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Wednesday, 31 January, 2001, 22:21 GMT
Fern eats up arsenic
Pteris vittata Nature/Ma
The arsenic builds up in the leaves of the plant
Scientists have discovered a fern that thrives on arsenic.

They suggest the plant, (Pteris vittata), could be used to clean up land and water that has been contaminated with the toxic element or its compounds.

Dr Lena Ma, of the University of Florida, US, and colleagues found the brake fern growing on a disused wood-preservation site that had been poisoned with arsenic.

When they examined its leaves, they found the concentration of arsenic to be up to 200 times higher than in the surrounding soil.

The brake fern, say the researchers, is hardy, versatile and fast growing. It has "great potential for the remediation of arsenic-contaminated soils", they write in the journal Nature.

Safely burnt

Brake fern is native to Africa, Asia and Australia, and is now widely naturalized in warm parts of the Americas. Unusually for a fern, it actually likes a sunny, open position.

The plants growing in uncontaminated soil were found by Dr Ma's team to have arsenic levels ranging from 11.8 to 64.0 parts per million.

But those growing in contaminated soil at a site in central Florida had arsenic levels of between 1,442 and 7,526 parts per million, most of which was found in the plants' long-fingered green leaves, or fronds.

The fern is able to absorb arsenic and its compounds very quickly, the team discovered. In lab tests, arsenic levels in ferns rose by a factor of 126 in as little as two weeks when they were transplanted into contaminated soil.

Research is now under way to devise a method of safely burning arsenic-enriched ferns that have been grown on contaminated sites. This would provide a source of energy and enable the element to be recovered in the form of a gas.

Water problems

Arsenic has wide industrial applications: it is used to remove iron impurities during glass-making, to manufacture semi-conductor wafers and even in the production of some fireworks.

But if the element or its compounds leak into the environment, their toxicity can cause health problems.

Dr Ma said that brake fern held out promise for helping Bangladesh, where between 35 and 77 million people out of a population of 125 million are at risk of being exposed to arsenic in their drinking water. Many have developed painful skin lesions; some cancers are also linked to the problem.

It all stems from the creation over the past two decades of tube wells that have been drilled into shallow rock containing naturally-occurring arsenic.

Dr Ma suggests the water in Bangladesh could flow through reservoirs planted with brake fern to filter out the arsenic.

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