Biodegradation and biotransformation of dicamba under different reducing conditions

We examined the anaerobic biodegradability and transformation of dicamba un der denitrifying, iron Fe(III) reducing, sulfate reducing, and methanogenic conditions. Anaerobic microcosms were established with dicamba treated agr icultural soil and golf course drainage stream sediments, which were each s piked with dicamba as the sole carbon source. Transformation of dicamba to 3,6-dichlorosalicylate via demethylation of the methoxy substituent (O-deme thylation) occurred in cultures under methanogenic conditions in cultures f rom both sites. In methanogenic enrichments from golf course sediments, the O-demethylated product (3,6-dichlorosalicylate) was reductively dechlorina ted to 6-chlorosalicylate and subsequently to salicylate, which was ultimat ely mineralized to CH4 and CO2. Sulfate reducing cultures from golf course drainage stream sediments O-demethylated dicamba and partially dechlorinate d 3,6-dichlorosalicylate to 6-chlorosalicylate (<10%). Neither denitrifying nor iron reducing conditions promoted the biotransformation of dicamba. Th is study shows the effect of different electron accepters on the transforma tion of dicamba in anaerobic environments and demonstrates the degradation pathway under methanogenic conditions. The work suggests that the electron accepters present will influence in situ degradation of herbicides in anoxi c soils and sediments.