Raquel Villarreal lives in a bright-yellow house in Mexico’s Monterrey metropolitan area with her family and nine cats. Here, the emergency medicine doctor has raised three daughters, one of whom died at the age of 14.
Just steps away is an industrial plant that operates 24 hours a day, emitting pollution that neighbors say blankets the neighborhood and which Villarreal says is hard to remove from her car.
In 2023, a prominent toxicology researcher at the Universidad Nacional Autónoma de México (UNAM), Martín Soto Jiménez, came to her gate and asked to test the soil and dust in and around her home.
Recently, Soto Jiménez and his team returned with bleak findings.
Samples taken by wiping the home’s indoor window sills found lead, which is neurotoxic, at levels 60 times higher than the level at which the US says action should be taken to fix the problem to avoid health consequences.
Additionally, the dust inside the Villarreals’ home had 14 times more cadmium than US health risk thresholds and was also very high in arsenic. Both are carcinogens.
“When I saw the numbers, I thought, ‘Oh my God, how scary, what’s going on?’” Villarreal said at her kitchen table as her two daughters, age 20 and 25, looked over her shoulder at a printout of the results.
“We have a toxic cocktail here,” said Soto Jiménez, who sampled soil and dust around the plant after being alerted to the issue by the Guardian and Quinto Elemento Lab, an investigative journalism non-profit.
Soto Jiménez has found even more alarming concentrations of pollutants at other homes and in a school surrounding the plant – sometimes hundreds of times higher than US risk thresholds.
The researcher has concluded that the contaminants came from the plant. The general director of the facility, for his part, says it follows “the highest standards” and complies with regulations.
What is the plant processing?
Among other things, vast quantities of America’s hazardous waste.
How toxic waste from the US ends up in a neighborhood in Mexico
Electric arc furnace
Steel
Images from Getty Images; basemap from OpenMapTiles.org and Bing Maps
The story begins in the US with discarded metal junk – such as cars and refrigerators. Steel plants vaporize it in “electric arc” furnaces to pull out the valuable steel. About 70% of American steel comes from this recycling process, according to the American Iron and Steel Institute.
Most of the contaminants in the scrap – such as plastic car components, paint and machine parts – are pulverized to dust and trapped in the steel plants’ pollution filters.
This dust, known as electric arc furnace dust, contains zinc but also other heavy metals such as brain-damaging lead and cancer-causing arsenic. It is recognized as hazardous waste in many countries, and as such the US requires it to have special handling when companies are processing and disposing of it.
American steel plants ship this dust to a facility in the Monterrey area, in northern Mexico, owned by a company called Zinc Nacional.
It has been processing this waste since at least the 1990s. In 2022 alone, US companies sent nearly 200,000 tons of this dust to Zinc Nacional – the equivalent of more than 90,000 new cars.
The plant profits off the dust by putting it through high-heat furnaces to reclaim zinc, which is sold for use in products such as fertilizer, animal feed and paint. A top company official says Zinc Nacional’s practices promote reuse by “transforming an industrial byproduct into valuable chemicals and finished products”.
But in the process, the plant releases lead, cadmium, arsenic and other toxic substances into the atmosphere as a fine dust, according to company emissions reports that are submitted to the Mexican government and were obtained by the Guardian and Quinto Elemento Lab.
Air emissions like these contribute to a huge air pollution problem in Monterrey, a metropolitan region and industrial hub of 5.3 million people.
Nearby residents complain that the plant is polluting their neighborhood with dust and smoke, and they allege it produces acid rain that destroys the paint finish on their cars.
Soto Jiménez tested 18 sites within a 2.5km (1.5 mile) radius of the plant.
They included homes, schools and streets. Several samples were taken from each site, including outdoor and, where possible, indoor samples.
Experts say the results are extremely concerning. And after reviewing them, an official from Mexico’s top environmental regulator, known by its acronym Semarnat, said it would seek an investigation to “learn in depth about the company’s compliance” with environmental regulation.
At most sites, lead levels in the outdoor dust and soil were higher than what the US Environmental Protection Agency considers a potential health risk for humans.
Three sites had outdoor lead levels five to six times greater than the US health risk threshold.
Lead wipe tests, which measured lead on indoor window sills, indicated levels that were higher than the US threshold at all locations where Soto Jiménez could collect samples.
One primary school had levels 1,760 times greater than the US threshold, and three homes had more than 400 times what the US considers a potential risk.
Cadmium, which can damage the lungs and kidneys, exceeded the US threshold at at least 14 out of 18 test sites.
And arsenic, which can cause cancer, exceeded the US threshold at every test site. Levels at many test sites also violated Mexican pollution standards, even though they are more lenient than those in the US.
Ultimately, nearly every site had concerning levels of several contaminants, according to these tests.
This raises the question of why US companies are sending hazardous waste to Mexico in the first place, and whether the country is equipped to handle it.
The steel dust that arrives here is part of a little-known and much larger trade in hazardous waste, the Guardian and Quinto Elemento Lab have found. In 2022, the most recent year for which data is available, US companies shipped 1.4m tons of their hazardous waste to Mexico, Canada and South Korea – ranging from old lead car batteries to industrial solvents and toxic sludge from factories.
The Monterrey region received nearly half of all hazardous waste the US exported in 2022, including not only steel dust but hundreds of thousands of tons of lead batteries.
And nearly one-seventh of the waste the US exported globally in 2022 was the contaminated steel dust that ended up at Zinc Nacional, in the Monterrey-area municipality of San Nicolás de los Garza.
Eduardo Alverde Villarreal, general director of Zinc Nacional, said in a statement that the company’s “circular economy approach” prevents steel dust “from ending up in landfills and saves valuable mineral resources in the ground for future generations”.
He added that Zinc Nacional was “committed to operating with transparency, in compliance with the law, and with a sense of social responsibility following the highest standards in the industry”.
Regarding the toxicology findings, he said: “We are not in a position to comment or discuss a study or its alleged conclusions since we do not know the study, its methodology, or its interpretation.”
He also said that the company regularly reports data about emissions, employee health, and impacts on soil, water and air, which confirms “that the operation at the company meets and fully complies with every criteria considered within regulations”.
Alverde Villarreal was provided with the findings reported in this story, and did not provide responses to a detailed list of questions about issues the piece raises, including pollutants released by the factory and whether they pose potential health risks to residents.
Numerous environmental experts questioned the safety of exporting US hazardous waste – including the toxic steel dust – to Mexico, a country they say has neither the government resources nor regulatory staffing to ensure the waste is handled in a way that does not harm residents’ health.
“The United States should reduce the generation of hazardous waste and not export it to Mexico or other countries,” said Fernando Bejarano González, a representative from the International Pollutants Elimination Network for Latin America and the Caribbean.
He described the export of hazardous waste from richer countries such as the United States to countries with weaker regulations such as Mexico as “a kind of toxic colonialism”.
As Soto Jiménez looped around the neighborhood to share his toxicology results in September, many residents expressed dismay.
One of the two schools tested – an elementary school about a kilometer away from the plant – had the highest levels of lead found in window sill wipes, at 1,760 times the US action level. It also had high levels of arsenic and cadmium. (This school has a large sign crediting Zinc Nacional for support on a wall near the entrance, but neither the school nor the company would share further details.)
Dr Yarelly Aguirre, a general practitioner who works at the other school – a nursery school with high arsenic levels – said she sees a surprising number of cases of respiratory allergies among students. Some parents told her that their children experienced rhinitis – inflammation of the nasal membranes – red eyes and other allergic symptoms at the school, but not at home. Even before learning of the sample results, Aguirre said she and the parents had worried that pollution might be affecting the children.
In recent years, she said, “what I have observed is that the cases of allergic rhinitis have increased”. Out of 430 children, approximately 80 to 100 have it, she said.
Soto Jiménez has not yet done the research to test whether pollution around the plant is connected to health problems in the neighborhood. Even so, there is vast research showing the harmful effects of lead, cadmium and arsenic. And exposure to a combination of toxic chemicals – as opposed to just one – compounds the risks. He plans to conduct further health studies, including testing the lead levels in the blood of children who live in the neighborhood.
After hearing the results, Guadalupe Rodríguez, general director from the regional public nursery school system, said the system was considering working with Soto Jiménez to test children who attend its schools for lead.
Raquel Villarreal is now asking whether pollution from the plant has played a role in her own family’s tragedies.
Eight years ago, her youngest daughter, Rebeca, then 10, was diagnosed with atypical sclerosing avascular rhabdomyosarcoma, a rare cancer. The treatment required surgery to remove Rebeca’s nose and rebuild her face, as well as two and half years of chemotherapy. Then, doctors detected leukemia. In 2020, she died – her mother said the death certificate listed cancer and Covid as the causes.
Looking at the soil and dust sample results, Villarreal remembered the many other people around her who have had cancer, including her father and at least five neighbors on her block. She and one of her surviving daughters have experienced hair loss and skin problems.
“You trust that the factory isn’t actually causing harmful emissions toward the community,” said Esther Gutiérrez, another of Raquel’s children. “Having it so close to my house honestly no longer makes me feel safe.”
Soto Jiménez, the toxicology researcher, has deep experience with this kind of testing. He performed similar studies around one of the world’s largest lead smelters, also in Mexico, which exposed generations of children to the neurotoxic metal.
He said a number of factors led him to conclude that the heavy metals around the Monterrey plant come from Zinc Nacional. The concentrations decrease the farther they are from the plant. There are large amounts of zinc, which the facility produces. And, Soto Jiménez explained, the zinc, lead, cadmium and arsenic observed in the findings are chemically associated with one another – in essence, they are traveling together.
Steel dust plants in the US have also been linked to high toxic emissions.
Two independent researchers who reviewed the findings said the contamination seemed reminiscent of the pollution found around several other now-closed plants that processed metals in the United States.
The samples showed concentrations of many other metals that were far above the levels at which they are expected to occur naturally. One of the earth’s rarest metals, a toxic element called tellurium, was found in concentrations in one dust sample of 3,100 times the tiny amount typically present in the earth’s crust.
“Anything and everything” can be in steel dust, said James Rybarczyk, a chemistry professor emeritus at Ball State University in Indiana, who consulted with environmental activists about a sister plant that Zinc Nacional opened in his state in 2022. “And that’s part of the problem.”
‘Clean steam’
There are business incentives for US steelmakers to send steel dust to Zinc Nacional in Mexico.
In 2022, the steel company Nucor sent 93,000 tons of steel dust from its plants in states including Alabama, Washington and Texas, according to EPA export records. Plants owned by Gerdau shipped 45,000 tons and CMC exported 21,000 tons from mills in southern states. The total amount going to Zinc Nacional has increased by nearly 50% over a four-year period.
Steel companies frequently pay Zinc Nacional to take the waste, according to court documents in a long-running case between Zinc Nacional and a US competitor. Other times, Zinc Nacional buys the waste. The alternative of disposing of it in a certified hazardous waste landfill in the US would be far more expensive for the steel companies, the documents suggest.
In response to questions about their exports of steel dust and potential environmental consequences in Mexico, Nucor, Gerdau and CMC referred reporters to the Steel Manufacturers Association.
Philip K Bell, president of the organization, said that recycling steel dust contributes to the production of zinc metal, which is “a critical mineral used in many renewable and transportation infrastructure projects”.
“Companies throughout North America have responsibly and beneficially reclaimed [electric arc furnace] dust for decades,” he said. “Regardless of location, these facilities operate pursuant to environmental permits, employ a variety of pollution controls and are subject to oversight by regulators.”
Zinc Nacional was founded in 1952 and is majority-owned by the Alverde Villarreals, a prominent business family in Monterrey. (Raquel Villarreal, the local resident, has no connection to them.) The company is part of a larger consortium of firms known as Grupo Promax. Zinc Nacional also owns or has stakes in arc furnace dust recyclers in Germany, Turkey and two plants in the US.
The company’s plant in Alabama has been criticized for high mercury emissions. Residents near a new plant in Indiana have expressed fears about heavy metal emissions.
In the average month, trains roll into the Monterrey plant carrying the equivalent of 624 semi truckloads of steel dust. It also receives steel dust from Mexican sources, and – according to Veritrade, a database of trade records – additional zinc substances from the two Zinc Nacional plants in the US.
Residents have long wondered what kind of pollution the facility emits into the neighborhood. Its chimneys and tall mounds of black material are visible from nearby streets.
In 2019, a group of neighbors sought to take action about what they said was soot and pollution coming from the plant. El Norte, a newspaper in Monterrey, wrote about their concerns and quoted a plant manager who responded that the fumes coming from the factory were “vapor limpio”, or clean steam.
Roberto Chavarría lives a few hundred meters from the plant and was part of the local group.
He said the local environmental agency placed a portable air monitor outside the plant for two years. But he said the results of the testing were never released to the neighbors.
“To this day, I have no report on what was achieved there,” he said.
The local government told the neighbors that it was unaware of any testing.
But government records obtained by the Guardian and Quinto Elemento Lab contradict the plant manager’s statement that Zinc Nacional’s emissions are simply “clean steam”. These records – which are not readily available to the public – detail the emissions of 1,000 companies in the state of Nuevo León, which are mandated to self-report to the Mexican government the quantities of pollution they emit.
The reporting team analyzed them and found that in 2023, Zinc Nacional reported emitting more arsenic than any other company in the state. The company was also a top emitter of lead and cadmium compounds.
And the company emits about 350,000 metric tons of earth-warming carbon dioxide each year – the equivalent of the emissions produced by 76,000 cars. (In its response to the findings of this story, the general director of the company said it “meets and fully complies” with regulations.)
Some who live around the plant acknowledge the work the company brings to local residents.
“Practically, most of the people here in the neighborhood work at the plant, either as employees” or contractors, said Sandy Ortiz, 32, who lives with her grandparents about 700m from the plant. Four members of her family work at Zinc Nacional. “My uncles have spent more than half of their lives there.”
Soto Jiménez took samples from the house next door to Ortiz’s home, where her uncle lives. It had some of the highest levels of heavy metals in the study – with lead wipe samples from its window sills containing lead levels 630 times higher than US action levels, as well as high levels of arsenic and cadmium.
At the small grocery store he runs next to his home, Isaías Izaguirre, 61, swept a finger along a shelf to show the gray-black dust that he says comes from the Zinc Nacional plant located just a stone’s throw away. Tests of the dust in his home showed lead levels 474 times higher than the amount the US would consider a hazard, as well as high levels of cadmium and arsenic.
“I know there’s pollution from the factory,” he said, gesturing in the direction of the giant plant, right behind his home. “We’ve lived here forever.”
But he also had some warm feelings for Zinc Nacional, which he said was in the neighborhood long before he arrived 30 years ago. He commended the company for the jobs it has given to neighbors and for responding to complaints when company equipment damages somebody’s property.
For his part, Alverde Villarreal, of Zinc Nacional, said that “for over 30 years, Zinc Nacional has promoted open dialogue and a trusting relationship with its neighbors through various programs, allowing a direct line of communication and working together to improve the community”. He did not provide details of the programs or improvements.
In any event, Izaguirre said he doesn’t believe the talk that the pollution is dangerous.
“This dust isn’t bad for us,” he said. “We’ve never had a study saying it could make us sick, so we’re not afraid of it.”
His 32-year-old daughter, Elena Marisol Izaguirre, who also lives in the house, had very different views.
She came out to the front of the store waving her X-rays from the frequent healthcare visits she has made trying to get rid of her persistent lung problems and infections.
“You get used to the smells, but I have friends who, when they come to my house, say it smells like plastic. The doctor told me it’s really harmful to live near factories.”
Mexico’s weak pollution enforcement
Environmental experts question whether the US, which has a per capita gross domestic product that is six times that of Mexico, should send its most dangerous waste to a poorer country with far fewer resources to manage it properly.
Mexico’s environmental practices rank far below those of the US, according to an international survey conducted by Yale and Columbia universities that compares how countries around the world handle such issues as waste disposal and air quality.
Meanwhile Mexico’s environmental regulator – the Secretariat of Environment and Natural Resources, known as Semarnat – relies on companies’ own reports about pollution emissions and controls. Zinc Nacional reports that its pollution controls operate at almost 100% efficiency.
The abilities of Mexican agencies to properly regulate hazardous waste are hindered by weak environmental laws, short staffing and, in some cases, corruption problems, said Carlos Álvarez Flores, an environmental consultant and president of the environmental organization México Comunicación y Ambiente.
“A developed country should not send its waste to a less developed one,” he said. “It’s an abuse.”
The standards for industrial emissions in Mexico are supposed to be revised every five years to ensure they are up to date, but many have not been. The standard for particulate emissions – such as smoke from a smokestack – has not been updated since 1993, even though the dangers of this kind of emission are now much clearer and the state government of Nuevo León, where Monterrey is located, estimates it causes 1,700 early deaths a year.
While specific standards for emissions of heavy metals, like lead, apply to some industries, such as battery recyclers and cement kilns, none of them apply to Zinc Nacional, according to Semarnat.
Moreover, the federal agency in charge of environmental inspection and enforcement, known by its acronym, Profepa, has had a budget cut of almost 50% over the past decade. In Nuevo León state, only eight inspectors are in charge of supervising 10,000 companies, according to 2023 records, as well as for protecting natural areas and wildlife. They conducted only 53 inspections that year.
Over the past nine years, government officials have inspected Zinc Nacional on two occasions. In the first inspection in 2020, inspectors noted problems with the uncontrolled release of emissions and ordered a partial lockdown of one of the furnaces until the company was able to prevent emissions contaminating nearby neighborhoods.
The second inspection, in 2021, was prompted by a video tweet posted by a local news website showing thick smoke pouring from a stack at the plant and lingering over the neighborhood.
But that inspection found no problems at the plant.
In theory, an industrial facility’s operating license would clearly specify which laws and pollution standards apply to the plant. But two experts who reviewed Zinc Nacional’s operating license said it was vague.
Javier Camarena Juárez, a professor of environmental law at Universidad La Salle México, said that based on its operating license, “these facilities are not adequately regulated in terms of how to measure emissions”.
He said there is no regulation “that clearly states the limit that must be complied with for the different metal compounds or metals themselves”, and it also did not include obligations to monitor emissions beyond the perimeter of the plant.
Belén Reyna Soto, an environmental consultant, agreed. She said that she was concerned that Zinc Nacional didn’t have to comply with more specific emissions regulations.
A government response amid growing fears
Soto Jiménez, the toxicology researcher, believes his findings should prompt action and further studies.
“The houses need to be cleaned, not only for lead, but for cadmium, zinc, arsenic and mercury, as well,” he said, adding that in more than 20 years of studies, he has seen few areas more contaminated with heavy metals than the neighborhood near the Zinc Nacional plant.
Dr Bruce Lanphear, one of North America’s leading experts on the health dangers posed by lead, who reviewed Soto Jiménez’s soil sample results, agreed.
“People shouldn’t be living in homes with hazards like this,” said Lanphear. His research has shown that even small amounts of lead exposure can eventually add up to thousands of extra cardiac deaths in a population, on top of long-known effects such as impairing kidney function and damaging brain development in children.
Mexico’s environmental regulator, Semarnat, said the results merit an investigation by Profepa (the government agency charged with conducting environmental inspections).
“The findings of the study justify an investigation by Profepa on the operation of the company with follow-up by Semarnat. As well as identifying other possible sources of concern in the area,” read a statement from Arturo Gavilán García, a director who works on hazardous waste imports and management at Semarnat.
It noted that Mexico’s constitution guarantees its population the right to a healthy environment and said it will seek to “learn in depth about the company’s compliance” with environmental regulation and to “detect possible impacts to the surrounding areas”.
Unconnected to Soto Jiménez’s research, in 2024 the state government secured promises from 10 companies, including Zinc Nacional, to improve their emissions equipment and change their processes over the next decade. It is an an effort to lower the overall pollution levels in the Monterrey area.
According to the government, Zinc Nacional has agreed to spend nearly $13m to meet this goal. Of the companies who promised to reduce pollution, Zinc Nacional’s spending pledge made up 3% of the total pledged.
There may be other reasons for concern about the Zinc Nacional plant.
Residents and visiting reporters have noticed piles of white bags, of the type usually used to store industrial powders in large quantities, around the edges of the plant.
Satellite imagery shows that from 2020 to 2024, thousands of these white sacks had begun to fill up many acres of empty land inside the plant site.
Several experts said they have no way of knowing what is inside the bags. They worry that if they contain toxic substances such as lead, contaminants could easily escape from such open-air storage. Zinc Nacional did not respond to a question about the sacks.
Gavilán García, of Semarnat, said whether this type of storage is allowable depends on what is in the bags.
“There shouldn’t be hazardous waste in the open air anywhere,” he said, when he saw the images. “That would be a violation of the law and would be punishable.” Alternatively, he said, “if they are finished products, they are not subject to those provisions”.
Another worry among environmental observers is whether the plant is producing dioxins, which are some of the most dangerous toxic compounds on earth.
Numerous studies have shown that dioxins are produced by Waelz kilns, the main technology used by Zinc Nacional in Monterrey.
Dioxins are extremely potent cancer-causing substances produced in some industrial processes, such as the burning of waste. They are dangerous even in tiny amounts. And because they take a very long time to break down, they can accumulate in human and animal tissues and contaminate entire food chains.
Zinc Nacional does not report releasing or disposing of any dioxins in its emissions reports to the federal government. However, it is not clear whether the plant tests for dioxin releases. The study by Soto Jiménez did not include a test for dioxins, which is expensive and difficult to perform.
The company did not respond to questions about whether it emits or monitors for dioxins. Another steel dust plant in Indiana, which is co-owned by Zinc Nacional, disclosed that it was releasing dioxins after concerned residents there pushed for such testing.
When Soto Jiménez came to Leticia Vázquez’s gate to tell her that dust in her home had high levels of lead, arsenic, cadmium and zinc, the 44-year-old mother appeared visibly shaken.
“What can we do?” she asked as she held her one-and-a-half-year-old daughter on her hip. Her five-year-old daughter was behind her in the family’s home, which sits just a few hundred steps from Zinc Nacional’s gate.
“It would be advisable to get blood lead level tests for your daughters, as children absorb lead at a higher rate than adults,” replied Soto Jiménez, handing her a written report of his findings in a yellow manila envelope.
The family had long known there was pollution in the neighborhood. Vázquez’s husband, Edelmiro Gómez, was raised in the area in the 1980s and remembers when dust from the plant was so intense that “white cars would turn yellow”, he said. But he felt it had improved a lot since back then.
“We believe, as neighbors, that they must have done something, maybe put in a filter or something different because it doesn’t happen anymore,” he said.
Other neighbors have expressed their dissatisfaction and concern with the plant’s progress on pollution.
Patricia Herrera, who lives on a hill overlooking the plant, said it seems to her that the smoke, dust and stink spewing from the factory have only gotten worse.
“My biggest concern is that I see more and more pollution,” said Herrera, who asks herself if fumes from the plant may have contributed to her chronic sinus issues or her daughter’s recent breast cancer. But there is no evidence either way, at least until experts further study the issue. “There are times when the smell is so noticeable that you can’t be outside.”
Raquel Villarreal, who lives just down the hill from Herrera, hopes that Soto Jiménez’s findings will result in new investigations to answer the question of whether health problems, such as the tragedies her family has faced, have any connection to pollution from the plant.
“We might be sitting on a time bomb without even knowing it,” she said.
Quick Guide
Methodology
Show
Hazardous waste export summaries were based on the EPA’s Waste Import Export Tracking System (WIETS) from 2018 to 2022, which was obtained through Freedom of Information Act requests. Although most exports were originally described in weights, some which were described as liquid volumes in liters were converted to estimated weights based on the weight of water. Some other shipments (usually contaminated soils) originally described in cubic meters were converted to estimated weights based on the weight of dirt.
Martín Soto Jiménez from the Universidad Nacional Autónoma de México (UNAM) and his team collected the soil and dust samples around the Zinc Nacional plant in Monterrey in July 2023. Samples included outdoor dust and soil and, where possible, indoor dust samples and wipes of windowsills.
Samples were not taken in locations with loose or peeling paint, to avoid the possible presence of lead-based paint.
The research also took into consideration expected background contamination levels in soil.
An unrelated 2024 study by a PhD student at the Universidad Autónoma de Nuevo León (UANL) tested lead, cadmium and zinc levels in road dust around the entire Monterrey region. While it found some very elevated lead levels in Monterrey’s commercial district (about 8km from Zinc Nacional’s plant), lead levels in the north-eastern region, where the plant is located, averaged 53 parts per million (ppm). This was far lower than the lead levels found at outdoor locations around the Zinc Nacional plant by Soto Jiménez, which averaged 323ppm.
The same UANL study tested natural background levels in nearby areas unaffected by human development. Again, levels of lead, cadmium and zinc (lead of 7.4ppm, cadmium of 0.25ppm and zinc of 70ppm) were far lower than levels discovered around the Zinc Nacional plant.
The UANL study did not test indoor locations. In the study by Soto Jiménez, the average lead level found in dust wipes taken inside homes around the plant was 10,900 micrograms per square foot. In contrast, the EPA’s action level is 40 micrograms per square foot.
While Zinc Nacional is in an industrial area, the closest other major reporter of lead, cadmium or arsenic emissions is a steel mill 4km to the south.
US health risk thresholds for lead, cadmium and arsenic were selected from the EPA’s Regional Screening Levels guidelines, which are considered to be protective for humans over a lifetime. The action level for lead found in indoor window sill dust wipes was from the new guidelines adopted by the EPA in October.
Mexican standards came from a 2004 regulation, NOM 147 of the Secretaría de Medio Ambiente y Recursos Naturales (Semarnat). The Guardian and Quinto Elemento Lab generally used the EPA’s risk thresholds for pollutants, which are lower and are updated more frequently based on the latest human health research. These would be the guidelines used if the waste were processed in the US.
Air emissions reports for Zinc Nacional and about 1,000 other companies in the Mexican state of Nuevo León were examined in the Mexican government’s Cédula de Operación Anual, which was obtained through public records requests. Top emitters of arsenic, carbon dioxide, lead and its compounds, and cadmium and its compounds were determined using the methodology employed by the EPA.
Thanks to the many academics and other experts who provided technical guidance for this report, including James Rybarczyk, emeritus chemistry professor at Ball State University, and Selene Martínez, executive director of the Citizens Air Quality Observatory of the Metropolitan Area of Monterrey (OCCAMM).
Bruce Lanphear of Simon Fraser University and Jill Johnston of the University of Southern California reviewed the soil sample data, noting it was reminiscent of pollution around shuttered plants in the US, and provided insight on possible health implications.
Thanks also to Monterrey resident Miguel Europa.
The Environmental Reporting Collective supported this project with a grant.
Editors: Alastair Gee, Alejandra Xanic
Data visualization and factchecking: Alvin Chang, Efraín Tzuc
Story factchecking: Bojana Pavlović
