Pesticide Runoff Research Articles

Revealing the Extent of Pesticide Runoff to the Surface Water in Agricultural Watersheds

Pesticides are beneficial in protecting crops from pests and improving agricultural productivity; however, concerns on pesticide pollution in water have increased due to their indiscriminate use and lack of adequate regulations. Many studies have focused on the risks of pesticides considering the limited number and types of pesticide residues in crops and soils, and duration, and very few have focused on surface water throughout the year. Therefore, this study comprehensively identified 308 pesticides in surface water samples collected monthly over one year in the Saemangeum Basin, Korea. Both targeted and non-targeted analyses were used to identify 171 and 24 pesticides, respectively. Results highlight the extensive extent of pesticide contamination. Among the quantified pesticides, bromobutide and pretilachlor consistently exhibited high concentrations and risk levels, as indicated by their elevated risk quotient (RQ) values. Seasonal variations in pesticide concentrations revealed distinct patterns with intensified herbicide use during summer and increased insecticide concentrations during autumn. This study highlights the presence, distribution, and associated ecological risks of pesticides in surface waters, emphasizing the necessity of comprehensive monitoring and regulatory measures to protect aquatic ecosystems. The high RQ values identified for specific pesticides underscore the urgent need to implement effective strategies to mitigate these environmental risks.

Performance of a pesticide fate model for predicting multi-year surface runoff contamination in a Mediterranean vineyard

Characterization of the risk of water contamination by pesticide runoff is an essential issue in the assessment of the environmental impact of pesticide use in agriculture. Models are valuable tools for this purpose. However, the use of pesticide runoff models implies that they can simulate the intra- and interannual variations in runoff contamination with a sufficient accuracy. In this study, we aimed to assess the performance of a modelling approach coupling Richards and convection-dispersion equations with the uniform mixing cell concept and an overland flow routine to predict the between- and within-year variability of the pesticide concentration in runoff water at the outlet of an agricultural field within a Mediterranean context. The model performance was evaluated by calibrating and validating model predictions to observed concentrations of two herbicides, diuron and glyphosate. The temporal structure of the model performance was analysed over 10 and 9 years for diuron and glyphosate, respectively. The results showed a favourable average model performance for runoff pesticide concentration prediction over approximately ten years. However, the annual performance largely varied, suggesting that at least 3 years of data are required to obtain reasonably precise runoff pesticides estimates in terms of the Nash–Sutcliffe efficiency in a Mediterranean climate. Although limited differences in the prediction performance were found between the two compounds, the within-year fluctuation of the predictions was more accurate for glyphosate than for diuron. This is interpreted by ageing effects that affect diuron sorption but not glyphosate sorption. Furthermore, the study results indicated that the parameters critical to precise estimation depend on the simulation objectives. The main parameter values to be determined include the pesticide half-life time when estimating chronic exposure to pesticide runoff and the sorption coefficient and mixing depth when predicting the maximum observed concentration during a given season.

Soil pitting mitigates runoff, erosion and pesticide surface losses in maize crops in the Belgian loess belt

Soils of the loess belt of Western Europe are intensively cropped and particularly prone to runoff and soil erosion, especially when planted with row crops such as maize or potatoes, characterized by a low soil cover during erosive spring storms. In this context, micro-basin tillage techniques could help mitigate these risks while being fairly easy to integrate into conventional cropping systems, yet very few studies have investigated the effectiveness of this technique in a maize crop. Soil pitting was therefore tested across 14 site*years of field trials in Belgium by a newly designed roller adapted to a seeding unit forming small depressions in-between maize rows. Runoff and surface losses of sediments and pesticides were measured on soil pitted plots under natural rainfall and compared with conventionally tilled plots. Seasonal runoff and erosion rates were reduced on average by 69% and 83%, respectively, following soil pitting. Median curve number (CN) values calibrated (λ = 0.05) on this dataset are 68 for the control, and 63 for the soil pitting treatment. Analysis of individual rainfall event data reveals that the mitigation effect remains consistent throughout the season, and is even slightly higher for highly erosive rainfall events than for light events. Whereas herbicide concentrations, and hence in-situ ecotoxicity risk indicators, were similar between control and soil pitted treatments at the experimental plot scale, at larger scales the environmental impact on water bodies would be mitigated by soil pitting thanks to the reduction in absolute runoff and soil loss. Future research should further investigate the impacts of soil pitting on crop yields under a broad range of rainfall conditions.

Pesticide extraction from soil into runoff under a rainfall simulator

Context Runoff estimation is an important aspect of pesticide environmental behaviour and is the major loss pathway to the environment. Aims To improve understanding of pesticide runoff. Methods Data from three rainfall simulator studies was used. Twelve pesticides were studied ranged from tightly sorbed (DDE, soil sorption coefficient (KD) ~15 000 L kg−1) to weakly sorbed (dimethoate, KD < 30). Key results Event runoff pesticide concentrations were closely related to soil concentrations (0–25 mm depth). The ratio of runoff to soil concentration (the runoff extraction ratio, ERO), was similar for pesticides with a wide range of sorption and across the three soils: runoff concentration (μg L−1) = 28 × soil concentration (mg kg−1). ERO decreased with time after spraying, presumably due to lower concentrations in the top few mm of soil. Conclusions This model provides improved or similar estimates of pesticide runoff than previous models. Similar ERO values between sites was probably due to similar hydrology (high rainfall intensity, surface sealing, moist subsoils) and erosion, and because the same masses of soil and water are involved in mixing. Reduction in runoff concentrations by leaching was not influential, because infiltration was small and soil sorption too high. Implications Conditions studied apply during summer storms on most cotton and grain land on clay soils in the northern grain and cotton lands in eastern Australia. The model should be applicable under these conditions.

Dynamic prediction of effective runoff sediment particle size for improved assessment of erosion mitigation efficiency with vegetative filter strips

The most widely implemented mitigation measure to reduce transfer of surface runoff pesticides and other pollutants to surface water bodies are vegetative filter strips (VFS). The most commonly used dynamic model for quantifying the reduction by VFS of surface runoff, eroded sediment, pesticides and other pollutants is VFSMOD, which simulates reduction of total inflow (∆Q) and of incoming eroded sediment load (∆E) mechanistically during the rainfall-runoff event. These variables are subsequently used to calculate the reduction of pesticide load by the VFS (∆P). Since errors in ∆Q and ∆E propagate into ∆P, for strongly-sorbing compounds an accurate prediction of ∆E is crucial for a reliable prediction of ∆P. The most important incoming sediment characteristic for ∆E is the median particle diameter (d50). Current d50 estimation methods are simplistic, yielding fixed d50 based on soil properties and ignoring specific event characteristics and dynamics. We derive an improved dynamic d50 parameterization equation for use in regulatory VFS scenarios based on an extensive dataset of 93 d50 values and 17 candidate explanatory variables compiled from heterogeneous data sources and methods. The dataset was analysed first using machine learning techniques (Random Forest, Gradient Boosting) and Global Sensitivity Analysis (GSA) as a dimension reduction technique and to identify potential interactions between explanatory variables. Using the knowledge gained, a parsimonious multiple regression equation with 6 predictors was developed and thoroughly tested. Since three of the predictors are event-specific (eroded sediment yield, rainfall intensity and peak runoff rate), predicted d50 vary dynamically across event magnitudes and intensities. Incorporation of the improved d50 parameterization equation in higher-tier pesticide assessment tools with VFSMOD provides more realistic quantitative mitigation in regulatory US-EPA and EU FOCUS pesticide risk assessment frameworks. The equation is also readily applicable to other erosion management problems.

Modeling of runoff water and runoff pesticide concentrations in upland bare soil using improved SPEC model.

The SPEC model (Predicted Environmental Concentrations in agricultural Soils) was developed and improved for the simulation of pesticide runoff. The model was applied to the Sakaecho upland bare soil field (Tokyo, Japan) to predict runoff water, sediment concentration in runoff water, pesticide concentrations in runoff water, and runoff sediment (clothianidin and imidacloprid) under artificial rainfall conditions. The results showed that the simulated time to first runoff agreed very well with the observed data. The simulated cumulative runoff, sediment yield, and imidacloprid concentration in sediment agreed well with the observed data (Nash-Sutcliffe Efficiency (NSE)>0.75). The simulated runoff rate agreed reasonably well with the observed data (NSE >0.5). The predicted clothianidin concentrations in sediment and in runoff water had acceptable agreement with the observed data (NSE >0). The results implied the model's potential to predict runoff water, sediment yield, and pesticide runoff.

Can Rice (Oryza sativa) Mitigate Pesticides and Nutrients in Agricultural Runoff?

Phytoremediation of nutrients and pesticides in runoff is a growing conservation effort, particularly in agriculturally intensive areas such as the lower Mississippi River Valley. In the current study, rice (Oryza sativa) was examined for its mitigation capacity of nitrogen, phosphorus, diazinon, and permethrin. Twenty-two high density polyethylene circular containers (56cm x 45cm) were used as mesocosms, with 12 mesocosms planted with rice and 10 mesocosms remaining unvegetated. Mesocosms were hydraulically connected and arranged in a series of two, with each system providing a 4h hydraulic retention time (HRT) for a total system retention time of 8h. Two treatments (RICE/RICE and RICE/BARE) of four replicates each were utilized, with three replicates of controls (BARE/BARE). Systems with RICE/RICE (8h HRT) significantly reduced diazinon (p = 0.0126), cis-permethrin (p = 0.0442), filtered orthophosphate (p = 0.0058), and total orthophosphate (p = 0.0123) compared to control systems. No significant differences were noted for trans-permethrin, nitrate, or ammonium. Results indicate promise in phytoremediation of agricultural runoff by rice. If further studies reveal contaminants are not transferred into seeds, then rice could potentially serve as both a remediation tool and food source in countries facing agricultural pollution challenges.

淀川の水稲移植後渇水，スーパー出水，秋季高濃度流出に対する高頻度農薬調査—弾力的で余裕のある面源負荷としての農薬流出調査の必要性—

淀川の水稲移植後渇水，スーパー出水，秋季高濃度流出に対する高頻度農薬調査—弾力的で余裕のある面源負荷としての農薬流出調査の必要性—

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.

Modeling Pesticide Runoff from Small Watersheds through Field-Scale Management Practices: Minnesota Watershed Case Study with Chlorpyrifos

Experimental studies of pesticide fate in surface runoff offer only a snapshot of the near semi-infinite parameter combinations that can and do occur in the environment, and mechanistic modeling is often used to supplement the often limited number of experimental observations. However, what has been lacking in pesticide surface runoff modeling is the impact of field-scale best management practices (BMPs) on the concentrations of pesticides found at the watershed outlet. A novel application of melding three agricultural models together was used to address field-scale BMPs and off-target pesticide environmental concentrations at the watershed scale resulting from agricultural surface runoff. These models were the pesticide root zone model [PRZM, an edge-of-field runoff and leaching model sanctioned by the US Environmental Protection Agency (USEPA)]; the United States Department of Agriculture-Agricultural Research Service watershed scale model, the soil and water assessment tool (SWAT); and the academic model, the vegetated filter strip model (VFSMOD). Watershed models such as SWAT, using high-resolution local input data, are capable of predicting watershed behavior but are limited when addressing field-scale BMPs. A unique method to approximate a small watershed as a linear combination of sub-basins and fields [hydrologic response units (HRUs)] is presented. Water, sediment, and pesticide runoff for each HRU are simulated using the USEPA field model PRZM. Daily edge-of-field PRZM predictions for pesticides in runoff water and eroded sediment are coupled with VFSMOD to address the effectiveness of a maintained vegetated filter strip (VFS) across the growing season in reducing pesticide loadings and water quality at the watershed outlet. Daily chlorpyrifos (CHP, insecticide) concentrations simulated for the Seven Mile Creek Watershed, MN, using the above modeling approach resulted in a spectrum of concentrations reported by the MN Department of Natural Resources. Simulated VFS effectiveness when used across all pesticide-treated fields ranged between 22% and 100% reductions in CHP mass across all runoff-producing events.

Evaluation of Three Models for Simulating Pesticide Runoff from Irrigated Agricultural Fields.

Three models were evaluated for their accuracy in simulating pesticide runoff at the edge of agricultural fields: Pesticide Root Zone Model (PRZM), Root Zone Water Quality Model (RZWQM), and OpusCZ. Modeling results on runoff volume, sediment erosion, and pesticide loss were compared with measurements taken from field studies. Models were also compared on their theoretical foundations and ease of use. For runoff events generated by sprinkler irrigation and rainfall, all models performed equally well with small errors in simulating water, sediment, and pesticide runoff. The mean absolute percentage errors (MAPEs) were between 3 and 161%. For flood irrigation, OpusCZ simulated runoff and pesticide mass with the highest accuracy, followed by RZWQM and PRZM, likely owning to its unique hydrological algorithm for runoff simulations during flood irrigation. Simulation results from cold model runs by OpusCZ and RZWQM using measured values for model inputs matched closely to the observed values. The MAPE ranged from 28 to 384 and 42 to 168% for OpusCZ and RZWQM, respectively. These satisfactory model outputs showed the models' abilities in mimicking reality. Theoretical evaluations indicated that OpusCZ and RZWQM use mechanistic approaches for hydrology simulation, output data on a subdaily time-step, and were able to simulate management practices and subsurface flow via tile drainage. In contrast, PRZM operates at daily time-step and simulates surface runoff using the USDA Soil Conservation Service's curve number method. Among the three models, OpusCZ and RZWQM were suitable for simulating pesticide runoff in semiarid areas where agriculture is heavily dependent on irrigation.

Pesticide runoff from energy crops: A threat to aquatic invertebrates?

The European Union aims to reach a 10% share of biofuels in the transport sector by 2020. The major burden is most likely to fall on already established annual energy crops such as rapeseed and cereals for the production of biodiesel and bioethanol, respectively. Annual energy crops are typically cultivated in intensive agricultural production systems, which require the application of pesticides. Agricultural pesticides can have adverse effects on aquatic invertebrates in adjacent streams. We assessed the relative ecological risk to aquatic invertebrates associated with the chemical pest management from six energy crops (maize, potato, sugar beet, winter barley, winter rapeseed, and winter wheat) as well as from mixed cultivation scenarios.The pesticide exposure related to energy crops and cultivation scenarios was estimated as surface runoff for 253 small stream sites in Central Germany using a GIS-based runoff potential model. The ecological risk for aquatic invertebrates, an important organism group for the functioning of stream ecosystems, was assessed using acute toxicity data (48-h LC50 values) of the crustacean Daphnia magna. We calculated the Ecological Risk from potential Pesticide Runoff (ERPR) for all three main groups of pesticides (herbicides, fungicides, and insecticides). Our findings suggest that the crops potato, sugar beet, and rapeseed pose a higher ecological risk to aquatic invertebrates than maize, barley, and wheat. As maize had by far the lowest ERPR values, from the perspective of pesticide pollution, its cultivation as substrate for the production of the gaseous biofuel biomethane may be preferable compared to the production of, for example, biodiesel from rapeseed.

Importance of Fine Particles in Pesticide Runoff from Concrete Surfaces and Its Prediction

Pesticides such as pyrethroids have been frequently found in runoff water from urban areas and the offsite movement is a significant cause for aquatic toxicities in urban streams and estuaries. To better understand the origination of pesticide residues in urban runoff, we investigated the association of pyrethroid residues with loose particles in runoff water from concrete surfaces after treatment with commercial products of bifenthrin and permethrin. In runoff water generated from simulated precipitations after 1 to 89 d exposure under dry outdoor conditions, over 80% of the pesticides was found on particles >0.7 μm for most treatments. The solid-water partitioning coefficient (K(d)) on day 1 was estimated to be 2.4 × 10(3) to 1.1 × 10(5) L/kg for permethrin and bifenthrin on these solids. Except for solid formulations, the pesticide-laden particles likely originated from dust particles preexisting on the concrete before treatment and the disintegration of the surficial concrete matter through weathering. We consequently tested a simple sponge-wipe method to collect and analyze the loose particles on concrete. Concurrent analyses (n = 30) showed an excellent linear correlation between the amount of pesticides transferrable to runoff water and that on the wipe (R(2) = 0.78, slope = 1.13 ± 0.11, P < 0.0001). The fact that the linear relationship has a slope close to 1.0 suggests that this method may be used to predict pesticide residues available for contaminating runoff water before runoff actually occurs. The importance of loose particles should be considered when developing practices to mitigate pesticide runoff contamination from urban residential areas.

National Assessment of Pesticide Runoff Loads from Grass Surfaces

Pesticide runoff loads from grass surfaces were estimated through simulation experiments for 37 chemicals registered for use on U.S. lawns and golf courses. Simulation runs were made for each chemical and surface (lawns, greens, fairways) using 100-year weather records generated for nine U.S. cities. Results were summarized as mean annual and 1-in-10 year annual maximum daily pesticide loads. These loads varied greatly with pesticide, grass surface, and city, ranging from less than one to over 400 g/ha for mean annual loads and from less than one to over 500 g/ha for 1-in-10 year maximum daily loads. Mean annual loads averaged over the 37 chemicals and three grass surfaces were found to be closely related to growing season precipitation. Variations among the nine cities were well-captured by three general climate categories: humid, represented by Atlanta and Houston; mesic, as with Albany, Columbus, Madison, and Olympia; and dry, represented by Bismarck, Fresno, and Roswell. Mean annual pesticide runoff...

Seasonal Changes of Macroinvertebrate Communities in a Stormwater Wetland Collecting Pesticide Runoff From a Vineyard Catchment (Alsace, France)

Agricultural land use may influence macroinvertebrate communities by way of pesticide contamination associated with agricultural runoff. However, information about the relation between runoff-related pesticides and communities of benthic macroinvertebrates in stormwater wetland that receive agricultural runoff does not currently exist. Here we show changes in macroinvertebrates communities of a stormwater wetland that collects pesticide-contaminated runoff from a vineyard catchment. Sixteen runoff-associated pesticides, including the insecticide flufenoxuron, were continuously quantified at the inlet of the stormwater wetland from April to September (period of pesticide application). In parallel, benthic macroinvertebrate communities, pesticide concentrations, and physicochemical parameters in the wetland were assessed twice a month. Twenty-eight contaminated runoffs ranging from 1.1 to 114 m3 entered the wetland during the study period. Flufenoxuron concentrations in runoff-suspended solids ranged from 1.5 to 18.5 μg kg(-1) and reached 6 μg kg(-1) in the wetland sediments. However, flufenoxuron could not be detected in water. The density, diversity, and abundance of macroinvertebrates largely varied over time. Redundancy and formal concept analyses showed that concentrations of flufenoxuron, vegetation cover, and flow conditions significantly determine the community structures of stormwater wetland macroinvertebrates. This study shows that flow conditions, vegetation cover, and runoff-related pesticides jointly affect communities of benthic macroinvertebrates in stormwater wetlands.

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.

Ecological Risk Assessment of Pesticide Runoff from Grass Surfaces

An ecological risk assessment was performed for runoff of 37 pesticides registered for use on grass surfaces (lawns and golf courses) in the U.S. The assessment was based on 100-yr simulations using TPQPond, a newly developed model of pesticide runoff and subsequent accumulation in a receiving pond. One-in-10 yr pond concentrations were compared with acute toxicity end points for fish, invertebrates, and algae. Simulations were performed for pesticides applied at label rates on lawns, fairways, and greens using weather data for nine U.S. locations. Runoff of 4 of the 37 pesticides produced potential acute risk to invertebrates or fish. Two chemicals posed a comparable danger to plants. Risk was highest with fairways and lowest for greens. Locations with long growing seasons and large amounts of precipitation produced the highest risks. The risk assessment followed the general protocols recommended by USEPA, but with different models, weather data, and scenarios. In spite of the differences, the results confirmed that most but not all of the pesticides which had survived the USEPA registration process were also demonstrated safe, with respect to acute risks, by this independent assessment. The five exceptions were explained by differences in models, simulation scenarios, and input data. These results do not mean that the studied pesticides are free of any ecological dangers. In particular, no attempt was made to evaluate chronic risk.

Parameter Importance and Uncertainty in Predicting Runoff Pesticide Reduction with Filter Strips

Vegetative filter strips (VFS) are an environmental management tool used to reduce sediment and pesticide transport from surface runoff. Numerical models of VFS such as the Vegetative Filter Strip Modeling System (VFSMOD-W) are capable of predicting runoff, sediment, and pesticide reduction and can be useful tools to understand the effectiveness of VFS and environmental conditions under which they may be ineffective. However, as part of the modeling process, it is critical to identify input factor importance and quantify uncertainty in predicted runoff, sediment, and pesticide reductions. This research used state-of-the-art global sensitivity and uncertainty analysis tools, a screening method (Morris) and a variance-based method (extended Fourier Analysis Sensitivity Test), to evaluate VFSMOD-W under a range of field scenarios. The three VFS studies analyzed were conducted on silty clay loam and silt loam soils under uniform, sheet flow conditions and included atrazine, chlorpyrifos, cyanazine, metolachlor, pendimethalin, and terbuthylazine data. Saturated hydraulic conductivity was the most important input factor for predicting infiltration and runoff, explaining >75% of the total output variance for studies with smaller hydraulic loading rates ( approximately 100-150 mm equivalent depths) and approximately 50% for the higher loading rate ( approximately 280-mm equivalent depth). Important input factors for predicting sedimentation included hydraulic conductivity, average particle size, and the filter's Manning's roughness coefficient. Input factor importance for pesticide trapping was controlled by infiltration and, therefore, hydraulic conductivity. Global uncertainty analyses suggested a wide range of reductions for runoff (95% confidence intervals of 7-93%), sediment (84-100%), and pesticide (43-100%) . Pesticide trapping probability distributions fell between runoff and sediment reduction distributions as a function of the pesticides' sorption. Seemingly equivalent VFS exhibited unique and complex trapping responses dependent on the hydraulic and sediment loading rates, and therefore, process-based modeling of VFS is required.

Detention and Recycling Basins for Managing Nutrient and Pesticide Runoff from Nurseries

Production nurseries may be significant sources of nutrients and pesticides in runoff as a result of the intensity at which fertilizers, pesticides, and irrigation water are applied. Concentrations of nutrients and pesticides in runoff from production nurseries are not extensively documented. Runoff from 11 production nurseries in southern California using either recycling or detention basins was monitored for nutrients and pesticides. For six sites, runoff volume was determined and nutrient loads in runoff were calculated. Water use data, percentage of water recycled, and construction costs were determined for sites with recycling systems. Nutrient concentrations, mass loads, and pesticide detections in runoff from some sites would have been of concern without the implementation of detention or recycle basins. There were few differences in nutrient concentrations or pesticide detections between runoff from irrigation and that from precipitation events. This suggests the need for management practices and technologies that address runoff from both irrigation and precipitation events. Water use and cost data suggested that the implementation of recycling systems may be more beneficial and cost-efficient for larger facilities.

Use of toxicity identification evaluations to determine the pesticide mitigation effectiveness of on-farm vegetated treatment systems

Evidence of ecological impacts from pesticide runoff has prompted installation of vegetated treatment systems (VTS) along the central coast of California, USA. During five surveys of two on-farm VTS ponds, 88% of inlet and outlet water samples were toxic to Ceriodaphnia dubia. Toxicity identification evaluations (TIEs) indicated water toxicity was caused by diazinon at VTS-1, and chlorpyrifos at VTS-2. Diazinon levels in VTS-1 were variable, but high pulse inflow concentrations were reduced through dilution. At VTS-2, chlorpyrifos concentrations averaged 52% lower at the VTS outlet than at the inlet. Water concentrations of most other pesticides averaged 20-90% lower at VTS outlets. All VTS sediment samples were toxic to amphipods (Hyalella azteca). Sediment TIEs indicated toxicity was caused by cypermethrin and lambda-cyhalothrin at VTS-1, and chlorpyrifos and permethrin at VTS-2. As with water, sediment concentrations were lower at VTS outlets, indicating substantial reductions in farm runoff pesticide concentrations.