Burned-Home Soils Reveal Uneven Lead & Arsenic After LA Fires

Here’s a truth that might unsettle you: the ash from the January wildfires in Los Angeles isn’t just a cleanup nuisance — it’s a toxic time bomb that could rewrite how we think about urban wildfire recovery. A new chemical analysis of residential soils and ash from homes burned by the Eaton and Palisades fires has found wide variation in contamination by lead, arsenic, and other harmful elements. And the patchwork pattern means you can’t assume any given lot is safe.

Published in Environmental Science and Technology Letters, the study collected samples from 16 properties in Altadena and Pacific Palisades — neighborhoods that burned in early 2025. The researchers, led by environmental chemist Dr. Laura Chen from the University of California, Irvine, found that lead concentrations ranged from below detection limits to over 1,200 parts per million in surface ash. That’s more than triple the EPA’s residential soil screening level of 400 ppm. But here’s the kicker: the contamination wasn’t uniform. Some properties next to heavily contaminated ones showed nearly clean soil.

Why the disparity? It comes down to what was inside the houses. Older homes built before 1978 often contain lead-based paint. When those homes burn, lead particles become concentrated in the ash and then settle into the soil. The same goes for arsenic, which can come from treated lumber used in decks and framing. The Eaton fire, which swept through Altadena — a community with many mid-century houses — produced higher average arsenic levels than the Palisades fire, where newer homes predominated. But even within the same fire zone, the variability was staggering.

“If you’re looking at a block of burned homes, one lot might be relatively safe while the next lot over has lead levels that would require remediation for a child care facility,” said Dr. Chen. “You simply cannot extrapolate from one property to another. This has huge implications for how we clear debris and protect returning families.”

The study found that total lead in soil averaged 278 ppm across all samples, but the range was so wide that the average is nearly meaningless. One sample hit 1,800 ppm. Arsenic averaged 18 ppm — below California’s residential screening level of 30 ppm — but again, extreme outliers existed. Soil pH also shifted dramatically: ash is highly alkaline, sometimes raising soil pH above 10, which can mobilize certain metals and affect plant uptake.

The Science of Post-Fire Toxic Soil

Wildfires have always altered soil chemistry, but urban wildfires are a different beast. When forests burn, most contaminants come from natural vegetation and underlying geology. When houses burn, you’re throwing in a cocktail of construction materials, electronics, paints, plastics, and household chemicals. This study is one of the first to systematically map that urban signature at a granular, property-by-property scale.

Dr. Michael Torres, a soil toxicologist at Stanford University not involved in the research, called the findings “a wake-up call for emergency management agencies.”

“We’ve known for decades that lead from paint and arsenic from pressure-treated wood can persist in soil for centuries,” Torres said. “But the fire concentrates these elements into a fine ash that can be easily inhaled or tracked indoors. The immediate health risks — especially for children who might play in the dirt — are very real. And we have no standard protocol for testing every parcel individually.”

The authors advocate for a tiered sampling approach: rapid field screening using portable X-ray fluorescence (XRF) analyzers to flag hot spots, followed by lab confirmation. That’s the kind of on-the-ground reality check that could prevent a second disaster — a chronic lead exposure crisis — on top of the acute trauma of losing a home.

It’s also worth noting that the risk doesn’t disappear with debris removal. Even after the bulldozers clear the charred structure, the soil underneath may still hold elevated levels. In some samples, lead concentrations in the top 2.5 cm of soil were double those in deeper layers — meaning that simply scraping off the surface ash won’t clean the lot. You’d need to remove and replace the topsoil, which is expensive and logistically challenging.

What This Means for Homeowners and Renters

If you’re a resident returning to a burned property, the message is clear: don’t assume the soil is safe. The Los Angeles County Department of Public Health has issued guidance urging people to wear masks and gloves during cleanup and to keep children and pets away from ash. But the study suggests that even after visible ash is gone, the ground may still require testing.

And here’s where the climate connection tightens. The January wildfires were fueled by a record-breaking drought followed by fierce Santa Ana winds — conditions made more likely by a warming planet. As climate change extends the fire season into winter, more urban areas will face this contamination dilemma. Communities from Paradise, California, to Boulder, Colorado, have already grappled with it. The LA fires, however, are a case study in the unevenness of contamination — a lesson that could inform how we prepare for heatwaves and other climate-driven disasters that interact with aging urban infrastructure.

The researchers also found that some contaminated areas overlapped with historically marginalized neighborhoods. Altadena has a significant proportion of older homes owned by low-income families who may not have the resources for expensive soil remediation. That raises urgent equity questions: who pays for testing? Who pays for cleanup? The Federal Emergency Management Agency (FEMA) covers debris removal, but long-term soil restoration often falls through the cracks.

A Long Road to Recovery

The Palisades and Eaton fires together destroyed more than 2,000 structures. The cleanup is ongoing, but the study suggests that lead monitoring should be a permanent part of the recovery process — not a one-off test right after the fire. Over time, rain and wind can redistribute contaminated ash to previously clean areas, creating new hotspots. The authors recommend periodic retesting for at least two years following a fire.

Dr. Chen and her team are now working with Los Angeles County to pilot a neighborhood-scale sampling protocol using XRF guns. They hope to create a map of contamination that residents can access online. “We owe it to these communities to give them data they can act on,” Chen said. “Not just a blanket ‘the area is safe’ or ‘the area is unsafe.’ People need to know what’s in their own backyard.”

The study’s findings also intersect with a broader conversation about urban resilience. Rebuilding after a wildfire isn’t just about stronger building codes and fire-resistant materials. It’s about understanding that the ground itself may carry the scars of the fire for decades — and that without careful remediation, those scars can become invisible health hazards.

Looking ahead, the researchers emphasize that this is only the beginning. A parallel study is already underway to examine airborne particulate matter during debris removal, and a long-term health survey of returning residents will track any correlations between soil contamination levels and blood lead levels in children. The results won’t be available for at least a year, but the pattern is already emerging: urban wildfire contamination is real, it’s unpredictable, and it demands a new kind of response.

For now, the takeaway is uncomfortable but actionable: if your home burned in the LA fires, test your soil. Not just once, but repeatedly. And don’t let the guy next door reassure you with his clean test results — because yours could be very different.