Mercury is a known persistent, bioaccumulative and toxic (PBT) trace metal that occurs naturally in coal at very low concentrations. The combustion of coal is considered the major anthropogenic source of this pollutant to the atmosphere.
According to data from the UNEP [49], combustion of coal in power plants, industrial boilers, residential boilers, heaters and stoves contributed with around 888 tonnes (46%) to the total global anthropogenic emissions in 2005.
Coal-fired power plants are one of the most important sources of mercury due to the large quantity of coal used for electricity generation. For example, about one-half of the anthropogenic mercury emissions in 2005 in the United States came from these plants, approximately 52.4 t/year [52].
Most of the mercury in the atmosphere is in the form of elemental mercury vapor; however, in water, soil, sediments, or biota it is found in both organic and inorganic forms.
Elemental mercury vapor is relatively insoluble and nonreactive, which is why it can remain aloft, carried by air currents over vast distances for very long periods—up to a couple of years—before it is finally deposited on land or in surface waters.
Once mercury is deposited, microbes can convert it into an organic form (methylmercury) that can be absorbed by other organisms and accumulated as it passes through food webs. Mercury has a variety of important ecological and human health impacts.
For example, mercury pollution is the most common cause of impairment of rivers and lakes in the United States, and many US states have issued warnings about eating fish from those water bodies.
Ingestion of mercury from eating contaminated fish can lead to impaired neurological development in fetuses, infants and children. In adults it can cause neurological damage [53]. The United States National Institutes of Health (NIH) estimates that one woman in 12 in the United States has more mercury in her blood than the amount considered safe by the Environmental Protection Agency.
According to NIH estimates, health impairment due to mercury cause nearly US$9 billion annually in higher medical costs and lost productivity in the workforce [47, 52].
