ARSENIC IN DRINKING WATER Page 2

MEASUREMENT

Accurate measurement of arsenic in drinking-water at levels relevant to health requires laboratory analysis, using sophisticated and expensive techniques and facilities as well as trained staff not easily available or affordable in many parts of the world.
Analytical quality control and external validation remain problematic.
Field test kits can detect high levels of arsenic but are typically unreliable at lower concentrations of concern for human health. The reliability of field methods is yet to be fully evaluated.

PREVENTION AND CONTROL

The most important remedial action is the prevention of further exposure by providing safe drinking- water. The cost and difficulty of reducing arsenic in drinking-water increases as the targeted concentration lowers. It varies with the arsenic concentration in the source water, the chemical matrix of the water including interfering solutes, availability of alternative sources of low arsenic water, mitigation technologies, amount of water to be treated, etc.

Control of arsenic is more complex where drinking-water is obtained from many individual sources (such as hand-pumps and wells) as is common in rural areas. Low arsenic water is only needed for drinking and cooking. Arsenic-rich water can be used safely for laundry and bathing. Discrimination between high-arsenic and low-arsenic sources by painting the hand-pumps (e.g. red and green) can be an effective and low-cost means to rapidly reduce exposure to arsenic when accompanied by effective health education.

Alternative low-arsenic sources such as rain water and treated surface water may be available and appropriate in some circumstances. Where low arsenic water is not available, it is necessary to remove arsenic from drinking-water:

The technology for arsenic removal for piped water supply is moderately costly and requires technical expertise. It is inapplicable in some urban areas of developing countries and in most rural areas worldwide.
New types of treatment 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 "point-of-use" removal of arsenic from water are few which includes reverse osmosis and have proven to be sustainable in each different setting.

Some studies have reported preliminary successes in using packets of chemicals for household treatment. Some mixtures combine arsenic removal with disinfection. One example, developed by the WHO/PAHO Pan American Center of Sanitary Engineering and Environmental Sciences in Lima, Peru (CEPIS), has proven successful in Latin America.

WHO'S ACTIVITIES ON ARSENIC

WHO's norms for drinking-water quality go back to 1958. The International Standards for Drinking-Water established 0.20 mg/L as an allowable concentration for arsenic in that year. In 1963 the standard was re-evaluated and reduced to 0.05 mg/L. In 1984, this was maintained as WHO's "Guideline Value"; and many countries have kept this as the national standard or as an interim target. According to the last edition of the WHO Guidelines for Drinking-Water Quality (1993)

Information extracted from:
Guidelines for drinking-water quality, 2nd ed.
Geneva, World Health Organization, 1996.