Mercury is emitted from a wide variety of natural and man-made (anthropogenic) sources. Anthropogenic releases of mercury result from combustion or industrial processes that involve mercury (mining, dental amalgam, chlorine manufacture, etc.). Fuel and waste combustion vastly dominate other routes of emission. Coal is by far the worst fuel from a mercury emission standpoint.

Mercury that is emitted when coal is burned falls into the categories of elemental and oxidized forms. The oxidized forms come to earth in precipitation in some spatial proximity to the smokestack but elemental mercury stays in the atmosphere for a long time and is distributed broadly. Mercury that is deposited to oceans, lakes and rivers, either directly of from terrestrial water runoff, is methylated by bacteria in sediment and enters the food chain as the methylmercury form. Although there are some exceptions, the mercury found in fish comes mostly from atmospheric mercury deposited to water bodies. About half the mercury in fish comes from human-related emissions and half from natural emissions.

There are obvious incentives to reduce the amount of mercury that bioconcentrates in fish and thus to reduce anthropogenic mercury emissions but the cost to to reduce mercury emissions from coal and waste combustion, both in the U.S. and globally, will be significant. The formulation of policies aimed at reducing mercury emissions will be (and has been) affected by both technical and political arguments. MTS has assembled links to some information on this subject to assist those with interest. Most of this information comes from U.S. Government websites due to the fact that regulations on mercury emissions from coal have been promulgated in the U.S. and most of the research to date has derived from the U.S. regulatory process.

The United States Environmental Protection Agency (EPA) has completed a study of mercury in coal and stack emissions for the nation's largest coal-fired electric utility boilers. Information generated by this study on the amount of mercury in coal by coal type is compiled on this website.