Arsenic is introduced into soil and groundwater during weathering of rocks and minerals followed by subsequent leaching and runoff. It can also be introduced into soil and groundwater from anthropogenic sources. Arsenic is emitted into the atmosphere by high-temperature processes such as coal-fired power plants, burning vegetation and volcanism. In water, particularly groundwater, where there are sulfide mineral deposits and sedimentary deposits deriving from volcanic rocks, the concentrations can be significantly elevated. Natural low-temperature biomethylation and reduction to arsines also releases arsenic into the atmosphere.
Long-term intake of arsenic contaminated water leads to arsenic poisoning or arsenicosis, with cancer of skin, bladder, kidney or lung or diseases of skin (colour changes, and hard patches on palms and soles), or blood vessels of legs and feet. Fresh evidence indicates possible association between intake of contaminated water to onset of diabetes, hypertension and reproductive disorders. WHO has had a stated position on the health risks of arsenic in drinking-water since 1958. Successive editions of International standards for drinking-water (1958, 1963, and 1971) and Guidelines for drinking-water quality (1984, 1993 and 2004) have published reviews of the data which have led to a progressive lowering of the standard or guideline value in response to emerging evidence of significant health concerns
In India, the states of West Bengal, Jharkhand, Bihar, Uttar Pradesh, Assam, Manipur and Chhattisgarh are reported to be most affected by arsenic contamination of groundwater above the permissible level.
Reducing arsenic exposure
Arsenic concentrations of 5 µg/l or lower using can be achieved by using any of several possible treatment methods. However, the focus should be to reduce contamination through anthropogenic source. The most common arsenic-mitigation strategies include use of uncontaminated or less contaminated wells, replacement of arsenic-contaminated sources by less-contaminated ones, and removal of arsenic from contaminated water before consumption. In places where is mitigating contamination is not possible careful process optimization and control, and a more reasonable expectation of 10 µg/l should be achieved by conventional treatment (e.g. coagulation)
Adopting rainwater harvesting/ watershed management practices will not only reduce water stress but also ensure arsenic free supply of water (naturally or through filtration).
Arsenic and human health
Arsenic have shown to cause widespread health effects in humans as a consequence of exposure through drinking-water when present in excessive quantities. Long-term exposure to arsenic in drinking-water is causally related to increased risks of cancer in the skin, lungs, bladder and kidney, as well as other skin changes such as hyperkeratosis and pigmentation changes. Soluble inorganic arsenic is acutely toxic, and ingestion of large doses leads to gastrointestinal symptoms, disturbances of cardiovascular and nervous system functions, and eventually death. In survivors, bone marrow depression, haemolysis, hepatomegaly, melanosis, polyneuropathy and encephalopathy may be observed. In few studies, increased risks of lung and bladder cancer and of arsenic-associated skin lesions have been reported to be associated with ingestion of drinking-water at concentrations below 50 µg of arsenic per litre.
