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]
Abstract
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.
