Factors controlling degradation of pesticides in soil

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 such degradation. The herbicides clomazone, ̄umetsulam, 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 ̄umetsulam has been shown to be regulated by sorption, even though the compound has a relatively low af®nity for the soil. The fate pathway for cloransulam-methyl shifts from mineralization to formation of metabolities, bound residues and physically occluded material as temperature increases. Atrazine degradation in soil may be controlled in part by the presence of inorganic nitrogen, as the herbicide appears to be used as a nitrogen source by micro-organisms. New insight Figure 2. Typical mineralisation plots; cumulative [C] carbon dioxide, 10mg litreÿ1 application. incubation 1, ^ incubation 2, & incubation 3, ~ incubation 4, control. * Correspondence to: Gerald K Sims, USDA-Agricultural Research Service, 1102 South Goodwin Avenue, Urbana, IL 61801, USA E-mail: [email protected] (Received 1 July 1998; accepted 5 January 1999) 598 Pestic Sci 55:566±614 (1999) Extended Summaries: IUPAC Conference