Sorption and Metabolism of Metolachlor by a Bacterial Community

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-¹⁴C]metolachlor (50 μg/ml) disappeared from the medium and accumulated inside the cells. The ratio of cellular ¹⁴C to ¹⁴C in 1 mg of supernatant reached a value of 1.1 × 10⁴ in a 10-day-old culture. ¹⁴C remaining in the medium consisted primarily of two dechlorinated products of metolachlor with m/z 233 and 263 as determined by mass spectrometry. The ¹⁴C-labeled material absorbed by the cells was strongly bound; only 2% of the ¹⁴C was released into deionized water after shaking for 3 h. Approximately 96% of the ¹⁴C 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.