Mercury 101…Let’s Be Clear on the Facts

                                    

ABEC has been talking about mercury issues for years. To be sure, mercury and methylmercury are very complicated issues, but keep in mind that substantial reductions in power plant mercury emissions will reduce only a small fraction of the methylmercury to which we are exposed.

Mercury occurs naturally in the earth’s core. About half the world’s airborne mercury emissions come from natural sources like oceans, soil, and forest fires, and the other half is attributable to sources associated with human activities, like burning coal, alkali and metal processing, medical and other waste, and mining of gold.

Coal-based power plants in the U.S. contribute about 40 percent of U.S. airborne mercury emissions associated with human activities, about 10 percent of U.S. emissions when natural sources are counted, and about one percent of total global emissions. To become methylmercury in fish, airborne mercury has to be deposited back to the earth, enter water bodies, be converted to methylmercury by microorganisms in the sediments, and be taken up by fish.

Human exposure to methylmercury comes from fish and most of the fish we eat come from the ocean. The methylmercury in ocean fish comes mostly from natural sources in the deep oceans, meaning that there has been methylmercury in ocean fish since there were fish. Global sources of man-made mercury could also contribute but given that U.S. power plants account for only one percent of global mercury emissions, eliminating them would have no detectable effect on fish, our biggest source of methylmercury exposure.

Most of the mercury that is deposited in the U.S. and is available to become methylmercury in freshwater fish comes from global sources. That mercury is both natural in origin and is associated with human activities, especially with power plants in India and China, which lack basic pollution control requirements. Further reducing or even attempting to eliminating U.S. coal-based power plants will have no impact on those sources.