Carbon and chlorine isotope fractionation of chlorinated aliphatic hydrocarbons by evaporation

Two pure solvents (trichloroethene and dichloromethane) were evaporated at room temperature (24±1°C). The carbon and chlorine isotopic compositions of the residual solvents were measured as a function of the fraction remaining. Isotopic fractionation factors (α) derived from these experimental results are 1.00031±0.00004 for C and 0.99818±0.00022 for Cl in trichloroethene, and 1.00065±0.00002 for C and 0.99952±0.00006 for Cl in dichloromethane. The negative correlation between δ13C and δ37Cl values caused by evaporation of chlorinated aliphatic hydrocarbons can be used to distinguish evaporation from biodegradation in contaminated systems.