2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 5
Presentation Time: 9:00 AM


GIBB, Connie L., Geosciences, Univ of Nebraska - Lincoln, 214 Bessey Hall, Lincoln, NE 68588-0340, clgneg0204@aol.com

Dicamba (3,6-dichloro-2-methoxy benzoic acid) is a highly mobile pre- and post-emergence anionic herbicide that has been detected in ground water throughout the U.S. We determined the potential of zerovalent iron (Fe0) to remediate ground water contaminated with dicamba and its common biological degradation product, 3,6-dichlorosalicyclic acid (DCSA). Mixing an aqueous solution of 100 mM dicamba with 1.5% Fe0 (w/v) resulted in an 80% loss of dicamba within 12 h. Solvent extraction of the Fe0 revealed that dicamba removal was primarily by adsorption. Dicamba dechlorination was accomplished when the Fe0-dicamba mixture was augmented with either Al or Fe(III) salts (4 mM). Extracting this Fe0 treatment yielded an unknown degradation product. Fe0-treatment of DCSA removed 96% from solution with 20% molar release of Cl-. When DCSA was treated with Fe0 plus Al or Fe(III) salts, DCSA destruction was 100% and we recovered 50% of DCSAs chlorides in solution. Extracting this Fe0 yielded the same unknown degradation product observed from Fe0 + Al or Fe(III) treatment of dicamba. These data indicated that Fe0 can either adsorb and/or dechlorinate dicamba and DCSA but removal mechanisms are dependent on Fe0 composition and may be related to the type of coordination complex formed on the iron surface. Mineralization experiments using 14C-labeled dicamba verified that 11% of the Fe0-adsorbed dicamba residues were available for subsequent biodegradation. This research indicates that anionic pesticides like dicamba and DCSA can react with Fe0 and possibly be treated with a PRB.

Abbreviations: Dicamba, 3,6-dichloro-2-methoxybenzoic acid; Fe0, zerovalent iron; DCSA, 3,6-dichlorosalicylic acid; Koc, organic carbon partition coefficient; HPLC, high performance liquid chromatography; LSC, liquid scintillation counting; ZPC, zero point of charge; IC, ion chromatography; a.i., active ingredient; VOCs, volatile organic compounds; PRB, permeable reactive barrier.