This delicate fern is a sucker for arsenic
What arsenic did for playwright Joseph Kesselring's "old lace" it's done for countless ranchers, orange growers, and golf-course managers: It's gotten rid of pests.
Used against everything from ticks on cattle and fungus on orange trees to weed killers, arsenic also figures into many industrial processes. Yet its use has left tens of thousands of sites worldwide badly contaminated.
In today's edition of the journal Nature, scientists in Florida report finding what may be a new ally in the battle against arsenic contamination - a lowly fern that, at least until now, state officials had branded an invasive pest.
The plant, commonly called brake fern, displays an appetite for arsenic that surprised its discoverers. Concentrations ranged up to hundreds of times higher in the plant than in the surrounding soil. Unlike many plants scientists have found thriving in metal-tainted soils, the brake fern uses its entire structure to sequester arsenic, not just its roots.
"This fern is really amazing," says Lena Ma, an associate professor in the Institute of Food and Agricultural Sciences at the University of Florida in Gainesville who led the research team that found the plant.
University of Northern Arizona biochemist David Salt agrees.
"The fern is exciting," he says, adding that even if other traits render the plant inadequate to clean up contaminated sites on its own, finding the genetic key to its ability to store arsenic could help researchers engineer more-suitable plants to clean tainted sites.
Dr. Ma notes that the fern, native to China but found worldwide, was one of a number of plants her team collected from an abandoned wood-preservation site in north-central Florida. The scientists were testing the plants to see which ones might prove useful for arsenic cleanup duty. She adds that dealing with arsenic-laced sites is a top priority for Florida environmental officials. The state has some 3,200 arsenic hot spots, she says.
When they returned to the lab with soil and fern samples, the researchers measured in the contaminated soil arsenic levels ranging from 18.8 to 1,603 parts per million (p.p.m.). Brake ferns growing in that soil displayed concentrations from 1,442 to 7,526 p.p.m. Even ferns growing in uncontaminated soils, where arsenic levels ranged from 0.47 to 7.56 p.p.m., held concentrations from 11.8 to 64 p.p.m. They also found that at certain concentrations, arsenic appears to act as food, boosting the brake fern's biomass by up to 40 percent over ferns grown in arsenic-poor soil.
One reason for the excitement over brake ferns lies in the frustration scientists have experienced in using plants to clean up sites tainted with metals such as arsenic, lead, zinc, cadmium, nickel, and cobalt.
Plants have been more successful cleaning sites contaminated by organic solvents and fuels, Dr. Salt says. Water often is enough to liberate these chemicals from soil particles for uptake by plants. Metals, however, are hard to liberate. He explains that if he were to place lead-contaminated soil in a glass of water, swish it around, then strain out the soil, the water would still be fit to drink.
Two key questions Ma's team is now trying to answer focus on the mechanisms the plant uses to extract the arsenic and the defense it has built against the poisonous concentrations it harbors.
"Why it accumulates arsenic is a real mystery," she says.
Despite the plant's glowing statistics, Salt notes that, as is, the fern's suitability for site cleanup duty is unclear.
"You need substantial biomass and substantial concentrations" taken up by plants to do the job, he explains.
Moreover, plants present their own disposal problems once they've done their job, although at the end of the cleanup the volume of plant material can be up to 1,000 times less than the volume of soil back hoes would have dug up to ship to landfills or incinerators.
Ma says her team also is looking into ways to safely dispose of the ferns once they've played their cleanup role.
(c) Copyright 2001. The Christian Science Publishing Society