C, Cl and H compound-specific isotope analysis to assess natural versus Fe(0) barrier-induced degradation of chlorinated ethenes at a contaminated site

摘要

Compound-specific isotopic analysis of multiple elements (C, Cl, H) was tested to better assess the effect of a zero-valent iron-permeable reactive barrier (ZVI-PRB) installation at a site contaminated with tetrachloroethene (PCE) and trichloroethene (TCE). The focus was on (1) using C-13 to evaluate natural chlorinated ethene biodegradation and the ZVI-PRB efficiency; (2) using dual element C-13-Cl-37 isotopic analysis to distinguish biotic from abiotic degradation of cis-dichloroethene (cis-DCE); and (3) using C-13-Cl-37-H-2 isotopic analysis of cis-DCE and TCE to elucidate different contaminant sources. Both biodegradation and degradation by ZVI-PRB were indicated by the metabolites that were detected and the C-13 data, with a quantitative estimate of the ZVI-PRB efficiency of less than 10% for PCE. Dual element C-13-Cl-37 isotopic plots confirmed that biodegradation was the main process at the site includingthe ZVI-PRB area. Based on the carbon isotope data, approximately 45% and 71% of PCE and TCE, respectively, were estimated to be removed by biodegradation. H-2 combined with C-13 and Cl-37 seems to have identified two discrete sources contributing to the contaminant plume, indicating the potential of delta H-2 to discriminate whether a compound is of industrial origin, or whether a compound is formed as a daughter product during degradation. (C) 2015 Elsevier B.V. All rights reserved.