Spatial assessment of pesticide leaching risk to groundwater: sub-national decision making and model output aggregation.

Background: This study compares standard regulatory methodology (fixed scenarios and models) to spatial modelling at a 1 km landscape resolution for the evaluation of predicted environmental concentrations of pesticides in groundwater. The use of spatial modelling in the decision-making processes is discussed and three options for the sub-national evaluation and restriction of substances based on spatial environmental fate modelling are examined. Wheat and sugar beet are tested with two modified FOCUS substances (A and D) in the PEARL and GeoPEARL models.

Considerations of temperature in the context of the persistence classification in the EU.

Simulation degradation studies for industrial chemicals, biocidal products and plant protection products are required in the EU to estimate half-lives in soil, water and sediment for the comparison to persistence criteria for hazard (P/vP) assessment, and for use in exposure assessments. There is a discrepancy between European regulatory approaches regarding the temperature at which degradation half-lives should be (1) measured in simulation degradation testing of environmental compartments, and (2) compared to the P/vP criteria. In this paper, an opinion is provided on the options for the experimental temperature and extrapolation to other conditions.

Interpretation of aged sorption studies for pesticides and their use in European Union regulatory leaching assessments.

First-tier regulatory exposure assessments for pesticides assume that pesticide sorption is instantaneous and fully reversible. In European Union (EU) regulatory guidance, an increase in sorption over time ("aged sorption") can be considered at the higher tier to refine predicted environmental concentrations in groundwater. Research commissioned by the UK Chemicals Regulation Directorate (CRD), funded by the Department for Environment Food & Rural Affairs (Defra), formed the basis of a draft regulatory guidance document proposing 1) a protocol on how to measure aged sorption of parent compounds in laboratory studies, 2) procedures to fit kinetic models to the experimental data, 3) criteria to test the reliability of the parameters, and 4) procedures for use of the parameters in the groundwater exposure assessment.

Nanopesticides: guiding principles for regulatory evaluation of environmental risks.

Nanopesticides or nano plant protection products represent an emerging technological development that, in relation to pesticide use, could offer a range of benefits including increased efficacy, durability, and a reduction in the amounts of active ingredients that need to be used. A number of formulation types have been suggested including emulsions (e.g.

Reanalysis of experiments to quantify irreversibility of pesticide sorption-desorption in soil.

Previously published research used an isotope-exchange technique to measure irreversibility of pesticide sorption-desorption in soil. Results indicated significant irreversibility (6-51%) in sorption in five pesticide-soil systems measured over 72 h. Here, we propose a three-site model to reanalyze the experimental data.

Impacts of climate change on indirect human exposure to pathogens and chemicals from agriculture.

Climate change is likely to affect the nature of pathogens/ chemicals in the environment and their fate and transport. We assess the implications of climate change for changes in human exposures to pathogens/chemicals in agricultural systems in the UK and discuss the effects on health impacts, using expert input and literature on climate change; health effects from exposure to pathogens/chemicals arising from agriculture; inputs of chemicals/pathogens to agricultural systems; and human exposure pathways for pathogens/chemicals in agricultural systems. We established the evidence base for health effects of chemicals/pathogens in the agricultural environment; determined the potential implications of climate change on chemical/pathogen inputs in agricultural systems; and explored the effects of climate change on environmental transport and fate of various contaminants.

Impacts of climate change on indirect human exposure to pathogens and chemicals from agriculture.

Objective: Climate change is likely to affect the nature of pathogens and chemicals in the environment and their fate and transport. Future risks of pathogens and chemicals could therefore be very different from those of today. In this review, we assess the implications of climate change for changes in human exposures to pathogens and chemicals in agricultural systems in the United Kingdom and discuss the subsequent effects on health impacts.

How does crop type influence risk from pesticides to the aquatic environment?

National-level risk mapping was undertaken to identify specific situations within England with the greatest potential for impacts on aquatic biodiversity from normal agricultural use of pesticides. Calculations of exposure via spray drift and drainflow were differentiated by landscape type, region, and crop and then compared with toxicity to the indicator organisms Daphnia magna and algae. The approach incorporated regional-level information regarding pesticide usage derived from farm visits.

Factors influencing degradation of pesticides in soil.

Degradation and sorption of six acidic pesticides (2,4-D, dicamba, fluroxypyr, fluazifop-P, metsulfuron-methyl, and flupyrsulfuron-methyl) and four basic pesticides (metribuzin, terbutryn, pirimicarb, and fenpropimorph) were determined in nine temperate soils. Results were submitted to statistical analyses against a wide range of soil and pesticide properties to (i) identify any commonalities in factors influencing rate of degradation and (ii) determine whether there was any link between sorption and degradation processes for the compounds and soils studied. There were some marked differences between the soils in their ability to degrade the different pesticides.

Lysimeter experiment to investigate the potential influence of diffusion-limited sorption on pesticide availability for leaching.

Pesticide leaching from soil has been shown to decrease with increasing time from application to irrigation. It is hypothesized that the availability of compounds for leaching decreases due to diffusion and sorption inside soil aggregates. Previous work showed that pesticide sorption inside soil aggregates increases significantly during the first days after application.

User subjectivity in Monte Carlo modeling of pesticide exposure.

Monte Carlo techniques are increasingly used in pesticide exposure modeling to evaluate the uncertainty in predictions arising from uncertainty in input parameters and to estimate the confidence that should be assigned to the modeling results. The approach typically involves running a deterministic model repeatedly for a large number of input values sampled from statistical distributions. In the present study, six modelers made choices regarding the type and parameterization of distributions assigned to degradation and sorption data for an example pesticide, the correlation between the parameters, the tool and method used for sampling, and the number of samples generated.

Impact of correlation between pesticide parameters on estimates of environmental exposure.

Monte Carlo techniques are increasingly used in pesticide exposure modelling to evaluate the uncertainty in predictions arising from uncertainty in input parameters and to estimate the confidence that should be assigned to modelling results. The approach typically involves running a deterministic model repeatedly for a large number of input values sampled from statistical distributions. A key decision in setting up a probabilistic analysis is whether there is correlation between any of the inputs to the analysis.

Pesticide sorption and desorption by lignin described by an intraparticle diffusion model.

Lignin was used as a model compound for soil organic matter to gain insight into the mechanisms that control the kinetics of pesticide sorption and desorption. Hydrolytic lignin was immobilized in a matrix of alginate gel, and sorption-desorption experiments were undertaken with isoproturon. Sorption increased with time and was close to equilibrium after 14 days.

Pesticide sorption and diffusion in natural clay loam aggregates.

Pesticide sorption in soils is controlled by time-dependent processes such as diffusion into soil aggregates and microscopic sorbent particles. This study examines the rate-controlling step for time-dependent sorption in clay loam aggregates. Aggregates (5 mm) were stabilized with alginate, and adsorption of azoxystrobin, chlorotoluron, and cyanazine was measured in batch systems equilibrated for periods between 1 h and 7 days.

Evaluation of simplifying assumptions on pesticide degradation in soil.

There is evidence that degradation of pesticides in simple laboratory systems may differ from that in the field, but it is not clear which of the simplifications inherent in laboratory studies present serious shortcomings. Laboratory experiments evaluated several simplifying assumptions for a clay loam soil and contrasting pesticides. Degradation of cyanazine [2-(4-chloro-6-ethylamino-1,3,5-triazin-2-ylamino)-2-methylpropiononitrile] and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at fluctuating temperature and moisture was predicted reasonably well based on parameters derived from degradation under constant conditions.

Inverse modelling for estimating sorption and degradation parameters for pesticides.

The leaching model PESTRAS was used to estimate sorption and degradation values for bentazone from three lysimeter datasets using the inverse modelling package PEST. Investigations were undertaken to assess the influence on calibration results of (1) values attributed to uncertain parameters not included in the calibration, and (2) starting values supplied to the inverse modelling package. Automatic calibrations with different realistic values for the Freundlich exponent n(f) yielded different combinations of K(om) and DT50.

Influence of kinetic sorption and diffusion on pesticide movement through aggregated soils.

Laboratory studies were carried out to investigate solute leaching at different times from application in relation to temperature and initial soil moisture. Aggregates of a heavy clay soil were treated with a non-interactive solute (bromide) and the herbicides chlorotoluron, isoproturon and triasulfuron. The soil was incubated at 90% field capacity and either 5 or 15 degrees C.

Sources of uncertainty in pesticide fate modelling.

There is worldwide interest in the application of probabilistic approaches to pesticide fate models to account for uncertainty in exposure assessments. The first steps in conducting a probabilistic analysis of any system are: (i) to identify where the uncertainties come from; and (ii) to pinpoint those uncertainties that are likely to affect most of the predictions made. This article aims at addressing those two points within the context of exposure assessment for pesticides through a review of the different sources of uncertainty in pesticide fate modelling.

Sensitivity analyses for four pesticide leaching models.

Sensitivity analyses using a one-at-a-time approach were carried out for leaching models which have been widely used for pesticide registration in Europe (PELMO, PRZM, PESTLA and MACRO). Four scenarios were considered for simulation of the leaching of two theoretical pesticides in a sandy loam and a clay loam soil, each with a broad distribution across Europe. Input parameters were varied within bounds reflecting their uncertainty and the influence of these variations on model predictions was investigated for accumulated percolation at 1-m depth and pesticide loading in leachate.

Calibration of pesticide leaching models: critical review and guidance for reporting.

Calibration of pesticide leaching models may be undertaken to evaluate the ability of models to simulate experimental data, to assist in their parameterisation where values for input parameters are difficult to determine experimentally, to determine values for specific model inputs (e.g. sorption and degradation parameters) and to allow extrapolations to be carried out.

Lysimeter study to investigate the effect of rainfall patterns on leaching of isoproturon.

The influence of five rainfall treatments on water and solute leaching through two contrasting soil types was investigated. Undisturbed lysimeters (diameter 0.25 m, length 0.