Inhaling Benzene, Toluene, Nitrogen Dioxide, and Sulfur Dioxide, Disrupts Thyroid Function in Captive American Kestrels (Falco sparverius)

摘要

Research investigating the effects of air contaminants on biota has been limited to date. Captive adult female American kestrels (Falco sparverius) were exposed to a mixture of benzene (0.6 ppm), toluene (1 ppm), nitrogen dioxide (NO_2; 2 ppm) and sulfur dioxide (SO_2; 5.6 ppm), in a whole-body inhalation chamber. Thyroid axis responses to meet metabolic demands were examined through thyroid histology, plasma thyroxine (T_4), and triiodothyronine (T_3), and hepatic outer ring deiodination (T_4-ORD). Plasma free (F) T_3 and T_4 were measured at baseline, and at 9 days and 18 days of exposure, whereas total (T) T_3 and TT_4, thyroid histology and hepatic T_4-ORD were determined at the final 18 day exposure. Inhalation of these contaminants significantly suppressed plasma FT_4 and TT_4, and depleted follicular colloid and increased epithelial cell height at 18 days, and significantly altered the temporal pattern of plasma FT_4. Significant histological changes in the follicular colloid: epithelial cell height ratio indicated sustained T_4 production and release by the thyroid glands. There was no effect on plasma FT_3, TT_3, or hepatic T_4-ORD. We hypothesize that contaminant-related activation of the hypothalamus-pituitary-thyroid axis in the kestrels increased elimination of plasma T_4 through Phase Ⅱ enzymes. Further research is required to test this hypothesis in wild birds.