Sorption and Metabolism of Metolachlor by a Bacterial Community

Abstract

A stable bacterial community absorbed and transformed the herbicide metolachlor [2-chloro- N -(2-ethyl- 6-methylphenyl)- N -(2-methoxy-1-methylethyl)-acetamide] from a liquid medium. About 80% of the added ring-[U- 14 C]metolachlor (50 μg/ml) disappeared from the medium and accumulated inside the cells. The ratio of cellular 14 C to 14 C in 1 mg of supernatant reached a value of 1.1 × 10 4 in a 10-day-old culture. 14 C remaining in the medium consisted primarily of two dechlorinated products of metolachlor with m/z 233 and 263 as determined by mass spectrometry. The 14 C-labeled material absorbed by the cells was strongly bound; only 2% of the 14 C was released into deionized water after shaking for 3 h. Approximately 96% of the 14 C associated with the biomass was extracted with acetone, and high-performance liquid chromatographic analysis of this fraction showed six peaks containing radioactivity. Since no metolachlor was detected by chromatographic analysis, it was concluded that the radioactivity recovered from the cells represented transformed products of metolachlor. Pure cultures isolated from the bacterial mixed culture were less effective in transforming and accumulating metolachlor. These results suggest that it may be advantageous to seed an aquatic environment with a mixture of microorganisms, rather than individual microbial species, as a method for removal or detoxification of metolachlor.