Understanding the tropospheric transport and fate of agricultural pesticides.

Many field monitoring studies have indicated the substantial role of the troposphere as both a sink and transport medium for pesticides. At the same time, this is the least studied and understood environmental compartment in regards to pesticide fate. Although the fundamental principles behind volatilization and tropospheric reactivity are well understood, it is becoming increasingly apparent that the ability to quantitatively measure flux and reaction rates in the air will continue to pose problems for researchers. To date, most deterministic models that try to simulate real world conditions generally fail to provide tropospherically relevant flux and reaction rates because it is virtually impossible to scale down all possible interactions occurring in a near-infinite reservoir. Better field methods for determining flux are emerging and more ambient air monitoring studies are being conducted. This growing database of information, together with an understanding of physicochemical properties and use of expert systems, has increased the predictive capability for estimating volatilization flux of pesticides. Unfortunately, there are very limited environmental data on the tropospheric reaction rates of pesticides, and more experimental studies using semivolatile to low-volatility pesticides or their more volatile homologues are required to validate existing structure-activity relationship (SAR) model predictions. The development of new analytical strategies using elevated temperatures for assessing semivolatile to low-volatility pesticide reaction rates and products may provide an alternative approach to the need for controlled environmental temperature data. Recent international workshops organized by the Health Council of The Netherlands for developing uniform approaches for assessing exposure risks to pesticides in air exemplify efforts to synchronize flux with environmental fate information for determining human health and ecological risks. When more detailed pesticide information is desired, especially in high-use agricultural areas, where exposure to humans and nontarget ecological communities is a major concern, field flux measurements and downwind monitoring, together with experimental fate studies, should be considered. The integration of models, empirical testing, and real world monitoring will provide the ultimate safety net needed for assessing exposure risks to airborne pesticides.