MPCA Finds Unexpected Rise in Sport Fish Mercury Levels
(From Minnesota Pollution Control Agency)
St. Paul, Minn. – An analysis of a 25-year record of mercury in northern pike and walleye from Minnesota lakes has found an unexpected rise in mercury concentrations in these predator fish. The Minnesota Pollution Control Agency (MPCA) study was reported in the peer-reviewed journal, “Environmental Science & Technology,” on Feb. 9, 2009.
“In the decade before the mid-1990s, the methylmercury concentrations in northern pike and walleye from the great majority of Minnesota lakes were decreasing,” said MPCA scientist Bruce Monson, who conducted the analysis. “However, the analysis showed that the fish-mercury concentration in the majority of lakes has been increasing since the mid-1990s.”
The analysis was based on tissue contaminant measurements obtained from fish collected from 845 Minnesota lakes. The finding is of concern because methylmercury, the form of mercury that contaminates fish, is toxic to humans and wildlife. Some of the mercury that is deposited from the air is converted to methylmercury by bacteria that live in the sediments of wetlands and lakes. Methylmercury accumulates in the aquatic food chain, with predator fish, such as pike, having the highest concentrations.
Because the trend is statewide, a local source of mercury is likely not responsible for the increase. Monson said the most likely cause is either increased global mercury emissions by sources outside the United States or factors associated with climate change, or both. Global mercury emissions increased between 1990 and 1995, due in large part to the increased production of electricity by coal-fired power plants in Asia, particularly in China and India. One effect of climate change is greater fluctuations in water levels, which results in more mercury being converted to methylmercury and being available for accumulation in the aquatic food web.
“Increased mercury pollution of fish underscores the need for nations worldwide to reduce mercury emissions to the greatest extent possible and address the problems brought on by climate change,” David Thornton, MPCA Assistant Commissioner, said. “Toward that end, Minnesota remains committed to working on mercury pollution with other states and the federal government as well as internationally.”
The MPCA shared the findings last year with a group of people representing diverse interests, who helped formulate a plan to reduce mercury emissions in Minnesota to improve the quality of the state’s surface waters.
“The change in trend in fish-mercury concentrations will not affect Minnesota’s obligation or resolve to achieve our goals for reducing mercury emissions, which were approved by the U.S. Environmental Protection Agency,” Thornton said.
The increase in fish mercury levels is not limited to Minnesota. Other scientists found a similar upward trend in mercury concentrations in coho and chinook salmon from Lake Ontario from 1999 through 2003.
“We are working with scientists from the other Great Lakes states and provinces,” Monson said, “combining our fish mercury data to create a Great Lakes mercury database that will allow us to look at trends throughout the region both geographically as well as over time. The project is being coordinated by the Biodiversity Research Institute in Gorham, Maine, which completed a similar project for the Northeast.”