Alterations in thyroid hormone status in Atlantic croaker (Micropogonias undulatus) exposed to Aroclor 1254 and selected PCB congeners
Many studies in animals and humans have demonstrated that exposure topolychlorinated biphenyls (PCBs) can interfere with the normal function of the thyroid system. In this study, Atlantic croaker (Micropogonias undulatus) were exposed to a PCB mixture (Aroclor 1254) or one of three individual congeners (ortho-PCB 153, ortho-PCB 47 or planar PCB 77) in the diet for 30 days to investigate the effects of PCBs on thyroidal status. Thyroid hormones, thyroxine (T4) and triiodothyronine (T3) were extracted from plasma samples and measured with an enzyme-linked immunosorbent assay. Both male and female croaker exposed to the PCB mixture Aroclor 1254 (0.2 and 1.0 mg/kg body wt/day) had decreased plasma levels of total T3 when compared to the parallel control groups, but the effects on total T4 levels were inconsistent. Exposure to PCB 153 (0.1 and 1.0 mg/kg body wt /day) significantly lowered both T4 and T3, while PCB 47 at the same doses had no effect on thyroid hormone levels. Fish exposed to PCB 77 had no effect on T4 or T3 levels except an increase in T4 levels at the highest dose employed (0.1 mg/kg body weight/day). However, this dose of PCB 77 caused partial loss of appetite and may be too high to be relevant for the effects observed after exposure to Aroclor 1254 considering the fact that it constitutes only 0.31% of the PCB mixture. The results of the present study demonstrate that exposure to synthetic endocrine disrupting chemicals, such as PCBs at the higher end of environmentally realistic concentrations can have profound effects on the thyroidal status of Atlantic croaker. The ability of Aroclor 1254, as well as ortho-PCB 153, to consistently disrupt the natural homeostasis of the thyroid system in croaker is an important finding that contributes to a better understanding of PCB endocrine toxicity in teleosts.