Page 802 - The Toxicology of Fishes

782 The Toxicology of Fishes

Contamination
1 Primary
2 2 Secondary
3 Tertiary
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2 2
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2 2 3
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FIGURE 19.2 Primary, secondary, and tertiary contamination associated with mining and smelting activities like those in
the watershed of the Clark Fork River. (Adapted from Moore, J.N. and Luoma, S.N., Environ. Sci. Technol., 24, 1279–1285,
1990.)

Geochemically, the upper and lower river waters are near neutral (pH 6.4 to 8.8), and hardness varies
from 75 to 350 mg/L. Geochemical characteristics, sediment loads, and stream discharge vary seasonally
and between years, as in most rivers of the semi-arid western United States. Mean daily stream discharge
on Silverbow Creek near Butte is 4 to 10 m /sec. The channel width at low flow is about 3 to 5 m. When
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the Clark Fork enters Lake Pend de Oreille, 550 km from its origin, mean daily flow in an average year
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is 634 m /sec, and it is the largest river leaving the State of Montana. Although the discharge of Silverbow
Creek is only 0.4% of the total discharge of the Clark Fork, enough metal contamination was transported
out of its watershed to contaminate the sediments throughout this massive river system.

Distribution of Contamination (Indicators of Exposure)
Dispersal of Contamination from Mining and Smelting

Mining and smelting create primary, secondary, and tertiary contamination (Figure 19.2). Primary con-
tamination is usually spread in a patchwork of tailings and waste rock deposits over the countryside nearest
the centers of mining and smelting activity. A pit lake at Butte was created when open-pit mining operations
were discontinued and dewatering of the mine was halted (Castro and Moore, 2000). Extensive tailings
deposits are confined above the headwaters and in ponds around Anaconda, with associated groundwater
contamination. Soil contamination is sufficiently widespread that dissolved and particulate loads of copper
increase 100-fold in storm drains during runoff events (Gammon et al., 2005). Smelting at Anaconda also
created air pollution, flue dust, and slag. Transport of the waste and contamination away from the mining
and smelting sites in streams or through the atmosphere generates secondary contamination in soils,
groundwater, and the rivers (Figure 19.2). If they leave the site, contaminated sediments, soils, and their
associated metals can be remobilized over and over, continuing their dispersal (tertiary contamination).
These processes extend the scale of contamination far beyond the visual disturbances of the landscape.

Effect of the Ore Body
Mineralized zones inherently have high metals concentrations in water and soil (soil anomalies). One
of the most contentious questions asked about mining impacts is how much of the contamination was
there naturally before the mineral deposit was disturbed and how much is a result of mining activity.