BEIJING -- China's pollution problems have damaged 10 million hectares, or one tenth, of the country's arable land, said the environment watchdog Tuesday as it called for expanding grass-roots monitoring staff in the rural areas.

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China faces "grave" soil pollution that jeopardizes the ecology, food safety, people's health and the sustainable development of agriculture, according to the State Environmental Protection Administration (SEPA).

It is estimated that each year 12 million tons of grain are contaminated by heavy metals in the soil, causing direct economic losses of more than 20 billion yuan (around 2.5 billion U.S. dollars), the SEPA said.

Irrigated sewage, scrap metal and acid rain are blamed for contaminated crops.

China has about 120 million hectares of arable land, 13 percent of its land area.

Despite the efforts of SEPA's 160,000 environmental officials, China's environmental picture shows little optimism.

Pollution prevention is weak, especially in the rural areas, the SEPA said, adding that there is currently no legislation concerning soil and poultry raising pollution.

Though an excess of one million factories in the country are generating pollution, there are only 50,000 environmental monitoring and inspection personnel at various levels, SEPA said.