National characterization of pesticide runoff and erosion potential to put USEPA standard ecological scenarios in context for pyrethroids

• Published in: Integrated environmental assessment and management Vol. 19; no. 1; pp. 175 - 190
• Main Authors: Ritter, Amy, Desmarteau, Dean, Hendley, Paul, Holmes, Christopher M.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.01.2023; John Wiley and Sons Inc
• Subjects: Agricultural environment; Agricultural watersheds; Catchment area; Catchments; Context; Crops; Decision making; Ecology; Environmental assessment; Environmental Impact Assessment; Environmental management; Environmental Policy & Regulation; Environmental protection; Erosion control; Erosion Vulnerability; Fluctuations; Hydrography; Hydrophobicity; Insecticides; Integrated environmental assessment; Mass; Meteorological data; Modelling; Pesticides; Pesticides - analysis; Protection; Pyrethrins; Pyrethroid; Pyrethroids; Regional development; Risk Assessment; Runoff; Runoff modeling; Soil - chemistry; Soils; Sustainability; Toxicology; United States; United States Environmental Protection Agency; Vulnerability; Water Pollutants, Chemical - analysis; United States; United States > US; Agricultural environment; Pyrethroid; Risk Assessment; Erosion Vulnerability; Runoff modeling
• ISSN: 1551-3777; 1551-3793
• DOI: 10.1002/ieam.4647

Decision‐making for pesticide registration by the US Environmental Protection Agency (USEPA) relies upon crop‐specific scenarios in a tiered framework. These standard modeling scenarios are stated to represent “…sites expected to produce runoff greater than would be expected at 90% of the sites for a given crop/use.” This study developed a novel approach to compare the pesticide runoff + erosion (SumRE) mass flux potential of a hydrophobic chemical using 36 of these ecological regulatory scenarios with national‐scale distributions of modeled SumRE from over 750 000 USA‐wide agricultural catchments to provide real‐world context for the simulated transport predictions used for regulatory decision‐making. For the standard scenarios and national scale modeling, “edge of field” SumRE mass flux was estimated using regulatory guidance for a hypothetical pyrethroid. The national‐scale simulations were developed using publicly available soil, hydrography, and crop occurrence /regional timings databases. Relevant soil and crop combinations identified by spatial overlay along with weather data were used in a regulatory model to generate daily SumRE estimates, which were assigned to the catchments. The resulting average annual total SumRE mass fluxes were ranked to produce distributions to compare with the standard regulatory scenario outputs. These comparisons showed that SumRE flux from 25 of the 36 USEPA ecological regulatory crop‐specific scenarios modeled ranked above the 99th percentile of pyrethroid runoff + erosion vulnerability from any catchment growing that crop; SumRE flux from six scenarios was more severe than any catchment. For 12 USEPA regulatory scenarios, the resulting eroded sediment corresponds to highly erodible land (HEL), which the US Department of Agriculture mandates should not be cropped without substantial additional erosion prevention controls for sustainability. Since the pesticide regulatory framework already incorporates many acknowledged assumptions to ensure it conservatively meets protection goals, these HEL observations suggest that the standard scenarios overestimate potential aquatic exposure and that the regulatory process is more protective than intended. Integr Environ Assess Manag 2023;19:175–190. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). KEY POINTS The US Environmental Protection Agency (USEPA) has developed a set of standard crop scenarios used in modeling for the regulatory risk assessment framework; results from this study show that several of the standard scenarios generate runoff and erosion mass output higher than the USEPA stated 90th percentile protection goal. This study simulated up to 271 340 unique soil and weather combinations per crop with the Pesticide Root Zone Model (PRZM) model covering a range of nine key pyrethroid crops. This study developed a novel approach to compare the pesticide mass flux of a hydrophobic chemical using 36 USEPA standard PRZM crop scenarios with national‐scale distributions of modeled mass flux from over 750 000 USA‐wide agricultural NHD + watershed catchments to put into a real‐world context.