Safe drinking

a simple filter based on sand and iron filings could effectively prevent millions of people being poisoned by arsenic in the water they drink. Nikalaos Nikolaidis, professor of environmental engineering as the University of Connecticut, usa , has created a filter that converts almost all the water-borne arsenic into insoluble compounds.

"Arsenic poisoning is one of the worst public health problems in the world today,' says Nikolaidis, "especially in countries like Bangladesh, where the soil is high in arsenic compounds and where people drink much more water than they do in temperate areas.'

The World Health Organisation's drinking water safety limit for arsenic is 10 micrograms per litre, but in nations such as Bangladesh and neighbouring Bengal in India, water from wells contains as much as 300-400 micrograms per litre. "And people of Bengal, working in the heat, consume as much as 15 to 20 litres of water every day,' says Nikolaidis. They experience a variety of symptoms, from skin lesions to kidney damage, and could suffer an early death.

The filter is a tube filled with sand and iron filings, designed to fit easily in a well outlet. In the presence of barium sulphate, which can be added if it is not in the water already, the iron particles oxidise and react with the arsenic to form arsenopyrite