Preliminary Study Of Application Of Compound-Specific Stable Carbon Isotope Analysis To Trace Biotransformation Of Polychlorinated Biphenyls In Common Carp

Compound-specific isotope analysis(CSIA) is a noval analytical technology developed in the last two decades, which has been widely applied to source identification and tracing the microbial degradation or restoration process of organic contaminants in the environment. Polychlorinated biphenyls(PCBs) are ubiquitous in environment with bioaccumulation,persistence and toxicity. Although PCBs’ manufacture and use had already been banned, PCBs’ residue are still of highly concerned and potentially threats the environment. The biotransformation of PCBs represent an important pathway of PCBs’ elimination. Numerous previous studies had reported the environmental and biological transformation process of PCBs, which mainly focused on the detection of metabolites of PCBs. However, metabolites of PCBs are often difficult to be detected,due to the complexity of biometabolism. Thus, some new technologies are needed to be developed to trace these metabolic processes.Fish represents an important source of human PCB exposure. Compared to the microbial degradation process,the metabolic process of PCBs in fish was still unclear. In the present study, the biotransformation of PCBs in fish were investigated by analysis of alternations in PCB congenener profile, the ennantiomer fraction of chiral PCB congeners and the stable carbon isotope compositon of individual PCBs in labratory experiment. The main aim of the present study was to verify and trace biotransformation of PCBs in fish by application of CSIA.Laboratory exposed experiments were conducted using common carp exposed to Aroclor 1262(in transformer oil) and Aroclor 1242(in hexane) commercial PCBs mixtures. The intestinal absorption efficiency of PCB congeners in common carp was found to be inversely correlated to the number of chlorine atoms in phenyl ring. Five OH-PCBs were detected in the serum of common carp exposed to Aroclor 1262 PCBs mixture, and the OH-PCBs pattern was similar to those reported in fish serum of the field study. This would suggest that those OH-PCBs found in wild fish were most likely due to formation and not bioaccumulation, even bioaccumulation may be an important exposure route of other OH-PCBs, those not quantified in this study, but found in abiotic matrices. No Me SO2-PCBs were above the limit of detection in the fish tissues in both Aroclor 1262 and Aroclor 1242 exposed experiments, which may be related to the extremely slow metabolism of the PCB parent copounds to the Me SO2-PCBs.The results of the CSIA indicated that the δ13C values of PCB 107/149,PCB 153/132、PCB 180/193、PCB183 and PCB 187 in Aroclor 1262 exposed experiment and PCB 5/8、PCB 18 and PCB 20/33 in Aroclor 1242 exposed experiment were increased compared with those in the standard, while PCB 141、PCB 151、PCB 174/181 and PCB 177 in Aroclor 1262 exposed experiment and PCB 47/48、PCB 49、PCB 52 and PCB 66 in Aroclor 1242 exposed experiment showed an obviously isotope depletion, which suggested a significant biotransformation of individual PCBs. However, the absense of related metabolites in present study may indicate some unknown biotransformation processes in fish.Chiral PCB congeners exposed experiment provided evidence of PCBs biotransformation in common carp. Common carp showed a selectively biotransformation of(+)-PCB 91 enantiomer and(–)-PCB95 enantiomer; while PCB 132 and PCB 149 were found to be racemic in fish throughout the course of the experiment.The results of the CSIA indicated that PCBs 91,95,132 and 149 in common carp were enriched in 13 C compared with that in the standard as a result of isotope fractionation during the metabolism in fish. With the decline of EF values of PCB 91, the δ13C of(+)-CB 91 increased, while no isotopic fractionation was found for(–)-CB 91, which indicated that common carp might selectively biotransformed(+)-CB 91. For PCB 95, heavy isotope enrichment were observed for both(+)-CB 95 and(–)-CB 95 but with different degree on enrichment. The isotope fractionation degree of(–)-CB 95 δ13C values were higher than those of(+)-CB 95, which indicated a different biotransformation rate between two eantiomers. For PCB 132 and PCB 149,the δ13C values of both enantiomers of each congener were changed in a same magnitude, which would suggest that both enantiomers were biotransformed at a same rate, that is, biotransformation was achiral. This was the first study of application of CSIA to trace the enantiomer selective biotransformation of chiral PCBs in fish.