Nature's Vacuum: A Fern That Sucks Up Arsenic

Arsenic cleanup is a top priority for the Environmental Protection Agency. In mid-January, federal regulators reduced the permitted level of arsenic in drinking water from 50 parts per billion to 10 ppb. To comply with this new standard, the American Water Works Assn. estimates at least 10% of the nation's water providers must do some serious cleanup.

To solve the problem completely, however, engineers also need to go to the source: hundreds of acres of soil contaminated by arsenic-laced waste from manufacturing plants and other businesses. Typically, that would entail carting away and storing thousands of tons of contaminated earth. New research published in the Feb. 1 issue of Nature suggests a better and cheaper way: enlisting the lowly brake fern.

The ability of plants and trees to vacuum up heavy metals such as zinc and nickel from soil has long been known. But until recently, no one had ever discovered a plant that could suck up arsenic. To find one that did so, Lena Q. Ma, a chemist at the University of Florida, collected 15 different plant species growing near arsenic-laden soil and tested them to see how much of the metal they had accumulated. Only the brake fern contained significant amounts of arsenic--as much as 7,500 parts per million, which is more than 200 times the level seen in the soil.

Ma notes that high levels of arsenic kill most plants, gumming up the inner workings of their cells. But the brake fern seems to thrive on the poison and actually grows better in its presence. Ma believes the plant actually stores the arsenic in a nontoxic form in its fronds. Once the metal is in the plant, it's no longer a hazard.

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