Return to Project List
Project Title: Neurochemical Biomarkers to Assess Health Effects of Toxic Substances to Great Lakes Wildlife
Chemicals Studied: Mercury, PBDEs
Geographic Areas: Great Lakes Region
Project Start Date: August 2009
Project Status: Completed
Synopsis: The specific aims of this project included:
(1) Exposure Assessment: to determine tissue mercury and PBDE levels in river otters and bald eagles from several Great Lakes states, with a focus on animals collected from existing statewide monitoring programs in Michigan and Wisconsin
(2) Health Assessment: to determine river otter and bald eagle health status by means of neurochemical biomarker studies on key receptors (muscarinic, glutamate) and enzymes (monoamine oxidase, cholinesterase) in physiologically important brain regions
(3) Risk Characterization: to determine if there is a statistical association between mercury and PBDE exposure and alterations in neurochemical biomarkers
(4) Education and Capacity Building: to build capacity among academic researchers and government/state managers and to disseminate results to scientific and regulatory communities.
Collection of Bald Eagles: Tissues (i.e., whole brain, liver, muscle, fur/feather) were obtained from 149 individual bald eagles. Because of the quality of tissue, none of the brains were separated into areas of physiological importance, rather they were analyzed in whole. For each eagle, the liver was obtained, and for many the muscle and feather were received. For all the eagles received, mercury (total) has been analyzed on nearly all brains and livers. Methylmercury has been analyzed in nearly all liver and brain samples. In a subset of 46 eagles, 15 different metals/elements were measured in both liver and brain. In a subset of 33 eagles from Michigan, a suite of PBDEs were measured in the liver. Four neurochemical biomarkers were measured in a majority of brain tissues. Tissue quality and certain QA/QC criteria did not permit all results to be of the highest quality (this is an innate hurdle in postmortem biomarker studies involving wild animals).
This study demonstrates that many bald eagles in the Great Lakes region accumulate substantial levels of Hg and provides evidence that Hg is associated with neurochemical changes. Similar changes have been identified in mink (Basu et al. 2007b), otters (Basu et al. 2007a), polar bears (Basu et al. 2009a), loons, and eagles (Scheuhammer et al. 2008), but the relevance of these subclinical changes is unknown. Considering that Hg is known to affect learning, memory, and motor coordination (Evers et al. 2008; Bennett et al. 2009; Spalding et al. 2000; Kenow et al. 2010), which are in part regulated by glutamate and GABA (Scholes 1965, Gibbs et al. 2008), changes in these neurotransmitters may impact ecologically important behaviors in wildlife. Future work should focus on identifying a threshold for Hg's subclinical effects on the brain and clarifying the relationship between subclinical changes and relevant behavioral changes.
Collection of River Otters: Tissues (e.g., brain, liver, fur, muscle) from 107 otters harvested on a 3-year cycle between the 2009- 2010 were collected by the Wisconsin DNR. Brains (n=107) were dissected into three regions (brain stem, occipital cortex, cerebellum). In a subset of 20 otters, 10 brain regions were also dissected to increase understanding of regional differences in mercury distribution. Total mercury analyses have been performed in nearly all dissected brain regions, as well as muscle, fur and liver samples. In a subset of 35 otters, a suite of PBDEs were measured in the liver. Two key neurochemical biomarkers were measured in each brain region for half the otters. Tissue quality and certain QA/QC criteria did not permit all results to be of the highest quality (this is an innate hurdle in postmortem biomarker studies involving wild animals).
Preliminary project results have been presented during the 2010-11 GLAD webinar series.
PBDE results are to be summarized in: Basu, N., Dornbos, P., Chernyak, S., Batterman, S. 2012. PBDE congener profiles in river otters and bald eagles from two Great Lakes States (Manuscript in Preparation).
Niladri Basu, Ph.D.
Dept. of Environmental Health Sciences
University of Michigan
Phone: (734) 764-9490