MICROBIAL UTILIZATION OF VADOSE ZONE ORGANIC-CARBON FOR REDUCTIVE DECHLORINATION OF TETRACHLOROETHENE

Aqueous extracts from a calcareous spodosol were used las the primary substrate to study the reductive dechlorination of tetrachloroethene ( PCE). A comparison was made between extracts obtained using pure water and water saturated with trichloroethene (TCE). The latter solutions were intended to simulate solutions formed by rainwater percolating th rough TCE-contaminated soils. The results indicated that TCE-saturated water apparently mobilized more organic materials than did pure water . The extracts obtained from TCE-saturated water were noticeably more turbid than those obtained using pure water, suggesting greater mobili zation of colloids. After centrifugation, the extracts contained simil ar amounts of dissolved organic carbon (DOG), 16 and 20 mg/L, respecti vely. Microcosm studies indicated that both centrifuged extracts were capable of sustaining reductive dechlorination of PCE as evidenced by the production of TCE, dichloroethene (DCE), and methane. These result s indicate that the inclusion of the transport of DOC from the surface and the vadose zone to the saturated zone may be important in bioreme diation and risk-exposure models.