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A fern that loves
toxic waste
US researchers from the Universities of Florida and Georgia report in this week’s Nature that brake fern Pteris vittata, originally from China, can accumulate in its fronds up to 10 times the concentration of arsenic found in the soil. The team stumbled on the fern flourishing at a site in Florida which had been contaminated with chromated copper arsenate. It was the only one of 14 plant species collected which had accumulated the arsenic in its leaves. Brake fern at the site contained up to 5000 parts per million (ppm) of arsenic, compared with only 65 ppm from ferns growing in an uncontaminated site. In subsequent laboratory experiments, researchers found that the fern accumulates arsenic very rapidly. In two weeks growing on soil which had been ‘spiked’ with 1500ppm arsenic, arsenic concentration in the fern leaves leapt more than 500 times from 29.4 to 15,861ppm. Increasing arsenic concentration even boosted the fern’s growth. Brake fern is one of very few plants which are able to accumulate arsenic and is the highest bio-accumulator so far known. It has potential for use in bioremediation of areas contaminated by arsenic, such as mining sites and old tick dip sites. India and Bangladesh in paricular have major arsenic soil contamination problems, and the poison is now finding its way into groundwater. Slow Grower Trials are being conducted in Australia using trees and crop plants to clean up sites contaminated with metals, petroleum products and other chemicals. One of the leading researchers, Dr Mike McLaughlin from CSIRO Land and Water said plants which take up toxic chemicals cope by storing the contaminants in vacuoles (vesicles within the cell), trichomes (bumps on the leaves) and in cells on the leaf surface. However, he said a major drawback in using ferns for bioremediation was their slow growth. Researchers were now focussing on understanding the mechanisms whereby ferns are able to tolerate such high concentrations of toxic substances. If these are under genetic control, then these genes could be transferred to faster growing species, such as potatoes and grasses to do a much faster cleanup. Abbie Thomas - ABC Science
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