Newest Research on Effects of Mercury Underscores Importance of Utility MACT

Catherine O'Neill

Oct. 28, 2011

As EPA’s long-awaited rule curbing mercury emissions from coal-fired power plants heads to OMB for its review, new scientific studies suggest that the harms of mercury contamination may be more severe and more widespread than previously understood. According to the report Great Lakes Mercury Connections: The Extent and Effects of Mercury Pollution in the Great Lakes Region, released October 11, “the scope and intensity of the problem is greater than had been previously recognized.”  Despite these harms, utilities have been relentless in their efforts to derail mercury regulation.   (The most recent attempts of this industry and its allies in 25 states to prop up the recalcitrant “old dirties” that still hope to avoid reducing their mercury emissions is discussed by my colleague Rena Steinzor.) These ongoing efforts to undermine protection of human and ecological health are unconscionable. The release of this recent collection of scientific data only underscores this point.    

The Great Lakes Mercury Connections report summarizes the findings of 35 new scientific papers that are the result of an ambitious multi-disciplinary effort to enlarge understanding about the impacts of mercury contamination in the Great Lakes region. According to the report, regulatory controls on the sources of mercury pollution, namely discharges to the water and emissions to the air, “have resulted in substantial progress, but have not yet addressed the full scope of the problem.” Importantly, the report concludes that mercury concentrations “still exceed human and ecological risk thresholds” throughout the Great Lakes region.

Mercury emitted to the air from coal-fired power plants gets deposited to surrounding land and waters; ultimately, it makes its way into the food web, including fish tissue, in the form of methylmercury. In terms of human health, methylmercury is well-recognized as a potent neurotoxin. Exposure to even small amounts of methylmercury in utero or during childhood can lead to irreversible neurological damage, placing the developing fetus and children at particular risk. Because fish consumption is the primary route of human exposure to methylmercury, those who depend on fish for food are at the greatest risk from mercury contamination. The report confirms that fish – ordinarily a healthful source of food – remain contaminated at levels of concern in the Great Lakes region:

“Average mercury concentrations in six commonly eaten fish species were above the U.S. EPA human health criterion (0.30 ppm) in 61 percent of the study grid cells. All study grid cells exceeded the Great Lakes Fish Advisory Workgroup recommended threshold for unrestricted consumption of fish by sensitive populations (0.05 ppm).”

In fact, mercury contamination does not burden everyone equally – among the most exposed are low-income fishers, Asian-Americans and Pacific Islanders, and members of the various fishing tribes.  In a recent national study of women of childbearing age, whereas 15.3% of self-identified “White” women of childbearing age had blood mercury levels above the level deemed safe by EPA, this figure more than doubles, to 31.5%, for women who identified themselves as “other” – a category composed primarily of Native Americans, Pacific Islanders, those of “Asian origin,” and those of “mixed race.”. Moreover, many American Indian tribes in the Great Lakes and elsewhere have rights to fish, including rights protected by treaties and other agreements with the United States. These rights secure the tribes’ continued ability to catch and consume fish – practices with cultural, spiritual, social, economic, and political dimensions.  

In terms of ecological health, mercury’s harms are felt throughout the food web.  The impacts on piscivorous species such as loons, kingfishers, eagles, and mink have been highlighted in the past, and the report amplifies earlier findings.  Among other things, the studies gathered in the report document a substantial increase in the number of species that harbor mercury at levels of concern. “For example, over the past two decades the number of bird species cited in the scientific literature as adversely affected by mercury has increased by a factor of six.” Moreover, “during recent decades, research on the toxicological impacts of mercury pollution has demonstrated that effects on fish and wildlife occur at lower mercury concentrations than previously reported.” 

Of particular note is a finding that several piscivorous fish species have mercury body burdens at levels that threaten their reproductive success and survival. While scientists had previously been aware of mercury’s negative impacts on other piscivorous species’ behavior and reproductive success, data had existed mainly for birds and mammals. However, as part of this series of studies in the Great Lakes, scientists documented mercury levels in walleye, smallmouth bass, and largemouth bass that potentially imperil the fish themselves. Based on more than 43,000 measurements of mercury in fish from over 2000 locations, scientists found levels of mercury that exceeded threshold-effect tissue concentrations at 8% (largemouth bass) to 43% (walleye) of sites. Moreover, at 3% to 18% of sites, respectively, these fish harbored mercury at levels “where an alteration in reproduction or survival is predicted to occur.” 

While these harms are registered throughout the food web, there are again unique impacts to the fishing tribes in the Great Lakes. As the tribes have explained in formal efforts to urge more ambitious mercury regulation, tribal health and well-being is tied to the health of tribal homelands. In comments to the EPA, for example, the Minnesota Chippewa Tribe noted mercury’s impacts on loons and mink, and stated “these animals are a value to the ecosystem they inhabit and they are clan symbols for tribal members. If these animals are threatened, tribal culture is threatened.” And walleye, smallmouth bass, and largemouth bass are vital to tribal fisheries. Threats to the reproductive success of these fish species have the potential to undermine tribal rights, including treaty-secured rights. 

In short, the harms of mercury contamination are serious and widespread, with repercussions for human and ecological health across a broad swath of species and environments. The harms visited on the fishing tribes of the Great Lakes and elsewhere are especially grave. Against this backdrop, that we are still waiting on meaningful federal regulation of mercury emissions from coal-fired power plants is our collective disgrace.

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