"Compared with air and water pollution, soil pollution is more difficult to control and remedy, taking a much longer time and needing more resources," said Chen Tongbin, research fellow with the Institute of Geographic Sciences and Natural Resources Research with the Chinese Academy of Sciences.

Twenty years ago, almost no one knew about soil pollution, and even today, many people are not fully aware of the severity of the problem, he said.

According to Chen, soil pollution is more hidden than air and water pollution.

"When a piece of land is polluted, it is usually hard to discover and sometimes it takes as much as 50 years for the problem to be found," he said.

SEARCH FOR A REMEDY

Chinese Premier Li Keqiang declared war on pollution during the March parliamentary session and pledged to fight it with the same determination the country battled poverty.

Following Li's words, a plan was passed in April to set up pilot projects in six heavily polluted regions, according to the Ministry of Environmental Protection. The government will allocate more than 1 billion yuan to each demonstration pilot to support soil pollution treatment.

The plan, together with a soil pollution law in the drafting stage, is expected to focus on protecting food supplies and ensuring that contaminated crops do not enter the food chain.

However, the pilot projects are small and cannot begin to redress the extent of the problem, according to experts. One of the major concerns is who will eventually pay for clearing up polluted soil.

Lan Hong, professor at Renmin University of China, said that the "polluter pays" principle has always been taken as an iron law for pollution treatment, but soil pollution has a long incubation period and many of its polluters are hard to find.

"Farmers who themselves are already victims of soil pollution should not be responsible for treating the problem, and it is necessary for the government to establish a special fund for soil remediation," he said.

Chen Tongbin is now studying phytoremediation, the engineered use of green plants to clean up contaminated soil.

"At present, foreign countries also lack successful experience in restoring polluted farmland on a large scale," he said. "New green methods that cause no secondary pollution are the way forward to treating soil pollution."

Wu Longhua, researcher with Nanjing soil research institute of the Chinese Academy of Sciences, said phytoremediation is still in a research and trial stage, and it also faces severe challenges, such as improving treatment efficiency, lowering costs and deciding who will pay for the treatment.