Eaton Fire Exposed 7M People To Toxic Lead Levels 80 Times Normal: Study

ALTADENA, CA — Smoke from the devastating Eaton Fire exposed nearly 7 million Los Angeles-area residents to airborne lead concentrations about 80 times higher than normal during a 24-hour period, according to a new Caltech study.

The findings, published Wednesday in the journal Science Advances, reveal the extent of toxic pollution released when thousands of homes, vehicles and other structures burned in the January 2025 fire.

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Researchers found that smoke from the Eaton Fire contained more than 50 times as much lead as smoke from a typical wildfire. It also contained seven times as much chlorine and bromine and three times as much arsenic.

The findings suggest that fires burning through populated urban neighborhoods pose different air pollution hazards than wildfires fueled primarily by plants, potentially exposing millions of people far beyond the fire zone to dangerous chemicals, researchers said.

The Caltech study focused on the Eaton Fire and separate ongoing research suggests residents near the Palisades Fire may face similar concerns about toxic pollution.

"With over 16,000 structures destroyed, the LA Fires released highly toxic pollutants, posing persistent exposure risks to affected communities," researchers for that study wrote.

UCLA researchers monitoring air quality in households near both fire zones found that certain toxic chemicals remained more concentrated indoors than outdoors after the fires, suggesting that contaminated building materials may continue releasing pollutants long after the flames are extinguished.

"Urban fire plumes are chemically distinct from those of wildfires. Now that we have these observational data about how they differ, we can go back and adjust our models to more accurately estimate how smoke might affect people," said Haroula Baliaka, the study's lead author and a Caltech researcher. "Smoke travels; it's not just about the burn area. What does a plume mean for people who are miles away from a fire but receive the smoke? We evacuate for fire, but we don't evacuate for smoke exposure."

Scientists were able to track the chemical composition of the Eaton Fire's smoke using an advanced air-monitoring station in Pico Rivera, about 11 miles south of Altadena.

Unlike traditional air-quality monitoring systems that collect samples periodically, the station continuously measures the chemical makeup of airborne particles, allowing researchers to track changes in pollution as the fire progressed.

The researchers compared the Eaton Fire's smoke with emissions from the Airport Fire, which burned about 24,000 acres of vegetation in Orange and Riverside counties in September 2024.

The differences were stark.

Lead concentrations spiked across eastern Los Angeles County and the San Gabriel Valley on Jan. 8 and 9, when the Eaton Fire was burning through residential neighborhoods. The highest concentrations were measured directly downwind of Altadena.

As the fire moved into the San Gabriel Mountains and began burning primarily vegetation, the smoke's chemical composition shifted toward that of a typical wildfire, researchers said.

Contrasted with the Airport Fire smoke, the plume from the Eaton Fire contained 50 times more lead, three times more arsenic, and seven times more halogens. At the peak of burning, about 7 million people were exposed for 24 hours to lead levels more than 80 times what's typical, researchers found.

Lead is a neurotoxin that can stunt children's development, lower IQ scores and increase blood pressure in adults. Scientists still don't know how short-term, high exposure to lead impacts human health. Arsenic exposure is associated with various cancers.

However, scientists said the health consequences of brief exposure to unusually high concentrations of these pollutants remain unclear.

"Unfortunately, Californians get exposed to fires all the time," Baliaka said. "What do all of these short-term but elevated air toxins, not just lead, mean for our health? We need to start figuring that out."

Ed Avol, a professor emeritus at USC's Keck School of Medicine who was not involved in the research, told The Associated Press that elevated heavy-metal exposure was consistent with what scientists would expect from burning buildings, but that the findings were significant because researchers previously lacked the ability to document such exposure in detail.

The study relied on instruments from the Atmospheric Science and Chemistry mEasurement NeTwork, or ASCENT, a federally funded network of monitoring stations that can measure the chemical composition of fine airborne particles in real time.

"With ASCENT, we are not only seeing how much particulate matter is in the air but what it is made of, and we can watch it as the event unfolds," Ng said.

Researchers said the technology could help emergency officials better predict where dangerous smoke will travel and determine how to protect residents during future fires.

The findings also raise questions about whether existing fire-response policies adequately address the dangers of large-scale urban fires.

The unusually high lead concentrations may have been influenced by the large number of older homes destroyed in Altadena, researchers said.