Arsenic-free water still a pipedream

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Decontamination plants fail to free millions from poisoned supply.

Decontamination plants installed at wells throughout West Bengal are failing to reduce arsenic in local drinking water to safe levels, according to a report. The authors suggest that efforts to supply safe water should instead focus on purifying surface water.

Of 18 arsenic-removal plants monitored over a two-year period, none reduced arsenic levels below the maximum safe value stipulated by the World Health Organization (WHO), says epidemiologist Dipankar Chakraborti of Jadavpur University in Calcutta, India, whose team carried out the tests (M. A. Hossain et al. Environ. Sci. Technol. 39, 4300–4306; 2005). The findings come as a blow to efforts to address what has been called the worst mass poisoning in history, in which millions of people were exposed to dangerous or fatal levels of arsenic in their water.

The high levels of arsenic in well water used for drinking and irrigation came to light in the early 1990s, after outbreaks of skin disease and cancers in West Bengal and Bangladesh. The arsenic comes from natural geological sources that weren't recognized when the wells were dug during the 1970s. An estimated 35 million people were drinking from such wells, dug by aid agencies so that locals wouldn't have to rely on rain and river water, which is often contaminated by carriers of diseases such as typhoid and dysentery.

Hard to swallow: millions of people in West Bengal are still drinking highly contaminated water. Credit: I. BERRY/MAGNUM PHOTOS

To try to fix the situation, some 2,000 arsenic-removal plants were installed in wells in West Bengal, and many more in Bangladesh, at an average cost of US$1,500 each. These plants aim to remove arsenic from water using a series of filters and extraction systems.

But controversy has persisted. Chakraborti has previously shown that methods for identifying safe wells are not always reliable. Now he says that the removal plants cannot be trusted either.

Chakraborti and his colleagues tested 18 such plants, from 11 different manufacturers in India, Germany and the United States. The average arsenic concentration in water treated during a two-year period was 26 micrograms per litre — more than twice the value recommended by the WHO. Only two of the plants met the Indian standard value for arsenic levels, which is five times higher than that of the WHO, and 80% of the local villagers tested had abnormal levels of arsenic in their urine.

Chakraborti believes that efforts should now focus on harnessing and purifying surface water. The United Nations Children's Fund (UNICEF), which initiated and funded the original well-drilling programme, supports the approach. “We're really pushing for rainwater harvesting,” says UNICEF emergencies coordinator Paula Plaza.

However, there are now plans to test arsenic-removal plants more thoroughly before they are licensed for use. A Canadian company called the Ontario Center for Environmental Technology Advancement is collaborating with the Bangladeshi government to develop performance standards for these systems.

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Arsenic contamination of Bangladeshi paddy field soils: implications for rice contribution to arsenic consumption

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Related external links

American Chemical Society paper

OCETA - Arsenic Mitigation Program

UNICEF - Arsenic Mitigation and Measurement Project

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Ball, P. Arsenic-free water still a pipedream. Nature 436, 313 (2005) doi:10.1038/436313a

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