Microbial transformation of metolachlor

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Abstract
Metolachlor is an important selective herbicide used for the control of several annual grassy weeds and certain broad‐leafed weeds in corn, soybean, peanut, and other crops. It is the most heavily used agricultural pesticide in Ontario. There is, however, very little information in the open literature on the aquatic fate and persistence of metolachlor, a fact that hinders the assessment of its ultimate impact on the aquatic ecosystem. This study showed that metolachlor was very stable in natural water systems. No apparent biodegradation or biotransformation of metolachlor was observed in three test lake waters after an incubation period of 170 days. With a polynuclear aromatic hydrocarbon (PAH) degrading bacterial culture as the test organism, metolachlor was estimated to have an environmental persistence much greater than medium molecular weight PAHs. Thus the extensive herbicidal use of metolachlor may have a long‐lasting impact on Canadian aquatic ecosystems. The white rot fungus Phanerochaete chrysosporium was able to biotransform metolachlor. Based on the three identified metabolites, a tentative metabolic pathway of metolachlor biotransformation by P. chrysosporium was proposed, involving demethylation, hydroxylation, and hydrolytic dechlorination. © by John Wiley & Sons, Inc.