Bio-Trap®–based in situ microcosm studies were conducted to evaluate EHC-M® stimulated degradation of mono-, di-, and trichlorobenzenes in anaerobic groundwater at a site in Michigan. The data show that the EHC-M® amendment stimulated an overall increase in microbial activity and a shift in the microbial community structure, indicating more reduced conditions. Stable isotope probing with 13C6-chlorobenzene demonstrated attenuation of chlorobenzene and subsequent separation and characterization of the 12C- and 13C-deoxyribonucleic acid (DNA) fractions were used to identify the attenuating microbes. These data clearly show the participation of an obligate aerobe in the chlorobenzene biodegradation process.
Decreases in concentrations of trichlorobenzenes were also observed in comparison to a control. Due to the thermodynamically favorable reducing conditions stimulated by EHC-M®, the mechanism of degradation of the trichlorobenzenes is presumed to be reductive dehalogenation. However, on the strength of the DNA-based analysis of microbial community structure, concurrent microaerophilic degradation of chlorobenzene or its metabolites was definitively demonstrated and cannot be ruled out for the other chlorobenzenes. © 2013 Wiley Periodicals, Inc.