Lead Concentration in Dust and Tap Water in the Aftermath of the Eaton Fire
On January 8, 2025, the Eaton fire rampaged through Altadena, destroying more than 9,000 buildings and taking 17 lives. Because more than 90 percent of the houses in Altadena were built before 1975, many were likely to contain lead-based paint and asbestos, materials that have been banned by the Environmental Protection Agency (EPA) for their danger to human health. In response to the growing concerns among the local community, between February 5 and 13, a team of isotope geochemists from Caltech collected samples from 52 houses in areas ranging from deep within the fire zone to neighborhoods miles away. The lead concentration data from the samples, collected outside and inside these homes, are presented below. Data for other toxic heavy metals (e.g., cadmium, arsenic, chromium) follow a similar pattern, and the conclusions shown below apply to these elements as well. Key takeaways are summarized at the end of this article.
Methods
At each house that the team visited, dust samples were collected on outdoor (e.g., windowsills, tables) and indoor (e.g., windowsills, table, countertops) surfaces using wet, clean wipes. The wet wipes were used to swab a predetermined surface area (using a stencil), and then placed in a clean centrifuge tube. The tubes were then transported back to the Isotoparium (Tissot Lab, Caltech), where a strong acid (4.5 M HNO3 + 0.01M HF) was added to the centrifuge tube to release the heavy metals from the wipe. The tubes, containing the dirty wipes and acid, were shaken for two hours, after which an aliquot of the solution was taken and heavy metal concentrations were measured with a Q-ICPMS: a high sensitivity mass-spectrometer capable of detecting parts-per-trillion levels of lead (which is a million times below the EPA limit for lead).
At all properties, an effort was made to sample, at least (i) one outdoor surface that had not been cleaned since the fire, (ii) one indoor windowsill that had not been cleaned since the fire, and (iii) one flat surface (e.g., table, desk, countertop, nightstand) that had been cleaned since the fire. In most cases, samples from both cleaned and non-cleaned indoor windowsills and flat surfaces were obtained. At each house still connected to the water lines, a centrifuge tube was also filled with tap water to check heavy metal contents in the tap water
Results
To preserve the anonymity of all participants, on all figures, the symbol for each house was placed randomly within a 100 m radius of its actual location. All results are reported in microgram per square meter (μg/m2). To convert to microgram per square feet, the units reported by the EPA, simply divide by 10: i.e., 10 μg/m2 ~ 1 μg/ft2. The color denotes the highest concentration measured for each house and surface type.
For comparison purpose, values exceeding the EPA limit for indoor windowsills (~400 μg/m2) are shown in dark red, and those only exceeding the indoor flat surface limit (~50 μg/m2, for floors) are shown in bright red. The markers indicate the highest lead concentration measured in each location. The highest lead (Pb) concentrations generally follow the wind patterns of the Eaton fire plume, moving from the northeast closest to the burn scar (darker gray region indicating damaged and destroyed structures) to the southwest. For homes that were located within or along the fire plume, even at a distance of more than seven miles away from the fire zone, measured samples indicated that most outdoor surfaces exceeded the EPA lead limit before cleaning. Samples were collected between February 5, 2025, and February 13, 2025.
The left and right panels show, respectively, Pb concentrations from indoor, uncleaned and cleaned windowsills and flat surfaces. The left panels show that most indoor surfaces that had not been cleaned have Pb levels above the EPA limit (dark and bright red squares). The right panels show that most (but not all) dust samples collected on an indoor cleaned surface showed Pb content reduced to below the EPA limit. Samples were collected between February 5, 2025, and February 13, 2025.
Here, WS stands for windowsills. The left panel shows data for uncleaned indoor surfaces, and the right panel data for cleaned indoor surfaces. In both cases, the highest Pb concentrations are found closest to the windows. Almost half of the uncleaned indoor surfaces have Pb levels above the EPA limits. Most, but not all, dust samples collected on cleaned indoor surfaces have Pb levels below the EPA limits, with ~10 percent of samples collected on cleaned indoor surfaces remaining at or above the EPA limits. Samples were collected between February 5, 2025, and February 13, 2025.
All tap water samples tested were found to be below the EPA action level of 0.010 mg/L, or 10 ppb. Samples were collected between February 5, 2025, and February 13, 2025.
Key Takeaways
- Lead (and other heavy metals) were clearly transported by the fire plume and have contaminated outdoor and indoor surfaces.
- Significant heavy metal contamination of outdoor and indoor spaces can occur even at large distances away from the fire zone.
- The majority of sampled indoor surfaces that had not been cleaned had Pb levels above the EPA limits.
- The amount of lead is highest near windows/doors, and ~10 times less on flat surfaces that are more than 1 meter away from the outside elements.
- About 90 percent of the sampled cleaned surfaces showed Pb levels below the EPA limit, indicating that cleaning is often, but not always, effective at removing heavy metals from surfaces.
- Tap water lead levels were all below the EPA action level.
What Next?
The data presented above shows that lead and other heavy metals, carried by the fire plume, penetrated inside most homes, even miles away from the burn zone. Given the risk that lead poisoning represents, particularly for children (see information from the Centers for Disease Control and Prevention and World Health Organization), proper cleaning of houses downwind of the fire zone is critical to remove as much as these contaminants as possible from one's immediate environment.
Our results are in agreement with the data gathered by residents affected by the Eaton Fire whose houses were tested by certified companies but show that the lead transport and infiltration in houses extends well beyond the burn zone. At this writing, professional remediation was recommended by testing companies for all 43 houses for which results have been shared on the Eaton Fire Residents United website.
This work was funded by NSF CAREER Award #2145780 and the Division of Geological and Planetary Sciences (GPS) Emergency Response Fund, through the generous support of private donors to the division.