The waters of a river contaminated by a mine


© Ashley Cooper / Nature Picture Library


One of the most serious problems associated with mining is water pollution caused by acid drainage. This is the result of chemical reactions involving the sulphide content of minerals commonly found in mines and typically associated with metals and carbon. The phenomenon occurs naturally on rock surfaces, but excavations and the waste dumps offer a far larger reactive surface area. The reaction is triggered by contact with water and oxygen and is exponentially accelerated by certain micro-organisms. As a result, water can become highly acidic and rich in heavy metals. Acidity has a harmful effect on aquatic life and fish may not survive high levels. That is just the start. As the acid becomes diluted, the metals contained in it form solid particles that stain the water with bright colours like orange and eventually deposit on the bottom. Small bottom-feeding organisms can no longer find nourishment in such an environment and die off, along with the creatures that feed on them. The surrounding soil also becomes contaminated, with serious repercussions for plant life.
Heavy metals persist in ecosystems and accumulate in organisms through water and the food chain. Damage to the ecosystem therefore means damage to human health. In man, heavy metals can build up in glands and organs like the heart, brain, kidneys, bones and liver, and can interfere with the process of absorbing mineral nutrients, compromising biological functions. Damage to human health is often accompanied by a reduction, sometimes critical, in drinkable water reserves and the corrosion of infrastructures. The duration of effects is another worrying aspect of mine drainage: acidity can continue to form at source for hundreds if not thousands of years.

Elena Sofia Grazian