Most mainlanders are familiar with air pollution, thanks to the thick smog that frequently envelops their cities, but many are unaware of the pollution affecting the ground beneath their feet.
In fact, the soil their food is growing in is no healthier than the foul air they are breathing.
As the government said in a recent document, it is not something "to be optimistic about". But just how pessimistic people should be is beyond the government's knowledge, the government said, even though it spent1 billion yuan (HK$1.24 billion) on a national survey conducted between 2006 and 2010.
In a policy directive issued late last month, the State Council ordered local governments to "attach great importance" to soil pollution and gain a thorough knowledge of the situation by 2015. Local governments should categorise land under their jurisdiction according to soil quality and establish a database with the information by the end of next year.
The orders came seven years after the central government launched its high-profile national survey of soil quality, the results of which have never been released.
In 2006, the State Environmental Protection Administration - now the Ministry of Environmental Protection - announced that it would spend one billion yuan over three-and-a-half years to determine pollution levels in soil across the mainland and establish a soil pollution database.
It estimated that more than 10 per cent of mainland farmland was polluted and that about 12 million tonnes of grain was contaminated by heavy metals every year. There has been no official explanation as to why the survey's results have never been released.
Some suspected they were so bad the government feared their publication would threaten social stability.
Professor Tan Shuhao, who specialises in soil science at Renmin University, said soil pollutants included heavy metals, pesticides and organic matter, with heavy metals - mainly cadmium, arsenic, chromium and lead - the main pollutants on the mainland.
Industrial discharges, exhaust fumes and solid industrial waste contributed the most to heavy metal contamination of soil, Tan said, adding that the abuse of fertiliser was also a problem.
"The effective utilisation rate of fertiliser in the mainland is only 30 per cent," she said. "The rest of the nutrients end up in underground water. Some of the excess nitrogen fertiliser, the most commonly used, becomes nitrate-nitrogen - a cancer-causing chemical - and phosphate fertiliser contains heavy metals, since it's made from phosphate rock."
The recent directive says the government aims by 2015 to "regularly monitor" the soil quality of 60 per cent of farmland and all drinking water sources that serve more than 500,000 people. For the first time, it also banned agricultural production in areas classified as seriously polluted.
Huang Hongxiang , a researcher at the Chinese Academy of Agricultural Sciences and a member of the Chinese People's Political Consultative Conference, said in a proposal at last year's CPPCC session that even if Chinese scientists invented more high-yield crops, such as the super rice of Dr Yuan Longping , they were unlikely to be grown in large areas because the quality of Chinese farmland was poor.
"On Chinese farmland, soil fertility contributes only 50 per cent of agricultural production, which is 20 percentage points lower than developed countries," he said. "We're consuming more than 30 per cent of the world's fertiliser on 8 per cent of the world's farmland."
He warned that China would be unable to achieve sustainable agricultural production without improving the quality of its farmland.
Ordinary people are more worried about the effect of poor soil on food safety.
In parts of Baiyin, in Gansu province, and Baotou, in Inner Mongolia , which are notorious for heavy metal pollution, many residents have suffered mysterious bone aches and deaths from cancer are abnormally high, Caixin magazine reported last month.
Chen Nengyang , a researcher at the Guangdong Institute of Eco-environment and Soil Sciences, warned that despite the central government's latest resolution, remedial work would be difficult.
He said that to improve its soil China must first train and certify professionals in soil clean-up.
"Many companies don't have any experience in remedying soil conditions," he said. "The work is much more complicated than people imagine. Without strict examination of companies and practitioners, the very limited farmland we have will be ravaged and become worse."