RESEARCH UNIT

Mercury is a toxic metal with no known essential function in living organisms, and it has been declared a primary pollutant of global concern. Of the 189 compounds identified as hazardous air pollutants in the 1990 Clean Air Act Amendment, only mercury was singled out for separate study to examine anthropogenic emissions and to define thresholds at which it affects human health and wildlife. Annual anthropogenic emissions of mercury in the United States were estimated at 159 metric tons in 1994-1995, with one-third of the mercury deposited through wet and dry deposition within the lower 48 states and the remainder transported out of the United States. Although government legislation reduced the acute toxicological effects of mercury contamination from point sources, regulatory control of emissions is lacking. Roughly 87 % of the emissions are from combustion sources such as fossil fuel and waste incineration, which contributes significantly to local and regional concentrations of mercury-adsorbed particulates in air and has been observed in association with other effects of rapid urbanization such as wild fires, brick manufacturing, and refuse burning. Thus, point sources for mercury emissions in the U.S.-Mexican border region, particularly in light o