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A weed that spreads rapidly spreads through ponds, lakes and rivers could provide a cheap yet effective way of removing arsenic from drinking water in developing countries, say researchers.

Arsenic contaminates drinking-water in parts of Asia and Latin America, posing a significant health threat to millions of people.

The problem is most severe in Bangladesh, where the World Health Organization (WHO) estimates that 250,000 people will die from cancer because of arsenic exposure.

The team from De Montfort University in Leicester, United Kingdom, showed that a powder made from the dried roots of water hyacinth (Eichhornia crassipes) removed nearly all the arsenic from tap water containing a high concentration — 200 micrograms per litre — of the toxic metal.

Within one hour of adding the powder to the water, the arsenic level had dropped to below the WHO's safety limit of ten micrograms per litre.

The research, led by Parvez Haris, was published online last week (7 March) by the Journal of Environmental Monitoring.

Andy Meharg, a biogeochemist at the University of Aberdeen, United Kingdom, says the approach could be an advance over methods that involve adding chemicals to water, because many households in Bangladesh have ponds or seasonally flooded fields where water hyacinth could grow.

Water Hyacynth
Photo: USDA / Ted Center

But the method would produce large quantities of contaminated root powder that would need to be disposed of safely, says Meharg.

Another concern is that potential health implications of drinking water that has been decontaminated using the powdered plant root are unknown.

"Before a technological solution can be deemed serious and suitable, more research is needed," Meharg told SciDev.Net.

The water hyacinth is an aquatic plant native to South America that has spread to many other parts of the world. It is considered to be a pest because it grows rapidly and can choke waterways, blocking sunlight from reaching underwater plants and so reducing the water's oxygen content.

Link to full paper in Journal of Environmental Monitoring
Reference: Journal of Environmental Monitoring DOI: 10.1039/b500932d (2005) (Advance Online Publication)

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