How are Mercury Sources Determined?

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USGS scientists use innovative isotopic identification methods to determine mercury sources in air, water, sediments, and wildlife.

Discriminating Mercury Sources Using Mercury Isotopes

Scientists are using new techniques to provide more certainty about mercury sources to air, water, sediments, and wildlife.

(Credit: Suzanne Roberts, U.S. Geological Survey. Public domain.)

Mercury is recognized as a neurotoxin that can accumulate in fish and move through the food chain to other wildlife and humans. Innovative techniques are used to measure differences in mercury isotopes and provide unique signatures that can differentiate mercury sources deposited from the atmosphere, released from local ongoing and legacy point sources, or mobilized from the watershed and transported downstream.


Scientists have used these techniques in the Great Lakes and the Northeastern United States to answer questions about mercury sources in fish.  For example:

Mercury signatures in Great Lake’s predatory fish were found to be more reflective of atmospherically sourced mercury than of sediment sourced mercury in each lake.

Mercury signatures in fish in Northeast U.S. Streams indicated atmospheric sources in fish within forested-rural areas, whereas mercury isotope signatures indicated past (legacy) and present local sources in fish within predominantly urban-industrial areas.

•Mercury isotopic signatures provided a tool to understand how mercury cycling and accumulation in a predatory fish in Lake Michigan was affected by changes in sources and by food web alterations.

Recently developed methods to separate methylmercury, the most bioaccumulative and toxic form of mercury in the environment, from other mercury forms and make isotope measurements will further improve methods to distinguish mercury sources in a wider array of settings.

These innovative methods inform efficient and economically sound mitigation actions that could reduce mercury exposure to fish, wildlife, and humans.