Carbon isotopic fractionation during photolysis of hexachlorobenzene

The occurrence of carbon isotope fractionation during dechlorination of hexachlorobenzene (HCB) to pentachlorobenzene (penta-CB) has been evaluated under ultraviolet irradiation in a photo-reactor. Stable carbon isotope ratios (δ¹³C) of HCB and penta-CB increase from -27.3‰ to 18.8‰ and from -33.9‰ to -19.5‰, respectively. The isotopic fractionations of the reactants and products are described with the Rayleigh model, and the following enrichment factors (ε) are obtained: -14.8‰ for the dechlorination of HCB and 22.7‰ for the dechlorination product (penta-CB). With the initial δ¹³C value of HCB, this enrichment factor can be used to estimate the fraction (f) of HCB remaining by Rayleigh equation. Strong enrichment of δ¹³C in HCB and penta-CB during photochemical dechlorination might serve as a powerful tool to monitor the photolysis process, such information may provide additional evidence to aid in further understanding of the biogeochemical processes these compounds will undergo in the environment.