Chlorpyrifos release rate from clay granules: experimental observations and simple algorithm development for use in computer-based exposure assessments
1998
Cryer, S.A. | Laskowski, D.A.
Environmental models can approximate pesticide mass leaving a treated field in runoff water and sediment but do not typically account for controlled-release formulations such as granules. Mathematical algorithms are developed from experimental observations to predict the environmental release rate of chlorpyrifos from a commercial formulation [Lorsban (trademark of Dow AgroSciences) 15G insecticide] into the surrounding soil environment. Chlorpyrifos release rates into flowing water were measured by HPLC analysis of water pumped through a column containing 15G granules. Analysis of these observations provides a basis for predicting water-induced release rates during natural precipitation events. Chlorpyrifos diffusion and volatilization rates from the granule in the absence of precipitation were determined from experimental observations using first-order kinetic modeling. Multiyear simulations and distribution analysis were performed using the GLEAMS model for the Midwestern corn belt region to determine release mechanism sensitivity and edge-of-field runoff potential for chlorpyrifos in 15G granules when the release mechanisms of advection, volatilization, and diffusion are accounted for. It is found that advection release was the dominate mechanism for chlorpyrifos release from clay granules, followed by diffusion and volatilization for Midwestern U.S. scenarios. Predicted losses of chlorpyrifos in runoff from soil incorporated applications are < 1% of applied.
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