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Chinese Fern Cleans up Heavy Metal-polluted Soil

One of China's leading soil cleaning experts Chen Tongbin uses a home-grown fern to accumulate heavy metals, mainly arsenic (As), out of contaminated soil near mines, which is encouraging to a country which has about 280,000 mines and heavy-metal polluted soil near those mines.

Chen, principal investigator at the Center for Environmental Remediation of the Chinese Academy of Sciences (CAS) Institute of Geographical Sciences and Natural Resources Research, and his team have improved the capability of Chinese brake fern, Pteris vittata, to collect heavy metals, mainly arsenic (As), from contaminated soil.

"The work we've done in Guangxi, Hunan, Yunnan, Zhejiang and Guangdong is quite impressive," Chen said here Monday in an interview with Xinhua.

The technology, scientifically named as soil remediation, includes assessment, clean-up, rehabilitation of soil polluted by chemicals, heavy metals, inorganics and radioactive wastes, which can be found near mines, oil fields, factories and waterways.

Chen's team discovered the arsenic-collecting Chinese brake fern, Pteris vittata, in 1998 in central China's Hunan Province. Besides Pteris vittata, the researchers found and cultivated a dozen more such pollution-extracting plants, called by scientists hyperaccumulators.

Investigation showed Chinese brake fern had a strong capacity to extract arsenic from soil, and had been proven to effectively aid recuperation of As-contaminated land. Chinese brake fern had extraordinary accumulating capacity for arsenic.

The concentration of arsenic was the biggest in leaves. It decreased to leafstalks and roots, which was rarely seen in other plants, Chen said.

According to their study, greenhouse cultivation doubled As accumulation in fern leaves than that in field samples. The highest concentration of arsenic reached 5070 mg/kg on a dry matter basis.

Besides the extraordinary tolerance and accumulation of arsenic, China brake fern grew rapidly with great biomass, wide distribution and easy adaptation to different conditions, he said.

The latest study of Chen's team -- "Arsenic Transformation and Volatilization during Incineration of the Hyperaccumulator Pteris vittata L." which was published in April in Environmental Science & Technology -- analyzed As behavior in incineration of As-hyperaccumulators, indicated that carbon originating from biomass incineration, during which furnace temperature was carefully controlled, might catalyze As reduction.

The next step might be to collect and reuse the arsenic and other heavy metals extracted from the plants, Chen said.

(Xinhua News Agency May 19, 2008)

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