Minamata Plus 50: Where Are We?
Dr. Leonard Levin
Electric Power Research Institute

Some 50 years after the direct discharge of methylmercury into Minamata Bay, and the "cats of Minamata," our understanding of environmental mercury has increased substantially, but mercury management methods remain less developed. Inventories of atmospheric sources show that not only do Asian industrial sources contribute half of the global burden, but that they contribute substantially to mercury additions to U.S. waterways by atmospheric deposition. Background sources, both natural sources such as hot springs and legacy sources such as abandoned mill sites, are roughly equal to industrial sources as emitters, but may play a lesser role in local and regional deposition.

Coal-fired electric power plants make up about one-third of current U.S. industrial emissions. These plants already remove about 40% of the mercury in the coal fuel before it is released from the stack, due to coal cleaning and current emissions controls. Studies show that additional levels of current controls, such as sulfur scrubbers or precipitators, become substantially more expensive when dedicated to mercury removal, and that advanced systems such as activated carbon are essentially unproven. This leaves unresolved the basic management question: will there be a substantial drop in fish mercury if there is a substantial cut in utility mercury emissions? This source-receptor relationship is not only unresolved, but is faced with increasing questions as scientific issues continue to be addressed. The possibility that emissions plumes chemically reduce the soluble divalent form of mercury to the globally-cycling elemental form has now been demonstrated initially in both field trials and laboratory measurements, but remains to be clarified. Modeling studies by EPA and others have recently shown a small contribution of utility emissions to deposition patterns at U.S. locations. These and other issues remain to be clarified.

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