Comparison of Reductive Dechlorination of Hexachloro-1,3-butadiene in Rhine Sediment and Model Systems with Hydroxocobalamin

Abstract

Transformation of hexachloro-1,3-butadiene were studied in columns packed with Rhine River sediment and in batch incubations containing titanium(III) citrate and hydroxocobalamin. Columns were operated under various redox conditions. Transformation was observed in a methanogenic column at influent concentrations of 4 and 400 nmol/L but not in columns where oxygen or nitrate were fed as terminal electron acceptors. Hexachloro-1,3-butadiene was reductively dechlorinated to (<I>E,E</I>)-1,2,3,4-tetrachlorobutadiene (>90%) and traces of a trichloro-1,3-butadiene isomer (<5%). (<I>E</I>)-1,1,2,3,4-Pentachloro-1,3-butadiene was detected as intermediary product. Reductive dechlorination in the column was ascribed to the activity of anaerobic microorganisms. In the batch experiments with titanium(III) citrate and hydroxocobalamin, hexachloro-1,3-butadiene (5 and 500 μmol/L) was transformed to an isomer of pentachloro-1,3-butadiene and two compounds with molar masses of 154 and 52, tentatively identified as trichloro-1-buten-3-yn, and 1-buten-3-yn respectively.