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

An industrial boom in Monterrey, Mexico’s manufacturing hub linked closely to US supply chains, is fuelling a severe air pollution crisis that local residents say is making them “breathe poison,” according to an investigation by the Guardian and Quinto Elemento Lab. Factories operating in the city—many owned by multinational corporations from the US, Europe, and Asia—are emitting levels of toxic heavy metals and carbon dioxide that surpass those reported in numerous US states and even exceed national emissions of nearly half the world’s countries. Data shows Monterrey’s fine-particulate pollution now ranks as the worst among metropolitan areas in North America, with daily exposure levels roughly double those in Los Angeles and, on particularly bad days, comparable to the most polluted cities globally.

The city, home to 5.3 million people just 150 miles south of the Texas border, has seen its urban footprint quadruple since 1990, transforming into a high-output industrial center. While vehicles and small businesses contribute to the pollution burden, government estimates attribute around 60 percent of harmful emissions to large industrial sources, including privately owned factories and public energy plants. These facilities produce goods destined for the US market—such as tractors, glassware, baked goods, and even recycled toxic waste sent from American facilities—raising concerns about the environmental and health costs borne by Mexican communities to sustain cross-border commerce.

Long-term exposure to such fine particulate matter is associated with thousands of premature deaths annually in the region. Yet despite this growing crisis, Monterrey remains one of the few major metropolitan areas in North America where air quality has not improved significantly in recent years, even as other cities report substantial reductions in harmful pollutants. Residents have taken to the streets in protest, holding signs that read “We want to breathe” and demanding government intervention. Environmental activist Aldo Salazar described the irony of only realizing the scale of pollution after hiking into the surrounding mountains, where he could look down on a persistent gray smog layer enveloping the city below—often obscuring the very peaks that frame the valley.

With industrial expansion continuing unchecked, the health toll is expected to rise unless regulatory action is taken. The findings underscore a troubling paradox: while Monterrey’s factories power global supply chains, their toxic output is poisoning the air that sustains the very communities producing goods for American consumers. The case highlights the urgent need for coordinated environmental oversight across borders to ensure that industrial progress does not come at the irreversible cost of public health.