Anaerobic transformation of alachlor, propachlor, and metolachlor with sulfide

The purpose of this work was to elucidate microbiological and abiotic transformations relevant to the environmental fate of the acetanilide herbicides alachlor [2-chloro-2',6'-diethyl-N-methoxymethyl)acetanilide], propachlor (2-chloro-N-isopropyl-acetanilide), and metolachlor [2-chloro-2'-ethyl-6'-methyl-N-(1-methyl-2-methoxyethyl)- acetanilide], Several attempts to retrieve aerobic and anaerobic microbial cultures capable of degrading alachlor from agricultural soils and pond sediments were unsuccessful with the exception of sulfate-reducing bacteria that partially transformed acetanilide herbicides during active sulfate reduction. The transformation products of alachlor and propachlor were more hydrophobic than the parent compounds. The transformations were associated with the activity of sulfate-reducing bacteria because the reactive species was sulfide and possibly other reduced S species produced during the bacterial reduction of sulfate. Transformation could he duplicated under abiotic conditions by reacting Na2S with alachlor, propachlor, and metolachlor. One of the reaction products of the abiotic reaction between alachlor and sulfide was identified by mass spectroscopy as a S-substituted dimer of alachlor. This compound was formed by the nucleophilic substitution of chloride by reduced S, with the subsequent oxidation to a disulfide.