Carbon isotopic fractionation during photolysis of hexachlorobenzene

Abstract

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 increased from −27.3% to 18.8% and from −33.9% to −19.5%, respectively. The isotopic fractionation 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 the biogeochemical processes of these compounds undergoing in the enivornment.

^* Supported by National Natural Science Foundation of China (Grant Nos. 40406021, 20577025), MCIIF(MIF1-CT-2004-510012), and the Ministry of Science and Technology, China (2004AA649140, 2003CB415007)

Keywords:

• hexachlorobenzene
• stable isotope fractionation
• photolysis
• isotopic ratio

Notes

^* Supported by National Natural Science Foundation of China (Grant Nos. 40406021, 20577025), MCIIF(MIF1-CT-2004-510012), and the Ministry of Science and Technology, China (2004AA649140, 2003CB415007)