Arsenic-Eating Fern Holds Hope for Tainted Soils
TACOMA, Wash. State pollution fighters planted a small patch of pitiful-looking plants inside a wire cage in Tacoma's Point Defiance Park and labeled them poison.
The 100 subtropical ferns inside the test plot near Fort Nisqually are part of a two-year, $30,000 experiment in pollution control that began in April on Vashon and Maury islands.
"We just want to know whether it's taking arsenic from the soil. We're watching for other things, but that's our primary objective," said Norm Peck, a state Department of Ecology investigator.
Four years ago, scientists in Florida found that Chinese brake ferns thrive on arsenic, sucking the poison out of soil and concentrating it in their fronds.
A company now markets the ferns as a pollution solution for arsenic-plagued communities.
Ecology Department officials decided to test whether the ferns will grow locally and reduce soil contamination in areas affected by windborne arsenic from the former Asarco smelter.
The Ruston smelter, which stood just outside Point Defiance Park, operated for nearly 100 years before it shut down in 1985.
Its smokestack and buildings have been demolished, but the site, adjacent neighborhoods and nearby shoreline are the focus of a federal Superfund cleanup.
Beyond that, elevated concentrations of arsenic, lead and cadmium still taint soils in a 1,000-square-mile area around Puget Sound.
Health officials have cautioned residents in many parts of Pierce and King counties to limit exposure to contaminated dirt because of the risks of long-term arsenic exposure. Children are particularly vulnerable.
The Point Defiance test plot represents a public relations turnaround for Metro Parks managers, who initially resisted outside efforts to test for soil contamination in children's play areas.
Earlier this year, Metro Parks agreed to allow the Tacoma-Pierce County Health Department to sample soils at about a dozen sites at Point Defiance and other Tacoma parks.
So far, about half -- including those in Point Defiance -- have been sampled.
Detected arsenic concentrations have not been high enough to warrant alarm, said Glenn Rollins, a health department environmental health specialist.
As for the ferns, scientists in the Florida laboratory experiments measured arsenic concentrations in them that were as much as 200 times higher than in the soil where the plants grew.
"The fronds themselves will become poisonous," said Marian Abbett, an environmental engineer who oversees the Ecology Department's Tacoma smelter project.
The wire cage around the Fort Nisqually test plot is designed to keep people and critters out, she said.
Pteris vittata, as scientists call the ferns, look a lot like native sword ferns. But Chinese brake ferns are considered invaders in Florida, where they dominate their habitat.
"We don't think it will be an invasive here. In fact, we're concerned whether we're going to keep it alive," Abbett said. "They like the warmer, tropical climate."
Bhaskar Bondada, a Washington State University plant physiologist who studied the fern in Florida, called it fascinating.
"The beauty of this plant is it only accumulates arsenic in the fronds," which are easily picked, he said.
But in the process, the fern also converts arsenate to arsenite, which is more toxic, he said.
In all, Ecology Department officials bought 750 plants for $5 each, from Edenspace, the Virginia company that markets the fern as an "arsenic-eating superstar."
In addition to the Fort Nisqually test plot planted Thursday, officials are growing the plants in a second patch near the park's maintenance shop.
They planted most of the ferns in April and May outside Chautauqua Elementary School on Vashon Island and in Dockton Park on Maury Island.
Rita Schenck, who runs the Institute for Environmental Research and Education on Vashon Island, said she thinks the ferns should be studied, but she urged caution.
They could prove to be invasive, she said. Besides that, the fronds might have to be buried in a hazardous waste repository.
"We have to harvest the leaves," Abbett said. "They can't just fall back on the ground."
Nor does the Ecology Department plan to compost them, she said. The plan is to test the arsenic concentrations and decide whether the fronds are hazardous before dumping. Regular soil testing also is planned.
Lois Stark, a Metro Parks planner, said she's confident Ecology Department officials will make sure the plant doesn't prove to be a problem in Point Defiance.
"They're not just planting them and walking away," she said.
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Source: Knight Ridder/Tribune Business News