A government study released last spring found that nearly 20 per cent of China's farmland is tainted by toxic metals and pesticides, and that pollution is making those who farm the land and consume the food grown on it sick, say environmental activists and some farmers.

The threat from pollution to China's food supply has been overshadowed by public alarm at smog and water contamination but is gaining attention following scandals over tainted rice and other crops.

The government was criticized last year when it refused to release results of a nationwide survey of soil pollution, declaring them a state secret.

This spring, it backtracked and released the study, which shows that the amount of contaminated farming soil is roughly the equivalent of all the farmland in Manitoba, Ontario, Quebec and the Maritime provinces combined.

Pesticides, metals and other toxins taint countryside

Complaints by farmers in China about lead and other pollutants in their soil and water supplies have led to protests against factories. (CBC) Industrialization has transformed China's landscape, and for some, the price of factories, mines and megacities has been high.

The explosive growth of Chinese industry, overuse of farm chemicals and lax environmental enforcement have left swathes of the countryside tainted by lead, cadmium, pesticides and other toxins.

Investigations by the Ministry of Environmental Protection have found "moderate to severe pollution" on 3.3 million hectares.

Han Jinchao is a resident in a village in Hunan province that is surrounded by toxic farming soil. He is sick and has not left his home in six years.

"My legs, I don't feel any strength. My hands are the same. It's even hard for me to carry a bowl when I eat," he said.

There is no proof that the soil is what has made Han sick, but many of his neighbours are ill, too, and they all believe it is from toxic soil.

"There are people with cancer. Also, some with diabetes. Also, many have cadmium levels that are higher than normal," said one of Han's neighbours.

High levels of cadmium in rice

Greenpeace environmental activist Wi Yixiu says the toxicity in collected rice samples is extreme.

"All the samples collected from this area were heavily contaminated by cadmium. Sometimes, the cadmium level is 20 times higher than the national standard," she said.

Chinese farmers say they are getting sick from working on polluted land. (CBC) Cadmium is a carcinogenic metal that can cause kidney damage and other health problems and can be absorbed into rice, the country's staple grain.

In May last year, authorities launched an investigation of rice mills in southern China after tests found almost half of rice supplies sold in Guangzhou, a major city, were contaminated with cadmium.

In February 2013, the newspaper Nanfang Daily reported tens of thousands of tons of cadmium-tainted rice was sold to noodle makers in southern China from 2009 to this year. It said government inspectors declared it fit only for production of non-food goods such as industrial alcohol but a trader sold most of the rice to food processors anyway.

Other toxic substances like lead and arsenic have been found in food as well, and only in the most extreme cases has the government prohibited using the land for farming.

Every consumer is vulnerable, says Greenpeace

But it will take decades before such soil is no longer toxic.

Every consumer in China is exposed to this kind of pollution. It is not just a remote issue. It can go to everyone's dining table. - Wi Yixiu, Greenpeace

The government is working on a long-range plan and expects to spend several billion dollars a year on the effort but has given few details. Scientists say one possible approach is to plant trees or other vegetation that will absorb heavy metals from the soil but will not be consumed by humans.

Complaints by farmers about lead and other pollutants in their water supplies have led to protests against battery factories.

"There have been a lot of scandals with the cadmium rice being found out in certain provinces and being sold at market," said Yixiu. "Every consumer in China is exposed to this kind of pollution. It is not just a remote issue. It can go to everyone's dining table."