MICROBIAL DECHLORINATION OF THE HERBICIDE METOLACHLOR

We studied the dechlorination of metolachlor by four microorganisms, Streptomyces sp., Phanerochate chrysosporium, Rhizoctonia praticola, and Syncephalastrum racemosum, in a growth medium containing 0.35 mM metolachlor. A significant amount of the herbicide was dechlorinated by all cultures, resulting in the formation of seven dechlorinated products as determined by high-performance liquid chromatography and mass spectrometric analyses. Transformation mechanisms included dehalogenation with subsequent hydroxylation of the chloracetyl group; further reactions led to ring formation between the acetyl group and the benzylic ethyl side chain. Dehalogenation in conjunction with demethylation at the N-alkyl substituent and hydroxylation at the aralkyl side chain were also observed. Streptomyces was the most active culture in dechlorinating metolachlor; 41% of the added herbicide was recovered as dechlorinated products after a 16-day incubation period. Dechlorinated products from P. chrysosporium, R. praticola, and S. racemosum amounted to 28.4, 26.8, and 13.5%, respectively, of the originally added metolachlor. Upon incubation of the dechlorination product G or I with Streptomyces, both compounds were further transformed, incdicating metabolism of the primary products.