Protecting China’s good earth


With China’s large and expanding population, it’s inevitable that pollution has crept in

THE “cadmium rice” scandal has raised awareness of the extent of heavy metal pollution in China, but the situation in Shanghai is considerably better. Zhang Qian talks to researchers mapping city pollution. Shanghai Daily reports

Cadmium discovered in rice from Hunan Province astonished Chinese residents once again, indicating a more pervasive food safety problem and focusing attention on the dangerous levels of heavy metal soil pollution.

The discovery of the toxic, cancer-causing heavy metal in Hunan rice came to light in February in Guangzhou Province. News reports said contaminated batches had been discovered over the years.

Scientists found that no cadmium was part of any chemical additives used after the rice was harvested, thus, leaving heavy metal soil pollution as the likely cause.

Cadmium, a known carcinogen, builds up in the body and damages the kidneys, lungs and bones, causing brittle bones and pain.

It is one of several toxic heavy metals that have leached from Hunan mines, mine tailings and chemical factories into waterways, mainly the Xiangjiang River and tributaries. Water from contaminated rivers, lakes and streams is typically diverted in rice paddies where metals settle into the soil and taint the crops.

Though less obvious than air and water pollution, soil pollution is now getting unprecedented public and official attention, with the revelation of “cadmium rice.”

Pollution maps

China’s Ministry of Land and Resources is said to be working on a nationwide soil pollution map, with checks on 81 chemical indexes (including 78 chemical elements) in the topsoil and deep soil all over the country.

The Shanghai Environmental Protection Bureau is also launching a soil pollution investigation of key industrial areas in the city.

Lead, mercury, cadmium, arsenic and chromium are the top five heavy metals frequently discovered in polluted soil near industrial areas. Antimony and selenium are also found in some regions. Heavy metals are essential in electronic gadgets and their batteries.

“Soil pollution is not a new issue, the problem has existed for more than a decade. But the polluted regions are expanding at an enormous speed in recent years,” says Professor Chen Zhenlou of Resource and Environmental Science School of East China Normal University.

“Generally speaking, heavy metal soil pollution in Shanghai is not as serious as that in Hunan and Jiangxi provinces, and there is no need to worry about ‘cadmium rice’ with the relatively low content of cadmium in local soil,” says Professor Chen. However, there are polluted areas and sources of pollution date back to the days before toxic discharges were banned.

Rice quality report

About one-fifth of China’s farmland, more than 20 million hectares, is polluted by heavy metal and farmland polluted by cadmium is found in around 25 regions in 11 provinces, according to a report issued in 2010 by institutes including the Agriculture Ministry’s rice quality test center.

The report, titled “Research on China’s Rice Quality, the Safety Situation and Development of Countermeasures,” indicates that the problem is most serious in regions south of the Yangtze River, including Hunan and Jiangxi provinces.

“The problem is that the soil cannot self-purify itself from heavy metals,” says Professor Chen, “Once the heavy metal pollution happens, it stays. Even pesticides degrade in 20-30 years, but heavy metals can never degrade the natural way.”

Using irrigation water polluted by domestic sewage and industrial waste was common in the 1970s and 80s.

Irrigating with such polluted water has been banned since the 1990s, but the heavy metals discharged before that period have persisted.