WP5 Wildlife Ecotoxicology
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() Age Specific Differences and Reversibility of Ammonium Perchlorate (AP) Effects on Avian Thyroid Function.

McNabb, F. M.1, Doernte, A. 1, Rainey, S. 1, Snyder, S.1, Burnette, S. 1, Queral, L.1, 1 Virginia Tech, Blacksburg, VA, USA

ABSTRACT- We have compared the effects of sustained AP exposure in drinking water on chicks and adults of Bobwhite quail by measuring plasma thyroid hormones (THs; indicative of organismal thyroid status), TG weight (indicative of hypothalamic-pituitary-thyroid, HPT, activation) and thyroid gland-TH content. Chicks were exposed to 0.013-4,000 mg/L and adults to .05-8,000 mg/L AP. In chicks, the effects of AP on thyroid function are greatest early in the exposure (2 weeks) then chicks adapt and recover thyroid function with continued exposure (up to 8weeks) at the lower AP concentrations. Chicks show partial compensation at mid-range AP but continue to have altered thyroid function at the higher AP concentrations. This experiment suggests that in quail chicks, AP exposure may alter the pattern of development of thyroid function. In contrast, adults tolerate higher AP and are less affected early in AP exposure than chicks but show increasing effects at all exposure levels with increased time (8 weeks). We also studied recovery from transient AP exposure (2 weeks at 0, 0.5 or 500 mg/L) at 2 and 4 weeks after the end of AP treatment. AP exposure at 500 mg/L for 2 weeks significantly decreased plasma thyroxine (T4) and triiodothyronine (T3) and significantly increased thyroid gland weight; TG-T4 and TG-T3 decreased in a dose-dependent manner. All thyroid variables recovered, i.e., did not differ from controls at both 2 and 4 weeks after the cessation of AP exposure. These studies suggest that the effects of short term AP exposure on thyroid function are reversible. Supported by SERDP contract #CU1242.

Key words: thyroid, perchlorate, development , birds

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