Biological transformations of 1,2-dichloroethane in subsurface soils and groundwater

The ability of naturally occurring microorganisms to biodegrade 1,2-dichloroethane was examined in soil/water microcosms prepared using aquifer material obtained from manufacturing sites in Louisiana and Texas with known histories of exposure to the compound, as well as in aquifer samples taken from a site in Oklahoma with no known history of 1,2-dichloroethane contamination. Biotransformation of 1,2-dichloroethane was noted under methanogenic or sulfate reducing conditions in all samples. Under anaerobic conditions, 1,2-dichloroethane was transformed to ethylene in a single step via reductive dihaloelimination. No other metabolites were detected in the reaction mixtures. Microbial adaptation appeared to be required for biotransformation of 1,2-dichloroethane. Lag periods ranging from 7 to 8 weeks preceded degradation in microcosms prepared with aquifer material from the Texas and Oklahoma sites. In contrast, no lag period was evident prior to biotransformation in microcosms prepared from the Louisiana manufacturing site, which is consistent with field evidence for natural biological attenuation in situ based on analysis of the groundwater chemistry. Aerobic biodegradation of 1,2-dichloroethane to carbon dioxide was also observed after 13 weeks in aquifer material from the Louisiana site, but was not evident in samples from the Texas or Oklahoma sites following 18 weeks of incubation. The ability of naturally occurring microorganisms to degrade 1,2-dichloroethane has bearing on assessments of the fate and lifetime of the compound in the environment, as well as having potential application in the remediation of contaminated groundwater.