Mercury in Lake Erie fish

Following the adoption of regulatory measures in the 1970s, studies showed a gradual reduction in mercury contamination in fish in the Great Lakes. However, this trend reversed in the 1990s.

This is what Environment and Climate Change Canada scientists have observed based on their analysis of data collected over the past 35 years on fish contamination in Lake Erie. Mercury concentrations appear to have either stopped decreasing or begun increasing in most species under study, including Walleye, Smallmouth Bass, Yellow Perch and White Bass. While the cause of this reversal remains unclear, scientists have proposed several hypotheses, including changes within the food chain relating to the introduction of invasive exotic species.

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© Brigitte Cusson and Denis Labonte, Environment Canada

Bioaccumulation is a phenomenon whereby the contaminant levels in organisms increase up the food chain. In fact, mercury concentrations can be as much as ten times higher in predators near the top of the food chain than the mercury concentrations in the water. For more information, please see the article on mercury in the food chain.

The downward trend in mercury levels appears to have started to slow following the introduction of Zebra and Quagga mussels and Round Goby into the Great Lakes in the late 1980s. Mussels have the capacity to filter water (approximately 1 L/day/mussel) and, especially, to concentrate various chemical contaminants such as mercury.

Since the Round Goby is a fish species that feeds on these mussels, mercury is transferred more or less directly up the food chain, potentially causing it to accumulate more quickly. The Round Goby is eaten in turn by predators such as Walleye, which has been found to exhibit the highest average mercury concentrations at 0.199 µg/g.

© Eric Engbretson, U.S. Fish and Wildlife Service

Despite the presence of mercury in fish tissue, the nutritional value of fish for human consumption remains excellent if the fish consumption advisories issued by the federal and various provincial and territorial governments are followed. In Ontario, consumption restrictions (zero to eight meals per month) for fish containing mercury begin at 0.26 µg/g for vulnerable populations (women of child-bearing age and children) and 0.61 µg/g for the general population (Eating Ontario Fish, 2017-2018).

Reference: Azim, M.E., A. Kumarappah, S.P. Bhavsar, S.M. Backus, and G. Arhonditsis. 2011. Detection of the spatiotemporal trends of mercury in Lake Erie fish communities: A Bayesian approach, Environ. Sci. Technol. 45(6): 2217-2226.