IN SITU VINYL CHLORIDE BIODEGRADATION REVEALED THROUGH CARBON ISOTOPE COMPOSITION

摘要

In situ biodegradation of vinyl chloride (VC) was documented by the change in the stable carbon isotope composition of VC within a groundwater aquifer. Isotopic specificity has been documented for stable carbon isotopes during the biodegradation of chlorinated ethenes, including VC. Biodegradation involves a preferential degradation of isotopically light ~(12)C-bearing VC. The preferential reaction results in accumulation of ~(13)C in the residual VC such that the isotopic composition of the VC becomes measurably ~(13)C enriched. This phenomenon was used to evaluate the effects of biodegradation on a large VC plume in a deep sandy aquifer at a manufacturing facility. Analysis of the stable carbon isotope composition of tetrachloroethene (PCE), trichloroethene (TCE), and VC demonstrated that VC was being biodegraded, provided an estimation of the degree of biodegradation in the source area and down gradient areas of the plume, and supported two independent biodegradation rate calculations that did not rely on VC concentration data. Stable carbon isotope analysis provided dramatic evidence for biodegradation and allowed an estimation of the degree and rate of VC biodegradation. The occurrence of biodegradation would have been assumed based on site specific geochemical changes and the presence of ethene in the groundwater. However, the significance of VC biodegradation would have been severely underestimated using concentration data alone and biodegradation rate calculations could not have been determined with existing data.