcher(®) SDB-RPS (0.05)>Chemcatcher(®) C18 (0.02), while the median logKPW (Lkg(-1)) decreased as follows: POCIS-B (4.78)>POCIS-A (4.56)>Chemcatcher(®) SDB-RPS (3.17)>SR (3.14)>Chemcatcher(®)C18 (2.71). The uptake of the selected compounds depended on their physicochemical properties, i.e. SR showed a better uptake for more hydrophobic compounds (log octanol-water partition coefficient (KOW)>5.3), whereas POCIS-A, POCIS-B and Chemcatcher(®) SDB-RPS were more suitable for hydrophilic compounds (logKOW<0.70). Overall, the comparison between passive sampler and time-integrated active sampler concentrations showed a good agreement and the tested passive samplers were suitable for capturing compounds with a wide range of KOW's in water.

Direct and indirect effects of climate change on herbicide leaching--a regional scale assessment in Sweden.

Climate change is not only likely to improve conditions for crop production in Sweden, but also to increase weed pressure and the need for herbicides. This study aimed at assessing and contrasting the direct and indirect effects of climate change on herbicide leaching to groundwater in a major crop production region in south-west Sweden with the help of the regional pesticide fate and transport model MACRO-SE. We simulated 37 out of the 41 herbicides that are currently approved for use in Sweden on eight major crop types for the 24 most common soil types in the region. The results were aggregated accounting for the fractional coverage of the crop and the area sprayed with a particular herbicide. For simulations of the future, we used projections of five different climate models as model driving data and assessed three different future scenarios: (A) only changes in climate, (B) changes in climate and land-use (altered crop distribution), and (C) changes in climate, land-use, and an increase in herbicide use. The model successfully distinguished between leachable and non-leachable compounds (88% correctly classified) in a qualitative comparison against regional-scale monitoring data. Leaching was dominated by only a few herbicides and crops under current climate and agronomic conditions. The model simulations suggest that the direct effects of an increase in temperature, which enhances degradation, and precipitation which promotes leaching, cancel each other at a regional scale, resulting in a slight decrease in leachate concentrations in a future climate. However, the area at risk of groundwater contamination doubled when indirect effects of changes in land-use and herbicide use, were considered. We therefore concluded that it is important to consider the indirect effects of climate change alongside the direct effects and that effective mitigation strategies and strict regulation are required to secure future (drinking) water resources.

The legacy of pesticide pollution: An overlooked factor in current risk assessments of freshwater systems.

We revealed a history of legacy pesticides in water and sediment samples from 19 small streams across an agricultural landscape. Dominant legacy compounds included organochlorine pesticides, such as DDT and lindane, the organophosphate chlorpyrifos and triazine herbicides such as terbutylazine and simazine which have long been banned in the EU. The highest concentrations of legacy pesticides were found in streams draining catchments with a large proportion of arable farmland suggesting that they originated from past agricultural applications. The sum of toxic units (SumTUD.magna) based on storm water samples from agriculturally impacted streams was significantly higher when legacy pesticides were included compared to when they were omitted. Legacy pesticides did not significantly change the predicted toxicity of water samples to algae or fish. However, pesticide concentrations in bed sediment and suspended sediment samples exceeded safety thresholds in 50% of the samples and the average contribution of legacy pesticides to the SumTUC.riparius was >90%. Our results suggest that legacy pesticides can be highly significant contributors to the current toxic exposure of stream biota, especially macroinvertebrate communities, and that those communities were primarily exposed to legacy pesticides via the sediment. Additionally, our results suggest that neglecting legacy pesticides in the risk assessment of pesticides in streams may severely underestimate the risk of ecological effects.

Analysis of monitoring data of pesticide residues in surface waters using partial order ranking theory.

In this investigation, a new and simple way to analyze, interpret, and generalize monitoring data of occurrence of pesticide active ingredients in surface waters was developed. The occurrence is quantified using the variables frequency of detection and the concentration level. These two parameters are associated with basically different ecotoxicological effects; for example, a high frequency of detection may be related to bioaccumulation problems, while the level of concentration also controls the acute toxicological effects. The active ingredients were ranked on the basis of the monitoring data in relation to both the frequency of finding and concentration level using the concept of partial ordered sets. The resulting rankings was correlated with other rankings based on descriptors such as sprayed area, applied dose, adsorption to soil organic carbon, vapor pressure, and soil dissipation half-life. A similarity index was applied in order to compare the ranking of the monitoring data with the ranking of the descriptors. It is shown how partial order theory can be used to evaluate the relevance of every single descriptor. The dosage is found to be the most important descriptor, followed by the sprayed area and the adsorption to organic carbon ending up a very close similarity between, respectively, the rankings using monitoring data and rankings using these three descriptors.

Evaluation of pesticide monitoring strategies in agricultural streams based on the toxic-unit concept--experiences from long-term measurements.

The European Water Framework Directive requires surface water bodies to have a good chemical and ecological status. Although relatively few pesticides are included in the list of priority pollutants, they pose, due to their intrinsic biological activity, a significant risk for the integrity of aquatic ecosystems. In this context, the pesticide (up to 128 pesticides including some transformation products) exposure pattern in four agricultural streams and two rivers was determined from 2002 to 2011 under the umbrella of the Swedish national monitoring program employing time-proportional and grab sampling strategies, respectively. After transforming the measured pesticide concentrations into toxic units, the European Uniform Principles for algae (chronic), invertebrates and fish (both acute), which are partly employed as benchmark for pesticide regulation, were only occasionally (<2%) exceeded. Moreover, this evaluation showed no long-term trends over the years. However, recent publications suggested that those thresholds are not protective for ecosystem structure and function, indicating a risk of up to 20% and 35% of the samples from the agricultural streams and the rivers, respectively. Moreover, the monitoring data show a continuous but rather low toxic potential of pesticides for all three trophic levels throughout the year, which suggests pesticides as an evolutionary force in agriculturally impacted aquatic ecosystems. However, the flow-triggered sampling, which was implemented as an additional sampling strategy in one of the agricultural streams starting in 2006, displayed an up to 7-fold underestimation of the maximum concentration in terms of toxic units for daphnids and fish during run-off events. The present study thus underpins that the optimal sampling design for pesticide monitoring strongly depends on its overall purpose. If the long-term exposure pattern is of concern a time-proportional composite sampling strategy is recommended, while for an assessment of peak exposures a flow-event-triggered high-resolution sampling strategy is superior.

Spatial variation in herbicide leaching from a marine clay soil via subsurface drains.

BACKGROUND: Subsurface transport via tile drains can significantly contribute to pesticide contamination of surface waters. The spatial variation in subsurface leaching of normally applied herbicides was examined together with phosphorus losses in 24 experimental plots with water sampled flow-proportionally. The study site was a flat, tile-drained area with 60% marine clay in the topsoil in southeast Sweden. The objectives were to quantify the leaching of frequently used herbicides from a tile drained cracking clay soil and to evaluate the variation in leaching within the experimental area and relate this to topsoil management practices (tillage method and structure liming). RESULTS: In summer 2009, 0.14, 0.22 and 1.62%, respectively, of simultaneously applied amounts of MCPA, fluroxypyr and clopyralid were leached by heavy rain five days after spraying. In summer 2011, on average 0.70% of applied bentazone was leached by short bursts of intensive rain 12 days after application. Peak flow concentrations for 50% of the treated area for MCPA and 33% for bentazone exceeded the Swedish no-effect guideline values for aquatic ecosystems. Approximately 0.08% of the glyphosate applied was leached in dissolved form in the winters of 2008/2009 and 2010/2011. Based on measurements of glyphosate in particulate form, total glyphosate losses were twice as high (0.16%) in the second winter. The spatial inter-plot variation was large (72-115%) for all five herbicides studied, despite small variations (25%) in water discharge. CONCLUSIONS: The study shows the importance of local scale soil transport properties for herbicide leaching in cracking clay soils.