More than 100 people have been made ill by the spillage of a toxic copper concentrate produced at one of Peru's biggest mines.
The Ancash state regional health office said 140 people were treated for "irritative symptoms caused by the inhalation of toxins" after a pipeline carrying the concentrate under high pressure burst open in their community.
Most of the injured had joined in efforts to prevent liquid copper slurry from reaching a nearby river after the pipeline linking the Antamina copper mine to the coast ruptured last week in the village of Santa Rosa de Cajacay, said the community's president, Hilario Moran.
The people used absorbent fabric provided by the mine but were not given gloves or protective masks, said Antonio Mendoza, the mine's environmental director. Shortly afterwards, people became ill, vomiting, suffering headaches and nosebleeds.
"That's unethical and irresponsible and they should know better," Greg Moller, a professor of environmental chemistry and toxicology at the University of Idaho-Washington State University, said of the mining company's enlisting villagers in the clean-up without proper protective gear.
Mr Mendoza said the substance that spilled "was not necessarily toxic". "It's a dangerous substance to the extent that it's an industrial substance," he said. "They are dangerous substances that require a particular handling but aren't necessarily toxic."
But Prof Moller said: "This was actually a toxic episode and these people are intoxicated." He added that the alkaline copper concentrate probably damaged lung tissue, causing chemical burns. He said it was his understanding that the rupture released a mist of concentrate, which could have created a fine cloud of toxic airborne particles. "There are a lot of chemical and physical irritants in that mix," he said.
About 30 people were taken to the San Pablo hospital in the highlands regional capital of Huaraz immediately after the July 25 rupture, Mr Moran said. "Some people continue to get sick and continue to go to Huaraz," he added. Meanwhile, the director of the private San Pablo hospital, Raul Guisse, refused to say how many patients were being treated there. Peru's Civil Defence agency said on July 28 that five children under 10 were among the sick.
Mr Moran said Antamina was paying the health care costs of those sickened by the spill. Antamina is a consortium that includes some of the world's biggest mining multinationals, BHP Billiton of Australia, Xstrata of Switzerland, TECK Cominco of Canada and Mitsubishi of Japan.
Peru's Environment Ministry has said it will release details of medical examinations of the victims.