Australian scientists combat water-borne arsenic threat
Scientists at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) have launched a project to assist millions of families in Bangladesh and India suffering from chronic arsenic poisoning caused by their drinking water.
It is estimated that more than 70 million people living in Bangladesh and West Bengal are drinking well-water containing dangerous levels of dissolved arsenic from the surrounding soil, says Dr Ravi Naidu of CSIRO Land & Water.
“About four million are sick and many are actually dying from the effects of arsenic poisoning. It causes skin diseases, keratoses, melanomas; it’s awful to see the plight of some families,” says Dr Naidu.
However he is also optimistic that work to be carried out by CSIRO Land & Water with backing from the Australian Centre for International Agricultural Research (ACIAR) offers potential solutions to the problem, and that it is possible both to save lives and to prevent chronic poisoning from occurring.
Arsenic occurs in groundwater in countries all round the world, including Thailand, China, Mongolia, Taiwan, Canada, New Zealand and some parts of Australia. It is naturally present in sedimentary soils of rich river valleys, usually bound up in pyrites or iron-rich minerals.
Changes in groundwater levels expose these arsenic-rich layers to the air, and soil microbes act on them. These actions can free up the arsenic so that it becomes digestible by humans – and starts to poison them.
In the case of Bangladesh and West Bengal, a shortage of clean drinking water led to the drilling of millions of tube wells to supply water for household use, livestock and agriculture. Many of these wells tap arsenic-laden groundwaters.
“The wells had to be drilled because there was an epidemic of diarrohea caused by polluted surface waters,” Dr Naidu explains. “Unfortunately much of the new water has this unintended side-effect.”
Another unintended effect is that humans can become addicted to arsenic, and that many people who drink the toxic water now find it more palatable than rainwater.
Australian scientists are already working on an absorbent tube in association with the University of Adelaide which contains a specially modified clay. If dropped in a bucket of water the clay rapidly takes up the arsenic, making the water safe to drink in a hour or so.
Another strategy is simply to let water which is rich in both iron and arsenic stand overnight in a tank or dam. The iron and arsenic bind together and sink to the bottom, leaving the water pure enough for use. The toxic sediments can then be removed using a simple filter made from wire mesh and hay.
“Solutions to this problem do not need to be high-tech or expensive – they can be simple, cheap and easy to use. But we do need to understand the precise nature of the problem first,” says Dr Naidu.
For example, shallow wells may be contaminated by arsenic, whereas wells which tap deeper aquifers may be pure. The challenge is to know which water is safe, and to monitor it for any adverse changes.
Testing water for arsenic is presently both costly and high-tech, and cannot be done for every one of Bangladesh’s 890,000 tube wells. There is a need for a cheap and reliable test.
Scientists also need to understand better the mechanisms which turn arsenic from a safe form (bio-unavailable) into a form toxic to humans and animals (bioavailable). This could be due to fluctuations in the water table, which expose previously submerged layers of soil to air and release arsenic, or the varying activity of different groups of soil microbes. “The situation is urgent in Bangladesh, but the knowledge we gain from tackling it will be useful in many countries round the world where similar problems occur,” he says.
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