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 (delta C-13) of HCB and penta-CB increases from - 27.3 parts per thousand to 18.8 parts per thousand and from - 33.9 parts per thousand to - 19.5 parts per thousand, respectively. The isotopic fractionation of the reactants and products are described with the Rayleigh model, and the following enrichment factors (epsilon) are obtained: - 14.8 parts per thousand for the dechlorination of HCB and 22.7 parts per thousand for the dechlorination product (penta-CB). With the initial delta C-13 value of HCB, this enrichment factor can be used to estimate the fraction (f) of HCB remaining by Rayleigh equation. Strong enrichment of delta C-13 in HCB and penta-CB during photochemical dechlorination might serve as a powerful toot to monitor the photolysis process, such information may provide additional evidence to aid in further understanding the biogeochemical processes of these compounds undergoing in the environment.