Arsenic in water — how much is too much?

The United States is in the throes of a fractious debate about what the permissible levels of arsenic in water should be.

The current US standard of 50 parts per billion (ppb), in place since 1942, is criticized as dangerous by public health watchdogs, who would like to see the level reduced to 10 ppb, a change proposed by the Clinton administration in January. EPA chief Ms Christine Todd Whitman has asked the US National Academy of Sciences (NAS) to review more data and to consider standards ranging from 3 to 20 ppb and has also asked an advisory council to study the potential costs of lower standards. Meanwhile, the current standard of 50 ppb remains in place.

The arsenic found in drinking-water is primarily from natural sources — it leaches into groundwater from rocks and soil. It can also enter the environment as a by-product of industrial and agricultural processes. WHO says prolonged exposure to arsenic in drinking-water causes cancer of the skin, lungs, bladder, and kidneys. In particular, the agency notes in a soon-to-be-published fact sheet, lung and bladder cancers have been observed at levels below 50 ppb — the international standard set by WHO in 1963. In 1993, WHO set 10 ppb as a ‘‘provisional guideline value’’ but notes that on health grounds this value ‘‘would be less than 0.01 mg/l [or 10 ppb]’’.

Countries where arsenic in drinking-water has been detected at concentrations above 10 ppb include Argentina, Australia, Bangladesh, Chile, China, Hungary, India, Mexico, Peru, Thailand, and the US. In at least four of these countries — Bangladesh, China, India, and the US — adverse effects on health have been documented, WHO says.

Catherine Dold, Boulder, Colorado, USA

World Health Organization Genebra - Genebra - Switzerland