Science Friday - Tracking The Toxic Fallout Of The LA Fires

Episode Date: January 23, 2026

This time last year, Los Angeles was on fire, and more than 16,000 homes and buildings burned to the ground. Cars, batteries, solar panels, insulation, and cleaning supplies went up in flames, releasing chemicals like lead, benzene, and asbestos into giant smoke plumes that wafted across the city.A year later, scientists are trying to understand the fallout of this urban wildfire—what chemicals got left behind, how to remediate them, and the threats to our health. Host Flora Lichtman talks with Yifang Zhu and Francois Tissot, who are at the forefront of this research. And for one of them, this work is personal.Guests:Dr. François Tissot is a professor of geochemistry at Caltech in Pasadena, California. Dr. Yifang Zhu is a professor of environmental health sciences at the University of California, Los Angeles.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flora Lichten, and this is Science Friday. Today in the show, the toxic fallout of urban fires. This time last year, Los Angeles was on fire. More than 16,000 homes and buildings burned to the ground. Cars, batteries, solar panels, insulation, cleaning supplies, all up in flames, releasing toxic chemicals into giant smoke plumes that wafted across the city. A year later, science. Scientists are trying to understand the fallout from this urban wildfire. What chemicals were left behind, how to remediate them, and what threats they pose to our health.

My next two guests have been at the forefront of this research, and for one of them, this work is personal. Dr. Francois-So is a geochemist at Caltech, and Dr. Ifung-Ju studies air quality and its health effects at UCLA. Welcome to you both to Science Friday. Thank you for having me. Thank you. I want to get into the toxicology in a second, but Francois, let's start with your personal story. What happened in your neighborhood? Yes. Well, our neighborhood was almost completely burnt down.

Our street, only the house that we used to live in, and another one didn't burn. Everything around is just complete desolation. The house is so contaminated with heavy metals and asbestos, and it's completely unlivable and unsafe. I mean, obviously this is so personal, but you also made it professional. Why? Well, we made it professional because we have the tools to make a difference and bring data that was missing. I guess the first thing I did when I saw that the fire was happening is I looked up if there was any paper that we're discussing how much lead and heavy metals and contaminants will be transported and how far and how, what are the risk I wanted to understand. but it turns out there is almost no literature on this kind of urban megafires.

There are new kind of threats. There is very little that is being known. And there was nothing for me to make an assessment of risk from. So I told my group that if anyone in a group wanted to work on this, we should really do it. And the response was very positive from them. And we got started immediately trying to answer very basic questions, such as the lead that had been seen in the air, how far did it go, how much was released, how much of a danger to human health is it?

What do you usually work on? My training is in a field called cosmochemistry and geochemistry, which is the study of planetary formation and solar system evolution using meteorites and chemical tools. typically we make very complex isotopic measurement, very precise measurements. Concentration measurements are much simpler for us. They're usually the step one of anything we do. Except in this case, for the fire concentrations are all you need to know because you just want to know if the element is present in what quantity so that you can assess how big of a risk it is. I mean, you must have felt desperate in some way to get these answers.

I was really shocked to see that there had been no systematic studies until now because urban fires are not a complete novelty, but I guess the magnitude and the scale of the devastation that those mega fires bring. This is novel. It has not been studied. And so, well, I guess we were at the wrong place at the right time to make a difference. Ifang, I know you have been collecting samples and testing the air for the last year. What have you found? Yeah. So we took three phases of measurements, right? We collected air samples during the active fire period. And then went back again and took measurements when the fire was about halfway contained. And then, you know, went out again another round to take air samples when the fire were completely put off.

So when we take measurements, we collect samples inside and outside people's home, both indoors and outdoors. I think the big surprise to us is how much higher some of those chemicals were inside homes comparing to outside after the fires were over. So this is especially true in homes where no one was living at a time, right? So we know there's lots of indoor sources, cleaning products, cooking, smoking, all can produce those VOCs. inside people's home, but the fact that we're seeing those high levels inside homes that is unoccupied really tells us there's some source going on in those homes. So this is a really, you know, an important public health message basically like, you know, saying that people really need to be aware about potential exposure at risk when they consider in returning homes, right?

When you say inside, was it air quality? Was it, you know, your sofa was loaded with these Toxic chemicals, what do you mean? Yeah, that's a very good question. We actually did two parallel projects where we're actually studying off-gassing from soft goose, household materials, like carbons and clothing, stuff, animals, pillows, those soft materials, they get soaked by the fire smoke

during the active fire period. And then, you know, after the fire is over, they were kept inside people's home and for security reasons or people just worry about, you know, outdoor air quality, oftentimes they just kept their home sealed. So those soaked materials, they would start to off-gassing, basically giving back those chemicals into the indoor space because the indoor space is now well ventilated. So they just got accumulated inside people's home. So like your rug or your couch absorbed all of these chemicals and then is just basically off-gassing, Exactly.

Francois, did you sample inside your own home, and what did you find? Yeah, my house was one of the first homes that we sampled, of course. We found what we find in any home in the burn area, elevated lead levels above the recommended safety limits from the EPA. We found very high levels of arsenic as well, both of which are coming from the constructions that burned around our house. For different reasons, lead was in lead paint and in lead pipes. And the houses in Altadina were all very old.

Most of them were built before the 1950s. So before any ban on lead or asbestos. And the arsenic was used as a termite treatment until the 2000s. And so all the wood from all the houses around us was containing this arsenic, and it released it when the house is burnt. Are people having to pay for testing for these chemicals themselves? It is one of the main problems that the local community is facing. It's that insurance companies, they have a guidebook that they follow on what to do after a fire.

But their guidebook is based on wildfires. And wildfires do not release arsenic or lead or any of those toxic elements because it's not in trees or the shrub or anything like this. So when I asked for testing in my house because I had already tested and I already shown that there was lead and arsenic and all of these elements, their response was we typically don't do this testing, so we're not covering for that cost. And also, there is no reason there should be lead in your house. My response was, of course, well, I have already measured that there is lead. And they said, well, you're not a credited lab. So we will have to have a professional lab tests, test your house. And when I ask it, they do it, they said, well, we don't do it in this instance.

So then there was this catch-22 where it is there. I showed it's there. But their guidebook does not say to do this testing unless there is a reason to think that there is lead, which just me saying it was not enough for them. Right. And they don't think that there's lead because there's no actual scientific research. There's not a lot of scientific research showing where you might find lead after an urban wildfire because it's a new kind of disaster.

It's, and this is something the National Academy has said, wildfires at the urban interface need to be studied because we don't know the risk, but it has not come to reality yet. Yeah, I mean, there's like a wide range of contaminants, right, from organics to heavy metals, arsenic. There's also benzene, twirling. They're all, like, say, have a serious,

health effects and insurance company, they're not obligated to test those chemicals at all because some of those, you know, they're not like have clear health standards published by or enforced by the government. So they're really limited testing going on in those homes during this post-of-fire recovery period. And we know they have house effects when people exposed to them for a long time. this is also why we started this work, because it is very needed for the next fire. And there will be one such next fire, because right now, one in three houses in the U.S. is in an environment that's called Wui, the wildland urban interface. This is where most of the expansion of the cities have happened.

And those are the places where very tightly packed houses interspaced with brush and other fuel can basically burn like L. Dina did. We have to take a break, but don't go away because when we come back, we're going to talk about where we go from here. Stay with us. Okay, we're back. Yvonne, can these toxic chemicals that we're talking about, you know, we're talking about asbestos and lead and benzene and others, can they be cleaned up from a house?

Yeah, that's a big question. It's just like a frank mention. We realized that there were, you know, how little knowledge that is all there in a scientific community, let alone guidance and post-of-fire remediation and all those uncertainties, I feel especially for vulnerable communities, is really challenging. So there are some insights, like general guidance, I think we feel comfortable to give to homeowners and residents. Like we know, for example, on the air side, we know, like, increased ventilations in your

indoor space could help running hippon air purifiers. especially with charcoal filters, could help reduce volatile organic compounds, remove particles, resuspended from deposit dust. You know, cleaning up your HVAC system is really important doing remediation, remove those smoke-impacted soft materials from the indoor spaces. All of those could help. But, you know, we really don't have enough data to give concrete answers

about which method is the most effective or cost-effective. active at this point. I mean, Francois, will you feel safe going back to your home? That's a very good question. Every expert that we have brought into our house, which has suffered extensive smoke damage and asbestos contamination, has said you have basically two options. You can either demolition rebuild and that will remove the contaminant, of course. Or you can strip down the house to the studs and then rebuild from there. And the rational for them is they do not know that they can clean the house by just cleaning the surfaces.

The only way that they can envision cleaning is removing the contaminant, removing all the coarse materials, including the walls and anything that was inside the walls. And that goes back to your question of can we clean? And it's an open question. when the amount of contamination is low, maybe a couple times above the EPA limit, yes, cleaning is possible. You can use wet wiping techniques and hepavacuuming and remediation companies know how to deal with that level of contamination. What this particular fire has brought to light is that some houses have been contaminated to such an extent

that we do not know if the cleaning techniques that we have are appropriate or efficient at all. And until research is done to answer this question, then the only approach is to remove the material itself. I mean, Ifung, how long will it take to know the health impacts from this fire? Yeah. So there's, you know, acute healthy facts. There's already studies being published like showing during the active fire period. The number of an ER visit went up. Not only the number of ER visit went up is also the abnormal blood test from those ER visits. it went up, like relative to the previous year of the same sort of like a generate timeframe. So the acute healthy facts is already being, you know, showing them and documented. The long-term healthy fast from those wind fires is really a big gap, knowledge gap.

Has there been any federal support for tackling some of those unknowns? So I have a penny and that you just grants and it's been pending for eight months. So it's supposed to be a rapid, rapid ground mechanism, but clearly not so rapid. So the funding climate at the federal agency levels is definitely also not helpful in this setting. Yeah, I guess I can jump in here. The climate of funding is really making it difficult to go after those kind of questions. The only reason that we've been fortunate enough at Caltech to do it is because Caltech was supporting this research from a few days after, the fire, they immediately said, whatever you guys need to do that can benefit the community,

do it and we will find the money for it. This is what federal agencies should do. This is what those rapid proposals that Yufeng was referring to should be doing. Clearly, this is not the priority right now. Francois, your usual research is on, you know, as you were saying, the solar system and how planets formed. What's it like to go from studying something? You know, know, wondrous and abstract to, is my house going to poison me? Like, has it changed the way that you think about science or your own research? It's definitely a different exercise. There is a sense of responsibility that comes with it that I'm very aware of, and I'm immensely proud of the work that my group has been doing, trying to address such a difficult situation. If this data had

existed before, it would have made everyone's life, myself included, so much easier. We wouldn't have to argue for months or years on end with insurance. We would, it would just, yeah, it would just have made it easier to face an already extreme challenge. If we, and by we, I mean my group and other researchers can bring answers that will prevent some further suffering. in future fires, then it will be worth it. Dr. E. Fengju studies air quality and its health effects at UCLA.

And Dr. Francois Tiso is a geochemist at Caltech. Thank you both for joining me today. Thank you so much for having us. Thank you. This episode was produced by Russia Auredi, and y'all, Russia needs your help. I'm about to pivot, so that's your warning. We are working on a show about games and gamification. and we want to hear from you.

Tell us about a time when a game changed your life. There's lots of different ways this could go. Maybe it's that first time you closed the ring on your Apple Watch and you turned into an exercise freak for life. Or maybe it was something more analog, like a game of truth or dare when you were a tween that you'll never, ever recover from. Tell us the story about how a game changed you for better or worse.

Please leave us a voicemail. 8774. sci-fry. That's 877 for sci-fry. Thanks for listening. Have a great weekend. I'm Florida Lichten.