Thyroid hormone status of Atlantic croaker exposed to Aroclor 1254 and selected PCB congeners

Abstract

Atlantic croaker ( Micropogonias undulatus) were exposed to the polychlorinated biphenyl (PCB) mixture (Aroclor 1254) or one of three individual congeners (planar PCB 77 or ortho-substituted PCB 47 and PCB 153) in the diet for 30 days to investigate the effects of PCBs on circulating thyroid hormones, thyroxine (T 4) and triiodothyronine (T 3). Aroclor 1254 (0.2 and 1.0 mg/kg body mass/day) decreased plasma T 3 levels consistently, but the effects on T 4 levels were inconsistent from year to year. Exposure to PCB 153 (0.1 and 1.0 mg/kg body mass/day) significantly lowered both T 4 and T 3, while PCB 47 at the same doses had no effect on thyroid hormone levels. The lower doses of PCB 77 (0.004, 0.01 and 0.02 mg/kg body mass/day) had no effect on T 4 or T 3, whereas the highest dose (0.1 mg/kg body mass/day) increased T 4 levels significantly. The results of the present study demonstrate that exposure to PCBs at environmentally realistic concentrations can have profound effects on the thyroid status of Atlantic croaker. The ortho-substituted PCB 153 appears to contribute at least partially to the deleterious effects of Aroclor 1254 on thyroid status, whereas the planar PCB 77 at concentrations present in the mixture is unlikely to alter thyroid hormone levels.