I suggest reading the whole article at the following link.https://www.scientificamerican.com/article/tunas-declining-mercury-contamination-linked-to-u-s-shift-away-from-coal/
By Richard Conniff on November 23, 2016
Levels of highly toxic mercury contamination in Atlantic bluefin tuna are rapidly declining, according to a new study. That trend does not affect recommended limits on consumption of canned tuna, which comes mainly from other tuna species. Nor does it reflect trends in other ocean basins. But it does represent a major break in the long-standing, scary connection between tuna and mercury, a source of public concern since 1970, when a chemistry professor in New York City found excess levels of mercury in a can of tuna and spurred a nationwide recall. Tuna consumption continues to be the source of about 40 percent of the mercury contamination in the American diet. And mercury exposure from all sources remains an important issue, because it causes cognitive impairment in an estimated 300,000 to 600,000 babies born in this country each year.
The new study, published online on November 10 by Environmental Science & Technology, links the decline directly to reduced mercury emissions in North America. Most of that reduction has occurred because of the marketplace shift by power plants and industry away from coal, the major source of mercury emissions. Pollution control requirements imposed by the federal government have also cut mercury emissions.
Progress on both counts could, however, reverse, with President-elect Donald Trump promising a comeback for the U.S. coal industry, in part by clearing away such regulations.
The new study comes as worldwide mercury emissions continue to rise, particularly in the Pacific, source of much of the tuna and other seafood consumed in the U.S. That increase of about 3.8 percent per year results largely from increased reliance on coal-fired power plants in China, India and other Asian countries.
Despite President-elect Trump’s campaign pledge to revive the coal industry in this country, economic factors, including competition from inexpensive natural gas, make a U.S. coal comeback unlikely. Even U.S. Senate Majority Leader Mitch McConnell, who for eight years blamed the Obama administration for the demise of coal, began to walk back the idea that Republican control in Washington, D.C., would make much difference: “Whether that immediately brings business back is hard to tell,” he told a Kentucky audience on November 11, “because it’s a private sector activity.”