title: Mercury exposure associated with altered plasma thyroid hormones in the declining western pond turtle (Emys marmorata) from California mountain streams.
abstract: Mercury (Hg) is a global threat to wildlife health that can impair many physiological processes. Mercury has well-documented endocrine activity; however, little work on the effects of Hg on the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in aquatic wildlife exists despite the fact that it is a sensitive endpoint of contaminant exposure. An emerging body of evidence points to the toxicological susceptibility of aquatic reptiles to Hg exposure. We examined the endocrine disrupting potential of Hg in the western pond turtle (Emys marmorata), a long-lived reptile that is in decline throughout California and the Pacific Northwest. We measured total Hg (THg) concentrations in red blood cells (RBCs) and plasma T3 and T4 of turtles from several locations in California that have been impacted by historic gold mining. Across all turtles from all sites, the geometric mean and standard error THg concentration was 0.805 ± 0.025 μg/g dry weight. Sampling region and mass were the strongest determinants of RBC THg. Relationships between RBC THg and T3 and T4 were consistent with Hg-induced disruption of T4 deiodination, a mechanism of toxicity that may cause excess T4 levels and depressed concentrations of biologically active T3.
authors.affiliation: Department of Biology, California State University, Fresno , 2555 East San Ramon Avenue, Fresno, California 93740, United States.
authors.forename: Erik
authors.initials: E
authors.lastname: Meyer
authors.forename: Collin A
authors.initials: CA
authors.lastname: Eagles-Smith
authors.forename: Donald
authors.initials: D
authors.lastname: Sparling
authors.forename: Steve
authors.initials: S
authors.lastname: Blumenshine
mesh_terms: D000818:Animals; D002140:California; D052244:Endocrine Disruptors / Q000032:analysis*; D004784:Environmental Monitoring; D005260:Female; D006046:Gold; D008297:Male; D008628:Mercury / Q000032:analysis*; D008906:Mining; D045483:Rivers; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D014426:Turtles / Q000097:blood*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D052244:Endocrine Disruptors; D014874:Water Pollutants, Chemical; D014284:Triiodothyronine; D006046:Gold; D008628:Mercury; D013974:Thyroxine