Anaerobic biotransformation of dicamba and chlorosalicylic acids under denitrifying, iron reducing, and methanogenic conditions.

The fate of dicamba in sediments is important with regard to ground water quality at sites of herbicide application and drainage. Herbicide application areas frequently contain high levels of nitrate in the ground water, and iron (III) is an important electron acceptor in many aquifers as well. Transformation of dicamba (3,6-dichloro-2-methoxybenzoic acid) to 3,6-dichlorosalicylate via demethylation of the methoxy substituent (O-demethylation) occurs both in the presence and absence of oxygen. We examined the anaerobic transformation of dicamba under denitrifying, iron (Fe-III) reducing, and methanogenic conditions. We also demonstrated utilization of related monochlorinated salicylic acids by denitrifying and methanogenic consortia. Enrichments were established with dicamba treated soil, and golf course drainage stream sediments which were spiked with dicamba or chlorosaliclyates. This study shows the effect of different electron accepters on the transformation of dicamba in anaerobic environments, and suggests that in situ degradation of herbicides in ground water and sediments will be influenced by the electron accepters present.