Arsenic in drinking water
Arsenic is 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 all over the world.
In Bangladesh, in West Bengal (India) and in some other areas, most drinking-water used to be collected from open dug wells and ponds with little or no arsenic. But the contaminated water transmitted diseases such as diarrhoea, dysentery, typhoid, cholera and hepatitis.
Over the past 30 years, programmes to provide "safe" drinking-water by digging tube wells have helped to control these diseases. Until the discovery of arsenic in groundwater in 1993, well water was generally regarded as safe for drinking. But it is now known that there can be unexpected side-effects caused by substances such as arsenic or fluorides contained in the groundwater. This then exposes the population to serious health problems.
There are between 8-12 million shallow tube-wells in Bangladesh. Up to 90% of the Bangladesh population of 130 million drink well water. Piped water supplies are available to a little more than 10% of the total population who live in the main urban areas and some district towns.
The most commonly manifested disease so far is skin lesions. Over the next decade, skin and internal cancers are likely to become the principal human health concern arising from arsenic. According to some estimates, arsenic in drinking-water will cause up to 270,000 deaths from cancer in Bangladesh alone.
Arsenic in drinking-water is a new and unfamiliar problem – both to the population as a whole as well as to professional health workers. There are millions of people who may be affected by drinking arsenic-rich water, whose health and well-being is now at risk, and even more people in the future are likely to suffer from the arsenic which is building up in their bodies as a result of water they have already consumed.
SOURCES OF ARSENIC
• Arsenic is widely distributed throughout the earth's crust.
• Arsenic is introduced into 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 disperse 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.
EFFECTS OF ARSENIC
• Chronic arsenic poisoning, as occurs after long-term exposure through drinking- water is very different to acute poisoning. Immediate symptoms on an acute poisoning typically include vomiting, oesophageal and abdominal pain, and bloody "rice water" diarrhoea. 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 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 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.
A simple solution?
A professor who developed an inexpensive, easy-to-make system for filtering arsenic from well water has won a $1 million engineering.
The National Academy of Engineering awarded the 2007 Grainger Challenge Prize for Sustainability to Abul Hussam, a chemistry professor at George Mason University in Fairfax. Hussam's invention is already in use today, preventing serious health problems in residents of the professor's native Bangladesh.
Hussam spent years testing hundreds of prototype filtration systems. His final innovation is a simple, maintenance-free system that uses sand, charcoal, bits of brick and shards of a type of cast iron. Each filter has 20 pounds of porous iron, which forms a chemical bond with arsenic. The filter removes almost every trace of arsenic from well water.
About 200 filtration systems are being made each week in Kushtia, Bangladesh, for about $40 each. More than 30,000 have been distributed so far. Hussam plans to use 70% of his prize to distribute filters to poor communities; 25% will be used for more research; and 5% will be donated to George Mason University.
The prize is funded by the Grainger Foundation of Lake Forest, Illinois. The aim of the contest was to target the arsenic problem. The challenge was looking for an affordable, reliable and environmentally friendly solution to the arsenic problem that did not require electricity.
The Grainger Challenge: www.nae.edu/nae/grainger.nsf?OpenDatabase
Read the World Health Organisation factsheet on arsenic in water: www.who.int