Abstract
Field-scale environmental models have been widely used in aquatic exposure assessments of pesticides. Those models usually require a large set of input parameters and separate simulations for each pesticide in evaluation. In this study, a simple use-exposure relationship is developed based on regression analysis of stochastic simulation results generated from the Pesticide Root-Zone Model (PRZM). The developed mathematical relationship estimates edge-of-field peak concentrations of pesticides from aerobic soil metabolism half-life (AERO), organic carbon-normalized soil sorption coefficient (KOC), and application rate (RATE). In a case study of California crop scenarios, the relationships explained 90–95% of the variances in the peak concentrations of dissolved pesticides as predicted by PRZM simulations for a 30-year period. KOC was identified as the governing parameter in determining the relative magnitudes of pesticide exposures in a given crop scenario. The results of model application also indicated that the effects of chemical fate processes such as partitioning and degradation on pesticide exposure were similar among crop scenarios, while the cross-scenario variations were mainly associated with the landscape characteristics, such as organic carbon contents and curve numbers. With a minimum set of input data, the use-exposure relationships proposed in this study could be used in screening procedures for potential water quality impacts from the off-site movement of pesticides.
Highlights
As part of the registration process, pesticides are evaluated for their potential to move off-site and impact non-target organisms
The logarithmic transformation was applied to EI_BASE according to preliminary analyses on pesticide concentrations detected in surface water of California [34]
The development of use-exposure relationships was demonstrated using crop scenarios developed by the U.S Environmental Protection Agency (USEPA) for California
Summary
As part of the registration process, pesticides are evaluated for their potential to move off-site and impact non-target organisms. Monitoring-based surface water risk assessments of pesticides are usually conducted at the watershed scale using measured concentration data from river sites, especially at watershed outlets. In-stream measurements of pesticides were assessed for U.S watersheds with spatial scales across 14 orders of magnitude [1,2]. Water flow from non-application areas and non-agricultural headwaters may significantly dilute pesticide concentrations in the river. In California’s Central Valley, one of the most productive agricultural areas in the world, pesticide concentrations are substantially higher in small creeks dominated by irrigation return flows, as compared to main streams where the majority of flow originates in Sierra Nevada mountains [3,4,5,6]. Assessments of aquatic risk generally focus on smaller water bodies close to the edge-of-field
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