BEIJING - Environmental experts warn China's food safety has been undermined by worsening farm land pollution from industrial pollutants and overuse of pesticides and fertilizers.

Pollution from poisonous chemicals and heavy metals had spread from land in cities to farm land and affected quality of crops and plants, a Nanjing Agricultural University professor Pan Genxing, who has long researched farm land environment, said in a recent interview with Xinhua.

Research of the Chinese Academy of Agricultural Sciences indicated about 16 percent of China's 120 million hectares of farm land had suffered from pollution at different levels and 10 million hectares were polluted by industrial pollutants.

The pollution was mainly caused by heavy metals and chemicals discharged by industrial projects and improperly disposed electronic and plastic waste, Pan said.

"The situation is worsening and might last for another three decades," he said.

Shan Yanhong, a researcher with the Nanjing Institute of Environmental Sciences under the Ministry of Environmental Protection, said, about half of the farm land in South China had been polluted by heavy metals such as cadmium, arsenic and mercury as well as petroleum organic compounds, while about 10 percent of the farm land in the Yangtze River Delta was barren due to heavy metal pollution. Both regions were the country's major industrial zones.

The country reported about 30 serious heavy metal pollution incidents in the past three years, including one in Liuyang of Central China's Hunan Province in 2009, in which cadmium-containing pollutants from a chemical plant affected more than 500 people and polluted the land within a radius of 500 to 1,200 meters of the plant.

"The pollution of such a level can usually not be self-cleaned by the land and pollutants will stay in the soil for hundreds of years without proper treatment," Pan said. "Sometimes the damage is irreversible."

Rampant use of pesticides and fertilizers worsened the situation.

Pesticide dosage reached about 1.3 million tons annually in China, 2.5 times of the world's average, Zhang Weili, a researcher with the Chinese Academy of Agricultural Sciences, said.

Du Guide, who heads the monitoring station of the Heilongjiang Provincial Agricultural Department, said, research showed that only 30 percent of pesticides and fertilizers worked to kill pests and benefited crops while the rest 70 percent were wasted and polluted the soil.

Pesticides also kill earthworms and frogs which can help the earth self-clean, Prof Pan said.

Experts strongly urged the government to reconsider the economic growth pattern that ignored environmental costs.

Although the central government has listed restructuring of economic growth pattern as its major target in the coming years, a number of local governments prefer pretty growth figures and some even try to cover up for polluters.

Zhang Weili suggested that more efforts should be made to encourage farmers to protect soil.

The state owns the land and farmers obtain land use rights through signing contracts with villages.

Since the land use rights can change hands every several years, farmers would not invest in protecting the soil, Zhang said.

In April, the Ministry of Land and Resources announced to invest 600 billion yuan ($9.52 billion) in treating 27 million hectares of the polluted and less productive farm land by 2015.