Rise in mercury in Great Lakes fish has scientists baffled
Trends are reversing in some locations
It’s not supposed to be like this.
Though advisories about toxic mercury in fish have continued in Michigan and the surrounding Great Lakes, with recommendations to limit consumption of certain species to a few times a month, the amount of mercury found in fish tissues has dropped steadily over decades since the 1970s. That corresponded with the reduction of pollution coming from Midwestern smokestacks as regulations tightened, pollution- prevention technology improved, and coal- fired factories and power plants went offline.
But over the past several years, that started changing. Scientists are finding mercury levels rising in large Great Lakes fish such as walleye and lake trout. Curiously, it’s occurring with fish in some locations but not others. Researchers are trying to figure out why.
The mercury levels are not surpassing Environmental Protection Agency thresholds. Yet researchers want to determine if what they are seeing is a temporary trend or a trajectory that’s only going to worsen. Mercury is toxic to humans and animals, and it remains in the environment for a long time.
The answer has large ramifications for Michigan’s vital sports fishing industry. Anglers spent $ 2.4 billion in trip- related expenses and equipment in 2011, according to the Michigan Department of Natural Resources.
At least for now, the mercury spikes are in isolated locations.
Scientists have only hypotheses. The trend of warming Great Lakes could be a factor, says Shane De Solla, an ecotoxicologist with Environment Canada and co- author of the recent study.
“The lakes are slightly warmer, and that increases the production of methylmercury,” a type of mercury that tends to be absorbed into fish tissues, De Solla says.
The region’s more frequent and intense storms in recent years also could be a factor, says Agnes Richards, a research scientist with Environment Canada. “That results in a lot of flooding and the re- suspension of sediments. What was buried before can become exposed, and that can increase the conversion of mercury to methylmercury.”