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Symposia on the Environment and Food

Contributions of Chemistry to Sustainable Food Production

Freie Universitat Berlin, August 1999
Thursday August 12, 9:00 - 13:00
Inorganic Chemistry Lecture Hall

Environmental Chemistry and Evaluation of Best Management Practices For Crop Protection Technologies
Allan S. Felsot, Professor, Washington State University, 2710 University Drive, Richland, WA 99352, USA, Email: [email protected]

Environmental chemistry has grown from orphan child to a valued discipline of study housed in a diversity of academic departments across the U.S. Such elevation in status reflects its multidisciplinary nature that makes it well suited to both delineating environmental problems and managing or eliminating them. Growing from isolated observational studies of both natural and anthropogenic phenomena, environmental chemistry now has a sound theoretical foundation. This foundation has been termed environmental chemodynamics. The need to manage exposures to environmental contaminants has led to the use of environmental chemodynamic principles for development of best management practices (BMPs) for crop protection technologies, especially the use of pesticides. The goal of BMPs as applied to agroecosystems and crop protection is to minimize adverse consequences of farming practices. The risk of adverse effects of pesticides is low when exposure of nontarget organisms is minimized. Exposure is determined by the distribution of the chemical in the environment. Thus, controlling that distribution leads to reduction in exposure.

Environmental chemodynamic studies are quite suitable for the task of controlling agrochemical distribution because it focuses on physicochemical properties, phase transfer characteristics, mass transport processes, attenuation reactions/kinetics, and modeling of environmental behavior. The chemodynamic approach has been most useful for identifying solutions to mass transport, including reductions in runoff, leaching, and volatilization. Numerous studies of pesticide runoff in relation to agronomic practices have been published in the last 20 years. These show that runoff can be controlled by tillage and row orientation practices, which slow water movement and reduce sorbed phase erosion. Controlled release formulations of some herbicides seem to allay leaching. We also know that residue aging increases sorption, thereby reducing leaching. Taking advantage of the extremely high solubility in water of the fumigant methyl bromide, its volatilization can be slowed significantly by flooding the soil after injection. Using a combination of prior field experience with older pesticides and applying fundamental chemodynamic principles to new compounds, we can now predict with some accuracy the fate of new chemicals before they are even used in the field.

Environmental chemistry has been equally useful for improving efficacy of agrochemicals. The efficacy of certain soil applied pesticides has decreased after numerous years of use. Studies have been conducted to help identify whether the problem was due to pest resistance, enhanced microbial degradation, or some peculiarity of soil chemistry. The development of controlled release formulations that both allay mass transfer and extend efficacy can be viewed as a joint effort between polymer chemistry and environmental chemistry. Advances in isolation and identification of insect pheromones has opened up new possibilities for "nontoxic" pest control, but the proper deployment of such technology will depend on a detailed knowledge of how these volatile chemicals disperse in the environment.

With all the good news about the development of BMPs for crop protection technologies, one dilemma looms on the horizon. We have gained some success in reducing agrochemical residues in the environment, but the demands for ever lower residues has increased. BMPs will not produce zero residues, yet society seems to be demanding just that.

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