4
1. Selenium Pollution Around the World
Sources and Impacts of
Selenium Contamination
Coal Mining and Combustion
One of the primary human activities responsible for mobilizing selenium in the environment is the procurement, processing, and combustion of coal for electric power production (Lemly 1985). Although
burning fossil fuels offers a cheaper and perhaps, seemingly, safer alternative to nuclear power production, especially in the aftermath of
the Three Mile Island and Chernobyl reactor incidents, it does not necessarily constitute an environmentally clean alternative-there are numerous contaminant problems associated with both raw coal arid its
waste byproducts. Literally all categories of solid waste and liquid effluents from the power industry are highly enriched with selenium as
compared to the Earth's crust and surface waters (Table 1.1). Enrichment factors for selenium in coal (ratios of selenium in coal to selenium in surrounding soils and mineral layers) can exceed 65, and are
among the highest of all trace elements (Ensminger 1981). When coal
is burned to produce electricity, the ash that remains is further enriched with selenium, perhaps by as much as 1250 times (Table 1.1,
coal versus precipitator ash). Thus, the potential for enrichment of
selenium in wastes arising from the power industry is compounded
because the raw materials have already undergone natural mineral
concentrating processes during their formation.
Selenium in freshly mined coal can be leached out of storage piles as
rainwater percolates through. It can also be leached out when the coal is
washed prior to being transported to power plants. Solid wastes from coal
combustion (fly ash, bottom ash, scrubber ash, etc.) present an even greater
risk of generating contaminated leachate because of their oxidation state
and alkaline pH, which promote dissolution of selenium anions (selenate,
selenite) on contact with water. Moreover, selenium can accumulate to
high concentrations in process and disposal waters in a very short period
of time. For example, using feed water with less than 10 f..lg SelL, a power
plant's flue gas desulfurization (FGD) once-through cleaning stream may
acquire as much as 2700 f..lg SelL during its passage through the system,
and a coal ash slurry stream may pick up over 1000 f..lg SelL within 15
minutes (Santhanam et al. 1979; Cumbie 1980). The power industry produces numerous waste materials that contain high concentrations of selenium. This selenium is readily mobilized during all phases of waste
collection, treatment, and disposal that involve aqueous processes or that
subsequently bring dry ash materials into contact with water. These two
factors, along with the potential for bioaccumulation and toxic effects in
aquatic life at very low waterborne concentrations (2-5 f..lg SelL, see Chap-
1. Selenium Pollution Around the World
Sources and Impacts of
Selenium Contamination
Coal Mining and Combustion
One of the primary human activities responsible for mobilizing selenium in the environment is the procurement, processing, and combustion of coal for electric power production (Lemly 1985). Although
burning fossil fuels offers a cheaper and perhaps, seemingly, safer alternative to nuclear power production, especially in the aftermath of
the Three Mile Island and Chernobyl reactor incidents, it does not necessarily constitute an environmentally clean alternative-there are numerous contaminant problems associated with both raw coal arid its
waste byproducts. Literally all categories of solid waste and liquid effluents from the power industry are highly enriched with selenium as
compared to the Earth's crust and surface waters (Table 1.1). Enrichment factors for selenium in coal (ratios of selenium in coal to selenium in surrounding soils and mineral layers) can exceed 65, and are
among the highest of all trace elements (Ensminger 1981). When coal
is burned to produce electricity, the ash that remains is further enriched with selenium, perhaps by as much as 1250 times (Table 1.1,
coal versus precipitator ash). Thus, the potential for enrichment of
selenium in wastes arising from the power industry is compounded
because the raw materials have already undergone natural mineral
concentrating processes during their formation.
Selenium in freshly mined coal can be leached out of storage piles as
rainwater percolates through. It can also be leached out when the coal is
washed prior to being transported to power plants. Solid wastes from coal
combustion (fly ash, bottom ash, scrubber ash, etc.) present an even greater
risk of generating contaminated leachate because of their oxidation state
and alkaline pH, which promote dissolution of selenium anions (selenate,
selenite) on contact with water. Moreover, selenium can accumulate to
high concentrations in process and disposal waters in a very short period
of time. For example, using feed water with less than 10 f..lg SelL, a power
plant's flue gas desulfurization (FGD) once-through cleaning stream may
acquire as much as 2700 f..lg SelL during its passage through the system,
and a coal ash slurry stream may pick up over 1000 f..lg SelL within 15
minutes (Santhanam et al. 1979; Cumbie 1980). The power industry produces numerous waste materials that contain high concentrations of selenium. This selenium is readily mobilized during all phases of waste
collection, treatment, and disposal that involve aqueous processes or that
subsequently bring dry ash materials into contact with water. These two
factors, along with the potential for bioaccumulation and toxic effects in
aquatic life at very low waterborne concentrations (2-5 f..lg SelL, see Chap-