Mean green plant which just thrives on heavy metal

Researchers in Florida have discovered a fern that so loves deadly arsenic that its fronds and stems could be classed as toxic waste. It should prove very useful for reclamation of lands poisoned with this dangerous heavy metal.

The brake fern, Pteris vittata, is the first plant found to "hyperaccumulate" arsenic, according to Dr Lena Ma, associate professor at the University of Florida's Institute of Food and Agricultural Science. She and colleagues report on the brake fern's abilities this morning in the journal Nature.

Arsenic is a dangerous poison and can also cause cancers. Yet it has often been used to kill vermin, as a herbicide and an insecticide and in wood preservatives.

The brake fern seems, however, to have a remarkable appetite for arsenic. "Why it accumulates arsenic is a mystery," Dr Ma said, but it does so with a staggering efficiency. In pristine soils on the campus, with arsenic at normal background levels of less than one part per million, the fern fronds have gathered up levels reaching 136 parts per million of arsenic.

The US Environmental Protection Agency has set a threshold of five parts per million for classification as an industrial level hazardous waste. This means the fern readily achieves the status of toxic waste.

The research team grew the fern on a site contaminated by a timber treatment which included arsenic. The soil had 38.9 parts per million of the heavy metal but the fern fronds accumulated 7,526 parts per million.

When the team artificially contaminated test soil with even more arsenic the plant obligingly sponged up enough to achieve a level of 22,630 parts per million. This meant that 2.3 per cent of the plant was composed of arsenic.

Pteris vittata joins a growing list of some 400 plants known to accumulate toxins, making it a prime candidate for "phytor emediation", the use of plants and trees to clean up toxic waste sites. "It has great potential for remediating these contaminated soils," Dr Ma said.

The brake fern, Pteris vittata, which consumes arsenic, could prove effective in reclaiming lands poisoned by toxic waste.