BEIJING - One million tons of untreated toxic industrial waste are piling up across China, risking environmental disasters like the recently exposed case in Yunnan province, a non-governmental organization has warned.

Earlier this month it was revealed that more than 5,000 tons of chromium residue were illegally dumped on roadsides and in mountains by a chemical factory in Yunnan's Qujing city, causing the deaths of 77 head of livestock.

Official tests found "excessive sexivalent chromium" in water in the area where the waste was dumped.

Tests of the groundwater near the factory by Greenpeace, an environmental protection organization, showed that the concentration of sexivalent chromium in the water was 242 times the national standard.

Chromium residue is a heavy metal and hazardous waste residue generated in the production of chromium metal and chromium salt.

Hexavalent compounds in the residue are the most toxic. The soluble and unstable chemical may cause health problems, such as kidney and liver damage, after entering human bodies through respiration, the skin, mucous membranes and digestion of food.

The International Agency for Research on Cancer (IARC), part of the World Health Organization, lists these compounds as carcinogenic for humans.

A national remediation scheme for chromium residue pollution in 2005 showed more than 4 million tons of the chemical had been stockpiled untreated in 19 provinces. This led to official demands that the waste be disposed of safely by the end of 2010.

"Most of the waste was not properly disposed of, but directly discharged into the environment. Some of it was even dumped in important water sources and densely populated areas," reported the scheme published on the website of the National Development and Reform Commission, the country's top economic planning agency.

It also said without decontamination, chromium residue had seriously polluted surface water, groundwater and soil, and posed a huge threat to people's lives and property.

According to the 2010 Report on the State of the Environment in China, 3 million tons of the residue in seven provinces have been treated, which means there are still 1 million tons left untreated in 12 provinces.

Wang Peilin, deputy secretary-general of the China Inorganic Salts Industry Association, said in previous interviews the figure was 1.3 million tons.

"This Yunnan incident also confirmed that disposal of the waste was not completed by 2010, and was a warning for other businesses which had not completed their disposal tasks. We can no longer be sluggish in the management of waste," she said.

Official data shows China is the world's largest producer and consumer of chromium with an annual production capacity of more than 300,000 tons. The chemical is widely used for the manufacture of stainless steel, leather and bicycle parts.

"Due to outdated technology, 3 to 5 tons of hexavalent chromium are generated when producing 1 ton of chromium," said Ma Tianjie, senior toxics prevention campaigner at Greenpeace.

He said this latest contamination incident once again showed the dangers of the development model of "pollution first, treatment later".

The organization urged the government to conduct an immediate nationwide evaluation of the surrounding environment where the waste is stored, and to use all possible means to prevent the public from being exposed to the contamination.