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| Fig. 1: Effects of Acid Mine Drainage. (Source: Wikimedia Commone) |
Modern mining is an industry that involves the exploration for and removal of minerals from the earth. Mining is vital: minerals are major sources of energy, as well as materials such as fertilizers and steel. It is necessary in order for nations to have adequate and dependable supplies of minerals and materials to meet their economic and defense needs at acceptable environmental, energy, and economic costs. Due to the fact that minerals are a renewable source, the life of mines is finite and represents a temporary use of the land.
The environmental responsibility of mining operations is protection of the air, land, and water. Even though there have been recent improvements to mining practices, environmental risks still remain. Mining can negatively affect the environment around it, but most notably, water. Water-pollution problems caused by mining include acid mine drainage, metal contamination, and increased sediment levels in streams.
AMD is a potentially severe pollution hazard that can contaminate surrounding soil, groundwater, and surface water. The formation of AMD is a function of the geology, hydrology, and mining technology employed at a mine site. [1] The primary sources for acid generation are sulfide minerals, such as pyrite, which decompose in air and water. [1] Many of these sulfide minerals originate from water rock removed from the mine or from tailings. If water infiltrates pyrite-laden rock in the presence of air, it can become acidified, often at a pH level of two or three. [1] This increased acidity in the water can destroy living organisms, and corrode piers, pumps, and other metal equipment in contact with the acid waters and render the water unacceptable for drinking or recreational use.
Dissolved heavy metals, commonly found in waters polluted by mine drainage, are toxic to the aquatic environment. In general, fish mortality depends on exposure to high metal concentrations, but continuous low exposure produces chronic effects, such as behavioral changes, reproductive failure, or fry mortality. [2] Both ultimately affect species survival. Toxic metals commonly released by mining are arsenic, cobalt, copper, iron, lead, mercury, nickel, and zinc. [2]
Sediment accrues in streams naturally, and at moderate levels can be a beneficial component of fish habitats. Major disruption of the system occurs when amounts of sediment become excessive. Deposition of excessive fine sediment on the stream bottom eliminates habitat for aquatic insects, and, consequently, reduces the density and diversity of these aquatic insects. [3] Toxic heavy metals can precipitate on sediment particles and remain in the aquatic environment to be released later. [3]
The effect of mining pollution on aquatic environments has been significant. Not only do water pollution problems from mines upset fisheries, it disturbs domestic water supply, swimming, irrigation, and other uses of streams. Although future protection of the aquatic habitat in mine areas looks promising, more funds are necessary to guarantee adequate safeguards. More research in developing reclamation measures is also needed. The aquatic environment should be treated as the important resource that it is.
© Lo'eau LaBonta. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] Hardrock Mining on Federal Lands (National Academies Press, 1999).
[2] L Järup, "Hazards of Heavy Metal Contamination," Brit. Med. Bull. 68, 167 (2003).
[3] M. Sengupta, Environmental Impacts of Mining: Monitoring, Restoration, and Control (CRC Press, 1993).
