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ARS Home » Research » Publications at this Location » Publication #94421
Title: FACTORS CONTROLLING DEGRADATION OF PESTICIDES IN SOIL

Author
item Sims, Gerald
item CUPPLES, ALISON - UNIV OF ILLINOIS

Submitted to: Pesticide Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The results of several soil pesticides studies were examined in order to illustrate the causes of variability in pesticide degradation rates. Factors that affected the dissipation of herbicides included a range of environmental variables and soil properties. The herbicides clomazone, flumetsulam, atrazine, and cloransulam-methyl, as well as the former insecticide naphthalene exhibited degradation pathways controlled by particular processes which, in turn, may be regulated separately by a variety of environmental factors. For example, volatilization and sorption in some cases competed differentially with degradation. For the herbicide cloransulam-methyl, metabolites formed depended upon soil temperature. The impact of the investigation is that it is necessary to measure several key environmental processes in the same experiment in order to understand how changes in conditions, such as temperature, moisture, pH, etc. control the fate of pesticides in the environment. These findings represent a new approach and will be beneficial to other scientists who are planning and conducting experiments on pesticide fate in the environment.

Technical Abstract: Rates of pesticide degradation in soil exhibit a high degree of variability, the sources of which are usually unclear. Combining data from incubations performed using a range of soil properties and environmental conditions has resulted in greater understanding of factors controlling pesticide degradation in soil. The herbicides clomazone, flumetsulam, atrazine, and cloransulam-methyl, as well as the former insecticide naphthalene offer examples of degradation kinetics controlled by coupling competing processes which may in turn be regulated separately by environmental conditions and soil properties. The processes of degradation and volatilization appear to compete for clomazone in solution; sorbed clomazone is degraded only after the solution phase is depleted. Similarly, volatilization of naphthalene is enhanced when degradation has been inhibited by high nutrient levels. Degradation of the herbicide flumetsulam has been shown to be regulated by sorption, even though the compound has a relatively low affinity for the soil. The fate pathway for cloransulam-methyl shifts from mineralization to formation of metabolites, bound residues and physically occluded material as temperature increases. Atrazine degradation in soil may be controlled in part by the presence of inorganic N, as the herbicide appears to be used as an N source by microorganisms. New insight gained from measurement of multiple fate processes is demonstrated by these examples.