Metal contamination can make water toxic to both aquatic biota and humans. Toxicity depends on the type of metal, the chemical interactions of the metal with other metals and the presence of organic compounds which may increase the availability and spread of the toxic metal. The flow rate and volume of water, the physical make-up of sediments, water temperature, pH and salinity also impact how toxic a metal is in a given environment (Davies and Day 1998).
Effluent from metal mines must be contained in hydrologically isolated waterbodies.
Source: Vogel 2005
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Heavy metals include cadmium, copper, nickel, zinc, chromium, arsenic, mercury, lead, etc. These metals are persistent in the environment and can be bio-accumulated in aquatic organisms. The main potential sources of metal pollution in the Kunene River are industries and mines through direct discharges of effluent, and diffuse seepage and runoff from polluted areas and waste dumps. Due to a lack of information in water quality issues within the Kunene River basin, assumptions can be made only on the basis of recent developments in the industry and mining sector, not on chemical analysis.
Although the current potential of pollution by heavy metals is still low, it is likely that the rapidly expanding industry and mining sector will lead to an increase in water pollution in near future. Heavy metal contamination also originates from urban storm water runoff from roads, parking areas and other impervious surfaces, ending up directly in the river. Toxic metals are also associated with some pesticides (Heath and Claasen 1999).
