BEIJING-Following a spate of metal pollution scandals around China, experts raised warning on land pollutions.

China needs to strike a balance between economic growth and safety, said experts.

"From a historical perspective, we see a growing number of land pollution cases associated with heavy metals in China over the past three decades," said Zhang Jianxin, a researcher with the Hunan Planning Institute of Land and Resources.

In Hunan province, 7,150 square km of land, or roughly 3.4 percent of the province's total area, has been contaminated by heavy metals, according to data from the Chinese Academy of Sciences.

Another recent study conducted by the Ministry of Land and Resources in Hunan identified elevated levels of heavy metals in a 250 km by 10 km belt adjacent to Dongting Lake, China's second-largest freshwater lake. Nearby crops, reeds and oysters have been found to be contaminated by cancer-causing cadmium.

Metal poisoning has also wreaked havoc in areas ranging from old industrial zones in the northeast to the economic powerhouse of Guangdong in the south.

A report from the Liaoning Provincial Committee of the Jiusan Society, one of China's non-communist parties, showed that wastewater from a zinc plant and several lead mines has caused severe land pollution in the cities of Shenyang, Jinzhou and Huludao.

In Guangdong, large amounts of farmland in the Pearl River Delta is contaminated with heavy metals discharged from information technology companies, according to a report released last year by 34 non-governmental environmental groups.

Experts say that heavy metal pollution is a side effect of China's manufacturing boom and that local governments across the country should consider creating a balance between economic development and environmental protection.

Chinese provinces have witnessed reductions in sulfur dioxide emissions and chemical oxygen demand - a measure of water pollution - as the world's second-largest economy vowed to shift away from its reliance on fossil energy and heavy industry.

However, heavy metal-related land pollution has not been taken seriously in some places, not only because it is invisible to the public in its primary stages, but also because officials put growth figures ahead of environmental protection, said Zhou Xinxin, deputy chief of the Hubei Provincial Bureau of Environmental Protection in central China.

Media reports in June last year said that the government of Leiyang, a city in Hunan province, failed to shut down a number of illegal smelting operations that had caused heavy metal pollution, in defiance of eight repeated orders from provincial authorities.

China has enacted laws against air and water pollution, but still lacks a policy framework and applicable laws to fight land pollution,  said Li Fasheng, a researcher with the Chinese Research Academy of Environmental Sciences.

Land pollution, if not brought under control, will become irreversible in a couple of years, posing serious threats to food safety and human health, he warned.

Heavy metals that accumulate in soil do not decay over time, so they are more dangerous and more difficult to remove than organic pollutants. But Chinese scientists have not yet found a method to decontaminate seriously polluted land in a fast and economical way.

"That's why provinces should launch an overhaul to find out the potential risks of metal poisoning outbreaks and start to repair land that is only moderately polluted," Li added.

The pollution has also become a source of social dissatisfaction and unrest, with the Ministry of Environmental Protection saying that metal poisoning outbreaks triggered 32 "mass incidents" in 2009.

"Some of the panics could have been avoided if governments and companies had been more transparent with the public by giving warnings and disclosing detailed information," Zhang said.

Minister of Environmental Protection Zhou Shengxian said earlier this year that "once we find a metal poisoning problem, we must solve it by giving the polluter a heavy blow as a warning sign for the likes of it."

In a plan outlined by his ministry, China will aim to cut heavy metal pollution in key areas by 15 percent by 2015.

The plan named 14 provinces and regions as major monitoring targets. A total of 4,452 companies, including mines, smelters and battery manufacturers, are on the list. In addition, local officials have been made accountable for the reduction targets.

In June this year, Daye, a central Chinese city known for its centuries-old mining and smelting industry, launched what is said to be the toughest campaign in history to crack down on polluters who left dangerous levels of cadmium, copper, lead and chromium on farmland and in a major lake.

Within two months of the crackdown's launch, 72 firms were closed and another 150 were ordered to cease production.

"Copper plants made our land infertile and water undrinkable. This campaign is what villagers have long waited for and we hope the government's resolution will not waver," said Liu Hengwen, resident of the village of Bajiaonao.