Biotic and abiotic degradation of 1,1,2,2-tetrachloroethane in wetland sediments: Geochemical and microbial community analyses

Additional microcosm experiments with the wetland sediment and groundwater at the Aberdeen Proving Ground, MD, site was presented to assist in elucidating the conditions under which these potentially competing biotic and abiotic degradation reactions for 1,1,2,2-tetrachloroethane (PCA) occur in the environment and to evaluate potential seasonal changes in degradation reactions. PCA concentration decreased to below detection within 21 days in the March 1999 experiment, while PCA was still present at day 35 in the July 1999 experiment. Compared to March 1999 experiment, peak concentrations of all daughter products except trichloroethylene (TCE) were delayed in the July 1999 experiment. The relative intensity of the peaks was directly related to the biomass present for each fragment length (bp, base pair). The relative intensities were lower in sediment collected in August 1999 than in March 1999, especially in the bp size range of ??? 160??-240??. These microbial community analyses, along with the geochemical analyses of the microcosms, provide evidence that abiotic production of TCE from PCA degradation is more significant under conditions of low bacterial biomass in the wetland sediments.