Revealed: Mexico’s industrial boomtown is making goods for the US. Residents say they’re ‘breathing poison’

Polluting facilities in Monterrey, which has close ties to the US, are pumping toxic heavy metals into the city's air and threatening residents' health

• Leer en espanol en Quinto Elemento Lab

An industrial boom in a US manufacturing hub in Mexico is contributing to a massive air pollution crisis that is threatening residents' health, according to new research by the Guardian and Quinto Elemento Lab.

The polluting facilities in Monterrey include factories that are operated by companies from around the world - including the US, Europe, Asia and Mexico - but export largely to the US.