A corner of the affordable-housing project in Wuhan, capital of Hubei province, which was found to have been built on the site of a previous chemical plant. Sun Xinming / for China Daily

Contaminated sites are becoming increasingly common in major cities, reports Li Jing in Beijing.

Soil pollution is spreading, and how to tackle it has been given priority status at the ongoing annual sessions of the National People's Congress and the Chinese People's Political Consultative Conference (CPPCC).

Environmental campaigns during the past five years primarily targeted air and water pollution, but now more attention is being given to the risks posed by contaminated soil.

Jia, who also heads the institute of fiscal science at the Ministry of Finance, said this week that land pollution already threatens the sustainability of economic growth and social stability.

Health Minister Chen Zhu said comprehensive evaluations of health risks from soil pollution are already under way.

Environmental Minister Zhou Shengxian has vowed repeatedly in recent months to strengthen efforts on curbing soil pollution during the 12th Five-Year Plan period (2011-2015).

China is already suffering direct economic losses caused by farmland pollution, which leads to reduced grain production and public questions over food safety, Jia said. In the long run, he said, land pollution will also take a toll on China's grain exports and threaten the country's ecological security.

But few people have noticed that soil pollution is not just an issue on farms, but also occurs in urban areas.

Affordable, but risky

Last November, an affordable-housing project in Wuhan, the capital of Hubei province, was found to have been built on the site of a previous chemical plant, according to news reports.

The compound, with 2,400 apartments, was constructed to meet the demand of middle- and low-income earners. Those who were qualified to purchase the property were considered lucky.

However, few of them knew their homes were constructed right where Wuhan Yangtze Chemical Plant once operated, the Beijing News reported. The project's developer didn't evaluate the site's health risks, the newspaper said.

It was not until construction was almost finished that an environmental review by China University of Geoscience discovered that the site was contaminated with antimony, a metallic element that can cause heart and lung problems, as well as with organic pollutants.

As a remedy, plastic sheeting was spread over 21,000 square meters to insulate the contaminated soil, and new soil was spread on top of the plastic. The measures cost the developer 6.8 million yuan ($1.03 million), according to the newspaper.

Local government officials said the compound is now safe to live in, but some residents aren't so sure. There's still 3,200 tons of contaminated soil buried beneath them.

'A growing concern'

Contaminated sites such as this, known as brownfields, are becoming increasingly common in major Chinese cities as urban sprawl has overrun many polluting factories, pushing them to new locations and leaving health risks behind.

In an extreme case, three construction workers were poisoned by toxic gas released from an old pesticide plant site as they drilled for Songjiazhuang metro station in Beijing in 2004.

"Pollution incidents associated with land contamination are becoming a growing concern in China," said Jian Xie, a senior environmental specialist at the World Bank. "Many brownfield sites, if not managed well, will pose an environmental and health hazard in China's most densely populated areas, as well as an obstacle to urban and economic development."

A recent study conducted by the World Bank shows that China's rapid urbanization has resulted in the need to redevelop industrial land once occupied - and contaminated - by old industries that sat on the cities' perimeters decades ago.

For instance, in Beijing, more than 100 polluting factories inside the Fourth Ring Road were relocated, leaving as much as 8 million square meters of industrial land to be redeveloped. Shanghai, Chongqing, Guangzhou and other big cities are in a similar situation.

Such sites are often heavily contaminated because pollutants leaked into the soil during previous production processes and because hazardous wastes weren't handled properly. In some cases, the concentration of pollutants in the soil can be hundreds of times higher than regulations permitted, according to the World Bank report.

Soil contamination usually involves toxic heavy metals from steel, iron and smelting plants; persistent organic pollutants (POPs) from pesticide residues; organic chemical compounds from petrochemical industries; and electronic wastes.

Heavy metals and POPs seldom break down over time and can accumulate in the environment. They can be absorbed into the body through drinking water and the food chain, causing harm to organs or even cancer.

Luo Yongming, a researcher from the Institute of Soil Science affiliated with the Chinese Academy of Sciences, said soil pollution is usually more difficult to identify than pollution in water and air. However, once the soil is contaminated, it can release toxic substances for decades.

"Redevelopment without proper remediation can be a hidden danger for people working or living on the polluted site," Luo said. For instance, volatile substances such as benzene and formaldehyde can enter the human body through breathing. And sometimes, children accidentally ingest dirt when they play on the ground.

A land pollution census conducted by the Ministry of Environmental Protection from 2007 to 2010 found that the soil quality is degrading in the country's economically well-off regions, such as the Pearl River Delta, Yangtze River Delta and Pan-Bohai Bay area, according to Jia, the CPPCC National Committee member.

Soil is already heavily polluted in some industrial zones and mining areas with heavy metals including cadmium, mercury, lead, chromium and arsenic, and with organic chemical compounds, such as oil hydrocarbons. The environmental risks are high.

Wang Yuqing, the deputy director of the CPPCC's Committee for Population, Resources and Environment, said the full results of the census will be published this year.