Mining, heavy metal contamination source

Water supplies are closely monitored for heavy metals, because they tend to be very toxic. Major sources of heavy metal contamination include landfills, industries, agriculture, mining, and old water distribution systems. 

In the field, soil can sometimes be a significant source of contamination. For example, in areas of mineralisation, heavy metals may occur naturally at elevated levels in soils. If there has been mining activity in the past this can exacerbate the problem by the spreading of mine spoil at the surface. Animals, particularly cattle, which tend to tug at forage rather than biting it, can ingest significant amounts of soil and metals can accumulate in tissues such as the liver. Plants may also take up elements from the soil that can accumulate in... 

Extractive industries include mining of mineral deposits (principally metal-bearing ores and coal deposits), oil and natural gas production, and quarrying for building and roadmaking materials. Poorly operated or abandoned mine sites are often significant sources of water contamination contaminants of particular health concern from these sources include heavy metals, and mineral-processing chemicals, such as cyanide. 

Other heavy metals are also toxic, but fortunately are less widespread and are present in smaller amounts. Mine tailings (waste rock remaining after the valuable minerals have been removed) and waste material from processing plants are major sources of such metals. Many major rivers and lakes have sources of metal contamination from industries whose processes were developed and facilities were built before control of waste was recognized as a major problem. 

The Pinal Creek basin in central Arizona, about 100 km east of Phoenix, is one of the most polluted acid mine drainage sites in the USA (Figure 9.2). Mining activities over a century, mostly in copper from porphyry deposits, have resulted in a plume of acidic groundwater in the alluvium and basin fill aquifer. The plume is laden with heavy metals. Many potential contamination sources, including mine tailings, heap leach, surface impoundments, and surface run-off and groundwater flow in the mineralized... 

Traces of heavy metals in waters are of industrial origin (waste waters from mining and treatment of ores, from metallurgical plants and rolling mills, metal finishing, photographic shops, from textile, leather, and chemical industry, and even from agriculture (e.g. cadmium from African phosphate fertilizers ). An additional source are atmospheric condensations contaminated by exhalations from combustion of fossile fuels and from motor vehicles. 

These considerations of the general behaviour of metals in aquatic and soil systems should be used to assess and control accumulation and mobilisation processes of trace metal ions. To evaluate the environmental impact of mining activities with regard to chemical contaminants, the following main steps of geochemical activities are recommended (1) estimate the extent of the local and regional contamination, (2) quantify the sources of heavy metals, chlorides, sulphates and thus the total acidity and salinity, as well as other contaminants and (3) define and control major sources, i.e. waste rock heaps, tailings, waste dumps and air pollution, etc. 

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