Gainesville, FL -- The solution to one of man's most vexing environmental problems may lie in one of nature's most remarkable plants.
In an article scheduled to appear Thursday in the journal Nature, University of Florida scientists report discovering a fern that soaks up arsenic from contaminated soil. The first plant ever found to "hyperaccumulate" arsenic -- a carcinogenic heavy metal often used as an herbicide -- the fern may prove useful in cleaning up thousands of sites contaminated by arsenic from industrial, mining, agricultural or other operations around the world.
"It has great potential for remediating these contaminated soils," said Lena Ma, an associate professor at UF's Institute of Food and Agriculture Sciences and lead researcher on the project. Ma's research team found that the brake fern, Pteris vittata, not only soaks up arsenic but does so with staggering efficiency. They measured levels as much as 200 times higher in the fern than the concentrations in contaminated soils where it was growing, Ma said.
In that example, from a site contaminated by lumber treated with chromium-copper-arsenic solution, the soil had 38.9 parts per million of arsenic, while the fern fronds had 7,526 parts per million of arsenic.
In greenhouse tests using soil artificially infused with arsenic, concentrations of the heavy metal in the fern's fronds have reached 22,630 parts per million -- meaning that a startling 2.3 percent of the plant was composed of arsenic, Ma said.
To their surprise, the research team found the fern even accumulates arsenic in soils that contain normal background arsenic levels of less than 1 part per million. For example, the team measured 136 parts per million of arsenic in fronds of a fern growing on UF campus in soil that contained just .47 parts per million of the metal.
Levels of arsenic in the plant easily eclipse the threshold of 5 parts per million for classification as an industrial-level hazardous waste based on the Environmental Protection Agency's standard test, a jarring fact when considered with the plant's verdant appearance.
The findings are all the more remarkable because arsenic often is used to kill weeds and other unwanted plants on golf courses and lawns, said Ma, a specialist in trace metal chemistry in the IFAS soil and water science department.
"Why it accumulates arsenic is a mystery," she said, adding that her future research will focus on how the plant takes up, distributes and detoxifies the arsenic.
The findings suggest the fern could become a star player in a burgeoning industry known as "phytoremediation," or using plants and trees to clean up toxic waste sites.
Currently, some 400 plants are known to accumulate toxins. Many are used in a small but growing phytoremediation market estimated to be climbing from a range of $16.5 million to $29.5 million in 1998 to a range of $214 million to $370 million by 2005, according to published reports. Because the fern accumulates 90 percent of the arsenic in its fronds and stems, the strategy would be to grow the plant on toxic sites, then harvest the fronds and stems -- its "above-ground biomass" -- and transfer them to a designated hazardous waste facility.
The approach could help address a major problem in Florida and worldwide, Ma said. Earlier this century, cattle ranchers in Florida often used the poison on their herds to combat fleas and other vermin. As a result of this activity alone, the state has more than 3,200 known sites contaminated by arsenic. Worldwide, there are tens of thousands of contaminated sites, the result of mining, milling, combustion, wood preservation and pesticide application, Ma said. The fern seems all the more promising to clean up many sites because it is an easy-to-grow perennial that prefers a sunny environment and alkaline soil. Arsenic is more easily extractable chemically in alkaline conditions, Ma said.
In the greenhouse tests done by Cong Tu, a postdoctoral student in Ma's group, the plant seems to fare better in soils with arsenic than in soils without arsenic. But Ma said she is not ready to conclude the plant needs arsenic to live.
In addition to Tu, other scientists involved in the research are Ken Komar, a former UF master's student under Ma's supervision; Weihua Zhang and Yong Cai of the Florida International University department of chemistry; and Elizabeth Kennelley at the IFAS Analytical Research Laboratory.
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