Carbon isotope fractionation during volatilization of chlorinated organic compounds†

Abstract

Chlorinated organic compounds (COCs) are industrially produced for different applications. These chemicals occur as common organic contaminants in soil and groundwater. Compound specific isotope analysis (CSIA) has been widely applied to delineate underlying transformation processes of organic contaminants. However, it remains unclear how volatilization processes would influence observed CSIA signals of different COCs, which is of special interest for remediation techniques such as soil vapor extraction and soil bioventing that rely on volatilization. To fill this data gap, our study developed an experimental setup and applied our optical CSIA approach to resolve carbon isotope fractionation of 12 different COCs during volatilization. Inverse carbon isotope fractionation was observed for all the target compounds, where positive carbon isotope enrichment factors (ε) were obtained. The extent of carbon isotope fractionation was correlated with the elemental compositions of the target compounds, indicating that chlorine substitutions lead to more pronounced inverse carbon isotope effects. Our study widened applications of the optical carbon CSIA method, and provided valuable data to evaluate volatilization-induced carbon isotope fractionation of different COCs.