Investigation of Stable C and Cl isotope effects of trichloroethene and tetrachloroethylene during evaporation at different temperatures

Abstract

There are variations of reported isotope enrichment factors of chlorinated organic contaminants in evaporation processes. Trichloroethene (TCE) and tetrachloroethylene (PCE) were chosen to study carbon and chlorine isotope effects during evaporation at different temperatures. Equilibrium vapor-liquid carbon and chlorine isotope effects experiments were also conducted. In the equilibrium liquid-vapor system, the ¹³C was enriched but ³⁷Cl was depleted in the vapor phase, being consistent with previous results. For evaporation average carbon isotope enrichment factor ɛ _C were +0.28‰±0.01‰ for TCE and +0.56‰±0.09‰ for PCE at temperature from 20 to 26 °C. Meanwhile, average chlorine isotope enrichment factor ɛ _Cl were −1.33‰±0.21‰ for TCE and −1.00‰±0.00‰ for PCE. The results indicate that during evaporation the equilibrium isotope effect attenuates the magnitude of carbon isotope fractionation whereas enhances the chlorine isotope effect. Isotope fractionation during evaporation is determined by both equilibrium and kinetic factors. Chlorine isotope fractionation is influenced by the evaporation rate which is linked to temperature. When using stable isotope to investigate the behavior of chlorinated organic contaminants in groundwater with slow biodegradation rate, the isotope fractionation resulted from evaporation should be taken into consideration. Furthermore, the environment conditions such as temperature are also factors to be considered.

Keywords

chlorine isotope / carbon isotope / evaporation / isotope fractionation / chlorinated organic contaminant / groundwater

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