A NEW TREATMENT: Workers bury heavy metal-polluted soil mixed with some kind of chemical reagent into a purification pit in Baiyin City, Gansu Province, on October 16, 2011 (NIE JIANJIANG)

A toxic-cadmium spill in January left 3.7 million residents in Liuzhou City in south China's Guangxi Zhuang Autonomous Region struggling to find a secure supply of drinking water.

Contamination was first detected in the Longjiang River on January 15 when hundreds of dead fish were discovered in the river's upper reaches. The river is a major tributary of the Liujiang River that runs through Liuzhou.

The Environmental Protection Bureau of Hechi, a city upstream on the Longjiang River, tested local water and discovered cadmium levels higher than those permitted by national safety standards. In the worst-hit areas, water samples indicated that cadmium levels were 80 times higher than permitted levels.

Experts with a task force charged with tackling the pollution estimated that about 20 tons of cadmium had been discharged into the Longjiang River, polluting a 300-km stretch of water.

Cadmium is a highly toxic heavy metal used in batteries, electroplating and some industrial paints. Overexposure can lead to fatal liver and kidney damage.

"The metal will have a long-lasting environmental impact on local fish and soil when it sinks into the riverbed," said Li Li, a researcher with the Chinese Research Academy of Environmental Sciences.

The incident has led to an overhaul of factories and facilities that use heavy metals along the Longjiang River. Investigators have identified Guangxi Jinhe Mining Co. Ltd. and the Hongquan Lithopone Materials Plant as the primary suspects behind the illegal discharge of cadmium. As of February 15, nine people were detained on suspicion they were responsible for the contamination.

Initial investigations show that a lack of pollution treatment facilities, the illegal discharge of toxic sewage and poor supervision by local authorities were the primary causes for the spill.

Ma Jun, Director of the Institute of Public and Environmental Affairs (IPEA), a Beijing-based environmental NGO, said that the pollution was a warning for Hechi, one of the country's most important mineral producing centers, to tighten regulation of the industry.

"Lack of proper monitoring in mines poses a threat to local people's health and damages the environment," Ma said.

Yet, the cadmium spill is just one of a series of major heavy metal pollution incidents reported in recent years.

Statistics from the Ministry of Environmental Protection (MEP) show that more than 30 serious cases of heavy metal pollution by chemical, photovoltaic, pharmaceutical and IT companies have taken place in 10 provinces across the country since 2009.

"Heavy metals have become one of the country's main pollutants, seriously threatening public health," Minister of Environmental Protection Zhou Shengxian said in a report to the Standing Committee of the National People's Congress, China's top legislature, on October 25 last year.

A growing threat

Heavy metals refer to a broad group of toxic elements such as cadmium, lead and chromium, most of which are extremely dangerous and can cause a range of ailments, from diseases of the central nervous system, to problems with internal organs, the skin, bones, and teeth. Unlike organic pollutants, heavy metals do not decay and thus pose a long-term threat to people and the environment.

Heavy metal contamination has become a serious problem in China's industrial regions. Although the government has invested heavily in efforts to curb spills and introduce safer handling of toxic substances, major incidents of heavy metal pollution remain regular occurrences.

A spate of lead poisoning cases and reports of cadmium-contaminated rice in recent years have further pushed the issue of heavy metal into the spotlight.