Beijing: China may be sitting on a potential environmental disaster as one million tonnes of untreated toxic industrial waste has piled up across the country, non government organisations have warned.

Earlier this month, it was revealed that more than 5,000 tonnes of chromium residue were illegally dumped on roadside and in mountains by a chemical factory in Yunnan's Qujing city, causing deaths of 77 livestock, state-run China Daily reported.

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 organisation, showed that the concentration of sexivalent chromium in the water was 242 times the national standard.

Chromium residue is 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 Organisation, lists these compounds as carcinogenic for humans.

A national remediation scheme for chromium residue pollution in 2005 showed more than four million tonnes of chemical has been stockpiled in 19 provinces. It 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 dumped in important water sources and densely populated areas," said a report 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, ground water and soil posed a huge threat to people's lives and property. According to the 2010 Report on the State of the Environment in China, three million tonnes of the residue in seven provinces have been treated, which means there is still one million tonnes to be treated, the report in the daily 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 tonnes.