Recent reports indicate that arsenic levels in the soil of some California wildfire burn areas can exceed environmental standards. Specifically, one report mentions that arsenic levels in the ash from a fire in Grass Valley were 20 times higher than the average in Western soil. The Los Angeles Times also reported on elevated levels of arsenic, lead, and mercury in yards of homes that survived the fires in Altadena and Pacific Palisades, including some areas already marked as clean by federal officials. The presence of arsenic and other heavy metals like lead and mercury is a concern due to their potential to cause a variety of health problems, including cancer, stunted development, and damage to the nervous system.
Here's a more detailed look at the situation:
Arsenic and other heavy metals in ash:
Wildfires can incinerate household items and construction materials, releasing pollutants like arsenic, lead, and mercury into the air and soil.
Health risks:
Arsenic is a known carcinogen, and prolonged exposure to lead can damage children's brains and cause kidney damage in adults.
Testing and monitoring:
The Los Angeles Times conducted independent testing of soil in the affected areas, revealing elevated levels of arsenic, lead, and mercury in some yards.
Federal agencies' response:
While federal officials initially did not test soil in burn areas, they have since taken steps to address the issue, according to The New Lede.
Long-term health impacts:
Studies are underway to assess the long-term health impacts of exposure to these toxins, particularly in children.
Rebuilding Los Angeles—on Toxic Soil?
By Hannah Miet
April 18, 2025
Soil testing
Los Angeles Department of Public Health
Reconstruction after January’s wildfires in Los Angeles County has begun in earnest, but many residents still don’t know whether rebuilding on their lots is safe.
The Federal Emergency Management Agency (FEMA) and the U.S. Army Corps of Engineers, responsible for the first two phases of debris cleanup, respectively, declined to test soil in the areas devastated by the Eaton and Palisades wildfires.
This decision—unusual in the history of the region’s fires—has left people without assurance that their land is free of such chemicals as asbestos, exposure to which can cause a plethora of cancers, or lead, which can damage the brain, especially in children.
Structure fires release into the environment a cocktail of toxic substances that were previously encapsulated in paint or insulation, among other materials. The resulting “ash footprint” can contain chemicals that are “not good to breathe or to have around”—such as carcinogenic arsenic, polycyclic aromatic hydrocarbons (PAHs), and dioxins, says Preston Brooks, a partner in the environmental practice at the law firm Cox, Castle & Nicholson.
“You can’t always see or smell toxic chemicals—that’s why you do [soil] sampling to make sure,” Brooks says.
Unconfirmed toxicity
Although soil sampling efforts self-funded by the L.A. County Department of Public Health and research institutions have filled in some gaps—USC is testing residents’ soil samples for lead, and researchers from UCLA, Loyola Marymount, and Purdue universities are offering full-panel soil testing—none of these groups have tested the soil on a parcel-by-parcel basis.
Preston Brooks, a partner in the environmental practice at the law firm Cox, Castle, & Nicholson.
Preston Brooks
That lot-by-lot testing is required to determine whether individual parcels are safe to reoccupy, says Brooks, who led the debris management section of Project Recovery, a report developed by ULI Los Angeles, UCLA, and USC that provides actionable recommendations to expedite recovery.
Residents who want to rebuild or reoccupy their houses have reason for concern—but they also face confusion. Victims of the Eaton fire in Altadena may know, for example, that 80 percent of preliminary soil samples in their area tested positive for lead at levels that exceed state health standards. But is their lot in the 80 percent or the 20 percent? It’s hard to know without hiring a soil testing company yourself, which comes with a steep price tag not always covered by insurance.
“I suspect most individuals . . . won’t be comfortable with generalities,” Brooks says. “People have different levels of insurance, and they want to understand from their insurance carriers whether debris removal is covered under their policies.”
Adding to residents’ plight: What the Corps of Engineers removes from each site is far from predictable. Brooks says that the Corps has leveled some sites completely, whereas on others, “they’ve left behind the driveway, tree roots, retaining walls, and pool structures,” which are now “essentially at a different elevation.” He adds, “It’s really tough, by the way, for residents to try to figure this all out on their own.”
Things are even more confounding downwind of the Pacific Palisades fire zone, where samples indicated less widespread contamination but showed isolated hot spots of heavy metals, including arsenic.
“I think it would be a real miss on the part of federal, state, and local authorities to leave [comprehensive testing] up to each individual property owner,” Brooks says. “This is an instance where government is best suited to provide what I’ll call a clean bill of health.”
Left in the lurch
FEMA and the Corps of Engineers’ decision represents a break with tradition. For nearly two decades, federal agencies funded and conducted comprehensive parcel-by-parcel soil testing (often called “confirmation” testing) after L.A. wildfires. Typically, the Corps would first scrape six inches of topsoil off each property and then test the newly exposed soil for a slew of different toxic chemicals. If those tests revealed contamination, federal crews would scrape further and retest.
“That’s really the only tried-and-true methodology,” Brooks says.
The 2018 Camp Fire in Paradise, a town in northern California, showed just how essential testing and rescraping can be. A third of the 12,500 properties authorities sampled there were dangerously contaminated—even after removal of the first six inches of topsoil. In fact, federal crews returned to each site as many as five times to remove more soil before the lots were deemed safe.
Despite pushback—including from a contingent led by U.S. Representative Laura Friedman (D-CA 30), among others—the agencies now maintain that the Corps of Engineers’ removal of six inches of topsoil, to level the ground to a rough, approximate grade, is sufficient.
Experts disagree. Project Recovery’s authors recommend the collection of soil samples—regardless of whether the lots are scraped—as well as analytical tests for lead and other contaminants at each of the 13,500 properties the Eaton and Palisades wildfires damaged or destroyed. According to Brooks, these steps are so important because of the heavy rainfall in L.A. since the fires. Rain tends to drive toxic chemicals “now in liquid form” deeper into the soil, Brooks says.
In response to these concerns, the L.A. County Board of Supervisors approved a motion on April 15, 2025, to reallocate $3 million from the county’s Lead Paint Hazard Mitigation Program to help residents in the Eaton Fire zone, or up to one mile downwind of it, cover the costs of lead testing. There isn’t a similar refund that covers testing for other chemicals, or for those conducted in the Palisades fire region.
“The findings shared by the Department of Public Health are concerning for our residents who live near the Eaton Fire burn area and are now facing the possibility of soil contamination,” said Board Chair Kathryn Barger—who introduced the motion—in a statement. “I’m aware [that] some of my constituents want to test their soil but are worried about the cost. This motion is about making sure they have access to resources and support to protect their health and their homes.”
This article is part of a series examining topics in the Project Recovery report. Join us next Friday for a new installment.
Related reading:
? Urban Land Institute, UCLA, USC Release Comprehensive Roadmap for Post-Wildfire Rebuilding in Los Angeles
? Rebuilding in the Aftermath of L.A.’s Unprecedented Urban Fires, Amid an Already Pressing Housing Crisis
? Holding on to Altadena: Rebuilding to Preserve Housing Wealth
? January 2025 Economist Snapshot: Los Angeles Wildfires Recovery Will Be Costly and Lengthy
? Los Angeles Fires Recovery: Real Estate Community and Key Stakeholders Present Innovative Rebuilding Plans
Hannah Miet
Hannah Miet is an award-winning writer based in Los Angeles. She launched the L.A. bureau of The Real Deal as its founding editor. Her feature writing has appeared in Newsweek and The New York Times.
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It's inaccurate to say that removing 6 inches of Los Angeles topsoil from forest fires does not improve arsenic levels in the soil. While the removal might temporarily lower arsenic levels in the immediate topsoil, it's a complex issue with no simple answer. Forest fires can alter soil composition, and the impact on arsenic levels depends on various factors, including the fire's severity and the pre-fire arsenic levels.
Here's a more nuanced explanation:
Factors affecting arsenic levels after a fire:
Fire Severity:
Severe fires can lead to increased arsenic mobility and potentially higher concentrations in the soil, while less severe fires might not have a significant impact.
Pre-fire Arsenic Levels:
The initial arsenic concentration in the soil before the fire is a crucial factor.
Soil Type:
The type of soil in the affected area can influence how arsenic behaves after a fire.
Ash Composition:
The ash produced by a fire can contain arsenic, which can be released back into the soil.
Plant Uptake:
Plants can absorb arsenic from the soil, and after a fire, new plants may take up arsenic from the soil or ash.
Erosion:
Fire can increase soil erosion, potentially washing away arsenic-rich topsoil or concentrating it in areas where erosion occurs.
Water Chemistry:
The chemistry of water interacting with burned soil can affect arsenic mobility and its form (e.g., whether it is soluble or not).
Removing topsoil:
Temporary Solution:
Removing the topsoil could temporarily lower arsenic levels in the area that was removed. However, this is a short-term fix and doesn't address the underlying issues.
Re-contamination:
If the area is not properly managed, the removed topsoil could be replaced by new topsoil, potentially with similar or higher arsenic concentrations.
Ecosystem Damage:
Removing topsoil can disrupt the soil ecosystem and affect the health of plants and other organisms.
In conclusion, removing 6 inches of Los Angeles topsoil from forest fires is not a definitive solution for reducing arsenic levels. It's a complex issue with multiple factors at play. A more sustainable approach would involve understanding the specific conditions in the affected area and developing a comprehensive plan that addresses the root cause of the problem and minimizes any potential environm |
