Sources and Impacts of Selenium Contamination
7
fly ash (Clean Air Task Force [CATF 2000]). At this time, there is no
treatment technology that eliminates serious environmental risks associated with disposal of this coal industry waste.
Gold, Silver, Nickel, and Phosphate Mining
Mining for precious and semiprecious metals has a long history of environmental problems, primarily associated with surface disposal of
waste rock and the water used to process ore (Lemly 1994a). Increasing values for gold, silver, and nickel have pushed exploration for new
deposits to the northern limits of the Canadian Arctic in North America.
In addition, new technologies have emerged that make profitable the
extraction of these metals, particularly gold, using ore grades that were
of little or no interest just a few decades ago. One example, the heapleach process, which percolates cyanide-laden water through ore piles
and dissolves/leaches out the gold, is a widely used practice in the
western United States at locations that were previously "mined out"
using traditional deep-shaft and open pit methods. However, there are
serious environmental risks and episodes of aquatic pollution associated with this practice. Many of the mines in North America have left
a legacy of environmental damage to lakes and fish populations due to
contaminants that leach from tailings and other surface residuals
(Lemly 1994a). Selenium is an important elemental component of the
mineral matrix of ore deposits. Although present in deceptively low
concentrations relative to other constituents (low parts-per-million for
selenium versus high parts-per-hundred or parts-per-thousand for the
metals being mined), selenium has the potential to rapidly affect aquatic
life because of its propensity to bioaccumulate and increase in concentrations as it moves up the food chain. Any mining operation that
mobilizes selenium from the ore and brings it into contact with water
activates this risk. Selenium has contaminated surface waters and impacted fish and wildlife near mine sites at locations ranging from the
Klondike in Yukon, Canada, to the Tobe near Capetown, South Africa
(see Table 1.2, Fig. 1.1). The best way to minimize the potential for
selenium issues in the mining industry is to minimize surface disposal
of tailings and wastewater. Practices such as backfilling of solids, recycling of process water, and in situ leaching can dramatically reduce
risks and improve the environmental performance of mines (Lemly
1994a).
Open-pit phosphate mining is an emerging selenium issue that poses
serious risks to aquatic life in the western United States (see Chapter
9). As with gold, silver, and nickel ore, selenium is associated with the
mineral matrix of phosphate deposits, some of which resemble lowgrade coal with respect to their carbon content. Selenium is present at
7
fly ash (Clean Air Task Force [CATF 2000]). At this time, there is no
treatment technology that eliminates serious environmental risks associated with disposal of this coal industry waste.
Gold, Silver, Nickel, and Phosphate Mining
Mining for precious and semiprecious metals has a long history of environmental problems, primarily associated with surface disposal of
waste rock and the water used to process ore (Lemly 1994a). Increasing values for gold, silver, and nickel have pushed exploration for new
deposits to the northern limits of the Canadian Arctic in North America.
In addition, new technologies have emerged that make profitable the
extraction of these metals, particularly gold, using ore grades that were
of little or no interest just a few decades ago. One example, the heapleach process, which percolates cyanide-laden water through ore piles
and dissolves/leaches out the gold, is a widely used practice in the
western United States at locations that were previously "mined out"
using traditional deep-shaft and open pit methods. However, there are
serious environmental risks and episodes of aquatic pollution associated with this practice. Many of the mines in North America have left
a legacy of environmental damage to lakes and fish populations due to
contaminants that leach from tailings and other surface residuals
(Lemly 1994a). Selenium is an important elemental component of the
mineral matrix of ore deposits. Although present in deceptively low
concentrations relative to other constituents (low parts-per-million for
selenium versus high parts-per-hundred or parts-per-thousand for the
metals being mined), selenium has the potential to rapidly affect aquatic
life because of its propensity to bioaccumulate and increase in concentrations as it moves up the food chain. Any mining operation that
mobilizes selenium from the ore and brings it into contact with water
activates this risk. Selenium has contaminated surface waters and impacted fish and wildlife near mine sites at locations ranging from the
Klondike in Yukon, Canada, to the Tobe near Capetown, South Africa
(see Table 1.2, Fig. 1.1). The best way to minimize the potential for
selenium issues in the mining industry is to minimize surface disposal
of tailings and wastewater. Practices such as backfilling of solids, recycling of process water, and in situ leaching can dramatically reduce
risks and improve the environmental performance of mines (Lemly
1994a).
Open-pit phosphate mining is an emerging selenium issue that poses
serious risks to aquatic life in the western United States (see Chapter
9). As with gold, silver, and nickel ore, selenium is associated with the
mineral matrix of phosphate deposits, some of which resemble lowgrade coal with respect to their carbon content. Selenium is present at