Mexican authorities say the mining company behind last week’s acid spill may have hidden the accident for several days, potentially endangering thousands of nearby residents and impeding cleanup efforts.
Residents and officials in the northern Sonora state were shocked when it was revealed last week that a catastrophic spill from the Buenavista copper mine had released more than 10 million gallons (40,000 cubic meters) of contaminated water into the Bacanuchi River, turning the river orange.
However, the Mexican water authority Conagua announced Tuesday that the spill may have happened as early as Wednesday, August 6, but that Grupo México, the mine’s owners, had deliberately kept the information from the public until residents reported the spill to authorities on Sunday.
Jorge Andrés Suilo Orozco, Sonora’s federal environmental ministry representative, told BBC Mundo that local representatives in the affected town of Arizpe were the first to inform civil defense authorities about the spill.
By Sunday, when state and federal officials finally became aware of the accident, the spill had already spread along more than 37 miles of the river, passing six towns and approaching the state capital of Hermosillo.
César Alfonso Lagarda, the Sonora representative of the National Water Commission (Conagua), said experts had detected potentially dangerous levels of heavy metals — including arsenic, cadmium, aluminum, iron, nickel and copper — in the contaminated river water. Lagarda warned that ingestion or contact with some of these elements could result in intestinal problems, skin irritation and other potential long-term health issues.
Residents are already reporting that fish and other animals living in and near the river have died as a result of the contamination.
The Bacanuchi River feeds into the 261-mile (420 km) Sonora River, which provides water for much of the northern border state’s population.
Water services were initially restricted in seven towns, affecting more than 20,000 of the area’s residents. On Sunday, Conagua also cut some water services to Hermosillo, a city of more than 800,000, even though just 3 percent of the city’s water comes from Sonora.
Grupo México has blamed a “structural failure” for the flood, saying a tube burst in a reservoir used for storing copper sulfate, releasing the acid into the nearby water supply. The company has not released any further comment on the accident.
Mexican authorities say they will enforce penalties against the company for the accident itself as well as the delayed response. The government will also investigate if the company was negligent in failing to inform authorities in a timely manner.
The spill comes just days after Mexican President Enrique Peña Nieto signed a new law opening up much of Mexico’s energy sector to private and foreign companies.
Sonora, one of the primary mining zones in Mexico, accounts for about a third of the country’s total mining production. The state is Mexico’s main producer of gold, copper and graphite.
The town of Cananea, where the Buenavista mine is located, is about 25 miles south of the Mexico-U.S. border.