DIRTY LAND: In Wangyuan Town of Yongning County, Ningxia Hui Autonomous Region, a piece of farm land is deserted due to pollution from a local pharmaceutical factory (XINHUA)

In the old section of Suzhou, east China's Jiangsu Province, a 40-hectare piece of land has been deserted for three years. Despite its prized location, few land developers have shown an interest in it. A real estate company had considered building a high-end residential community there. However, after learning about the land's "secret," they were scared away. In fact, the soil of the land is so severely polluted that without intensive detoxification, the land is not available for development.

The extreme pollution is a legacy of the land's former owner. This tract of land is the site of the former Suzhou Chemical Factory. The factory, founded in 1956, was a large state-owned enterprise that mainly produced pesticides; it was shut down in 2006. Although the factory's warehouses and production facilities have been removed, chemicals such as chlorobenzene have saturated the soil as well as the water table in the area.

Dirty land like this tract is not exceptional in China. Statistics show that a large proportion of land in China is in poor condition due to unscientific cultivation practices and the abuse of chemical fertilizer. All in all, about 10 percent of China's land is more or less polluted.

Dirty land can trigger problems such as contaminated food as well as an increase of plant diseases and insect pests. In addition, it also inhibits crops from absorbing beneficial nutrients. "The poisonous chemical substances will eventually enter into the human body through the food chain," said Zhao Qiguo, an academician of the Chinese Academy of Sciences (CAS). Zhao is a famous soil scientist in China. He also said some chemicals can affect soil for more than 30 years.

A survey conducted by the Institute of Applied Ecology under CAS in Shenyang shows that pesticides, antibiotics and pathogenic bacteria are becoming sources of soil pollution. In China, about 20 million hectares of farm land—or 20 percent of the total farm land in China—are threatened by pollution from heavy metals including cadmium, arsenic, chromium and lead.

Some organic pollutants in the soil can also produce harmful gases that can be absorbed through the air. Experts say living around pollutants that persist in the environment for dozens of years or even a hundred years affects the immune system, causing cancers or genetic diseases.

"Strengthening soil pollution prevention has become the most important task in environmental protection. We must pay close attention to heavy metal pollution prevention, pilot projects for dirty soil purification and cleaning the polluted land in a comprehensive way," said Zhou Shengxian, Minister of Environmental Protection, at a national conference on environmental protection in 2010.

In fact, many scientists in China have already made progress in "washing" dirty land.

Invisible battle

Compared with water pollution and air pollution—to which humans are very sensitive—soil pollution is hard to identify and can often be neglected.

"Generally speaking, soil pollution and its effects on the health of humans and livestock can only be determined through examination of soil quality," said Professor Wang Shuyi, Director of the Research Institute of Environmental Law at Wuhan University. Wang is also leader of a team charged with drafting a law for prevention and control of soil contamination. According to Wang, soil, air and water are the three main elements of the human environment and almost all pollutants will ultimately contaminate soil.

Through tests and analysis of soil at different depths, scientists can learn about soil pollutants. After understanding regional hydrologic information, they can then make plans for detoxifying the soil.

"There are two main methods for treating polluted soil. One method is to deal with pollutants after the soil has been dug out and moved to another place; the other method is to treat the polluted soil in place," said Liao Xiaoyong, a researcher at the Institute of Geographic Sciences and Natural Resources Research (IGSNRR) under CAS.