Endocrine Abstracts

The lifelong exposure to mixtures of endocrine disrupting chemicals raises serious concerns about their deleterious effects on human health. Polychlorinated biphenyls (PCBs) had widespread use in numerous industrial applications, and were massively produced for several decades. After the discovery of the adverse effects of PCBs in the 1970s, brominated flame retardants (BFRs) were established as the major chemical flame retardant. Both chemicals persist in the environment and biomagnify in the food chain, hence their cocktail effect on thyroid gland can be assumed.

This experimental study was aimed to assess effects of repeated relatively low doses (corresponding low to high environmental human exposures) of these persistent organic pollutants on thyroid homeostasis in adult animals. Rats were randomized into control and treatment groups. Animals were treated by oral gavage for 28 days with either PCBs solution in corn oil or polybrominated diphenyl ether (BDE-209) suspension in dimethyl sulfoxide, or their combination. Animal groups were receiving BDE-209 suspension or commercial mixture of Aroclor 1254 at five different dose levels for each chemical. Nine groups were receiving different combinations of BDE-209 and PCBs. Treatment of all animals was performed by oral gavage, each day, during 28 days. Thyroid hormones were investigated in serum samples obtained from blood samples collected at necropsy.

Applied doses of PCBs induced dose dependent decrease in T4, while BDE 209 caused increase in T4 and decrease in T3 levels, compared to respective controls. However, no interaction at tested dose levels of PCBs and BDE-209 were observed implying that PCBs and BDE-209 as chemicals which act by similar modes at the level of thyroid homeostasis, exert additive effects in mixture.

The study implicates that exposure to low, environmental doses of these chemicals interferes with thyroid function and raises an issue of their additive thyroid toxicity in mixtures.