Fern soaks up arsenic with “staggering efficiency”

Researchers from the University of Florida (UF) in Gainesville announced on 30 January that the common brake fern, or Pteris vittata, is the first plant ever found to hyperaccumulate arsenic, showing levels as much as 200 times higher in the fern than the concentrations in contaminated soils where it was growing.

Lena Ma, an associate professor at UF’s Institute of Food and Agriculture Sciences and lead researcher on the project, said that in one experiment on 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 showed 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% 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 one 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 0.47 parts per million of the metal. This means that arsenic levels in the plant easily eclipse the threshold of five parts per million for classification as an industrial-level hazardous waste based on the Environmental Protection Agency’s standard test. The findings are all the more surprising to researchers because arsenic often is used to kill weeds and other unwanted plants on golf courses and lawns.

“Why it accumulates arsenic is a mystery,” Ma said, adding that future research will focus on how the plant takes up, distributes and detoxifies the arsenic, but the findings suggest the fern could become a major player in the phytoremediation industry. Because the fern accumulates 90% 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, and transfer them to a designated hazardous waste facility. The fern is further aided because it is an easy-to-grow perennial that prefers a sunny environment and alkaline soil, and arsenic is more easily extractable chemically in alkaline conditions.

The approach could help address a major problem in Florida and worldwide, Ma said. Florida alone has more than 3,200 known sites contaminated by arsenic, however, Bangladesh is the country most affected by arsenic poisoning. According to the United Nations, around 25 million Bangladeshis are at risk of disability or death from arsenic poisoning in much of the country’s drinking water (see related story).

Edenspace, a Virginia-based company, has already bought rights and begun to market the fern commercially.

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.