| This study examined the dietary bioaccumulation and biotransformation of an Aroclor mixture of polychlorinated biphenyls (PCBs) in rainbow trout (Oncorhynchus mykiss) and the effects of PCBs on trout thyroidal status. Considerations such as the physico-chemical properties of PCB congeners, temperature and cytochrome P450 (CYP) induction, which are thought to be important in the bioaccumulation and biotransformation of persistent organic pollutants but rarely directly studied, were also assessed. A strong relationship between half-life (t½) and octanol/water partition coefficient (KOW) for the entire range of PCB congeners was identified, validating previous findings for a subset of recalcitrant PCBs. The slope of this relationship was robust over differing fish body sizes, various water temperatures, and CYP induction, although the intercept of the t½ varied. A number of PCB congeners fell below this relationship, indicating biotransformation, and this was related to chemical structure, water temperature, and CYP2B-like enzyme induction. This is the first study to demonstrate in vivo CYP2B-like enzyme induction and biotransformation of PCBs in fish and to provide biotransformation rates. Biotransformation of PCBs was verified by demonstrating stereoselective degradation of certain chiral PCB congeners, and, more definitively, by the bioformation of hydroxylated PCB (OH-PCB) metabolites. Hydroxylated PCBs bioformed in this study were similar in concentration pattern to those observed in wild fish, indicating that biotransformation is likely an important source of OH-PCBs in wild fish. There were relationships between PCBs and some indices of thyroid status in fish (thyroid epithelial cell height and T4 outer ring deiodination) but alterations were dependent on temperature. Thyroid changes in the PCB-exposed fish were compensatory in nature and the thyroid system was capable of maintaining circulating hormone concentrations. Results of this work suggest that exposure to PCBs, along with additional stress factors may impact the heath of fish in the wild but that additional research is required before we can fully understand the magnitude and implications of these effects. |
