Mexican mine was slow to report leak, officials say
A private copper mine in north-west Mexico did not immediately alert the authorities that large quantities of a toxic chemical were spilling into a river last week, Mexican officials say.
The authorities in Sonora state said the spill only came to light the next day, after residents downstream noticed the river had turned orange.
Some 40,000 cubic metres (10 million gallons) of sulfuric acid have leaked into a tributary of the Sonora river.
The mine is owned by Grupo Mexico.
"The company deliberately concealed the accident," said Cesar Lagarda, an official at the National Water Commission, according to Mexico's La Jornada newspaper.
But the Associated Press news agency reports that Arturo Rodriguez, the head of industrial inspection for the Attorney General for Environmental Protection, said the Buenavista mine did advise his agency about the spill almost a day afterwards, just within the 24-hour time limit for filing such reports.
He said lax supervision at the mine, along with rains and construction defects, appeared to have caused the spill on 7 August, AP says.
Water supplies to 20,000 people have been cut.
Local reports say the contamination has killed fish and cattle in the area.
Lime has been dumped into the river to neutralise the acidity of the leaked chemical.
The mine is located in Cananea in Sonora state, near the US border.
More than a quarter of Mexico's mining activity is located in the north-western region, making it the country's top producer of gold, copper and graphite, according to the AFP news agency.