Ground water contaminated by arsenic poses a risk to the health of millions of people, especially in the densely populated river deltas of Southeast Asia. To date, no method had been available for identifying high-risk areas without conducting costly sampling campaigns. Now, researchers have developed a model that allows vulnerable areas to be pinpointed using existing data on geology and soil properties. It also has enabled them to detect high-risk areas in regions where ground water studies had not previously been carried out, such as in Myanmar and on Sumatra.
Scientists from Eawag, a Swiss-based
aquatic research institute, have described a method that allows
to be identified without the need for ground water analysis. The
led by geologist Lenny Winkel and environmental chemist Michael Berg,
existing geological data from Bangladesh, Myanmar, Thailand, Cambodia,
Vietnam and Sumatra to produce a uniformly classified map.
The data related only to
surface sediments and soil properties; surprisingly, this combination of data
permits sufficiently accurate conclusions to be drawn concerning chemical and
physical conditions in ground water.
The scientists then studied
the statistical relations between 30 surface parameters, including geological,
hydrological and climate data, and arsenic concentrations, finally
incorporating the eight most relevant variables into a logistic regression
model. In particular, young river deposits with organic rich sediments proved
to be indicators of ground water arsenic contamination. This finding is
apparent from the maps in which the probabilities calculated for elevated
arsenic concentrations are presented in a graphical form.
Worldwide, more than 100
million people are exposed to excessive amounts of arsenic in drinking water.
Arsenic occurs as a natural component of underground rocks worldwide, with
small quantities being dissolved in ground water as a result of weathering. The
inorganic salts of arsenic are tasteless and odourless, but highly toxic to
humans. If ingested over long periods, even low concentrations can damage
health, including hyper-pigmentation of the skin, disorders of liver and kidney
function, and various types of cancer.
Problems arise from the fact
that arsenic concentrations can vary widely at the local level, and that, in
many areas, people are completely unaware of the risk because their well water
or ground water never has been tested for arsenic. Arsenic concentrations below
10 µg/L are deemed to be safe, and therefore, are recommended by the World
Health Organization as a guideline value for arsenic in drinking water.
In the deltas of the Red
River and the Mekong, Eawag detected arsenic concentrations exceeding 100 µg/L
in one in five of the samples analyzed, with maximum values as high as 3,000
µg/L. In Myanmar’s Irrawaddy delta, another study found arsenic concentrations of
more than 50 µg/L in two-thirds of the sampled wells.
The latest findings from Southeast Asia are part of the Water Resource Quality (WRQ) project,
a research program studying the occurrence of geogenic contaminants in ground water
worldwide. Methods also are being developed to allow the affected populations to
treat contaminated water using appropriate technologies. To date, the work has
been carried out on a very coarse scale, but now has been successfully refined,
thanks to the project in Southeast
Asia. The new model is of
particular interest for regions where no ground water measurement data are yet
Accordingly, the Swiss
aquatic research team applied the model to the Indonesian island of Sumatra, where an area covering 38,610 square miles on the
eastern coast was found to be at high risk for arsenic contamination. The
researchers subsequently used about 100 ground water samples to verify the
probabilities predicted by the model for a region on the border between a low- and
a high-risk area. Once again, the results of analyses were found to agree with
the predictions: 94 percent of the wells in the low-risk area showed arsenic
concentrations below 10 µg/L. The maps also indicate an increased risk of
elevated arsenic concentrations in ground water in the Irrawaddy delta and along the Chao
Phraya river north of Bangkok, Thailand – both areas where the risk had not previously been
Scientists Develop Model to Map Likely Arsenic Contamination
July 16, 2008