"The land suffers from a high level of arsenic pollution and it's hard to wash it away with water or chemicals, which can of course lead to secondary pollution," said Chen. Crops grown from the arsenic-polluted land are inedible.

But experts have a secret weapon that can absorb the poisons from the soil-Eremochloa ciliaris Merr, a plant nicknamed "chilopod grass." The plant has a good appetite for heavy metals such as arsenic. Once the plant takes up the pollutants, scientists can retrieve contaminants from its leaves and convert them into useful industrial materials.

It's reported that Chen Tongbin is the world's first scientist to discover the plant. As early as 1987, he realized that arsenic pollution could pose a huge environmental problem for China. For 10 years he led a team to find the best plant for cleaning up heavy metal soil pollution. He knew that, based on the climate, soil and biodiversity in China, such a plant was likely to exist.

Chen speculated that such a plant might grow near arsenic sulphide mines, so he traveled to one in Hunan Province's Shimen County that was known to have been operating for 300 years. He stayed there for three years before finding a grass that grows as tall as a person and very quickly. Results of tests performed on the plant excited Chen-every kg of the plant can take up as much as 10,000 milligrams of arsenic, an amount that is tens of thousands of times higher than normal plants.

In 2000, it was found that Chenzhou, Hunan Province was seriously polluted with arsenic; large plots of land had been deserted and two villagers had died as a result of the poison. Chen established the world's first arsenic-polluted soil recovery project that used the grass to treat the soil. After three years, the pollution problem was primarily solved.

"After each plant was reaped, the arsenic content in the soil it was growing on decreased by a large margin," said Chen. He estimated it would take five years to restore the productivity of the soil. "It is the fifth year of the experiment. When the technology is mature and promoted widely, farmers will be able to carry out treatment on their own land." In the meantime, scientists are experimenting with ways to grow the grass among crops to increase productivity while treating the soil.

Scientists around the world are racing to develop plants that can clean soil because of the safety of the approach and its low cost and efficiency. They have found more special plants to cure polluted soil. After research, analysis and experimentation, Chinese scientists have discovered metal-absorbing plants in 200 mines that can uptake heavy metals like bronze, lead, zinc, cadmium and cobalt. Scientists have also developed organic solutions and microorganism additives from these plants that can enhance the treatment effect.

Chen also attacks the problem of urban sludge treatment along with his work on soil pollution. Authorities usually treat the raw sewage but do not know how to deal with the sludge that results. In some places it was sold to farmers as a cheap fertilizer, but crops died after it was applied to farmland. And the sludge cannot be buried underground, as the odor would infest the area and the harmful substances leaching out of it would pollute groundwater.

Chen established a model project in Henan Province to conduct sludge disposal harmlessly and convert it into fertilizers for plants. The first step of the process is to neutralize the bad smell, which results from absence of oxygen. So scientists pump oxygen into it. Chen invented a special probe to monitor real-time oxygen levels and give feedback to the control system.

Oil Cleansing

Several years ago, Beijing-based Tsinghua University chemical engineering professors began using bacteria and fungi to treat oil-polluted soil.

"Oil pollution comprises a large part of the overall chemical pollution," said Professor Liu Zheng. In their Henan Province experiment zone, grass does not grow around drilling platforms and oil pipelines that cut across otherwise productive farmland.

But Liu said fungi can degrade petroleum polymers, breaking down complex hydrocarbons in the oil. The results are then fed to bacteria, which further dissolve them first into smaller molecules and then, finally, into carbon dioxide and water.

After the experiments were carried out, treated soil samples were sent to the Beijing Academy of Agriculture and Forestry Sciences for comprehensive analysis. The results confirmed that the treated soil had been retuned to normal earth that could be safely used as productive farmland.

The method has proven effective, and experts say that the polluted soil can be rendered safe after one year of treatment.