Millions of Los Angeles residents were exposed to elevated levels of lead and other toxic metals from the smoke of the 2025 Eaton Fire, according to a new study published by researchers at Caltech. The study found that lead concentrations in the fire's plume soared to 80 times normal levels, posing a significant public health concern.
Comparing the chemical composition of the Eaton Fire's smoke with that of a typical wildfire, the study concluded that the urban blaze released a far more toxic mixture. The research article stated that compared to wildfire smoke, the urban plume was enriched more than 50-fold in lead, seven-fold in halogens, and three-fold in arsenic. This toxic cocktail is linked to the burning of vehicles, electronics, and building materials, which differs fundamentally from the conventional vegetation fuel of wildland fires.
The findings underscore the distinct dangers posed by fires that occur in densely populated areas, where the combustion of urban materials can release hazardous pollutants into the air over large populations.
"Unlike wildfire smoke that has been the focus of decades of air quality research, this plume represents an emerging class of urban fire air pollution that demands revised exposure frameworks and emergency response protocols as fires increasingly burn into cities," the study noted.
The lead author, Haroula Baliaka, a Caltech PhD student, initiated the research to better understand Los Angeles's persistent air pollution issues. Baliaka and co-author Ryan Ward utilized an air-monitoring system from the Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT) to collect real-time data on the chemical makeup and particle sizes in the air.
"ASCENT has the unique capability to measure the chemical components and the size of these different particles in real time," said Caltech professor Nga Lee "Sally" Ng, who was also involved in the study.
The Eaton Fire, which began on January 7, 2025, alongside the Palisades Fire, resulted in significant destruction. At least 31 fatalities were reported, and over 16,000 structures were destroyed across the two incidents. Residents faced mandatory evacuations, with many businesses in the Pacific Palisades area being completely lost. The widespread exposure to smoke raised immediate concerns, and the new findings highlight the lingering health risks beyond the immediate fire threat.
High levels of lead exposure can have severe health consequences, including impacting the development of children and damaging the nervous and kidney systems of individuals of all ages. In extreme cases, lead exposure can be fatal.