ARSENIC IN DRINKING WATER
Arsenic may be found in water which has flowed through arsenic-rich rocks. Severe health effects have been observed in populations drinking arsenic-rich water over long periods in countries world-wide.
- Arsenic is widely distributed throughout the earth's crust.
- Arsenic is introduced into the water through the dissolution of minerals and ores, and concentrations in groundwater in some areas are elevated as a result of erosion from local rocks.
- Industrial effluents also contribute arsenic to water in some areas.
- Arsenic is also used commercially e.g. in alloying agents and wood preservatives.
- Combustion of fossil fuels is a source of arsenic in the environment through dispersed atmospheric deposition.
- Inorganic arsenic can occur in the environment in several forms but in natural waters, and thus in drinking-water, it is mostly found as trivalent arsenite (As(III)) or pentavalent arsenate (As (V)). Organic arsenic species, abundant in seafood, are very much less harmful to health and are readily eliminated by the body.
- Drinking-water poses the greatest threat to public health from arsenic. Exposure at work and mining and industrial emissions may also be significant locally.
- Chronic arsenic poisoning, as occurs after long-term exposure through drinking- water is very different from acute poisoning. Immediate symptoms of acute poisoning typically include vomiting, oesophageal and abdominal pain, and bloody "rice water" diarrhea. Chelation therapy may be effective in acute poisoning but should not be used against long-term poisoning.
- The symptoms and signs that arsenic causes, appear to differ between individuals, population groups, and geographic areas. Thus, there is no universal definition of the disease caused by arsenic. This complicates the assessment of the burden on the health of arsenic. Similarly, there is no method to identify those cases of internal cancer that were caused by arsenic from cancers induced by other factors.
- Long-term exposure to arsenic via drinking-water causes cancer of the skin, lungs, urinary bladder, and kidney, as well as other skin changes such as pigmentation changes and thickening (hyperkeratosis).
- Increased risks of lung and bladder cancer and of arsenic-associated skin lesions have been observed at drinking-water arsenic concentrations of less than 0.05 mg/L.
- Absorption of arsenic through the skin is minimal and thus hand-washing, bathing, laundry, etc. with water containing arsenic do not pose a human health risk.
- Following long-term exposure, the first changes are usually observed in the skin: pigmentation changes, and then hyperkeratosis. Cancer is a late phenomenon and usually takes more than 10 years to develop.
- The relationship between arsenic exposure and other health effects is not clear-cut. For example, some studies have reported hypertensive and cardiovascular disease, diabetes and reproductive effects.
- Exposure to arsenic via drinking-water has been shown to cause a severe disease of blood vessels leading to gangrene in China (Province of Taiwan), known as black foot disease? This disease has not been observed in other parts of the world, and it is possible that malnutrition contributes to its development. However, studies in several countries have demonstrated that arsenic causes other, less severe forms of peripheral vascular disease.
- According to some estimates, arsenic in drinking-water will cause 200,000 ?270,000 deaths from cancer in Bangladesh alone (NRC, 1998; Smith, et al, 2000).
Guidelines for drinking-water quality, 2nd ed.
Geneva, World Health Organization, 1996.