title: Suppressed adrenocortical responses and thyroid hormone levels in birds near a mercury-contaminated river.
abstract: Much of the research on sublethal, adverse effects of mercury (Hg) has focused on impairment of neurological function and reproduction in fish and fish-eating vertebrates. Here we examined the associations between Hg and endocrine function (adrenocortical responses and plasma thyroid hormone concentrations) of insectivorous tree swallow nestlings adjacent to a Hg-contaminated river and nearby reference rivers in Virginia. Nestlings from the contaminated sites had blood Hg concentrations that exceeded those from the reference sites by more than an order of magnitude (354 +/- 22 vs 17 +/- 1 ppb wet weight). A regression of age and Hg concentrations suggested dietary Hg at the contaminated sites exceeded the nestlings' capacity to eliminate Hg through deposition into growing feathers. Although blood Hg concentrations among nestlings at the contaminated sites were lower than those typically associated with abnormal behavior or altered physiology in young birds, adrenocortical responses, plasma triiodothyronine, and thyroxin concentrations were suppressed, relative to reference levels, by the end of the nestling period. These results suggest that (1) Hg may disrupt endocrine systems of terrestrial avian young and (2) adverse effects of Hg on endocrine systems may be most evident once endocrine axes are fully developed.
authors.affiliation: Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, 100 Cheatham Hall, Blacksburg, Virginia 24061, USA. haruka@vt.edu
authors.forename: Haruka
authors.initials: H
authors.lastname: Wada
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Cristol
authors.forename: F M Anne
authors.initials: FM
authors.lastname: McNabb
authors.forename: William A
authors.initials: WA
authors.lastname: Hopkins
mesh_terms: D000302:Adrenal Cortex / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001717:Birds; D004703:Endocrine System / Q000187:drug effects*; D004784:Environmental Monitoring / Q000379:methods; D008628:Mercury / Q000633:toxicity*; D012044:Regression Analysis; D045483:Rivers; D013963:Thyroid Hormones / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood; D014768:Virginia; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D013963:Thyroid Hormones; D014874:Water Pollutants, Chemical; D014284:Triiodothyronine; D008628:Mercury; D013974:Thyroxine