Lowering of Serum Thyroxine and Triiodothyronine Levels in Yearling Coho Salmon, Oncorhynchus kisutch, by Dietary Mirex and PCBs

Abstract

Yearling coho salmon, Oncorhynchus kisutch, were fed diets contaminated with PCBs (500 μg or 50 μg/g dry feed), Mirex (50 μg or 5 μg/g dry feed), or a mixture of Mirex and PCBs (5 μg Mirex + 50 μg PCB/g dry feed) daily for 2 or 3 mo. Serum T3 and T4 levels were significantly reduced in fish fed the high Mirex diet for 2 or 3 mo. Serum T3 levels were reduced in fish fed the high PCB diet for 3 mo. Serum T3 and T4 levels were significantly reduced in fish fed the mixed Mirex–PCB diet for 3 mo. The significant increase in serum T4/T3 ratios in fish given the high Mirex or high PCB diet was not evident in fish given the mixed Mirex–PCB diet, suggesting a synergistic effect that is different from the effect of individual contaminants. Fish given the high PCB or high Mirex diet had significantly lower body weights than the control fish. Key words: organochlorines, teleost fish, thyroid gland, hormones, endocrines, synergism, pituitary gland

Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?

“…Changes in thyroid histological appearance and plasma thyroid hormone levels were reported in coho salmon (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha) collected in Great Lakes (Leatherland, 1993). Salmonids were fed by Aroclor mixtures to determine if PCBs caused these changes, but no conclusive results could be obtained (Leatherland and Sonstegard, 1978;Leatherland and Sonstegard, 1980). Given the equivocal impact of experimental exposure of PCB mixtures on trout and salmon thyroid measures, it was concluded that other factors than PCBs may cause thyroid disruption of the Great Lakes salmon (Leatherland, 1993).…”

Effects of chemical contaminants on blood chemistry of teleost fish: A bibliography and synopsis of selected effects

“…In laboratory studies in which both rainbow trout and coho salmon were fed mirex and polychlorinated biphenyls (PCBs), serum levels of both thyroxine (T,) and triiodothyronine (T,) were significantly reduced in fish fed 500 pg mirex per gram food; however, no significant changes were observed in fish fed 500 pg Aroclor 1254 per gram food [139,146]. No changes in thyroid histology were observed, suggesting the changes in thyroid hormones were due to altered peripheral metabolism of the hormones.…”

Toxic effects in C57B1/6 and DBA/2 mice following consumption of halogenated aromatic hydrocarbon-contaminated Great Lakes coho salmon (Oncorhynchus kisutch Walbaum).

“…The serum T3 levels in DBA/2 mice were elevated following consumption of coho salmon from the Pacific Ocean. Hypothyroidism has been reported in rats following dietary consumption of Lake Ontario coho salmon (23,24) and in coho salmon following dietary exposure to mirex and PCBs (25). The health problems associated with hypothyroidism in adult humans may be correctable with dietary supplements; however, the level ofrisk to the developing fetus is potentially very serious and may affect embryonic physical and mental development.…”