Use of dual element isotope analysis and microcosm studies to determine the origin and potential anaerobic biodegradation of dichloromethane in two multi-contaminated aquifers

Abstract

Many aquifers around the world are impacted by toxic chlorinated methanes derived from industrial processes due to accidental spills. Frequently, these contaminants co-occur with chlorinated ethenes and/or chlorinated benzenes in groundwater, forming complex mixtures that become very difficult to remediate. In this study, a multi-method approach was used to provide lines of evidence of natural attenuation processes and potential setbacks in the implementation of bioremediation strategies in multi-contaminated aquifers. First, this study determined i) the carbon and chlorine isotopic compositions (δ 13 C, δ 37 Cl) of several commercial pure phase chlorinated compounds, and ii) the chlorine isotopic fractionation (εCl =-5.2 ± 0.6‰) and the dual C-Cl isotope correlation (Λ C/Cl = 5.9 ± 0.3) during dichloromethane (DCM) degradation by a Dehalobacteriumcontaining culture. Such data provide valuable information for practitioners to support the interpretation of stable isotope analyses derived from polluted sites. Second, the bioremediation potential of two industrial sites contaminated with a mixture of organic pollutants (mainly DCM, chloroform (CF), trichloroethene (TCE), and monochlorobenzene (MCB)) was evaluated. Hydrochemistry, dual (C-Cl) isotope analyses, laboratory microcosms, and microbiological data were used to investigate the origin, fate and biodegradation potential of chlorinated methanes. At Site 1, δ 13 C and δ 37 Cl compositions from field samples were consistent with laboratory microcosms, which showed complete degradation of CF, DCM and TCE, while MCB remained.

Dehalogenation of Polybrominated Diphenyl Ethers and Polychlorinated Biphenyls Catalyzed by a Reductive Dehalogenase in Dehalococcoides mccartyi Strain MB

“…Our findings may also contribute to a better understanding of the attenuation of halogenated POPs at sites contaminated with multiple groups of organohalide pollutants. Multiple organohalide compounds are frequently found at contaminated sites (e.g., soil and sediment adjacent to e-waste recycling facilities), , and such co-contamination is conventionally thought to impair bioremediation efforts. , However, in the current study, we found that some organohalide pollutants (i.e., penta-BDEs and PCE in the case of D. mccartyi strain MB) could act as growth-supporting substrates to stimulate cell growth for attenuation of the more persistent organohalide pollutants (i.e., PCBs) that do not support the growth of the given OHRB.…”

“…Multiple organohalide compounds are frequently found at contaminated sites (e.g., soil and sediment adjacent to e-waste recycling facilities), 31,63 and such co-contamination is conventionally thought to impair bioremediation efforts. 52,64 However, in the current study, we found that some organohalide pollutants (i.e., penta-BDEs and PCE in the case of D. mccartyi strain MB) could act as growth-supporting substrates to stimulate cell growth for attenuation of the more persistent organohalide pollutants (i.e., PCBs) that do not support the growth of the given OHRB. It should be noted, however, that the co-metabolic dechlorination stimulated by metabolically dehalogenated substrates in a specific strain most likely occurred because dehalogenation of each organohalide was attributed to the same RDase, MbrA, and may not be a general feature of OHRB that employ separate RDases to dehalogenate different organohalides.…”

Alleviating Chlorinated Alkane Inhibition on Dehalococcoides to Achieve Detoxification of Chlorinated Aliphatic Cocontaminants

“…The present study ranked chloroform as the most detrimental cocontaminant inhibiting microbial reductive dechlorination of DCEs by Dehalococcoides -containing consortia, followed by 1,1,1-TCA and 1,1,2-TCA. Notably, both chloroform and 1,1,1-TCA demonstrated evident inhibitory effects on DCE dechlorination at concentrations ≥ 5 μmol/L, which is within the environmental detection levels of these pollutants at contaminated sites. ,, This underscores the necessity of accounting for these cocontaminants when conducting bioremediation with Dehalococcoides . Interestingly, we also found that dechlorination of trans -DCE was more susceptible to cocontaminant inhibition compared to cis -DCE in the investigated Dehalococcoides -containing consortia, providing an alternative explanation for the more frequent detection of trans -DCE than cis -DCE at contamination sites .…”

“…Bioremediation employing Dehalococcoides populations capable of detoxifying chloroethenes has been widely applied to clean up relevant contamination sites. − Field bioremediation efforts and laboratory investigations have indicated that cocontamination with other chlorinated solvents significantly affects the effectiveness of bioremediation for chloroethenes. ,− Despite the recognition of this issue for a long time, a comprehensive evaluation of the toxicity of environmentally relevant chlorinated cocontaminants on the metabolic activity of Dehalococcoides and other associated syntrophic microorganisms is lacking. The present study ranked chloroform as the most detrimental cocontaminant inhibiting microbial reductive dechlorination of DCEs by Dehalococcoides -containing consortia, followed by 1,1,1-TCA and 1,1,2-TCA.…”

“…In spite of the significant advancements achieved over the past four decades in bioremediation of chloroethenes through the utilization of Dehalococcoides , instances with unsatisfactory remediation outcomes (e.g., accumulation of toxic intermediates and incomplete removal of pollutants) remain far from uncommon. − A pivotal determinant contributing to these compromised bioremediation results is the inhibition of microbial reductive dechlorination induced by chlorinated cocontaminants. The metabolic activity of OHRB, particularly Dehalococcoides , is prone to suppression in the presence of other chlorinated cocontaminants that often coexist with chloroethenes. ,− For instance, chloroform at environmentally relevant concentrations (2.5–14.0 μM) severely inhibited dechlorination of chloroethenes in most Dehalococcoides isolates. , Similarly, 0.2–2.0 μM 1,1,1-trichloroethane (1,1,1-TCA) has been demonstrated to result in an approximately 50% reduction in dechlorination of vinyl chloride in commercial dechlorinating consortia (KB-1, OW, and BDI) . Although these pioneering studies separately investigated the inhibitory effects of individual groups of cocontaminants on dechlorination of chloroethenes, a comprehensive comparison of the inhibitory potential of various chloroalkanes is currently lacking.…”