One of the first and most severe cases of mercury (Hg) poisoning through the consumption of fish occurred in the mid-1950s in fishing villages along the coast of Minamata Bay, Japan. A petrochemical company, located in the coastal city of Minamata, had been dumping tons of mercury into the bay for decades. The mercury, in the form of methylmercury, had bioaccumulated in the fish and shellfish that were a staple of the local diet. Known as Minamata Disease, hundreds of victims died as a direct result of fish and shellfish consumption, while thousands more suffered neurological damage, cognitive and sensory impairments, and birth defects.
By the late 1960s and early 1970s, mercury contamination had also become a serious issue in the Great Lakes region of North America. Activities such as chlorine production, metal smelting, mining, waste incineration, and wastewater discharge all contributed to toxic levels of mercury being released. As a result, commercial fishing bans were implemented by both Canada and the United States, industrial plant shutdowns occurred, and a growing environmental movement had begun.
The tipping point for this emerging movement was the Cuyahoga River Fire of 1969 in Cleveland, OH. It brought national attention to the issue of unchecked industrial pollution and became a symbol of overall water pollution in the United States. The establishment of the Environmental Protection Agency (EPA), the passage of the Clean Water Act, the Clean Air Act, and others soon followed.
Since the passage of the Clean Water Act in 1972, point source discharges of mercury into surface waters are regulated by the National Pollutant Discharge Elimination System (NPDES). Through this permit program and decades of clean-up efforts, mercury in the aquatic environment has been significantly reduced. However, mercury continues to be released through human activities. Today, most mercury that is deposited in surface waters can be traced to atmospheric deposition through the burning of fossil fuels (coal) that contribute to fish consumption advisories in the U.S. and Canada.
Here in South Dakota, a collaborative effort between the SD Departments of Agriculture & Natural Resources, Game, Fish & Parks, and Health sample and analyze fish from a variety of waterbodies each year to determine the concentration of various contaminants to protect public health. The Department of Health issues consumption advisories when mercury concentrations found in fish flesh are greater than the Food & Drug Administration (FDA) recommended criterion of 1.0 parts per million (ppm).
There is growing evidence that zebra mussels may be affecting the level of mercury in fish tissue by altering contaminant cycling in inland lakes. In a recent study from the University of Minnesota, researchers compared Hg concentrations of fish collected from lakes with and without zebra mussels. Results showed that mercury concentrations were significantly higher in walleye and yellow perch in lakes invaded by zebra mussels than those that were not. While the mechanism of this increase needs to be further studied, it likely means that fish consumption advisories will increase for those lakes invaded by zebra mussels.
Additional Information
- The Extent and Effects of Mercury Pollution in the Great Lakes Region—A Summary, Great Lakes Commission.
- Fish Consumption Advisories, South Dakota Agriculture & Natural Resources.
- Fish Consumption Advisories, South Dakota Department of Health.
- Study reveals elevated mercury levels in fish associated with zebra mussel invasions, UMN Water Resources Center.
- Increased mercury concentrations in walleye and yellow perch in lakes invaded by zebra mussels, Science of The Total Environment.
