Development of Groundwater Pesticide Exposure Modeling Scenarios for Vulnerable Spring and Winter Wheat-Growing Areas

摘要

Wheat crops and the major wheat-growing regions of the United States are not included in the 6 crop- and region-specificrnscenarios developed by the US Environmental Protection Agency (USEPA) for exposure modeling with the Pesticide Root ZonernModel conceptualized for groundwater (PRZM-GW). The present work augments the current scenarios by definingrnappropriately vulnerable PRZM-GW scenarios for high-producing spring and winter wheat-growing regions that arernappropriate for use in refined pesticide exposure assessments. Initial screening-level modeling was conducted for all wheatrnareas across the conterminous United States as defined by multiple years of the Cropland Data Layer land-use data set. Soil,rnweather, groundwater temperature, evaporation depth, and crop growth and management practices were characterized forrneach wheat area from publicly and nationally available data sets and converted to input parameters for PRZM. Approximatelyrn150 000 unique combinations of weather, soil, and input parameters were simulated with PRZM for an herbicide applied forrnpostemergence weed control in wheat. The resulting postbreakthrough average herbicide concentrations in a theoreticalrnshallow aquifer were ranked to identify states with the largest regions of relatively vulnerable wheat areas. For these states,rninput parameters resulting in near 90th percentile postbreakthrough average concentrations corresponding to significantrnwheat areas with shallow depth to groundwater formed the basis for 4 new spring wheat scenarios and 4 new winter wheatrnscenarios to be used in PRZM-GW simulations. Spring wheat scenarios were identified in North Dakota, Montana, Washington,rnand Texas. Winter wheat scenarios were identified in Oklahoma, Texas, Kansas, and Colorado. Compared to the USEPA’srnoriginal 6 scenarios, postbreakthrough average herbicide concentrations in the new scenarios were lower than all but FloridarnPotato and Georgia Coastal Peanuts of the original scenarios and better represented regions dominated by wheat crops.