The impact of prolonged cadmium exposure and co-exposure with polychlorinated biphenyls on thyroid function in rats

Endocrine-disrupting chemicals currently represent one of the major concerns and this study was aimed to investigate the effects of different doses of cadmium, widespread toxic metal, on the levels of thyroid hormones and to calculate Benchmark doses for these effects. Furthermore, the effects of co-exposure to cadmium and polychlorinated biphenyls on thyroid function were investigated. Six orally-treated groups of rats were receiving 0.3, 0.6, 1.25, 2.5, 5 and 10 mg Cd/kg b.w./day, five groups were orally treated with 0.5, 1, 2, 4 and 8 mg PCBs/kgb.w./day, while nine groups of rats were orally-treated with different dose combinations of Cd and PCBs (0.6, 1.25 and 2.5 mg Cd/kgb.w. and 2,4 and 8 mg PCBs/kg b.w./day), during 28 days. Thyroid hormones were adversely affected by cadmium, with most prominent effect observed on triiodothyroxine levels indicating Cd interference with thyroid function at extrathyroidal level. Calculated Benchmark doses for Cd effects on thyroid hormones indicate triiodothyroxine as the most sensitive one that can be used as a basis for risk assessment. This study also implicates possible synergistic effects of Cd and PCBs on thyroid function as a consequence of their interference at different levels of thyroid homeostasis.