Science Friday - The Toxic Aftermath Of An Urban Fire

Episode Date: February 3, 2025

After nearly four weeks of burning, the fires in Los Angeles are almost fully contained, and cleanup is underway. But as the dust literally settles, people in LA are left with major questions, like: What is actually in the ash? What’s in the air? And how do I stay safe?Flora Lichtman talks with two experts in public health and toxic substance exposure about the chemicals left behind after an urban fire as well as what science needs to be done to fully understand the issue. She speaks with Dr. Rima Habre, associate professor of environmental health and spatial sciences at the University of Southern California in Los Angeles; and Dr. Mark Wilson, director of exposure science at Chemical Insights Research Institute (CIRI) in Marietta, Georgia.Transcript for this segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This is Science Friday. I'm Flora Lichten. Today on the podcast, the fires in Los Angeles are fully contained, but now residents are dealing with a different problem. The toxic chemicals left behind. It's definitely an open question in terms of how much cleanup, how deep of a cleanup, how often should you keep cleaning up until you can feel safe again in your home. As the dust literally settles, people in L.A. are left with questions, like what is in that? ash coating my backyard. What's in the air and how do I stay safe? Today we've got two experts in public health and toxic substance exposure on the line to talk about the chemicals left behind after an urban fire, how much is known, and what science really needs to be done in order to understand this problem. Let me introduce my guests. Dr. Rima Haber, Associate Professor of Environmental Health and Spatial Sciences at the University of Southern California in L.A.

And Dr. Mark Wilson, Director of Exposure Science at the Chemical Insights Research Institute in Marietta, Georgia. Welcome to Science Friday. Thanks so much for having us. Hi. Thank you for having me. Rima, give me a sense of what's happening in L.A. right now. Where are we with the cleanup process? We are now at the point where people are starting to go back to their homes.

Some of them have been cleared through what we call phase one. others are still waiting. But the cleanup hasn't really kind of finished yet. I would say it's not even maybe halfway. It's massive and like the scale is unprecedented. So there's so many questions people are having right now. I mean, is it safe for people to go back to burned structures? I think that's what we're all struggling to answer as accurately and as kind of in the most helpful way as possible. You know, a burned structure obviously. see is very dangerous and I'd love to hear Mark's thoughts on that. But where we're struggling the most is many people are going back to not so damaged structures, but that have a lot of ash outside and

around them and perhaps in them and got a lot of smoke damage. And even when you clean that up, you have a lot of lingering questions around what's possibly safe or not even in the longer term. Yeah, I agree with that it is. is very difficult to understand just what safe means, given the vast differences in level of impact that are going to be experienced at different locations. And there are very significant unknowns associated with what chemical hazards as well as physical hazards exist within the residual materials and how those may be trafficked in the environment. and how they may ultimately impact health.

Well, what are some of those unknowns specifically? The nature of the residues is heavily influenced by the fuels, the combustion fuels that were associated with the event. And those can vary widely from location to location, even residents to residents. So things like age of properties can be important covariates associated with whether you are likely to see things like heavy metals from legacy building materials like lead in paint or lead service lines in water versus newer residences

which may have things like solar panels and power walls and e-vehicles. So it's very difficult to have a broad understanding of what types of hazards you anticipate being present. Yeah, absolutely. I mean, you know, I think it's exactly what Mark said. And also, let's say, asbestos, which, you know, we know that might not travel too far, but it's so hard to know given how complex the plumes were, how windy things have been. But also, you know, we are worried about kind of what we call multimedia exposures now to people going back.

So let's say some of the really open questions are exactly what Mark said, like how much of that is remaining inside my home or right outside. Lead and asbestos are particularly concerning, especially if you have kids who like to play on the floor and, you know, get their hands in their mouth or track in the outdoor dust and dirt. But also, even for the smoke itself, we know that a lot of these kind of volatile compounds, you know, tend to like, glue themselves onto surfaces and will take a lot of time to start off gassing and stay in the air even after you clean up. I'm not saying that is maybe the most scary thing or concerning thing right now, but it's definitely an open question in terms of how much cleanup, how deep of a cleanup, how often should you keep cleaning up until you can feel safe again in your home. So you're saying that even if you've cleaned up all the ash, there could be,

small volatile organic compounds that are stuck in your couch or that could sort of re-off gas. Is that right? 100%. And I, you know, we've been talking about this a lot and I worry that sometimes we're making people panic about every little thing that could be there. I'm not saying those VOCs are maybe my biggest worry relative to lead and asbestos, right? And the things that Mark mentioned, especially with these newer materials. We're not sure exactly what's in them. But all of these are still open questions, and we're trying hard, you know,

especially in our exposure science community, like Mark and I are specialized, to kind of get people more actionable information and answers. Like, how do you figure these things out? Well, what kind of chemical monitoring is happening right now in Los Angeles? We're trying to deploy a lot of, of air sensors and monitors. Right now, the air quality is much better, to be honest, but also sometimes the ash gets kicked around. We're trying to measure more of the chemical species

within the particles and the gases and volatile organics in the air. But we're also trying very hard to deploy into homes to measure what's in the dust and the soil, especially like ash impacts or remaining kind of air contamination, water contaminations. The tricky part is these are, you know, very intensive, very complicated studies, and they need so many things to line up together to be able to do them. So we're not fully out there yet, but we're working very hard around the clock to try to do that. Let's talk about air quality a little bit because I know this is on people's minds. I want to play a question from one of our L.A. listeners. Hi, my name is Sandin Totten and I live in Los Angeles, California. A lot of what I'm scared about and wondering about is like, you know, there's these particles we've heard we can't really measure things like asbestos or benzene. And how much of that is in the air?

Like, should I be wearing a mask when I go outside? And I've heard N95 don't quite catch all the smaller particles. So, you know, should it be full-fledged gas mask like a P-100? You know, it feels like that really is post-apocalyptic. I also have a young child. He's four years old. And I don't know. Should I be keeping him indoors?

When will we know it's safe to let them run around and take, you know, big, healthy gulps of air again? Mark, any thoughts? I think it's important to recognize that the caller brought up two distinct classes of hazards. They brought up benzene, which would be a volatile organic, which we were just talking. about and also asbestos. If you are going to use something like an N95 respirator, that might provide a good level of protection associated with something like particles or fibers like asbestos. But depending on the type of respirator, like in the absence of a VOC cartridge, wouldn't provide any protection at all for gases.

So until we have a better understanding of kind of the holistic picture of what the chemical hazard landscape looks like, both in the air and in soils and water and dusts, it's going to be very difficult to make definitive statements associated with safety. Mark, would you be wearing an N95 or a more heavy-duty respirator if you were in L.A. right now? If I was personally there, yes, I would wear respiratory protection. I would focus a lot on hygiene, so hand washing and things like that. I would certainly consider if I was going to interact with any kind of impacted area that I would want to probably wear disposable gloves, clothes,

clothes-toed shoes, long pants, long-sleeve shirt. But we also have to acknowledge that the personal protective equipment has to be appropriate for the hazards. And when we don't have a real clear picture of what those are, it's difficult to identify exactly what level of protection is necessary. Rima? Yeah, I definitely agree with. that, Mark. I think I just want to make a couple of clarifications because we're also getting a lot of

these questions. So I think Sandin was our caller's name. And basically, like, I'm in L.A. right now. I'm going around as normal, not wearing anything. In general, day-to-day life, not in impacted areas, right? But there is a distinction. When the fires were burning, of course, we're worried because all these things are being emitted very quickly and in large volumes, right? So I would wear protection if I'm going outside, or at least I would consider it if you're in the general L.A. area and not very close to the burn or very adjacent to it or downwind of the smoke. But right now, I think if you are going into impacted areas like Mark said or trying to clean up your house or, you know, you were very close to it or in the middle of it, that's when I would wear protection

for sure, and exactly like Mark said, right? I do think another important thing that Sand and our caller mentioned is their child, who's four years old. And with children, we worry more, of course, because they're in such a sensitive developmental stage of their life. And the kind of the open questions we have now are, you know, if they're out playing in a sandbox or on the playground. And yes, there's a little bit of leads that kind of deposited at,

one of these events, perhaps ash and asbestos, how much cleanup should happen to make sure they are safe. The really important question is sort of how much deposited on these surfaces that the kids are playing in, especially when it comes to lead and ash and metals and asbestos. So, you know, just keep in mind that lots of open questions, but still, as Mark said, If the air quality is good outside and you're not right in the zone, you're probably fine. After the break, why is the chemical fallout from an urban fire so difficult to study? In a world that is completely not impacted by resource limitations, I would build a city and then create a very large-scale fire in a mock city and see what happens. Stick around.

Did these air quality indices pick up on some? some of these other chemicals that stand in and that we've mentioned. I mean, if you look at AQI, like, is it actually going to give you a picture of whether the air is safe? So here's the thing. I think people are kind of doing unfair comparisons with the AQI because the AQI was designed as a communication tool, you know, and it's done so much public health good and benefit. The AQI can only use information that we measure regularly, and that's, you know, particles and

maybe NO2 and ozone, depending on what's around. We don't have measurements of VOCs and these toxic as regularly and as intensively as some of these other things. That said, the AQI is still a very good indication of whether, you know, you should be worried yes or no and it should help you plan your life, but also your nose can tell you a lot if you're smelling smoke, you know, or seeing smoke in ash. Rima, what long-term health effects are you concerned about? So there's mental health effects, of course, and trauma from the entire disaster. But, you know, we worry about cancer effects because some of these toxins are more hazardous than your average particle. We worry about cardiovascular effects, longer term respiratory effects.

You know, ash is very irritating as it is, let alone now with all these urban fires like Mark was explaining, you know, we don't know what kind of damage that could have caused. So this is, again, not to alarm people, but when you look at like an entire community that was exposed over the long term, across all these people, we definitely. you know, we'll be monitoring to see what the chronic health outcomes will be. Mark, we've talked a lot about how there are so many unknowns right now. You know, if we wanted to understand fires and chemical exposure on a scale like this, what is the ideal science experiment that you would do?

That's such a good question. I want to know. I mean, in a world that is completely not impacted by research, limitations, not impacted by time. You know, I would build a city. I would geotag everything within the city so I could account for point sources of various things like homes that contained lead, e-vehicles, internal combustion vehicles, et cetera, and then create a very large-scale fire in a mock city and see what happens. You'd burn it down. that that's you know that's not a practical approach do you do this on a smaller scale in your lab

we do try to recreate scenarios that are associated with various fire fuels but one of the biggest challenges with lab scale reconstructions is that it is literally a matter of scale So things like temperature of combustion or combustion efficiencies are difficult to impossible to recreate at a small scale. Mark, do you have any cleanup tips for people who are going back to their house and maybe there's ash around or they're near an affected site? What should they do? One of the kind of critical things that I would do myself would be using a. as highly rated air filtration system as my HVX system could deal with. So MIRV-13 or better. And I would engage in cleaning practices that were not stirring things up. So mopping would be

better than using a broom, for instance. But the ultimate answer is that there isn't a very clear criteria to establish how you clean all things all of the time. When do you think we'll start having some answers? And what should people be doing in the meantime? I think over the next few weeks, because a lot of people are mobilizing, and I'm so glad I met Mark through Science Friday, because I will need your help, please, and expertise as well, and I'll reach out. But I think over the next few weeks, you'll start to see data coming out. I want to say, in the meantime, though, there's so much good. practical information out there on how to clean, how to be safe, listen to people you trust.

Don't panic. But if you're in impacted areas, try to be safe about these things. If you're in a general area that's not as impacted, you can go about your day-to-day life and hopefully try to help as much as you can with anyone around you who needs help. Thank you for joining me today. Thank you for having me. Thank you for having me. Haber, an associate professor of environmental health and spatial sciences at the University of Southern California in L.A. and Dr. Mark Wilson, Director of Exposure Science at the Chemical Insights Research Institute in Marietta, Georgia. And that is about all we have time for. Lots of folks helped make the show happen, including...

Floresa Males, Danielle Johnson, Beth Rami, Santiago Flores. I'm Flora Lickman. Thanks for listening.