How Much Lead and Other Toxic Metals are Present after the Eaton Fire?

On the evening of January 7, 2025, Caltech professor of geochemistry François Tissot evacuated his Altadena home with his family as the Eaton fire spread. Fires in Altadena and surrounding communities ultimately took 17 lives and destroyed over 9,000 buildings, causing widespread damage estimated to cost more than $10 billion. Tissot's home sustained heavy smoke, ash, heat, and fire damage: melted windows and roofing, compromised waterproofing, cracks in several walls, and more.

The Eaton fire was unique in that 90 percent of the homes that burned had been built before 1975, meaning that they likely contained some amount of lead paint and asbestos, building materials that are now banned by the Environmental Protection Agency (EPA) for their danger to human health. In the aftermath of the fire, Tissot saw an opportunity to help by leveraging his laboratory's state-of-the-art techniques to measure the presence of toxic metals like lead in the debris. As a geochemist, Tissot has deep expertise in studying the chemical signatures of elements like lead and uranium in meteorites to learn about the early solar system, and these methods could be applied to samples like ash from the fire. High winds had carried ash from the fires throughout the region, reaching neighborhoods across Los Angeles that were miles from the burn area.

"I was being impacted so heavily, I personally had no bandwidth," Tissot says. "But I messaged my group, 'We have the instrumentation and the expertise. I think we have a chance to rapidly bring answers to questions that everyone is worried about. Are you willing to participate in producing data for the community that will be helpful?' Within half an hour, they had all responded, 'Whatever you need, just let us know.'"

In the weeks after the fires, Tissot's team collected more than 300 samples from 52 homes from sites ranging from deep within the fire zone to neighborhoods miles away like Highland Park. The data collected are now publicly available. As his team prepares papers for peer review, we spoke with Tissot about his initial readings of the data and what it could mean for longer-term fire recovery.

Tell us about your findings.

My group has expertise in techniques to easily measure the concentration of most elements, and heavy metals in particular, in samples like meteorites. So, immediately after the fire, we sampled dust around the four geological and planetary science buildings on campus: North Mudd, South Mudd, Linde, and Arms. We took 100 samples from windowsills, desks, other flat surfaces and stairwells, and looked at the levels of lead, cadmium, chromium, and arsenic, primarily. We found that samples close to a window have 10 times more lead than those farther from the window. The good news is that cleaning those surfaces removed about 90 percent of the lead that's been deposited, bringing most of them below the EPA limit of 50 micrograms per square meter.

Now, we've taken data from deep in the fire zone to all of Pasadena, South Pasadena, out to San Gabriel, a bit to Sierra Madre. We looked at the dominant direction of the wind at the time and extended the sampling area to La Cañada Flintridge and Glendale. We've built heat maps showing the concentrations of lead as a function of distance from the fire zone. You might think that as you go farther from the fire, there is less lead, but that's not a given. The way elements are transported by the fire depends on whether they can easily vaporize, and lead is quite volatile, so it will easily be transported long distances. For instance, the amount of lead we found on surfaces that had not been cleaned since the fire in houses in the Pasadena area were as elevated as those in my house, which was deep in the fire zone. But my home received 100 times more arsenic than houses in Pasadena.

Our data is publicly available here.

What are your takeaways from this study?

I think there are four main takeaways.

First, our measurements indicate that lead was transported by the fire and then deposited in areas that extend far beyond the burn area. Our data shows that lead was transported by the fire plume and winds in the area more than 7 miles away from the burn zone. Second, the data on non-cleaned surface shows that lead penetrated inside most homes. The amount of lead is highest the closer you are to a window and about 10 times less on flat surfaces that are more than 1 meter away from the outside elements. Third, at a similar distance from a window, surfaces that had been cleaned showed 10 times less lead than surfaces that had not been cleaned. So is it imperative to do a proper cleaning to remove as much of the ash particulates and lead that was transported with those particulates. And four, continuous cleaning to remove any remaining particulates is a good idea, especially in areas close to windows and doors, which are the entry point for new particles and lead that might be present outside the home.

I need to emphasize that before proper cleaning, the majority of indoor surfaces we tested had elevated lead levels, well above the EPA limits. This is particularly of concern for children. According to the CDC [US Centers for Disease Control and Prevention] and WHO [World Health Organization], there is no safe dose of lead in one's blood stream, especially for a child. The CDC goes on to say that even low levels of lead in the blood stream of a child have been associated with developmental delays, difficulty learning, and behavioral issues. The bottom line is that cleaning is critical because it's not safe for children to be exposed to lead that they can breathe in or ingest.

And finally, the last measurement we took was to sample tap water. We sampled water from all taps that were connected during the sampling window and none of the samples taken had traces of lead that were close to or above the EPA limit.

What actions can people take with this new information?

I hope that our work can help people to better understand the potential impact of the fires in their region and enable them to take the informed steps to protect themselves and clean their environment as best they can. At the very least, one can go buy some cleaning wipes, put on protective equipment—gloves, goggles, N95 masks—wipe everything down and vacuum with a HEPA vacuum. It's important to use a HEPA vacuum, because it's the HEPA filter that will catch the fine particles. Without it, a regular vacuum just throws back into the air the fine particulate that one wants to remove.

There is a lot that we will continue to study in the months ahead. For instance, my instruments are not able to measure for asbestos, and, given the age of the buildings that burned, it is expected that asbestos was released during the fires as very fine particles, which poses a great health risk. A student in Julia Tejada's [assistant professor of geobiology; William H. Hurt Scholar] lab is collecting larger ash samples to look for asbestos fragments, and then we plan to measure heavy metals and other elements in the same samples.

The Eaton fire was not just a wildfire, it was an urban firestorm. If mostly trees had burned, what you're going to breathe in, in the worst case, is potassium, which is not particularly dangerous. Here, because it burned a populated area of older buildings, you have the potential to breathe in car batteries, lithium, and lead particulates from all the materials that burned in the built environment.

As remediation and demolition are underway, what do people need to be aware of?

Until all the debris removal is completed, I am concerned personally. The greatest danger that the ash represents is when people resuspend it in the air, like with a leaf blower. Not only does the leaf blower put the ash in the air, it also—if the ash particles are big enough—breaks those particles into smaller ones that people breathe. That's one of the main ways you can poison yourself with lead. Once it's in your lungs, it doesn't come out; it stays in the body. This is going to be one of the main dangers for many months to come as the debris is being removed and ash particles continue to be disturbed and dispersed from all the cleanup efforts in the fire zone, so it will be important for people to monitor the air quality and wear a mask when particulate levels are high.

Paul Wennberg [R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering] has started a project called PHOENIX, an array of sensors across the region that are measuring air quality in real time. It shows the amount of particulates in the air, though it doesn't specify exactly what they are. Regardless, if the air quality index (AQI) is elevated, it would make sense to mask up.

How did you work with the community to take samples?

In January, we did a webinar about our samples at Caltech, and, afterward, we received a lot of requests from people asking, ‘Can you check my house?' We had about 400 people volunteer to have their homes tested and the capacity to do only about 50 homes.

I went to a first-year student, Merritt McDowell, who was interested in cosmochemistry, and said, ‘This is not cosmochemistry, but it's incredibly important. You would gain the training that you need, but it's going to be super intense. You'll have to put everything else on pause, go sample houses, and it will need to happen on a very short timescale.' And she was amazing. She interfaced with everyone, built a small team of students from my group and beyond, and within one week and a couple of days had successfully completed the sampling of 52 houses. Finally, teaming up with Théo Tacail, a postdoc in my team, she finalized the analysis and interpretation of metal concentrations in over 30 metals across approximately 300 samples.

At each house, she sampled an outside window, an inside windowsill, a clean inside surface, tap water, and any other surface the participants wanted. The outside windowsill is the dirty surface that is going to tell us how much lead from the fire made it that distance from the fire; the indoor windowsill is going to tell us how much of it made it inside the house; the clean surface inside the house is going to tell us how much of a health hazard is left after you've cleaned; and the tap water is just in case anything made it into the distribution system.

Since the fires, LA has had a few days of heavy rain—does that change anything about the concentration of these metals?

The rain actually is really good. Lead is pretty soluble, so it is going to go from the ash on the ground and infiltrate into the ground. In the ash, the amount of lead is quite high. But if you dilute it into the ground, you'll maybe multiply by two the amount of lead naturally present there, which is not that much higher than usual.

You can imagine it with sugar: If you spread powdered sugar on the ground and then you use a leaf blower before it rains, you're going to put a lot of powdered sugar everywhere in the air—and you might not see it, but you will breathe it. If it rains, and the sugar goes into the ground, there's more sugar in the ground, but it's not going to be picked up as easily.

Tissot is part of a group of Caltech researchers studying the effects of the Eaton fire funded by the Division of Geological and Planetary Sciences (GPS) along with the GPS Chair's Council. Additional researchers studying the fire's aftermath are Jean-Philippe Avouac, Christian Frankenberg, Mike Lamb, Victoria Orphan, Alex Sessions, Julia Tejada, Paul Wennberg, and Zhongwen Zhan. Donors to the division have provided over $275,000 for the projects to date.

Find more insights from Caltech researchers on the 2025 Los Angeles fires on the Caltech Science Exchange.