Soils have long memories, and the fires simply exposed what was already there.
In the wake of the January 2025 Eaton and Palisades wildfires that killed 31 people and erased more than 16,000 structures across Los Angeles, researchers discovered that fire does not merely destroy — it reveals. Duke University scientists found that the flames had concentrated lead and arsenic from decades-old building materials into the ash and soil of burned neighborhoods, exposing a contamination that was always present but hidden beneath the surface of daily life. A federal cleanup removed millions of tons of hazardous material and measurably reduced the danger, yet conflicting state and federal safety standards left returning residents uncertain about what safety even means. The story of these soils is, in many ways, the story of every American city: the past does not disappear, it waits.
- Wildfire ash from pre-1970s homes in Altadena and Pacific Palisades contained dangerously variable levels of lead and arsenic, with older structures — built when lead paint was standard — showing the highest concentrations.
- A grassroots network of volunteer homeowners, organized by a garden designer, collected 300 soil and ash samples across more than 30 burned properties, giving scientists the raw material to map the contamination before authorities had acted.
- The EPA and Army Corps of Engineers responded with a sweeping remediation, scraping six inches of soil and debris from foundations and hauling away nearly 2.4 million tons of hazardous material — yet conducted no independent testing to confirm the cleanup had worked.
- Duke's before-and-after sampling filled that evidentiary gap, showing substantial reductions in lead and arsenic at the most contaminated sites — offering residents one of the only data-backed assurances available.
- A collision between California's stricter lead standard and the federal EPA limit is generating public confusion about whether cleaned properties are truly safe, with researchers calling for a formal technical review to resolve the discrepancy.
- Scientists warn that the contamination uncovered in Los Angeles is not an anomaly — urban soils across the country carry the chemical residue of their own industrial and architectural histories, and wildfires are simply the force that makes the invisible visible.
When the Eaton and Palisades wildfires swept through Los Angeles in January 2025, killing 31 people and destroying more than 16,000 structures, they left behind more than rubble. Researchers at Duke University, working with a volunteer network organized by a local garden designer named Robin Jones, collected 300 samples of soil and ash from over 30 burned properties in Altadena and Pacific Palisades. What they found was uneven and alarming: lead and arsenic concentrations varied dramatically from one property to the next, with the highest levels concentrated in homes built before the 1970s, where lead-based paint had been standard construction practice. Fire had not introduced these metals so much as liberated and concentrated them.
The study, published in Environmental Science and Technology Letters, was led in the laboratory by Anselme Dossou, a doctoral student under soil scientist Daniel Richter at Duke's Nicholas School of the Environment. As the data took shape, the team shared their findings with the Los Angeles Public Health Department. Then, in June and July, the EPA and Army Corps of Engineers mounted a large-scale cleanup — scraping six inches of ash and soil from foundations and removing nearly 2.4 million tons of hazardous material. Crucially, the federal agencies conducted no post-cleanup testing of their own. Richter's team returned to 17 of the original sites and collected more than 100 new samples, producing some of the only before-and-after evidence available. The results were encouraging: contamination levels had dropped substantially in scraped areas, particularly where the hazard had been greatest.
Yet the findings also illuminated a structural problem. California's residential lead standard is less than half the federal EPA limit, and the existence of two competing thresholds leaves residents uncertain about what safety actually means for their property. Richter called for a technical review to resolve the discrepancy. More broadly, the research serves as a reminder that the soils beneath American cities carry the chemical memory of everything built and burned and buried within them — and that Los Angeles, in this regard, is not exceptional. The fires simply made visible what was already there.
In the months after the Eaton and Palisades wildfires tore through Los Angeles in January 2025, killing 31 people and destroying more than 16,000 homes, a different kind of hazard settled into the soil. Researchers at Duke University conducted a chemical analysis of ash and dirt from burned residential properties in Altadena and Pacific Palisades, looking for metals that fires had released and concentrated in the rubble. What they found was troubling and uneven: lead and arsenic contamination varied wildly from house to house, with the highest concentrations appearing in homes built before the 1970s—structures where lead-based paints had been standard.
The study, published in Environmental Science and Technology Letters in May, began almost by accident. While the fires were still burning, Daniel Richter, a soil scientist at Duke's Nicholas School of the Environment, was connected through a Los Angeles colleague to Robin Jones, who runs a small garden design business called Honey Girl Grows. Jones organized a team of volunteer homeowners to collect samples from more than 30 burned properties. By March, they had gathered 300 samples of soil and ash and shipped them to Richter's laboratory for analysis. Anselme Dossou, a doctoral student in Richter's lab, led the work of preparing and testing the material, assisted by other student volunteers.
What emerged from the data was a portrait of contamination shaped by the age and construction of the homes themselves. Fires had released metals from structural materials and household products, but they had also concentrated those metals in the ash left behind—ash that could seep into the surrounding soil and pose a risk to residents returning to rebuild. The variation was significant enough that some properties showed dangerous levels while others nearby did not. The researchers shared their findings with the Los Angeles Public Health Department as the work progressed.
Then came the cleanup. In June and July, the U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers conducted a massive remediation effort, removing nearly 2.4 million tons of burned and hazardous materials from the affected areas. The work was thorough: crews scraped away six inches of ash and soil from house foundations and structural debris. Richter's team returned to 17 of the original sites and collected more than 100 additional samples from within a meter of where they had sampled before the cleanup began.
The post-cleanup analysis showed something encouraging: the removal effort had substantially reduced concentrations of lead and arsenic in the areas that had been scraped, particularly at sites where contamination had been highest. This was significant because, as Richter noted, the Army Corps of Engineers had conducted no testing after the fires to measure whether their work had actually reduced the hazard. The Duke study provided some of the only before-and-after data available.
But the findings also exposed a deeper problem. California maintains its own standard for lead in residential soil—one that is less than half the federal limit set by the EPA. The existence of two different standards, Richter argued, creates unnecessary confusion for the public and obscures whether a given property is actually safe. The discrepancy, he said, demands a technical review.
Beyond Los Angeles, the research points to a broader reality about American cities. The soils underlying communities across the nation carry the chemical signatures of their own histories—leftover metals from decades of industrial use, old paint, and other sources. The contamination found in Altadena and Pacific Palisades is not unique. As Dossou put it in language Richter quoted in the study: soils have long memories. The fires had simply exposed what was already there, and what remains in countless other places.
Citações Notáveis
Homes often contain metals in structural materials and household products, and fires release metals in smoke but also concentrate metals in structural ash that can potentially contaminate residential soils.— Daniel Richter, Duke University soil scientist
The two lead concentrations needlessly confuse the public, and they critically need a technical review.— Daniel Richter, on conflicting state and federal lead standards
A Conversa do Hearth Outra perspectiva sobre a história
Why did the contamination vary so much from house to house? Was it just the age of the homes?
Mostly, yes. Homes built before the 1970s used lead-based paints, and when those structures burned, the lead concentrated in the ash. But it's also about what was inside each house—different products, different materials. The fire didn't create the contamination; it released what was already there and concentrated it.
So the cleanup actually worked?
In the areas they scraped, yes. The data showed real reduction in lead and arsenic after the EPA and Army Corps removed that top layer of soil and ash. But here's the thing—they didn't test to know that. The Duke study is one of the only before-and-after comparisons that exists.
What about the lead standard problem?
California says one thing, the EPA says another. The state's limit is stricter, which sounds good, but it creates confusion. People don't know which number applies to their property. It muddies the whole conversation about whether a place is safe.
Is this a wildfire problem or a soil problem?
Both. The fires exposed it, but the contamination was already in the soil. That's what Dossou meant about soils having long memories. Every city in America has this—old paint, old industrial use. The fires just made it visible and urgent.
What happens to people rebuilding in those areas now?
They're dealing with soil that's been partially cleaned but still carries some contamination. The question is whether the cleanup went deep enough, and whether the standards being used to measure safety actually protect them.