Mercury temporal trends in top predator fish of the Laurentian Great Lakes
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Mercury (Hg) contamination is widespread in the Laurentian Great Lakes region and is a serious environmental concern. In anaerobic environments such as lake sediments, mercury is transformed into methylmercury (MeHg) and can biomagnify up the food chain to toxic concentrations. The Great Lakes Fish Monitoring Program (GLFMP), administered by the US EPA Great Lakes National Program Office (GLNPO), aims to monitor temporal trends of mercury in the five Great Lakes using top predator fish as biomonitors. Total Hg (THg) concentrations were measured in Great Lake fish collected between 1999 and 2009. Single factor ANOVA determined that average fish THg concentrations over this time period in the five lakes were significantly different from one another in the order of Superior > Huron > Michigan > Ontario > Erie. By fitting the data to three different models (linear, quadratic, and two-segment piecewise), it was determined that Hg concentrations in top predator fish (lake trout, or walleye in Lake Erie) are currently increasing in Lake Erie and the Apostle Island sampling site in Lake Superior. Significant decreasing trends are evident in Lakes Michigan, Ontario, and the Rockport sampling site in Lake Huron, although all of the lakes exhibit elevated concentrations in fish compared to historic concentrations. As new Hg emission controls are implemented in the US, continued monitoring of Hg in Great Lakes fish will be needed to determine if they influence the current concentrations and trends.
KeywordsMercury Lake trout Salvelinus namaycush Walleye Sander vitreus Great Lakes
The authors would like to thank Marylin Mayer for her contribution to analytical method development and 2004–2005 data; GLFMP Manager Elizabeth Murphy; Molly Middlebrook of CSC; Kenneth Miller for intricate data review; Xiaoyan Xia for help cataloging and organizing fish samples, and for continuous constructive project input; and Jiaoyan Huang for help with statistical analysis. In addition we would like to acknowledge the fish collection teams from both federal and state agencies, and all other collaborators from across several universities. We thank our peer reviewers for their guidance with earlier manuscript versions. Funding for this work was provided by the Great Lakes National Program Office under the United States Environmental Protection Agency, grant no. GL 96594201. Although the research described in this work has been partly funded by the US EPA, it has not been subjected to the agency’s required peer and policy review and therefore does not necessarily reflect the views of the agency and no official endorsement should be inferred.
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