Abstract
Natural attenuation (NA) processes represent a valuable option in groundwater remediation. At a heavily 1,2-dichloroethane (1,2-DCA) contaminated site, Compound-Specific Isotope Analysis (CSIA) in combination with Biological Molecular Tools (BMTs) were implemented as a rigorous characterization approach to evaluate the occurrence of Natural Attenuation in the proximity of the source area. By the use of microcosm experiments, the potential for natural and enhanced biodegradation under anaerobic conditions was documented, following the dichloroelimination pathway. Enrichment factors of −9.1‰ and −11.3‰ were obtained for 13C while Geobacter spp. and reductive dehalogenase genes (rdhs) were identified as main site-specific biomarkers. At pilot scale, enrichments of 13.5‰ and 6.3‰ for δ13C and δ37Cl, respectively, high levels of reductive dehalogenase (rdh group VI) along with the dominance of Geobacter spp. indicated the occurrence of significant dichloroelimination processes in groundwater under anaerobic conditions. By using the site-specific enrichment factors, degradation extents over approximately 70–80% were estimated, highlighting the relevant potential of NA in 1,2-DCA degradation in the vicinity of the source area at the site. The proposed fine-tuned protocol, including CSIA and BMTs, is proven to be effective as a groundwater remediation strategy, properly assessing and monitoring NA at site scale.
Highlights
Chlorinated hydrocarbons are among the most frequent groundwater contaminants in many industrialized countries, as they are used as chemical intermediates, refrigerants, solvents, cleaners etc. [1]
Frequently detected in aquifers and sediments, Dehalobacter spp., Dehalococcoides spp. and Desulfitobacterium spp. are primarily responsible for the conversion of 1,2-DCA, mainly using reductive dehalogenases (RDs), a class of enzymes which are capable of eliminating chlorine from molecules [5,6,7]
Abiotic controls showed a slight decrease in 1,2-DCA concentrations for natural attenuation (NA) microcosms only throughout the incubation period (15% maximum over 15 days, data not shown), most likely due to volatilization processes; such decrease in concentration due to abiotic process was taken into consideration during estimation of the kinetic parameters and enrichment factors
Summary
Chlorinated hydrocarbons are among the most frequent groundwater contaminants in many industrialized countries, as they are used as chemical intermediates, refrigerants, solvents, cleaners etc. [1]. Vinyl chloride (VC) is formed as an intermediate of the dehydrodechlorination step due to the cleavage of one atom of chlorine using H as an electron donor and 1,2-DCA as a terminal electron acceptor This step can be followed, in specific conditions, by a hydrogenolysis to ethane. Another possibility is dichloroelimination, where two chlorine atoms of 1,2-DCA are removed, converting the contaminant into ethene without production of toxic chlorinated intermediates (such as VC, which is even more toxic than the precursor). The latter presents the favored process for the remediation of polluted groundwater. Aerobic biodegradation of 1,2-DCA is feasible, occurring via enzymatic oxidation or hydrolytic dehalogenation reactions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
