Episode 3: Lead in the Environment, an Update

Julia Ehlert Nair: Welcome to After the Fires, from the Caltech Science Exchange. I'm Julia Ehlert Nair, a writer and science communicator at Caltech. In this limited series, we're sharing what Caltech scientists on campus and at JPL are learning in the wake of the LA fires, as they're learning it.

Today, we're bringing you an update on research into lead that was released into the environment during the Eaton fire. As we've discussed on this podcast before, the Eaton fire was different from other wildfires. So much of what burned was man-made material, and a lot of it included metals from things like cars, batteries, and appliances, as well as the lead house paint that was commonly when many of the homes in Altadena were built.

François Tissot: If we zoom in now to the Altadena and Pasadena region, there are more than 7,000 houses that have been burnt, and over 90% of them were built before 1975, which means they're very, very likely to contain lead-based paint.

Julia: You may recognize that voice from episode 1. That was Caltech geochemist and Altadena resident François Tissot.

François's expertise is in studying the chemical signatures of elements like lead and uranium in meteorites to learn about the early solar system, but in January, he started applying these methods to heavy metals released in the fire.

In this episode you'll hear from François and other Caltech scientists who are testing the ash and dust outside and in homes, plus a colleague from Chapman University who is testing soil on properties near the Eaton fire.

As we have more updates and research results, we'll bring them to you on the Caltech Science Exchange website and in this podcast. Now, let's turn to the researchers. First, about why they chose to dive headfirst into this research, setting aside other ongoing projects and working overtime in the lab.

A quick note, the audio you'll hear in this episode is from a Caltech webinar in mid-April.

François:

The very unusual nature of the fire means that there is very little guidance. The guidebook that has been used for typical fire does not quite apply. And so given the risk that lead represents for health, especially for young children. We have a deep need for data. And so we see the work we're doing as a public service to try to bring clarity to the community and try to help moving forward.

Julia: Next is Christine O'Connell, an Assistant Professor of Biological Sciences at Chapman University, who is focused on measuring lead and other toxins in the soil after the fires.

Christine: I live in North Pasadena. I have a toddler daughter and a very beloved dog. And basically, I got started on this project because during those initial 48 hours of being displaced, I wrote to a bunch of soil scientist friends to ask what I thought would've been maybe a simple question, which is can my daughter play in the backyard again? And can we eat the food in our garden this year and next year? And that led down this rabbit hole of realizing, just as Francois said, maybe we know some things about that after some fires, but this fire probably has some major distinctions from those other wildland urban interface fires. It became this enormous thing where I wanted to answer that question for my own family, but also for the tens of thousands of families who are also either living in the fire zone or in the smoke plume downwind.

Julia: Of course, passion and know-how are not quite enough to get these urgent projects off the ground—you also need funding. The studies you'll hear about today were funded by the National Science Foundation CAREER and RAPID awards, and private donors to Caltech's Division of Geological and Planetary Sciences Emergency Response Fund.

Back to François and graduate student Merritt McDowell who tested dust on surfaces inside and outside homes downwind from the fire plume.

François: And so the very peculiar nature of the fuel of the houses that have been burning, especially in the Eaton fire, means that heavy metals will be present in the plume, transported by the winds, and deposited along the way. And the questions that we have of course is to what extent were heavy metals present? How much was deposited along the plume? To what distance? This is a question we've had many, many times, how far is far enough to be safe? And so safety is defined typically by the EPA clearance level.

Julia: The Environmental Protection Agency, EPA, sets regulations in micrograms per square feet, which describes the legal concentrations of hazardous materials like lead measured in that one-foot by one-foot square area. François's group works in micrograms per square meter. To convert the numbers in this episode to the units the EPA uses, divide Francois's and Merritt's numbers by 10 and you'll be very close.

François: And so we wanted to know where are the heavy metals? Is cleaning effective? Those are our motivating questions.

Merritt: We started out with a very large volunteer pool of residents who offered their homes for testing. We ended up with a pool of around 400 volunteers, which given the manpower and feasibility of coordinating sampling, we weren't able to visit all. But we distilled this volunteer pool down to 52 houses covering as even and as wide of a spatial distribution as possible around the Pasadena and Altadena area, then expanding that pool to areas as far west as Glendale, south as Highland Park, and then east as Sierra Madre. Over the course of around February 5th through the 13th, we went around and sampled these 52 houses.

François: And we thank the people that volunteer their houses, this would not have been possible without them. We took over 450 samples of what we call dust, which is the fine particles. You might not be able to see that particle, but it might have been deposited inside the house on flat surfaces, on windowsills, on the floor. And we went back to the lab and we measured the concentration of heavy metals. We are focusing here on lead because it is one of the most, if not the most risky element for health, the highest health concern.

Merritt: We also tried our best to sample indoor and outdoor samples, as outdoor samples would give us an indication of how much lead actually made it from the fire to the home, and then indoor samples giving us insight into how much lead actually made it into the home once it reached that location. And so, in addition to those sets of samples, we also wanted to measure cleaned versus unclean surfaces.

Julia: What do they mean when they say clean? Any surface that was wiped down with water or a wet cloth of some kind, whether that was by a professional cleaning company or the resident. And to be extra clear: The team did not take measurements on the same surfaces before and after cleaning. They took some measurements from surfaces that had been cleaned and some from surfaces that hadn't, so they could compare those two sample sets.

Merritt: And so once all of these samples were collected, we then brought them back to the clean lab here at Caltech. Once we have all of these solutions processed and ready, we can put them into an instrument called an ICPMS, which is an inductively coupled plasma mass spectrometer. Essentially what this instrument does is that for each element in the sample, it will count the number of atoms, or more specifically ions to give us an indication of the concentration of that particular element in the sample. And because we're counting atoms, we can get this down to about a part per trillion level of lead concentration.

Julia: So, after all this high-precision work, what did they find?

François: What the map shows is that everywhere in Pasadena and along the plume trail, we have very high concentrations of lead on outdoor surfaces, which means that the lead that was released by the fire was carried very large distances, at least we've measured all the way to seven miles along the fire plume, and we still see the same elevated amount of lead.

Now, this is what is outside. What is much more of a concern is what makes it inside the houses. And we're going to start with windowsills because windowsills and flat surfaces and tables and floors have different EPA limits. Here, the limit from the EPA recommendation is 400 micrograms per square meter of lead on the windowsills.

Julia: The team found that before cleaning, a substantial number of houses—about a third of them—had lead concentrations above the EPA limit on their windowsills.

François: After surfaces that had been cleaned, we see a much better situation with much less lead on the windowsills. A few houses still have windowsills with elevated lead above the EPA limit. And from this data, we can conclude that most but not all of the cleaned windowsills have reduced level of lead below the EPA limit.

Now if we move further inside a home, we look at flat surfaces. Here we're meaning a table, a coffee table, a nightstand, anything that is not immediately the windowsill. The majority of houses that we've visited, especially in the Pasadena area have lead above the EPA limit on their floors and flat surfaces before cleaning. Surfaces that have been cleaned. Only a few remaining points are above the EPA limit. It seems to be rather random. And what it indicates is that most of the time, cleaning is effective and brings back the lead levels below the EPA limit, but it is not all the time; it is not a certainty that the cleaning will work. We're not sure what makes the difference yet, but this is what the data indicates.

Julia: For three of the windowsills tested, the team was able to determine that high lead levels were not necessarily due to the fire, but to soldering used on the windowpanes.

François: For all of the other points, we were not able to identify any other source than the fire. Yes, we have to think that the lead is coming from the fire. If you're within a meter of a windowsill, there is about 10 times more lead than if you are more than a meter away from the window. On average, clean surfaces have 30 to 10 times less lead than unclean surfaces.

Merritt: We also went, and at each house that we visited, we took a small sample of tap water to check to make sure that lead in particular was not making its way into the water distribution system. All of the tap water samples that we collected, all of them remain below the EPA action level of 10 nanograms per milliliter. That is very encouraging to see.

François: We have also data on cadmium, arsenic, chromium, all the heavy metals that people are concerned about. We only presented the lead because lead is much more enriched because of the nature of the fire because of the lead present in the houses. We see similar patterns for other toxic metals like cadmium and chromium and arsenic, but the amount of the element present is much less, 100 times less on average. After the debris removal will be completed, we will do a follow-up study, the same sampling that we did to hopefully the same houses or nearby to assess what remains in the environment now that everything is supposed to have been removed. But this will be taking place in a few months only.

Julia: Thank you to François's group for all their work to bring us this useful, if sobering, information.

So far, we've focused on the very fine dust that seeped into homes after the fires. But what about larger particles of ash that have been deposited in the region, on streets and in yards.

Isaac Aguilar is a graduate student in the lab of Caltech professor Julia Tejada, a geobiologist. He has studied forest management practices, and fires are part of his history.

Isaac: I grew up in San Diego County where wildfires were also a frequent concern. And I clearly remember two fires that occurred near my childhood home and the anxiety from having to evacuate in the middle of the night. So, when the Eaton fire happened, I really wanted to help with the response efforts to understand the environmental impacts. And by focusing on lead specifically, I think I hope to address community concerns in addition to tracking some of the ecological impacts of lead in the environment.

Julia: On to the ash.

Isaac: Ash is defined as the coarse residue from incomplete combustion of wildland vegetation and urban infrastructure. This is different from dust, which is a mix of fine ash particles, soot, and aerosols. And so this distinction is important because we discovered that they don't behave the same way.

And we collected samples of ashes from outdoor street surfaces between January 14th and the 25th.

Julia: Which means they started a week after the fire.

Isaac: Around the wildland and urban burn scar, and then areas in the southwestern wind direction. These ashes can be categorized in three distinct sources, the first of which was ashes from the urban fire scar in Altadena where there was a high density of damaged structures. The second type of ashes that we collected were ashes from the wildland fire scar along the periphery of the urban interface with the San Gabriel Mountain wildlands. And then the third type of ashes we collected were the ones that were blown outside of the fire perimeter. And we targeted the ashes along this northeast to southwest trending axis to try to understand how far ashes from the urban fire specifically may have been distributed by the Santa Ana winds.

Isaac: We did use the same ICPMS technique in the Tissot lab with the help of his amazing postdoc, Theo, to measure the concentration of lead in the ashes from the Eaton fire. And overall, we found that the concentration of lead in the ashes from the wildland burn scar had much lower lead than ashes from the urban burn scar in the Altadena area where there was a higher density of damaged structures. The urban fire ashes had over 300 micrograms of lead per gram of ash, while the wildland fire ashes had lead levels that were between 10 to 30 micrograms of lead per gram of ash, which was more similar to unpolluted soils that we also sampled from the Eaton Canyon. And the ashes southwest of the urban burn zone in Altadena still had high lead concentrations even though they were sampled from outside of the fire perimeter. The ashes we collected towards the east and Sierra Madre and towards the west and La Cañada Flintridge had lower lead concentrations. And it was only up to about five miles southwest of the Altadena burn scar where we saw that steep drop off in the concentration of lead in the ashes. And it was the winds that were blowing along that northeast to southwest trending axis that transported ashes with the high lead levels from the urban fire in Altadena at least five miles southwest of the burn scar perimeter. After that, it seemed like the lead level seemed to drop off.

Julia: I'll note that, unlike for the dust that Francois and Merritt sampled, there is no EPA regulation or threshold for lead in ashes.

But Isaac's team didn't stop there, they also checked for another dangerous substance: asbestos. Once commonly used in building materials, asbestos was linked to lung cancer and mesothelioma. Its use was restricted in the 70s and all-out banned by the EPA in 2024.

Here, there is actually a bit of good news.

Isaac: Asbestos can be challenging to detect in ashes because the high heat from fires can consume or degrade asbestos and into smaller fragments, and that's why we decided to send some of our ashes that we collected to a professional service lab that specializes in asbestos quantification methods. We got our results back just this week that found no asbestos detected in any of the ashes that we submitted. And so this suggests that the ashes from the outdoor street surfaces where we sampled didn't have any asbestos in them, but we can't extend this interpretation to any other types of samples like dust debris or aerosols because we didn't test for those types of samples.

Julia: Especially when it comes to high-impact, community-relevant research, collaboration and knowledge-sharing are essential parts of the scientific process, helping to inform the public, policymakers, and fellow scientists with accurate data and sparking ideas for new research.

In the spirit of collaboration, we'll turn to a researcher from another Sothern California institution who is contributing to what we know about the environmental effects of the fires: Christine O'Connell from Chapman.

She's the researcher you heard at the beginning of the podcast who wanted to know if her toddler and dog could play in the yard after the fire.

Instead of looking at the ash and dust directly deposited by the fire, like the last two researchers we heard from, Christine's team is testing surface soils to see what heavy metals have made their way into gardens, lawns, and yards.

Christine: Our core question is what contaminants are on residential soils in and around the Eaton fire? What forms are they in? What might be coming off of them and what are the present and longer term risks? These are some really large questions that are going to involve longitudinal studies, will require many different dependent variables and different types of measurements. But today, I'm going to present the initial survey results that we've collected.

Julia: To measure their samples, Christine's team used a portable x-ray fluorescence analyzer. We're going to call this an XRF analyzer.

Here's a slightly technical explanation of how this technology works, then we'll get back to the results.

Christine: The way these analyzers work is they send out a burst of x-rays towards a sample, a material, whatever you want to measure, and they excite the atoms in that sample. Those atoms, as they get excited, send back fluorescence. And the analyzer can use that fluorescence to calculate what materials and what elements are present in that sample. A huge benefit of an XRF analyzer approach is that you get results very fast and you can take many of them. What you're giving up in that trade-off is that your precision at low concentrations isn't as strong. For that reason, we're really only presenting lead results because lead is present in high enough concentrations that even though we're using a less precise survey data method, we're really confident in the lead results. For metals that are present at much lower concentrations, this kind of baseline extensive survey data probably isn't as valuable of an approach. What did we do in and around the Eaton fire? We have followed 20 residential properties, 10 that have burned structures and 10 that do not have burned structures on the property. And for every visit to those properties, we've taken between 10 and 50 scans per site per visit. The reason that the number of scans and observations varies is we are only looking at garden, lawn, and yard soils, so it depends on how big the lawn or garden is of those properties. This sampling is ongoing; it's over a longer time period. The data that I'm going to show here represents about 430 samples we took from only surface soils. Lead in the surface soils of gardens, lawns, and yards in our data set exceeded the California recommendation for residential soils in about a third of our observations and exceeded the EPA limit in about 7% of observations. By definition, all of these data are from soils that are not slated to be removed during the FEMA/Army Corps of Engineer debris removal. We only tested soils that were outside of the debris shadow. None of these soils would be scraped during the conventional debris removal process that you might've read about in the news in which the top six inches of soil are slated to be removed directly underneath fallen debris. These are the remaining yard and garden soils that will remain on your property if you have a burn structure that's having debris removal conducted by the Army Corps of Engineers. There is substantial variation in lead both within and across properties in surface soils. And within the yard of a given home, there are some areas in which we read much higher lead levels than not. If something burned down in your garden or yard, think things like a heater, an electric or gas fire pit, a grill or barbecue, or if they melted, those probably aren't going to be on your mind as the core part of the debris that you need to be thinking about, but we have been opportunistically taking samples immediately adjacent in the soils right around things like your barbecue, your fire pit, your portable heater by your picnic table, stuff like that, and we see some really, really high numbers; not always, but often enough. If you live on a property in which you had fire damage to one of these smaller pieces of debris, you might potentially take care to proactively remove the soils right around that item. But we didn't immediately see a correlation between lead concentrations making it into soil and distance of the closest burn property. That's in keeping with what we just learned from the last three speakers. We weren't incredibly surprised by this finding just because we know the smoke plume moved lead very far. We're continuing to investigate this dynamic.

Julia: Something else Christine's team noticed was that there was actually more lead in the tiny particles of soil than in the larger particles that you might see or feel on your skin. This is not so good news.

Christine: These fine soil particulates, which we're going to define here as less than or equal to 250 microns in size, are the soil particles that are more mobile, they're more ingestible. These are the particles that can electrostatically stick to skin, food, clothing, hair, pet hair, and you might not necessarily notice them. These are also the particle size at which you don't really notice it inside of your mouth the way you would with a larger piece of soil, piece of sand, et cetera. These fine soil particles we think of as the readily ingestible soil particles that are actually making it into your digestive system and then potentially allowing that lead be mobilized into your bloodstream. Soil particulates that are these fines, these 250 microns in size or smaller, were on average in enriched by 61% in lead in comparison to the bulk surface soil samples. Why does it matter? I guess one of our core takeaways is that the soils around you, these fine particulates, your bulk measurement that you might get out of testing isn't necessarily going to represent what your child or your pet might be ingesting. Here, the general interventions that you can make is just to limit your exposure to these very fine particulates, which again, you're not necessarily visually seeing or feeling inside of your mouth.

Again, the standard ways to mitigate your exposure is hand washing, frequent hand washing, remove shoes on your way indoors. It's just trying to limit how much of this dust gets into your house where you're eating food, having your kid play on the floor, sitting on the ground, et cetera.

Julia: Christine and her colleagues are digging deeper into how much of the lead from fine soil particulates could be making it into our bloodstreams—also known as its bioaccessibility. To do this, they simulate a human stomach in the lab. This is the type of data that could inform public health department recommendations on lead levels in residential soils.

We also asked Christine how long lead would stick around in the soil.

Christine: I think it's fair to say it's more on the orders of months to years, not days to weeks. We're two months into the sampling; we have not seen a statistically significant reduction in these lead levels. We've done some limited sampling in the immediate wake of a rainfall, and we did not find a drop in lead levels, so we're anticipating some level of persistence. There's a lot of unknowns. How long these sorts of contaminants can stay in soil is going to depend on the form of the contaminant, the speciation of that metal aspects of soil hydrology, the soil science of the different particulates in soil. Some soils are more sticky to metals than others. Our soils around here aren't going to get a ton of rainfall as well, which can potentially influence mobilization of these sorts of metals.

Julia: Overall, Christine's work suggests that soils in and around the Eaton fire burn zone could be a source of lead above the recommended levels. So how do you know if your property is affected?

Christine: If you're doing this testing yourself, we advocate for using a composite surface sample, which means only bother getting the top centimeter or two of your soils. Walking around your yard, getting a bunch of samples at once, putting it into the same baggy or jar, mixing it all together, that'll get you with fewer samples, more holistic composite of what might be going on in your yard. And if your lead levels are elevated above that EPA limit advocate for soil removal and replacement.

Julia: Armed with this information, what did Christine decide when it came to her daughter and her dog?

Christine: I'll say just personally, I live less than a mile downwind. We did do professional remediation inside of our home. Outside of our home, we are mostly implementing mitigation strategies to limit our ingestion of these fine soil particulates, hand washing, shoes off in the house, wet mopping around the doors. But in our yard, we're putting down a new layer of mulch and we planted a bunch of native plants. Finally, I think something that a lot of people might want to consider is speaking with their doctors, pediatricians or veterinarians about having vulnerable people in the household, have their lead blood tests done on some recurring schedule. I will say, my daughter went to the pediatrician yesterday to get her blood tested, and our dog is going to the vet tomorrow to get his blood tested. Maybe our approach has been like trust but verify or cautiously proceed. We are letting her play in the backyard. That makes me a little nervous, but you have to balance your kid's happiness a bit too.

Julia: Back to the results we heard earlier in the show, you can also take indoor lead testing into your own hands.

François: If you are in a zone where you think your insurance is going to cover for this kind of thing, you should definitely ask your insurance. If not, there are some lead tests that you can buy. The EPA recommends three of them. One of them is the lead check test, which is just a little stick that you take and wipe a surface. And if it has more than a few microgram of lead on the surface, it will turn bright red.

Julia: And if you live in the LA area, the Department of Public Health is offering free testing to check blood lead levels. For more information Visit public health dot lacounty dot gov slash media slash Wildfire

Thank you to all the people who contributed to these studies—the researchers you heard from, the students and staff in their labs, the donors, and those who volunteered their homes for testing.

For now, thank you for listening.

I'm Julia Ehlert Nair signing off for After the Fires, a limited series from the Caltech Science Exchange.

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This episode was produced by the Caltech Office of Communications and External Relations and Caltech Academic Media Technologies.