AFP/Mexico City

Authorities in Mexico said Monday they have closed about 80 schools after sulphuric acid leaked from a copper mine in the country’s northwest and contaminated the Sonora River.

“About 5,000 students from around 80 schools will not have classes this week because of a lack of water and in some locations their proximity to the river,” said the director of the Sonora state civil protection agency, Jesus Arias.

On August 6, some 40,000cu m of sulphuric acid used to dissolve copper from ore for processing leaked out of a holding tank at the Buenavista copper mine, one of the largest in the world.

The chemical turned a 60km stretch of the Sonora River orange, causing authorities to shut off the municipal water supply to 20,000 people in seven towns.

The mine has poured tons of lime into the river to neutralize the acidity, but experts warn the water supply still poses a health risk because sulphuric acid releases heavy metals from the surrounding environment.

Potential risks for the local population include cancer, genetic deformities and developmental problems in children.

The government and the mine, which is owned by Latin American mining giant Grupo Mexico, say they have distributed 4mn litres of water to most of the affected communities.

The mine produces 200,000 tonnes of copper a year, and is seeking to increase annual output to 510,000 tonnes by 2016 with a $3.2bn investment.

Prosecutors have said it could face a $224,000 fine for the leak.