Abstract
Chlorinated ethanes, such as 1,1,1-trichloroethane (1,1,1-TCA), are environmental pollutants frequently found in soil, groundwater and the atmosphere, and are commonly identified in many industrial contaminated sites. Removal of 1,1,1-TCA can be achieved via abiotic transformation or biodegradation by dechlorinating organisms such as Dehalobacter (Dhb). In this study, we analyzed samples from groundwater microcosms and an industrial site where a mixture of granular zero valent iron (ZVI) and guar gum was injected for 1,1,1-TCA remediation. Abiotic and biotic transformation products were monitored and microbial community changes were tracked using quantitative PCR (qPCR), with primers targeting the Dehalobacter 16S rRNA gene and two functional genes cfrA and dcrA encoding the reductive dehalogenases capable of converting 1,1,1-TCA to 1,1-dichloroethane (1,1-DCA) and 1,1-DCA to chloroethane (CA), respectively. The abundance of genes targeted by the cfrA and dcrA qPCR primers tracked dechlorination activity in a highly consistent and specific manner. The two reductive dechlorination steps were catalyzed by two distinct Dehalobacter populations harboring two closely related but distinct reductive dehalogenase genes. Using cell yields established in microcosms along with Dhb 16S rRNA, Dhb cfrA- and dcrA-like gene copies in site samples, the biotic component of 1,1,1-TCA transformation at a complex field site was estimated.