Remediating dicamba-contaminated water with zerovalent iron

Dicamba (3,6-dichloro-2-methoxybenzoicacid) is a highly mobile pre- and post-emergence herbicide that has been detected in ground water. We determined the potential of zerovalent iron (Fe-0) to remediate water contaminated with dicamba and its common biological degradation product, 3,6-dichlorosalicylic acid (DCSA). Mixing an aqueous solution of 100 muM dicamba with 1.5% Fe-0 (w/v) resulted in 80% loss of dicamba within 12 h. Solvent extraction of the Fe-0 revealed that dicamba removal was primarily through adsorption; however when the Fe-0 was augmented with Al or Fe(III) salts, dicamba was dechlorinated to an unidentified degradation product. In contrast to dicamba, Fe-0 treatment of DCSA resulted in removal with some dechlorination observed. When DCSA was treated with Fe-0 plus Al or Fe(Ill) salts, destruction was 100%. Extracts of this Fe-0 treatment contained the same HPLC degradation peak observed with the Fe-0 + Al or Fe(III) salt treatment of dicamba. Molecular modeling suggests that differences in removal and dechlorination rates between dicamba and DCSA may be related to the type of coordination complex formed on the iron surface. Experiments with C-14-labeled dicamba confirmed that Fe-adsorbed dicamba residues are available for subsequent biological mineralization (11% after 125 d). These results indicate that Fe-0 could be potentially used to treat dicamba and DCSA-contaminated water. (C) 2003 Elsevier Ltd. All rights reserved.