Department of Civil and Environmental Engineering, University of Iowa, Iowa City, IA, 52242, 319-335 5054
Herbicides have been detected with increasing frequency in ground water supplies throughout the United States. Some of these compounds mineralize readily and others may persist for some time. During herbicide degradation, products are formed; some of these could be environmental hazards. These metabolites may also be short-lived and subsequently degraded, or they may persist in the environment. The behavior of these herbicides and their products becomes increasingly important as herbicide use increases. Alachlor, a commonly used herbicide, is known to be biodegradable to varying degrees under various electron acceptor conditions (aerobic, denitrifying, sulfate reducing and methanogenic) depending on experimental conditions and the organisms present. Alachlor is a suspected human carcinogen. Of 6 million wells surveyed in 1987, 1% contained alachlor residuals, with 1200 of these wells exceeding the maximum contaminant level of 2 µg/l as set by the Environmental Protection Agency. A survey of the literature indicates that little documentation exists on the degradation and transformation products of alachlor.
Enrichment cultures were developed on synthetic media under three terminal electron acceptor conditions (denitrifying, sulfate reducing and methanogenic). Under denitrifying conditions with acetate-fed organisms and resazurin (a color indicator of redox potential) present, acetyl alachlor, diethyl aniline, aniline and m-xylene were positively identified as transformation products of alachlor. Acetyl alachlor, a reductive dechlorination product, and diethyl aniline were expected metabolites. Aniline and m-xylene, however, have not been previously reported as metabolites of alachlor under denitrifying conditions. Aniline, a poison that poses a severe health risk, and m-xylene, a compound that damages the human nervous system, are of particular concern. An abiotic reaction mediated by resazurin was implicated in the formation of these two compounds. On-going research is focusing on the specific role of resazurin and other electron carriers in the production of these alachlor metabolites. The goal is to determine which transformation steps are biologically mediated and which are abiotic. Acetyl alachlor and diethyl aniline were also major metabolites in sulfate-reducing and methanogenic systems.
alachlor, metabolites, biodegradation
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.