Arsenic risk high in Sumatra, Myanmar, Cambodia, according to study

Channel NewsAsia 12 Jul 08;

PARIS : Eastern Sumatra, the Irrawaddy delta in Myanmar and Cambodia's Tonle Sap lake are among areas in Southeast Asia facing a high risk of arsenic contamination in the water, according to a study published on Friday.

The researchers use innovative digitalised techniques, drawing on geology, geography and soil chemistry, to compile a "probability map" of naturally-occurring arsenic concentrations in five Southeast Asian countries and Bangladesh.

The map is intended as a useful pointer for health watchdogs, urban planners and water engineers worried about concentrations of this poison in groundwater supplies but lacking the funds to carry out wide-scale analysis of water samples.

Published online in the journal Nature Neuroscience, the Swiss-led study combined several methods to compile its probability model.

These included knowledge about sediments whose textures and chemical or bacterial properties could release arsenic from the local ore, thus contaminating aquifers.

Also factored in were areas with flat, low-lying topography. Arsenic contamination is rarely found in places with slopes.

The benchmark for risk was the World Health Organisation (WHO) guideline of 0.01 milligrams of arsenic per litre in drinking water.

The study predicted that in Bangladesh -- which has the worst arsenic contamination in the world -- the risk of water breaching this guideline was highest in the south-centre of the country and in the northeastern Sylhet basin.

This prediction concurred with water samples previously taken and analysed from tube wells in Bangladesh.

High probabilities of arsenic contamination were also seen for the deltas of the Irrawaddy in Myanmar and the Red River in Bangladesh, for the Chao Praya basin in central Thailand and for the organic-rich sediments of the flood plain of Cambodia's Tonle Sap lake.

The computer model said an area of about 100,000 square kilometres (38,600 square miles) on the east coast of Indonesia's main island, Sumatra, was likewise "prone to high risk" of contamination above the WHO benchmark.

This prediction was then borne out by samples taken from a zone in Sumatra deemed to have high-risk and low-risk aquifers.

However, many wells in this area are deep and draw water from below the water-bearing sediments which have the arsenic problem, the study says.

"The prediction map is a useful tool for identification of areas at risk of arsenic contamination, but... understanding the local geology as a function of depth is of vital importance for specific areas," it cautions.

In Bangladesh, tens of millions of people are potentially exposed to arsenic-tainted water, boosting the danger of skin lesions, respiratory illness and cancer.

The risk comes from so-called shallow tube wells which were drilled in the 1970s and 1980s, ironically in a bid to provide rural Bangladeshis with safe water. Millions of these pipes were installed.

The new study is lead-authored by Michael Berg of the Swiss Federal Institute of Aquatic Science and Technology in Duebendorf.

- AFP /ls