Over the last century the discharge of crude or partially treated sewage has probably been the most widespread, most documented and certainly the best understood form of pollution entering the aquatic environment. In the past two decades, however, there has been an increasing public aware ness of the potential hazards that exist from the contamination of the freshwater environment by toxic substances associated with the mining industry. World demand for minerals has intensified the exploitation of natural resources. In most western and newly developed countries significant mining proposals...