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Mercury-Contaminated Fish--Is it Old or New Mercury?

Scientist in a white protective suit spraying 202Hg solution on plants

Applying 202Hg as part of the METAALICUS study of the fate of mercury from atmospheric deposition in pristine lakes.

An international consortium of scientists has undertaken a major experiment to determine just that. The experiment is called METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the United States), and it takes place at the Experimental Lakes Area (ELA) of the Department of Fisheries and Oceans Canada, located in northwestern Ontario.

Recent dramatic increases in the instance of mercury fish-consumption advisories, which now occur in 42 states, demonstrate that mercury is a serious national problem, as well as an issue of global concern. In fact, mercury is responsible for over three quarters of all contaminated fish-consumption advisories. An international team of researchers that includes scientists from the USGS is trying to determine if the widespread mercury problem is a result of current mercury emissions into the atmosphere or if it is due to "old" mercury that is already in the environment from 100 years of mercury emissions by a variety of industries. The answers to these questions could help regulators determine what the response of ecosystems will be, in terms of reduced exposure levels of mercury to humans and wildlife, if emissions are reduced. The U.S. Environmental Protection Agency and the U.S. Department of Energy currently estimate that emission controls for mercury would cost approximately $2 billion a year to operate. The scientific community's current understanding of the fate of mercury in the environment cannot guarantee or provide reasonable assurance that significant environmental improvements would result from reduced emissions of mercury. To address this important question, the METAALICUS project has been given permission by the Canadian government to add trace amounts of specific mercury isotopes to an entire watershed to simulate "new" mercury entering the watershed. Because specific isotopes are being used, scientists can differentiate it from the mercury already in the watershed as it moves and reacts in the watershed and presumably ends up in the food chain. The research team developed new methods to detect mercury at extremely low levels for this project, which allowed the team to add mercury isotopes in amounts that would not pose a significant threat to the watershed's ecosystem. This experiment is unique because of the opportunity to trace the cycling of mercury on a whole-watershed scale and to observe the response of the whole ecosystem to atmospheric deposition of mercury. The results of this experiment will allow the research team to determine precisely how much and how quickly recently added mercury enters food webs.

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