BEIJING (Reuters) - A spill from a tailings dam at a molybdenum mine in northeast China on Saturday has contaminated water up to 110 km (68 miles) downstream, environmental authorities said on Wednesday.
Tailings dams are commonly used by mining firms to store waste remnants of ore but they have come under close scrutiny since the collapse of one in Brazil last year killed more than 250 people.
In China's Heilongjiang province on Saturday, water containing waste molybdenum ore - mined for the metal used in stainless steel and tools - flowed out of a tailings pond belonging to Yichun Luming Mining Co Ltd and into a river system.
There were no casualties reported.
Testing of water in the Hulan river some 110 km southwest of the mining site in Yichun showed the molybdenum content was 2.8 times higher than standard levels on Tuesday, Heilongjiang's department of ecology and environment said.
The Hulan flows into the Songhua river, the fifth-longest in China, in a northern district of provincial capital Harbin.
The petroleum content was 1.4 times above standard levels at the same spot and the chemical oxygen demand (COD) - a measure of water quality - was 5.7 times higher. A high COD reading indicates a greater threat to aquatic life.
"Molybdenum itself is not toxic. The issue with tailing water is the flotation agent - oil," one molybdenum industry source said. Flotation agents are used to help extract minerals from ore.
Levels were even higher closer to the spill site, the readings published by the Heilongjiang environmental department showed.
A report posted on the website of the Ministry of Ecology and Environment said 2.53 million cubic metres of waste had been discharged from the tailings pond. The official Xinhua news agency said the leak was plugged on Tuesday.
Yichun Luming Mining, a subsidiary of state-run China Railway Resources Group, did not immediately respond to a request for comment on the production status of its mine.
"Nowadays, most risks from tailing ponds have been brought to the attention of regulatory bodies," said Ada Kong, head of Greenpeace East Asia's toxics campaign. "Yet tailing ponds and dams are ticking bombs due to their sheer volume, and the challenge to local authorities is still significant."
(Reporting by Tom Daly; Editing by David Clarke)