Reducing mercury pollution to lakes can lower methylmercury contamination in fish within just a few years according to research reported today in the online version of the journal Nature. The findings suggest efforts to control mercury emissions can reduce the risk of human exposure through fish consumption.

Mercury released because of human activity can find its way into aquatic ecosystems, where it is converted into methylmercury, a potent neurotoxin that accumulates in fish and poses a health threat to humans. There is limited understanding of the effectiveness of controls on mercury emissions in removing methylmercury from the food chain.

Two people in boat.

Researchers in the Experimental Lakes Area of Canada adding mercury isotopes to study lake. Contributed photo.

A 15-year study on the effects of mercury control efforts on the recovery of fish contamination was conducted on a remote, undisturbed Canadian lake and its watershed. Wisconsin Sea Grant Director Jim Hurley was part of the research team that also included scientists from binational regulatory agencies and other academic institutions in the U.S. and Canada.

“This study shows the value of long-term multi-disciplinary, consistent research. We were able to observe the impacts of both an increase and decrease in contaminant loading over several years. Both showed rapid responses in the chemistry and biology of the lake and its watershed,” Hurley said.

Close-up of two men pouring liquid from one jug to another jug.

Jim Hurley (left) and Todd Kuiken, Canada Department of Fisheries and Oceans, homogenize the mercury isotope solution to ensure the carboys on each boat have the same concentration. Photo: Chris Babiarz

This whole-ecosystem experiment for seven years supplied specific isotopes of mercury to the ecosystem. During this period, the researchers recorded an increase in the uptake of this isotopically labelled mercury as methylmercury in the fish. Methylmercury concentrations increased by 45–57% in invertebrates (plankton, for example) and small fish (such as yellow perch), and by more than 40% in large fish, such as pike and whitefish.

Then, mercury additions ceased and the effects on the food chain were observed for eight years. Labelled methylmercury quickly diminished in the smaller fish, with concentrations dropping by at least 85% by the end of the study period. This triggered a subsequent reduction of labelled methylmercury in the larger fish, with concentrations declining by 76% in pike and 38% in whitefish.

The rapid reductions in methylmercury contamination observed in these experiments demonstrates the potential for mercury emission controls to improve the safety of fish for human consumption, the authors concluded. 

 

The post Study in Nature shows reduction of mercury pollution in waterways reaps relatively quick benefit first appeared on Wisconsin Sea Grant.

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Moira Harrington

Study: Fish can recover from mercury pollution faster than thought

Mercury pollution remains a problem in many parts of the Great Lakes, but new research from Canada’s Experimental Lakes Area in northern Ontario shows that efforts to reduce the amount of mercury going into a lake can have quick and dramatic effects on the levels of the pollutant in fish populations. 

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Brian Owens

Methylmercury uptake rate in phytoplankton is among the highest recorded   

Sept. 22, 2021
By Moira Harrington

A recently published study in the journal of the American Chemical Society, Environmental Science and Technology, found that while Great Lakes waters harbor low methylmercury concentrations, the rates of methylmercury transfer to phytoplankton are extremely high, higher than rates observed in open oceans. Phytoplankton are the smallest organisms in an aquatic food web.

Researchers, including a UW-Madison-supported postdoctoral scientist, say this is important because the bioaccumulation of methylmercury into phytoplankton sets the baseline for methylmercury levels in fish.

Methylmercury is highly toxic and is the form most encountered by people. This is generally through eating fish and shellfish, which is why advisory consumption guidelines are issued, particularly targeted toward pregnant women and young children. However, monitoring fish and shellfish varieties—some have higher levels of methylmercury—and consumption frequency, people can still enjoy the health benefits of omega-3 fatty acids found in the food.

From 2010 to 2018, the U.S. Geological Survey Mercury Research Lab in Madison, Wisconsin, teamed up with the U.S. EPA and its research vessel the Lake Guardian to monitor inorganic and methylmercury dynamics in the five Great Lakes. This was done through a combination of vertically, seasonally and spatially comprehensive water quality measurements and analysis of seston collections, which is the suspended particle mass in the lakes made up of plankton, bacteria, bugs and detritus.

Ryan Lepak, a postdoctoral scientist (Ph.D. UW-Madison, 2018) through the University of Wisconsin Water Resources Institute and its sister organization, Sea Grant and stationed at the U.S. EPA Mid-Continent Ecology Division in Duluth, Minnesota, said, “Ultimately, the study concluded the very low concentrations of dissolved organic carbon, the substrate which competes with phytoplankton for methylmercury but also can serve as a source of sustenance, in these lakes likely create a scenario where methylmercury transfer to phytoplankton is facilitated. The planktonic methylmercury levels are quite low, but exceedingly higher than we’d expect considering the extremely low methylmercury levels in the waters in which they reside.”

Ryan Lepak aboard the U.S. EPA RV Lake Guardian sampling for methylmercury. Contributed photo.

Lepak continued by explaining the transfer of methylmercury up the lower food web, from phytoplankton to herbivorous zooplankton and then to omnivorous zooplankton, was not statistically different. Finally, he and the team tested whether water-mercury concentrations have declined over the study period and determined that without more routine continuous monitoring, trends could not be identified because unresolved sources of variability masked data trends.

“The conditions that make the Great Lakes highly susceptible to methylmercury bioaccumulation are common to the world’s great lakes,” Lepak said. “These global water bodies should serve as excellent sentinels to track the impacts mercury reductions at local, regional and global scales have on biota. This paper’s important finding could aid those planning global mercury monitoring networks aimed at tracking mercury reductions due to actions resulting from the Minamata Convention on Mercury, a multilateral environmental agreement the U.S. signed in 2013 and which would reduce global mercury pollution.”

 

The post Methylmercury water concentrations low, but Great Lakes fish consumption advisories persist—new research documents one probable culprit first appeared on WRI.

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News Release | WRI

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https://www.wri.wisc.edu/news/methylmercury-water-concentrations-low-but-great-lakes-fish-consumption-advisories-persist-new-research-documents-one-probable-culprit/

Moira Harrington

Methylmercury uptake rate in phytoplankton is among the highest recorded  

 A recently published study in the journal of the American Chemical Society, Environmental Science and Technology, found that while Great Lakes waters harbor low methylmercury concentrations, the rates of methylmercury transfer to phytoplankton are extremely high, higher than rates observed in open oceans. Phytoplankton are the smallest organisms in an aquatic food web.

Researchers, including a UW-Madison-supported postdoctoral scientist, say this is important because the bioaccumulation of methylmercury into phytoplankton sets the baseline for methylmercury levels in fish. 

Methylmercury is highly toxic and is the form most encountered by people. This is generally through eating fish and shellfish, which is why advisory consumption guidelines are issued, particularly targeted toward pregnant women and young children. However, monitoring fish and shellfish varieties—some have higher levels of methylmercury—and consumption frequency, people can still enjoy the health benefits of omega-3 fatty acids found in the food.

From 2010 to 2018, the U.S. Geological Survey Mercury Research Lab in Madison, Wisconsin, teamed up with the U.S. EPA and its research vessel the Lake Guardian to monitor inorganic and methylmercury dynamics in the five Great Lakes. This was done through a combination of vertically, seasonally and spatially comprehensive water quality measurements and analysis of seston collections, which is the suspended particle mass in the lakes made up of plankton, bacteria, bugs and detritus.

Ryan Lepak, a postdoctoral scientist (Ph.D. UW-Madison, 2018) through Sea Grant and its sister organization the University of Wisconsin Water Resources Institure and stationed at the U.S. EPA Mid-Continent Ecology Division in Duluth, Minnesota, said, “Ultimately, the study concluded the very low concentrations of dissolved organic carbon, the substrate which competes with phytoplankton for methylmercury but also can serve as a source of sustenance, in these lakes likely create a scenario where methylmercury transfer to phytoplankton is facilitated. The planktonic methylmercury levels are quite low, but exceedingly higher than we’d expect considering the extremely low methylmercury levels in the waters in which they reside.”

Ryan Lepak aboard the U.S. EPA RV Lake Guardian sampling Great Lakes waters for methylmercury. Contributed photo.

 Lepak continued by explaining the transfer of methylmercury up the lower food web, from phytoplankton to herbivorous zooplankton and then to omnivorous zooplankton, was not statistically different. Finally, he and the team tested whether water-mercury concentrations have declined over the study period and determined that without more routine continuous monitoring, trends could not be identified because unresolved sources of variability masked data trends.

“The conditions that make the Great Lakes highly susceptible to methylmercury bioaccumulation are common to the world’s great lakes,” Lepak said. “These global water bodies should serve as excellent sentinels to track the impacts mercury reductions at local, regional and global scales have on biota. This paper’s important finding could aid those planning global mercury monitoring networks aimed at tracking mercury reductions due to actions resulting from the Minamata Convention on Mercury, a multilateral environmental agreement the U.S. signed in 2013 and which would reduce global mercury pollution.”

 

The post Methylmercury water concentrations low, but Great Lakes fish consumption advisories persist—new research documents one probable culprit first appeared on Wisconsin Sea Grant.

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Moira Harrington

Former University of Wisconsin Water Resources Institute researcher, and now a post-doctoral fellow at the U.S. EPA Mid-Continent Ecology Division in Duluth, Minnesota, Ryan Lepak has been awarded the 2021 Raymond L. Lindeman Award from the Association for the Sciences of Limnology and Oceanography (ASLO). It is the leading professional organization for researchers and educators in the field of aquatic science.

“I am thrilled that our team was selected for this prestigious award. It represents work that would not have been possible without strong monitoring efforts like those at the Great Lakes Fish Monitoring and Surveillance Program at the EPA,” Lepak said. “Across the board, at UW-Madison’s Environmental Chemistry and Technology Program, the U.S. Geological Survey Mercury Research Lab and the Great Lakes Toxicology and Ecology Division Laboratory at EPA, this work exemplifies the innovative and multidisciplinary approaches requisite to creating impactful science. I am honored to tell this story alongside these colleagues.”

Researcher Ryan Lepak sampling Lake Michigan sediments for peer-reviewed findings that led to winning the prestigious Lindeman Prize. Contributed photo.

Each year, ASLO recognizes a young scientist for leading an outstanding peer-reviewed, English-language paper in the aquatic sciences. Lepak’s paper, on which he was the lead author, is “Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan,” published in Proceedings of the National Academy of Sciences (PNAS) of the United States of America.

Lepak and a team of researchers used a novel combination of mercury, nitrogen and carbon isotope analysis, which he termed “fingerprinting,” on archived samples of lake trout from 1978 to 2012. From the same period, Lepak also examined archived samples of sediment taken from the lakebed to compare trends of mercury sources to sediments and fish.

The study years included a time when the Great Lakes were spared higher amounts of added mercury, in part because hospitals and municipalities stopped burning waste. That decline could have been expected to lessen mercury levels in fish. Yet, there had not been an obvious decrease in the mercury concentrations of sport fish.

The culprits behind this are invasive zebra and quagga mussels that exploded in Lake Michigan and now are estimated to number in the trillions. The mussels have caused significant shifts in lake trout feeding habits, forcing the fish to consume food that provides less energy while being more enriched in mercury.

In a statement released today by the organization, ASLO President Roxane Maranger said, “It is our pleasure to award Dr. Lepak the Lindeman early-career award for this outstanding paper. His work will certainly have far-reaching implications for assessing the combined influence of changes in contaminant source and concentrations as well as food web alterations in the study of mercury and other contaminants in aquatic ecosystems. We look forward with excitement to Dr. Lepak’s continued contributions to aquatic science!”

The Lindeman Award will be presented to Lepak at the 2021 ASLO Aquatic Sciences virtual meeting in June.

Collaborators to the study published in PNAS include the U.S. EPA Great Lakes National Program Office; U.S. EPA Office of Research and Development; University of Wisconsin-Madison; Minnesota Science Museum; St. Croix Watershed Research Station; and the Chinese Academy of Sciences, Institute of Geochemistry.

The study was funded by the Great Lakes Restoration Initiative; U.S. Geological Survey National Institutes for Water Resources, University of Wisconsin Water Resources Institute; and the Wisconsin Alumni Research Foundation through the University of Wisconsin Office of the Vice Chancellor for Research and Graduate Education.

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Moira Harrington