Arsenic in Drinking Water.

Sources

Arsenic exposure has a number of sources:

* 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.

* In some areas, industrial effluents contribute arsenic to water.

* 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 is also used commercially (e.g., in alloying agents and wood preservatives).

* 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 or pentavalent arsenate. Organic types of arsenic, abundant in seafood, are 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, as well as from mining and industrial emissions, may also be significant locally.

Effects

Chronic arsenic poisoning, as occurs after long-term exposure through drinking water, is very different from acute poisoning. Immediate symptoms of an acute poisoning typically include vomiting, esophageal 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 signs and symptoms of long-term arsenic poisoning appear to differ among individuals, population groups, and geographic areas. Thus, there is no universal definition of the disease caused by arsenic. This circumstance complicates the assessment of the burden arsenic places on health. Similarly there is no method of distinguishing cases of internal cancer that were caused by arsenic from cancers induced by other factors.

Nevertheless, the following information is known about the effects of arsenic exposure on health:

* Long-term exposure via drinking water can cause cancer of the skin, lungs, urinary bladder, and kidneys.

* Increased risks of lung and bladder cancer and of arsenic-associated skin lesions have been observed at arsenic concentrations of less than 0.05 milligrams per liter (mg/L) of drinking water.

* Absorption of arsenic through the skin is minimal, and thus handwashing, bathing, and doing laundry with water containing arsenic do not pose health risks.

* With long-term exposure, the first changes are usually observed in the skin: pigmentation changes, 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. Some studies have reported hypertensive and cardiovascular disease, diabetes, and reproductive effects.

* In a province of China, exposure to arsenic via drinking water has been shown to cause a severe disease of the blood vessels leading to gangrene. This disease, known as "black-foot disease," has not been observed in other parts of the world, and it is possible that malnutrition contributes to its development. Studies in several countries have, however, demonstrated that arsenic causes other, less severe forms of peripheral vascular disease.

Prevention and Control

The most important remedial action is prevention of further exposure through provision of safe drinking water. Alternative low-arsenic sources such as rainwater and treated surface water may be available in some circumstances.

Where low-arsenic water is not available, it is necessary to remove arsenic from drinking water. The cost and difficulty of this process increase as the targeted concentration lowers. They also vary with the concentration of arsenic in the source water; the chemical matrix of the water, including interfering solutes; the availability of alternative sources of low-arsenic water; mitigation technologies; and the amount of water to be treated.

* The technology for arsenic removal from piped water is moderately costly and requires technical expertise. It is inapplicable in some urban areas of developing countries and in most rural areas worldwide.

* New technologies, including co-precipitation, ion exchange, and activated alumina filtration are being field-tested.

* There are no proven technologies for the removal of arsenic at water collection points such as wells, hand pumps, and springs.

* Simple technologies for household removal of arsenic are few, must be adapted to, and must be proven sustainable in each setting.

* Some studies have reported preliminary successes with packets of chemicals for household treatment. Some mixtures combine arsenic removal with disinfection.

Activities of the World Health Organization

The World Health Organization's (WHO's) norms for drinking-water quality go back to 1958. In that year, the International Standards for Drinking Water established 0.20 mg/L as an allowable concentration. In 1963, the standard was re-evaluated and reduced to 0.05 mg/L. In 1984, the 1963 standard was reaffirmed as WHO's "Guideline Value," and many countries have kept it as a national standard or an interim target. The last edition of the WHO Guidelines for Drinking-Water Quality, from 1993, established a new provisional guideline value of 0.01 mg/L.

A summary of an updated International Programme on Chemical Safety Environmental Health Criteria Document on Arsenic, published by WHO, is available at [less than] http://www.who.int/pcs/ehc/summaries/ehc_224.htm#English[greater than].

A United Nations report on arsenic in drinking water has been prepared in cooperation with other U.N. agencies. It provides a synthesis of available information on chemical, toxicological, medical, epidemiological, nutritional, and public-health issues; develops a basic strategy for coping with the problem; and advises on removal technologies and water quality management. A draft of the report is available at [less than]http://www.who.int/water_sanitation_health/Arsenic/ArsenicUN Reptoc.htm[greater than].