Biodegradation and Biotransformation of Dicamba under Different Reducing Conditions

We examined the anaerobic biodegradability and transformation of dicamba under denitrifying, iron Fe(III) reducing, sulfate reducing, and methanogenic conditions. Anaerobic microcosms were established with dicamba treated agricultural soil and golf course drainage stream sediments, which were each spiked with dicamba as the sole carbon source. Transformation of dicamba to 3,6-dichlorosalicylate via demethylation of the methoxy substituent (O-demethylation) occurred in cultures under methanogenic conditions in cultures from both sites. In methanogenic enrichments from golf course sediments, the O-demethylated product (3,6-dichlorosalicylate) was reductively dechlorinated to 6-chlorosalicylate and subsequently to salicylate, which was ultimately mineralized to CH4 and CO2. Sulfate reducing cultures from golf course drainage stream sediments O-demethylated dicamba and partially dechlorinated 3,6-dichlorosalicylate to 6-chlorosalicylate (<10%). Neither denitrifying nor iron reducing conditions promoted the biotransformation of dicamba. This study shows the effect of different electron acceptors on the transformation of dicamba in anaerobic environments and demonstrates the degradation pathway under methanogenic conditions. The work suggests that the electron acceptors present will influence in situ degradation of herbicides in anoxic soils and sediments.