Evaluation of Three Watershed‐Scale Pesticide Environmental Transport and Fate Models¹

Abstract

The U.S. Environmental Protection Agency (USEPA) Office of Pesticide Programs (OPP) has completed an evaluation of three watershed‐scale simulation models for potential use in Food Quality Protection Act pesticide drinking water exposure assessments. The evaluation may also guide OPP in identifying computer simulation tools that can be used in performing aquatic ecological exposure assessments. Models selected for evaluation were the Soil Water Assessment Tool (SWAT), the Nonpoint Source Model (NPSM), a modified version of the Hydrologic Simulation Program‐Fortran (HSPF), and the Pesticide Root Zone Model‐Riverine Water Quality (PRZM‐RIVWQ) model. Simulated concentrations of the pesticides atrazine, metolachlor, and trifluralin in surface water were compared with field data monitored in the Sugar Creek watershed of Indiana’s White River basin by the National Water Quality Assessment (NAWQA) program. The evaluation not only provided USEPA with experience in using watershed models for estimating pesticide concentration in flowing water but also led to the development of improved statistical techniques for assessing model accuracy. Further, it demonstrated the difficulty of representing spatially and temporally variable soil, weather, and pesticide applications with relatively infrequent, spatially fixed, point estimates. It also demonstrated the value of using monitoring and modeling as mutually supporting tools and pointed to the need to design monitoring programs that support modeling.

Exposures of Aquatic Organisms to the Organophosphorus Insecticide, Chlorpyrifos Resulting from Use in the United States

“…The model has undergone extensive validation, in which the results were compared with measured concentrations from numerous studies of field-scale runoff and leaching, conducted for pesticides in the United States (Carousel et al 2005;Jones and Russell 2001). Moreover, PRZM has been integrated into several watershed assessment models in the U.S. (Parker et al 2007;Snyder et al 2011).…”

Evaluation of Watershed‐Scale Simulations of In‐Stream Pesticide Concentrations from Off‐Target Spray Drift

“…This monitoring dataset was collected from streams in two watersheds within The Dalles region of Oregon, the details of which are provided in the accompanying supplemental material. The SWAT model has been identified from a pool of 36 models as one of the most appropriate for watershedscale simulation of pesticides (Quilbe et al, 2006), has been used globally for watershed management and assessing agrochemical fate and transport (Borah and Bera, 2004;Gassman et al, 2007;Parker et al, 2007;Payraudeau and Gregoire, 2012;Arnold et al, 2012b;Mottes et al, 2014;Boithias et al, 2014), and was recently used in higher tier pesticide ecological exposure risk assessments (Whitfied Aslund et al, 2017). An evaluation of its performance in simulating drift-driven pesticide concentrations is of current interest.…”

Risk assessment considerations with regard to the potential impacts of pesticides on endangered species

“…In addition to the Parker et al () study, numerous watershed‐level modeling studies have been conducted to assess pesticide exposure in various locations across the United States. For over 20 years, the USEPA Chesapeake Bay program has been using HSPF to estimate pesticide concentrations in the Chesapeake Bay watershed, an area of more than 68 000 square miles.…”