The physico-chemical properties that influence the environmental fate and transport of chlorpyrifos (CPY) and CPY-oxon (CPYO) are briefly reviewed. These include vapor pressure, air-water and soil-water partition coefficients, half-lives in the atmosphere, water, and soils, and the kinetics of CPYO formation from CPY. The relatively high vapor pressure of CPY results in appreciable volatilization during and shortly after spraying, resulting in atmospheric concentrations at the site of application in the range 10 to 1000 ng/m3. The plume disperses and degrades, notably to CPYO, thus causing long-range atmospheric transport (LRAT) in the days following application. CPY and CPYO are thus subject to deposition to terrestrial and aquatic systems in the hundreds of km downwind of sources as is confirmed by monitoring data, from the Central Valley and National Parks in California, the Mid-West and Eastern US, and Canada. A LRAT model suggests a characteristic travel distance for CPY of some 65 km, over which two-thirds of the CPY is degraded or deposited, but this distance is very sensitive to hydroxyl radical concentrations. A tentative mass balance model of dispersion, formation of CPYO, and deposition is outlined.  It has the potential to simulate concentrations in air and other media such as precipitation yielding results that are broadly consistent with monitoring data. This model serves as a foundation for a more quantitative and site�specific quantification of the fate, transport and long-range transport, and potential effects of CPY and CPYO.

Towards a model of the environmental fate and long-range atmospheric transport of chlorpyrifos and its oxon

246th National Meeting (2013)

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