Bioavailability of soil-sorbed pesticides and organic contaminants

Abstract

Toxic organic chemicals find their way into our environment as a result of industrial and agricultural activities. There are at least 75,000 toxic chemicals in common use worldwide (US EPA 2005). In the U.S., about 2.2 billion kilograms of chemicals are used as pesticides each year, with agricultural usage accounting for 77% (Kiely et al. 2004). Many pesticides and other organic chemicals have been found to accumulate in nature because the release rates exceed the rates of microbial and chemical degradation. Low biodegradation rates can be attributed to: (1) limited biochemical potentials, i.e., chemicals with structures foreign to nature are less likely to be degraded without a long adaptation period; and (2) limited bioavailability of contaminants or other substances (e.g. electron acceptors) to microorganisms. Our understanding of pesticide bioavailability has important ramifications for environmental fate modeling, risk assessment and remediation. Limited bioavailability may lead to unexpected chemical persistence in soils hence increasing the likelihood of ground-or surface-water contamination (Pignatello et al. 1987). In the remediation of contaminated soils, bioavailability affects the clean-up time, cost, and the end-point of the process. Bioavailability of pesticides and other organic contaminants has been identified as a major limitation to complete bioremediation of contaminated soils (US EPA 1999).