Geogenic contamination

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Fig.2.1 Overview of contaminant types leading to water- and sanitation- related diseases (Terms of use: Cite original source from Handbook)

NOTE: Article from the Geogenic Contamination Handbook

Contamination in drinking water, both chemical and microbiological, can originate from a range of sources, most of which are anthropogenic, such as agriculture, industry or human settlements (Fig. 2.1). As the name suggests, geogenic contamination derives from geological sources. It stems from interactions between aquifer rocks and groundwater that lead to the release of substances from the aquifer rock or sediment into the water. Such interactions are always taking place – in fact, rocks and sediments largely control water chemistry – but if a particular substance is released in quantities that are high enough to have a detrimental effect on life forms, then it is termed a geogenic contaminant.

Only a very small number of the 98 naturally occurring elements have the potential to be geogenic contaminants. There are three critical factors:

  • their concentration in rocks and sediments,
  • their solubility under at least some environmental conditions and
  • their presence in soluble form in concentrations that are toxic to humans.

The most common soluble ions in groundwater are sodium (Na+), magnesium (Mg2+), calcium (Ca2+), chloride (Cl-), bicarbonate (HCO3-) and sulphate (SO42-). While these can make water unpalatable, they do not pose a direct threat to health. Contamination with dissolved iron (Fe) and manganese (Mn) can occur in groundwaters with little or no oxygen. High levels of these elements are also more of an aesthetic than a health concern, though there is increasing evidence that exposure to manganese in drinking water can cause neurological problems (e.g. Wassermann et al., 2006). Of all inorganic groundwater contaminants, arsenic (As) and fluoride (F) clearly represent the greatest threat to human health. Many millions of people are affected worldwide. Other elements, such as selenium (as selenate), uranium (carbonated anions), boron and chromium (as chromate), can be important locally but are not as widespread as arsenic and fluoride.

References and Handbook chapter

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