Prospective aquatic exposure modeling is one of several tools used to assess the potential for impacts in Biological Opinions (BO) for pesticides. The Biological Evaluation (BE) prepared by the EPA for the insecticide carbaryl provides aquatic exposure estimates by using well-established pesticide fate and transport models (e.g., PRZM, VVWM, AgDRIFT) applied to a standardized set of crop/soil/weather scenarios with reported aquatic concentrations generally limited to 30 annual maxima values. Variability in aspects such as spatial proximity, the incorporation of Percent Crop Area, distribution of pesticide treated acres, and temporal aspects of exposure have been identified as areas for possible refinement in recent BEs and BOs and are employed to better inform the risk evaluation. This paper describes a highly efficient, structured approach that builds on the EPA’s aquatic modeling to increase the spatial/temporal context and resolution of exposure estimates to listed species and produces well-defined and reproducible species-specific estimated aquatic concentrations. Utilizing data for each species, the set of NHD+ catchments, landscape-based crop proximity and density, pesticide usage (e.g., Percent Crop Treated), and additional user-selected options (e.g., PCT multiplier, alternate application rates), inputs were processed to produce refined exposure concentrations suitable for aggregation at multiple spatial scales appropriate for the species being examined. Temporal aspects were examined using multiple endpoints of the 30-year dataset (e.g., 1-in-15 year, median of annual maxima, 95<sup>th</sup> percentile of daily) as well as daily distributions. Individual PWC output files (labeled use/HUC/aquatic bin/proximity/application method) were scanned using Python scripts to develop summary concentration profiles for differing time periods and distribution points to provide inputs for refined modeling. Options for results presentation integrated into existing R-Plots from Services’ BOs will be illustrated. The spatially explicit aquatic modeling results provide valuable information to help inform localized mitigations for individual species and across specific use patterns. Aspects of efficiency, transparency and documentation were all addressed in the generation of this framework. This presentation describes the purpose, design decisions, and results of these post-screening refinements as related to the recent carbaryl BE.

Integrating species-specific landscape information into aquatic exposure estimates for endangered species assessments

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ACS Fall 2022

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