Microbial molecular and isotopic biomarkers of chloroethene (PCE, TCE, DCE, CV) biodegradation to evaluate natural attenuation contaminated plumes: which added value?

Abstract : The extensive use of aliphatic chlorinated hydrocarbons (e.g. tetrachloroethene (PCE) and its degradation products) as solvents and their hydrophobic proprieties has resulted in their accumulation and persistence in aquifers worldwide, representing a serious risk for human health and the environment. The monitoring of polluted sites (and their natural attenuation) benefits from the classical physical-chemical assessment of the plume. In addition, the evaluation of the potential of chlorinated hydrocarbons’ degradation relying on molecular biomarkers may be valuable for site diagnosis. In the framework of this research project (BioDisspol: Applicability of microbial biomarkers for evaluating natural attenuation of polluted sites) financed by ADEME (French Environment and Energy Management Agency), we evaluate the relationship between PCE, TCE, DCE and CV degradation and specific functional and taxonomic bacterial genes to eventually develop the role of biomarkers in a coherent framework of monitored natural attenuation (MNA). Groundwater was sampled biannually for two years in 12 piezometers at a contaminated site in France. Four parallel analytical approaches were coupled: (i) ground water physical-chemical parameters, (ii) compound-specific isotope fractionation analysis (CSIA) of chlorinated hydrocarbons, (iii) the quantification of taxonomic and functional genes, and (iv) microbial profiling with next generation sequencing (Illumina MiSeq). In addition to this onsite monitoring, the possible degradation capacities of specific molecules were assessed in batch assays, indeed validating the possibility of biological attenuation. Altogether, our results highlight the value of biological characterization of polluted sites to guide remediation strategies and site management.