China has a bagful of environmental challenges. You name it, they got it. Polluted waterways, contaminated air, greenhouse gas emissions that confound attempts to measure them - the lot. When it comes to China's land situation, we commonly focus on desertification - the exhaustion and degradation of arable farmland and its transformation into sterile desert. Now the focus is shifting - to land pollution.
Nowhere is the global push to restore degraded land likely to be more important, complex and expensive than in China, where vast swaths of the soil are contaminated by arsenic and heavy metals from mines and factories.
Scientists told the Guardian that this is likely to prove a bigger long-term problem than air and water pollution, with potentially dire consequences for food production and human health.
Zhou Jianmin, director of the China Soil Association, estimated that one-tenth of China's farmland was affected. "The country, the government and the public should realise how serious the soil pollution is," he said. "More areas are being affected, the degree of contamination is intensifying and the range of toxins is increasing."
Other estimates of soil pollution range as high as 40%, but an official risk assessment is unlikely to be made public for several years.
...Unlike in Europe where persistent organic pollutants are the main concern, Chen Tongbin of the Chinese Academy of Sciences said China's worst soil contamination is from arsenic, which is released during the mining of copper, gold and other minerals. Roughly 70% of the world's arsenic is found in China – and it is increasingly coming to the surface with horrendous consequences.
"When pollution spills cause massive die-offs of fish, the media usually blames cadmium, but that's wrong. Arsenic is responsible. This is the most dangerous chemical," he said. The country's 280,000 mines are most responsible, according to Chen.
But the land – and food chain – are also threatened by lead and heavy metals from factories and overuse of pesticides and fertilisers by farmers. The risks are only slowly becoming well known. The Economic Information Daily reported this week that pollution ruins almost 12bn kilograms of food production each year, causing economic losses of 20 billion yuan.
Cleaning up China's contaminated farmland is going to be no simple matter because most of the toxins and heavy metals arrive in airborne form.