By Marie E. Zhuikov
Researchers around the world now have a new tool for determining the source of mercury contamination, and the results so far have been surprising.
Wisconsin Sea Grant Director James Hurley was part of a team of researchers with the U.S. Geological Survey (USGS) and the University of Wisconsin-Madison responsible for the tool.
“Determining where mercury comes from is important because it helps us figure out the best way to minimize inputs of this harmful element into the environment,” Hurley said.
The two-year study found that in lakes Superior and Huron, most mercury comes from the atmosphere. In lakes Erie and Ontario most mercury comes from industrial activity or runoff from the land surrounding the lakes and the other waters that flow into the lakes (also known as watershed sources). Lake Michigan is beset in general by relatively equal combinations of all three contributing sources: atmospheric, industrial and watershed. The results were published in December 2015 in “Environmental Science & Technology Letters.”
“This project is our first opportunity to show what our lab is capable of,” said Ryan Lepak, a graduate student in civil and environmental engineering at UW-Madison advised by Hurley. “The instrument we’re working with is new, the techniques are new to our group, and the science itself is fairly new.”
Researchers collected sediment samples from 58 locations around the Great Lakes for the project.
They analyzed them for stable isotopes of mercury and used those chemical “fingerprints” to determine sources. They compared the mercury signatures in the lakes against those previously found in lake trout and burbot collected in lakes Michigan, Superior and Ontario. Results showed the mercury in the fish more closely resembled mercury from the atmosphere than mercury from lake sediment. That surprised Dave Krabbenhoft, a mercury researcher from the USGS. “This shows that atmospheric mercury needs to be emphasized, even when the sediments in the lakes show relatively
little atmospheric mercury accumulation.”
The mercury fingerprinting tool can also help resource managers distinguish mercury deposited by past industrial practice, known as “legacy mercury,” from newer sources.
A naturally occurring element, mercury can have toxic effects on people’s brains, kidneys and lungs. In certain environments, with the right microbes, it transforms into methylmercury, which is far more toxic. In addition, methylmercury can accumulate in the tissues of fish and other aquatic organisms, resulting in higher doses when people or other animals eat them.
“In general, methylmercury concentrations in Great Lakes trout are lower than in top predatory fish in many inland lakes, but due to other organic contaminants, it is important to follow state consumption advisory guidelines,” said Lepak.