Study finds LA fire smoke held 80 times more lead than normal
New research shows millions of residents inched closer to toxic thresholds during the January 2025 blazes.
By Bianca Herrera ·
A study published Wednesday in Science Advances reports that Los Angeles residents breathed air with toxic lead levels 80 times higher than typical background rates during a 24-hour period in January 2025. The findings come from a new analysis of the Eaton Fire, which ignited on Jan. 7, 2025, and killed at least 31 people while destroying more than 16,000 structures. Researchers at the California Institute of Technology analyzed the chemical makeup of the urban smoke plume and found it contained distinct heavy metals not found in standard wildfire smoke.
The study authors compared the Eaton Fire emissions to a 2024 wildfire in Riverside County that burned mostly vegetation. The urban smoke from the Los Angeles fire contained 50 times more lead, three times more arsenic, and seven times more halogens than the wildland smoke. Halogens include chlorine and bromine, which often come from burning vehicles, building materials, and electronics. Nga Lee “Sally” Ng, an author of the study, said the fundamental difference between the two smoke types was the primary finding. With new measurement technology, her team could see the detailed components of the particles people were breathing.
Co-author Haroula Baliaka noted that understanding these chemical differences fills a gap in research as urban growth pushes fires into cities. She said monitoring and emergency response systems will need to adapt as wildfires become larger and more frequent due to warmer and drier weather. The team used the Atmospheric Science and Chemistry mEasurement NeTwork, or ASCENT, to measure trace elements in fine particulate matter every hour. Ng described ASCENT as the first U.S. network capable of measuring airborne particle composition in real time. This allowed researchers to track how smoke composition changed over the fire’s duration and estimate exposure across the city.
Experts outside the study confirmed the results align with their expectations. Ed Avol, a professor emeritus in the Keck School of Medicine at the University of Southern California, said high heavy metal exposure is consistent with what he has seen in air pollution research. He noted that while the specific documentation is surprising, the presence of metals is not. Avol praised the study for its hourly measurement frequency, noting that standard air quality checks usually happen only a couple of times per week.
Yaguang Wei, an assistant professor at Icahn School of Medicine at Mount Sinai, said the findings reinforce his own recent work on wildfire smoke toxicity. He explained that burning homes releases toxic substances from lead paint, plastics, and electronics. Wei, who was not involved in the new study, stated that his research found PM2.5 from wildfire smoke is more toxic than particulates from other sources. He called the new findings “not surprising” given the materials in urban homes.
Wei said the study has important policy implications. He suggested governments invest in more wildfire monitoring, public alerts, and prescribed fires to protect public health. Avol added that the findings remind residents to be cautious as urban and wildland areas intersect. He noted that people will not stop using materials containing metals and halogens in their homes, so society must find ways to protect people from exposure.
The study highlights the specific health risks of lead and arsenic. Lead is a neurotoxin that can stunt children’s development and lower IQ scores, while it can increase blood pressure in adults. Scientists do not yet know how short-term, high-level lead exposure impacts health. Arsenic exposure is linked to various cancers. The Eaton Fire and a simultaneous blaze in Pacific Palisades destroyed thousands of homes and released these chemicals into the air. Millions of people across the United States are exposed to smoke annually, which has been linked to tens of thousands of deaths. A separate recent study found that metal mixtures from the 2023 Maui wildfires harmed lung health in nearby residents long after the fires ended.
