California Department of Pesticide Regulation’s Surface Water Protection Program (SWPP) is developing a modeling approach to evaluate pesticide products submitted for registration in California. A receiving waterbody model is a crucial component of the modeling system. The model describes the transport and fate of pesticides in aquatic systems and predicts environmental concentrations for exposure characterizations. Model development was divided into two stages – 1) review of modeling theory, and 2) development of California-relevant receiving waterbody scenarios for agricultural and urban settings. Three regulatory receiving waterbody models – Variable Volume Water Model (VVWM), AGRO-2014, and Toxic Substances in Surface Waters (TOXSWA) – were reviewed. In these models, a receiving waterbody is conceptually formulated into a compartmental system consisting of a water compartment, a sediment compartment, and several sub-compartments. Various processes are considered to describe pesticide behavior in the system, including mass transfer between water and sediment, sorption, degradation, volatilization, sediment/sorbed pesticide burial, system inflow/outflow, and environmental processes (e.g., precipitation and evaporation). The models were compared in the simulation of these processes, and we concluded that VVWM is the most promising model for use by SWPP for pesticide registration evaluation. Modeling scenarios are under development to represent California conditions. Spatial and monitoring data on hydrography and water quality are being examined.

Development of a California-based receiving waterbody model for pesticide registration evaluation

253rd National Meeting (2017)

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