Selenium:mercury molar ratio in eared grebes (Podiceps nigricollis) as a possible biomarker of exposure |
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| Institution: | 1. Division of Life Sciences, Rutgers University, Piscataway, NJ, USA;2. Consortium for Risk Evaluation with Stakeholder Participation, Rutgers University, Piscataway, NJ, USA;3. Environmental and Occupational Health Sciences Institute, Rutgers University, Piscataway, NJ, USA;4. Division of Birds, U.S. Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA;5. Environmental and Occupational Medicine, Robert Wood Johnson Medical School, Piscataway, NJ, USA;1. Department of Applied Physics, School of Physics and Electronics, Hunan University, Changsha 410082, China;2. Changsha Environmental Protection College, Changsha 410004, China;1. China Nuclear Power Design Co., Ltd. (Shenzhen) of China General Nuclear Power Group, Shenzhen, Guangdong, 518172, China;2. China Nuclear Power Engineering Co., Ltd. of China General Nuclear Power Group, Shenzhen, Guangdong, 518120, China;1. Department of Food Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa;2. Department of Animal Sciences, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa;3. Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South Africa |
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| Abstract: | Mercury and selenium have adverse effects on health, and in the past their individual levels in tissues have been used as biomarkers of environmental contamination. These selenium:mercury molar ratios has been proposed as an alternative way to anticipate possible health risks to organisms. We examine selenium and mercury levels, their molar ratios, and variability in the ratios in the brain, liver, muscle, and feathers of a common waterbird, the eared grebe (Podiceps nigricollis), at several locations and phases of their annual cycle. We found: (1) Mean total mercury, for any site or tissue, ranged from 0.15 ppm in the brain to 29.2 ppm in breast feathers; (2) In any tissue, mean mercury levels varied by as much as 10-fold while selenium varied by 3-fold; (3) Mercury and selenium levels were correlated only in liver; (4) Selenium:mercury molar ratios varied significantly in regular patterns among tissues (less than 1 in feathers, up to 23 in brain), sites, and stages of annual cycle; (5) Molar ratios were affected by body weight (but not age), and the heaviest birds had the lowest ratios; and (6) Molar ratios varied more for brain than in other tissues. Low molar ratios are generally considered harmful, although no threshold ratio has been identified. Despite wide variation of molar ratios, field studies of eared grebes have not detected overt adverse effects. Before being adopted as a biomarkers, we suggest that selenium:mercury molar ratios be used in conjunction with studies of individual metal levels, and in accordance with detailed studies of selected species, to provide a baseline of variation in different organisms and tissues. |
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| Keywords: | Selenium:mercury molar ratio Biomarker Brain Liver Muscle Feathers Grebe |
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