There is ongoing concern that authorized pesticide use practices are in compliance with the Endangered Species Act (ESA). Of particular concern in the Pacific Northwest is the protection of ESA listed salmonid species. Assessing potential harm requires understanding of how pesticide use practices may adversely impact salmonids, their food web, and habitat. While registration under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) requires evaluation of environmental fate of the parent pesticide and products of concern, little is known regarding their concurrent fate at the landscape scale.  We present a case study demonstrating a modeling approach using the Soil and Water Assessment Tool (SWAT) to investigate the fate of chlorpyrifos and its degradates in the Zollner Creek watershed, Willamette Basin, OR. Through participatory modelling employing probabilistic methods, daily surface water concentrations were estimated for chlorpyrifos and its degradates over a 2 year period. SWAT estimates of chlorpyrifos daily surface water concentrations were evaluated using both grab and passive surface water sampling data. As degradate monitoring data is generally not available, model estimates of degradate fate are based primarily on first principles of product formation and degradation, as well as expected degradate characteristics that determine mobility relative to the parent pesticide. Data needs to improve model performance will be discussed.

Modeling the co-occurrence of pesticides and degradation products in surface water at the landscape scale

2019 Fall National Meeting

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