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’ healthLeer en español en Quinto Elemento LabAn 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. Continue reading...
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.And the facilities are pumping more toxic heavy metals into the city’s air than the totals reported in many US states, the analysis finds for the first time, as well as more earth-warming carbon dioxide than nearly half the nations in the world.The industrial pollution in Monterrey, a metro area of 5.3 million people that is 150 miles (241km) from the Texas border, has contributed to it ranking as the metro with the worst fine-particulate air pollution in Mexico, the US or Canada in a recent study that looked at trends up to 2019.The problem persists. On a daily basis, residents here live with about twice the levels of fine particulate air pollution as those in Los Angeles, which has long been the most polluted major metro in the US. And on bad days, the area sometimes has among the worst pollution levels in the world.Long-term exposure to this kind of air pollution has been linked to thousands of deaths per year in the area.Monterrey is one of the only major metro areas in the three nations where such air pollution has remained stubbornly high, at a time when most cities are accomplishing vast reductions in harmful pollutants.The findings come as residents have mounted protests about the air quality in Monterrey, with some carrying signs saying “We want to breathe” and demanding that the federal government take action.“You have to wonder: How are we not suffocating?” said Aldo Salazar, an environmental activist, who said he didn’t realize he was living in a fishbowl of pollution until he began hiking into the mountains that surround Monterrey, where he could stand in the clear sunshine and look down at the gray basin of smog beneath him. The mountains themselves are frequently not visible from the city owing to the dirty air.About 40 residents in a neighborhood in San Nicolás de los Garza protested near the Zinc Nacional recycling plant on 20 April 2025. They demanded the cease of operations of the company in this area. Photograph: El NorteThe Monterrey urban area has quadrupled in size since 1990 as it has become an industrial boomtown. And although vehicles and small businesses also contribute to pollution, about 60% comes from industrial emitters, including privately owned factories and public energy plants, according to a government estimate. This pollution consists of fine particles that are harmful if inhaled, and can include small quantities of dangerous metals.Many of the major factories in Monterrey produce goods that go to the US market – ranging from tractors and beer mugs to chocolate cookies – or recycle toxic waste and scrap metal sent from the US, the research shows. Among the top emitters are factories that recycle US car batteries and hazardous waste, and those that ship finished products back to the US.In one example, the analysis found that a single European steel company reported emitting more lead – which can cause brain damage in children – into the air in a year than all the companies combined in the New York/New Jersey metropolitan area, the most populous metro in the US. The company acknowledged these emissions but said future reports would show less pollution.The analysis also revealed that some facilities in Monterrey emit carcinogenic cadmium and arsenic at levels that are rarely reported in densely populated areas of the US.Top Mexican officials have promised to address air-quality problems in Monterrey. Alicia Bárcena, Mexico’s secretary of environment and natural resources, said in a statement to the Guardian and Quinto Elemento Lab that her administration is aware there is a problem with pollution and “actions are being taken to address this,” including updating emissions standards and improving industrial monitoring. She added that “there is a long-term trend towards improvement” in pollution levels.A view of the Santa Catarina river and Fundidora park in the city of Monterrey, seen with pollution on 19 November 2024 and without pollution on 2 November 2025. The mountains of the Sierra Madre (left) and Cerro de las Mitras (right) sometimes disappear from sight in days with bad air.Credit: José Villasaez, El NorteMexican President Claudia Sheinbaum said in July that she was awaiting research about Monterrey’s air pollution that was being coordinated by the “best scientists in our country on these issues”, and which would show “who is polluting, how much they are polluting and where they are polluting.”While industry representatives argue that facilities serving the US market have modern and effective pollution controls, some experts say the industrial growth in Monterrey may come at the price of residents’ health and lives.“Monterrey is paying a price for being too aggressive in getting foreign investment,” said Rafael Fernández de Castro, director of the Center for US-Mexican Studies at the University of California San Diego.“This will backfire,” he said. “Because this pollution is going to result in a big-time impact on public health. The remedy is going to be very, very costly and it will offset the short-term benefits of this very hot market that is Monterrey.”Polluting plants operate in highly populated areasTo find the top industrial polluters, the Guardian and Quinto Elemento Lab combed through emissions reports for thousands of facilities, which journalists obtained through records requests and government databases, as well as a leaked government inventory.The emissions reports used in this investigation, which companies self-report to the Mexican government, are not complete. There are gaps for certain plants, pollution types and years. But they provide an overall picture of what the companies themselves say they are pumping into the air.The investigation revealed that Monterrey contains a huge number of polluting industrial plants operating in highly populated areas. Particularly troubling were some that report emitting large amounts of heavy metals into dense, urban neighborhoods.Producers of metals, glass, ceramics and cement, as well as power plants and a government-run refinery, dominate the emissions reports.Chronic exposure to even small quantities of the heavy metals have been shown to cause an array of health effects like kidney dysfunction, nervous system disorders, birth defects, and cancer, as well as causing increases in learning disabilities and behavior problems in children that can affect the economic prospects of an entire population.The US has cracked down on air emissions of these metals due to their very harmful effects. But evidence suggests Mexican residents near plants making and recycling goods for US customers are still breathing in lead, cadmium and arsenic.The emissions numbers for each heavy metal are striking.Lead emissions more than that of all companies in many US statesPlants in Monterrey reported releasing a total of 4,362lbs (1979kg) of toxic lead into the air per year on average between 2021 and 2023 – more than all the companies in many US states.Top emitters in recent years included two steel plants and a half dozen companies that recycle old car batteries, often shipped down from the US. Among these is US company Clarios, which owns five plants that reported lead emissions in the Monterrey area.In response to questions, the company did not dispute its emissions but said that it operates “in full compliance with – and often exceed[s] – the environmental, health, and safety regulations in Mexico.”In another example, Ternium, a steel company headquartered in Luxemburg that supplies metals crucial to the North American auto industry, reported releasing over 1,000lbs (458kg) of lead into the air in 2023 from a factory in a crowded Monterrey neighborhood. That is more than all companies combined in the New York/New Jersey metropolitan area, the United States’ most populous metro.Ternium said that its treatment system captures 99% of lead emissions, and that its forthcoming lead and cadmium reports would show substantial decreases. “If we compare our emissions, they are similar to or lower than those reported by steel plants in the United States and Europe,” the company said.Hazardous cadmium emissionsIn the case of cadmium, which is considered even more hazardous because of its significant carcinogenic potential, facilities here reported emitting a total of 301lbs (137kg) in the average year.A general view shows Mexican state oil firm Pemex’s refinery in Cadereyta, on the outskirts of Monterrey, Mexico, in 2021. Photograph: Daniel Becerril/ReutersThat is more than in all but four places in the US – but those places are mostly rural locations far from dense populations, such as in Alaska’s Northwest Arctic Borough. The only place where comparably large amounts of cadmium were emitted near an urban population in the US was around two solar panel plants that are 10 miles (16km) south of Toledo, Ohio.Top emitters included zinc and steel plants, and power plants providing electricity to the city.US-owned glass producer Crisa Libbey reported emitting 45lbs (20kg) of cadmium into the air. The company did not respond to requests for comment.Top arsenic emittersMeanwhile, facilities reported emitting 66lbs (30kg) of arsenic per year into the air.Zinc Nacional, which recycles steel dust sent from the US to recover zinc, was the largest reporter in this category in recent years.It recycles US hazardous waste in a tightly packed neighborhood and has reported emitting about 20lbs (9kg) of arsenic per year since 2017.By comparison, most plants that emit large amounts of arsenic in the US operate well away from large urban populations. Only one US plant that reports arsenic at these levels operates in a dense neighborhood in a major metropolitan area – the US Steel plant in Gary, Indiana.Zinc Nacional disputed that its emissions are this large. It said that its reports are only estimates that do not take into account its pollution-control technologies and that “our actual emissions are considerably lower.”Zinc Nacional plant seen in Monterrey, Nuevo Leon, on 13 September 2024. Photograph: Bernardo De Niz/The GuardianAn industry group, the Institute for the Environmental Protection of Nuevo León, which advises Zinc Nacional and many other major Monterrey companies went further, saying in a statement that emissions reports submitted to the Mexican government “may include materials retained in filters or chimneys, or treated” and should only be used as “trend indicators”.However under the law, “only what is emitted into the air should be reported, without considering what is retained by the control equipment,” said an official from the Mexican environmental regulator, Semarnat.Other top arsenic emitters included the multinational cement company Cemex, a refinery and several energy plants.Cemex said that it is in full compliance with regulations and is investing in technologies to reduce its emissions, including using real-time air monitors and drones to detect and control any increased emissions. The company has “a long history of seriously embracing our environmental commitment.”Overall, about 40% of the heavy metals emissions reported came from a handful of companies operating plants within 5 miles (8km) of each other in the most densely populated area of Monterrey, called San Nicolás de los Garza. Its population of mostly working-class residents has exploded over the years.“Many of these factories have been there for 80 or 90 years and now they are absolutely surrounded by people living there, so that makes this problem a lot bigger,” said Glen Villarreal Zambrano, a state legislator who lives in the area and was, until recently, the head of the Nuevo León parks and wildlife department.“We are victims of our own success,” he said. “We have economic growth – now we have to put order to it.”‘We’re breathing in a capsule of poison’The health consequences are becoming increasingly clear to residents. Chronic exposure to fine particulate air pollution causes as many as 2,500 deaths every year in the Monterrey metropolitan region, as well as contributing to a multitude of chronic ailments, ranging from respiratory and neurological problems and cancer, according to a 2023 study issued by the state of Nuevo León.Guadalupe Rodríguez, director of the regional public nursery school system, has long worried about the effects of Monterrey’s air pollution on her young students. On the worst air quality days, when winds pick up dust to mix with the industrial pollution, monitors hung in the rafters of schools scattered around the city report air quality levels so high that they are symbolized with pictures of children wearing old-fashioned gas masks.Guadalupe Rodríguez, director of the regional public nursery school system, organized lead testing for all the children in her schools. Photograph: El Norte“We’re breathing in a capsule of poison throughout the entire metropolitan area,” she said. “Out of a school month, I’d say we get five good days and 15 bad ones”.She says about half the children, from infants to six year olds, suffer some kind of health condition, including repeated respiratory infections and allergies. She is also concerned about high rates of autism among her students.But it wasn’t until the Guardian and Quinto Elemento Lab published an investigation in January into Zinc Nacional that she was able to organize lead testing for all the children in her schools.That investigation revealed heavy metals contamination in homes and schools surrounding Zinc Nacional, which recycles hazardous waste from the US steel industry.Children play at a school in the municipality of San Nicolás de los Garza, near numerous facilities that have reported large emissions of heavy metals, in September 2024. Photograph: Bernardo De Niz/The GuardianZinc Nacional responded that the investigation was based on a study “that lacks scientific validity and institutional backing”. It said that its recycling process is crucial. “If these materials were not recycled, they would end up landfilled or released into the environment, posing real ecological risks”This spring medical teams began showing up at nine nursery schools to prick the fingers of children three to six years old whose parents signed up for the testing, which is ongoing.Rodríguez, who is also a state legislator, said she and other environmental activists have been trying to draw attention to the worsening air pollution problems for years, without tangible results.“There are laws, but they aren’t enforced,” she said.Guadalupe Martínez, 63, lived for 30 years in a neighborhood that sits in near several of the plants reporting the highest heavy metal emissions in the region.One morning in 2021, she began coughing and spitting up blood and her children took her to the emergency room, according to Martínez and her son. Her condition was so critical that she spent six months in an induced coma and more than a year in the hospital. Today she can barely speak because of her tracheotomy tube and is dependent on oxygen and constant care.“I don’t drink, I don’t smoke, I don’t stay up late,” said Martínez, whose family now wonders if living in the midst of so much pollution might have affected her health.Ricardo González and his mother, Guadalupe Martínez, who depends on oxygen and wonders whether living near several of the plants reporting the highest heavy metal emissions in the region has affected her health. Photograph: Courtesy of El NorteHer son, local attorney Ricardo González, is taking legal steps to demand that the government investigate the health effects of pollution in the urban area.“The authorities are failing to fulfil their duty to guarantee legal, physical and material safety for the people,” he said. “And by doing so, they are enabling and allowing the population to be poisoned.“CO2 emissions and outdated environmental regulationsThe Guardian and Quinto Elemento Lab investigation also examined the region’s top emitters of carbon dioxide, a measure which shows not only how much of this global-warming gas each factory is sending into the atmosphere, but is often also an indicator of air pollution.In 2022, the roughly 200 plants that reported their annual CO2 releases in Monterrey emitted more of the greenhouse gas than more than 100 countries, and were similar to Paraguay, Panama and Costa Rica.One of the highest emitters in recent years was the Cadereyta refinery, run by Mexico’s state-owned oil company Petróleos Mexicanos (Pemex). The plant can also be seen from satellites in space as one of the biggest emitters in the world of sulphur dioxide, which contributes to smog.The company did not respond to a request for comment.Experts said Pemex emissions have worsened in recent years, as the previous presidential administration ramped up processing of dirtier oil. Mexico’s refineries, including the nearly 50-year-old Cadereyta, are in a poor state of repair.The Cadereyta refinery has been “operating purely on inertia, without filters or anti-pollution measures – it simply degraded into what we’re seeing now”, said Gonzalo Monroy, an energy consultant.Since 2015, investment in refinery maintenance has decreased dramatically.“Most of the sulfur [capturing equipment] in the refineries and in the gas processing plants in Mexico are out of operation for lack of maintenance”, said Francisco José Barnés de Castro, an oil industry expert and former head of the Mexican Petroleum Institute.The Guardian and Quinto Elemento Lab investigation also raised concerns about the effectiveness of Mexico’s environmental regulation of industrial facilities.Companies that would face tight air pollution regulation in the US are able to operate under decades-old Mexican environmental standards. These “are a real disgrace”, said Samuel García, the governor of Nuevo León, Monterrey’s home state, in a social media post this summer. They allow thresholds for air and heavy metals pollution that are “extremely high”.Additionally, emissions records for toxic chemicals at many facilities are missing, while others are removed from the record by the Mexican environmental regulator because of doubts about their accuracy.A ‘circular economy’ gone awry?Experts say the city’s relationship as a supplier to the US is crucial in explaining the pollution crisis. Monterrey has long prided itself on its entrepreneurial spirit and centuries-long history of teaming up with US businesses.Monterrey is still a place “where the factory, the facility, the smokestack is a source of pride,” said Eduardo Enrique Aguilar, a professor of political economics at University of Monterrey.But he said, since the North American Free Trade Agreement opened the trade borders between the US and Mexico in the 1990s, Monterrey has seen an over-accumulation of factories.“They come here, pay very low wages, and offload all the environmental harm – which is ultimately borne by us, by the people who live here,” said Aguilar.Since 2006, international exports from the metro have tripled. About 90% in sales go to the US – totalling at least $46bn dollars in 2024.As part of this manufacturing boom, he said the region has become a “recycling hub” for the US companies, who want to process US waste into new goods in what is now dubbed “the circular economy.”Some of the highest emissions figures found by the Guardian and Quinto Elemento Lab came from factories recycling waste and scrap exported out of the US for Mexican companies to process and use as raw materials.These imports included hazardous waste from the US, including toxic steel dust and millions of old car batteries.But Monterrey also receives vast quantities of everyday recycling that US consumers throw into their bins, including household paper recycling, and nearly 2m metric tons a year of scrap metal.“Ultimately, the United States has to send its waste somewhere, and clearly, there was already infrastructure here – highways, energy usage, and technological capacity,” said Aguilar, who said the pollution it foists upon the population is “a real injustice.”But an industry group, advising Ternium, Zinc Nacional, Clarios and numerous other large companies on environmental issues, pointed to Monterrey’s role in recycling US materials as an environmental benefit to the planet.“These are not uncontrolled wastes, but valuable inputs that are reprocessed under federal permits and supervision,” the group, Instituto para la Protección Ambiental de Nuevo León, said in a statement. Recycling can “replace primary mining, reduce global emissions and deforestation, and promote the circular economy.”The group said that Monterrey’s industrial boom has been accompanied by hundreds of millions of dollars in investments in environmental improvements in the region.“The industrial boom and nearshoring have gone hand in hand with an unprecedented process of industrial modernization in environmental matters,” it said.‘Mexico is not the trash dump for the US’Calls for action on the industrial pollution problems have intensified since the journalistic investigation earlier this year.Neighbors have staged several protests outside the Zinc Nacional plant, with signs such as “Mexico is not the trash dump for the United States”, and government officials have instituted five different temporary closures of the plant. The company announced it would move some of its operations elsewhere. (It said it followed all applicable regulations, and that the wellbeing of the community was a priority.)State and federal officials have responded by saying they will crack down on industrial polluters citywide.“The metropolitan area of Monterrey is one of the most polluted regions in terms of air quality in our country,” said Mariana Boy Tamborrell, the federal attorney for environmental protection, appointed last fall, who said her agency plans to step up inspections and sampling to make sure industry complies with the laws.“We want to prevent companies from merely simulating compliance or engaging in greenwashing,” Boy Tamborrell added.García,Nuevo León’s governor, has amplified that message in various statements this summer, saying that “there will be zero tolerance” for those who pollute and that “industry has completely failed” to handle pollution.But Hugo Barrera, an air pollution researcher, said solutions might not come so easily. His organization, the Mario Molina Center for Energy and Environment, has recommended that government and industry should work together to relocate polluting factories outside the urban area.But companies “don’t seem interested”, he said. “It’s very costly to move industry, and it’s both politically and economically difficult.”Ultimately, activists hope the huge groundswell of public anger that has now built around the air pollution issue in Monterrey will spark meaningful improvements.“If people don’t know the air is dangerous, the government doesn’t have to act,” said Vivianne Clariond, who is pushing for the government to do something about the smog.Clariond’s own background is a sign of how broad the movement has become. Her grandfather founded a major steel mill, which was later bought by the international conglomerate Ternium and is now considered one the biggest polluters in the city. She is also the daughter of a former governor, and has herself served as a councilor in local government.People take part in a protest demanding the closure of the Pemex refinery, blaming it for polluting the air, in Monterrey, Mexico, on 28 January 2024. Photograph: Daniel Becerril/ReutersNow a wide array of Monterrey residents – from the affluent to the working class – are joining the fight to reduce pollution. And many hope that Sheinbaum, a trained climate scientist, will take up the cause and make the changes to environmental law and enforcement that will be needed to improve the situation.“What we need is someone with the guts to act,” Clariond said. “When Mexico City was the most polluted city in the world, they introduced vehicle inspections, bike lanes, cable cars, a metro. They made decisions – even if unpopular.”“Here in Nuevo León, nobody wants to sacrifice the economy or their political capital.”El Norte newspaper contributed reportingTo find the top industrial polluters in Monterrey, the Guardian and Quinto Elemento Lab analyzed emissions data for the region from multiple viewpoints. This included filing public records requests to obtain a database of each facilities’ reports to the Mexican government, as well as their itemized accounts of their releases from each part of their operation. We also obtained a leaked draft of an emissions inventory that was never published. Ultimately the numbers we decided to publish in this piece are from the Mexican government’s Registro de Emisiones y Transferencia de Contaminantes program, which compiles emissions data to share with the public and the international community through the North American Pollutant Release and Transfer Register (NAPRTR) initiative.We downloaded these from a webportal run by the Commission for Environmental Cooperation (CEC), an international organization created as a side accord to the 1994 free trade agreement (Nafta) between the US, Canada and Mexico to facilitate cooperation on environmental issues across the three countries.The reports only include emissions from facilities that are federally regulated (generally industrial facilities in sectors like chemicals, metals, automotive components and power; and those that generate more than 10 tons of hazardous waste each year.)We gathered data on all facilities that reported their emissions in the most recent three years available (2021-2023) and used their most recent report for each type of pollutant. Some facilities had no reports for certain types of pollutants in certain years. To calculate the total amount of heavy metals emitted – lead, cadmium and arsenic, and their compounds – we used three-year averages for each.To calculate CO2 emissions for the entire metro region, we used 2022 emissions reports. It was the year with the most complete dataset, due to the fact that many of the largest reporters’ records were removed from the 2023 final report by the government as “inconsistencies”, which the regulator said meant there were reasons to suspect the reliability of the information. (Some heavy metals reports are also disqualified for being “inconsistent”.)To compare emissions in the US and Mexico, we analyzed analogous reports submitted by US polluters. The CEC itself publishes such national comparisons and has an initiative to improve the comparability of pollution reporting.But there are some differences in the data gathered in the US and Mexico – most notably the minimum reporting thresholds. For instance, in the case of lead, US facilities that use 45kg per year must report their lead emissions; while, in Mexico, plants that use 5kg must report. In the case of cadmium and arsenic, Mexico requires reporting by plants that use at least 5kg of a substance; whereas the US standards do not require reporting by facilities unless they handle at least 4,530kg. We found that the vast majority of emissions in both countries come from large reporters. The comparisons were designed to focus on large reporters.As part of our right-of-reply process, we sent letters outlining our findings to the top emissions reporters. In consequence we removed reports from two facilities, Forja de Monterrey and Tenigal, from our heavy metal emissions totals because the companies demonstrated that their reports were in error.Comparisons of Monterrey’s fine-particulate pollution with other metro areas, including Los Angeles, are based on a 2025 study led by researchers at George Washington University. They used data from satellites, air monitors and computer models to look at pollution levels in 13,189 metro areas around the globe over a 20-year-period. We analysed this data to focus on metros with populations over 1 million in the North American free trade zone countries of Mexico, the United States and Canada. The year 2020 was excluded from this analysis because of the pandemic, when emissions temporarily plunged in many places (though fine-particulate pollution estimates increased in Monterrey that year as well).Editors: Alastair Gee, Alejandra XanicData editor: Will CraftData visualization: Andrew WitherspoonFactchecking: Bojana Pavlović
