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Chinese Farmers Pin Hope on ^Soil Doctors ̄ to Cure Polluted Land

Editor:Sharon Lee
Updated:2009/5/26 16:05:29

  NANNING, May 25 (Xinhua) -- Eight years after his arable land was polluted by heavy metals, Zhou Xiaobing finally saw hope of a harvest out of the infertility.

  "I don't know what magic they used, but, you see, the land is covered with plants again," said the 37-year-old farmer in south China's Huanjiang County, Guangxi Zhuang Autonomous Region.

  In 2001, flood water from the Huanjiang River carried mineral processing industry wastes from tailings dams of three major mining companies on the upper reaches to lower watercourses, causing infertility in more than 5,000 mu (about 333.3 hectares) of arable land including Zhou's 0.6 mu.

  "This place didn't even grow a blade of grass at that time," Zhou said, standing beside his land, which, he claimed, used to yield 500 kilograms of grains a year.

  Now it is part of a 30-mu soil recovery base set up by one of China's leading soil cleaning experts Chen Tongbin and his team in 2005.

  Chen uses plants, such as a home-grown fern, to "suck up" heavy metals like arsenic, copper and zinc, from contaminated soil.

  The team, nearly 40 members in total, engaged in soil recovery projects in Hunan, Guangxi, Yunnan, Guangdong and Beijing, with an aggregated area of more than 200 mu. The base set up in Chenzhou, central China's Hunan Province, in 2001 was the first arsenic-polluted soil recovery base in the world.

  "Unlike the first base that only use the fern to rehabilitate the land, we tried intercropping in this base," said Chen, principal investigator at the Center for Environmental Remediation of the Chinese Academy of Sciences (CAS) Institute of Geographical Sciences and Natural Resources Research.

  They arranged the fern and cash crops including maize, sugar cane, and mulberry in alternate rows.

  "We can rehabilitate the land and have yields at the same time," he said. "It could help to increase farmer's income."

  Last year, the maize in the base grew so good villagers flocked to harvest them, Chen said. His team members had to be on guard to tell the villagers the maize was not safe yet for eating as poisonous elements had not been cleaned up.

  "Farmers are quite pragmatic," he said. "If it has no economic benefit at all, the technology can hardly be promoted for wider use."

  The center estimated that with an annual input of 2,000 to 3,000 yuan (about 437.7 U.S. dollars) per mu, the farmer could expect a net income of 1,000 to 1,500 yuan in return.

  Through three years of rehabilitation in the base, the soil's PH value got back to normal, the amount of arsenic in the soil was cut by 12 percent, the yield and quality of mulberry leaves had not been affected, and heavy metal contained in silk and silkworm pupa did not exceed the national level, according to the Center for Environmental Remediation.

  Compared to water and air, soil contamination is the most dangerous because it is hidden and can only be reversed by human intervention as nature cannot do it, Chen said.

  "It'll take at least three to five years for even the moderately-polluted land to recover," he said.

  Arsenic and many of its compounds are especially potent poisons and commonly used as pesticides, herbicides, and insecticides.

  "Long-time exposure to arsenic might induce cancer, and high-dose arsenic could lead to death," he said.

  "In arsenic-polluted areas, the amount of arsenic in people's hair was several times higher than the normal level," he said.

  Arsenic aroused the memory of a spate of tragedies in China last year.

  A high concentration of arsenic was recorded in water from Yangzonghai Lake in southwest China's Yunnan Province last June caused by leakage in a sub-standard waste water pool at a nearby factory.

  In September last year, 26 local officials were given administrative punishment (ranging from a warning through to demotion and the sack) in relation to the case, including the removal of 12 from their posts.

  In a separate case in October, 2008, 450 people were sickened after drinking contaminated water in Hechi city in Guangxi, including four with arsenic poisoning.

  Hechi City authority said a typhoon triggered torrential rain in September in the area. Waste water containing arsenic overflowed from a company's premises and polluted nearby ponds and wells.


  A global leader in technology for collecting arsenic from soil, Chen's team discovered Chinese brake fern, Pteris vittata L., which had a strong capacity to extract arsenic from soil in 1999.

  Besides the brake fern, the researchers found and cultivated a dozen more such pollution-extracting plants, called by scientists "hyper-accumulators". They had also developed technologies to recycle and further processed the plants into useful industrial materials by biomass incineration.

  "It's proven that the hyper-accumulators are the best possible choice for soil recovery as the technology is of lower cost and has lower risk of secondary pollution," Chen said.

  China has the largest proven reserves of arsenic with about 70 percent world share, while 61.6 percent of the Chinese reserve was concentrated in Guangxi, Yunnan and Hunan areas, statistics from the Center for Environmental Remediation showed.

  "Mine exploration usually leads to soil pollution," the 46-year-old scientist said.

  In the early years of his research in the early 1990s, Chen focused on the impact of arsenic pollution and rules of its transfer.

  "It was like you knew what disease the patients had but had no drug to cure them," he said. "So from 1995 on, we decided to find ways to repair the contaminated soil."

  At that time, soil remediation was still an emerging division for academic research in China.

  Less than ten researchers in the country were studying renovation of heavy metal-polluted soil, Chen said. "In contrast, more than 100 institutes and universities are working on the subject now."

  "Now soil remediation almost becomes a fashionable word," he said.

  Chen's team has been engaging in risk assessment and clean-up of soil in recent years, or "physical examination" and "hospitalized treatment" as Chen described the tasks.

  "We can't renovate each piece of land that was polluted because it¨s quite costly," he said. "That's why we have to assess the severity and distribution of polluted fields and give treatment accordingly," he said.

  "We usually don't recommend patients with a cold to go to hospital," he said.

  Chen, however, admitted it was a pity there was no "clear picture" of soil pollution situation in the country, though some experts estimated one fifth, or about 20 million hectares, of China's arable land had been polluted.

  Zhang Shanling, soil office head of the Department of Nature and Ecology Conservation under the Ministry of Environmental Protection, said a national soil pollution survey has came to its final stage of data collection, and the result was expected to be worked out by the end of this year.

  The government launched China's first soil pollution survey in 2006 backed by a budget of 1 billion yuan.

  The program aimed to assess soil quality across the country by analyzing the amount of heavy metals, pesticide residue and organic pollutants in the soil.

  Chen Tongbin said his team was now engaging in promoting the use of soil remediation technology through plants to wider regions across the country.

  "We hope we can set up more bases in different parts of the country to see to more patients," he said.

  "China is a country with a vast territory and varied climates. Though the core technology and engineering application are there, we have to test them in different areas and make adaptations accordingly," he said.

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