The Pyrethroid Working Group (PWG) is conducting a probabilistic refinement of aquatic exposure estimates for agricultural pyrethroid uses. Landscape variability as it affects the potential for pyrethroid runoff and drift loads to enter receiving water bodies was identified for quantification in this analysis. In a national assessment, for every NHD+ catchment included in a HUC12 watershed containing the crop of interest (CoI), potential vulnerability was estimated using the percent of CoI in the 200m proximity zone around NHD+ stream reaches to reflect potential drift loading. Erosion/runoff loading potential of each NHD+ catchment was ranked using crop area-weighted 30-yr median PRZM model output for all CoI cropped soils in the catchment using local weather stations. These two parameters were plotted for each catchment to characterize the distribution of nationwide landscape vulnerabilities for the CoI for further probabilistic modeling and for comparison with the EPA tier II scenario (which assumes 100% cropping and a 90th centile worst case erosion potential. The results showed that the combination of vulnerability factors used by EPA for standard lower tier aquatic exposure modeling occur very infrequently for most crops.

Refining pyrethroid aquatic exposure assessments by incorporating measured landscape and environmental variability using probabilistic approaches, II: Characterizing nationwide landscape vulnerability for several pyrethroid crops

248th National Meeting (2014)

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