Caltech Study Shows Eaton Fire Exposed Millions to Toxic Metals
Nearly 7 million people in the L.A. metro area breathed in air containing lead concentrations 80 times higher than normal during the peak of the Eaton Fire, according to a Caltech study published in Science Advances. The catastrophic blaze killed 19 people, burned over 14,000 acres, and destroyed nearly 10,000 homes. Researchers discovered that the smoke generated by the disaster carried a chemical signature drastically different from typical wildfires because burning structures and vehicles released massive amounts of toxins into the atmosphere.
Advanced Air Monitoring Tracks Urban Smoke Plume
The smoke’s movement from Altadena toward the San Gabriel Mountains was followed by an advanced air monitoring station located in Pico Rivera that operates as part of the National Science Foundation’s ASCENT network. Analysis by researchers revealed that the urban smoke plume contained 50 times more lead, 7 times more chlorine and bromine, and 3 times more arsenic. Haroula Baliaka, a PhD student and lead author of the study, noted that urban fire plumes are chemically distinct from standard wildfires. Baliaka co-authored the report with graduate student Ryan Ward, using four instruments to continuously measure airborne particles downwind.
Timeline of Lead Spikes and Shifting Smoke Chemistry
On January 8 and 9, lead levels surged dramatically across the San Gabriel Valley and eastern L.A., with peak measurements recorded downwind of Altadena. As the fire moved out of urban neighborhoods and into the San Gabriel Mountains, lead levels decreased while potassium ratios increased, approaching typical wildfire compositions by January 11. This trajectory contrasted sharply with the 2024 Airport Fire in Orange and Riverside counties, demonstrating how urban structures fundamentally alter the toxicity of wildfire smoke.
Health Risks and Ongoing Contamination Concerns
The severe lead contamination was likely driven by older structures burning in Altadena. In April 2025, Pasadena issued a public health advisory after initial soil tests revealed extreme lead contamination, which prompted the Environmental Protection Agency to test dozens of homes in early 2026. Howard Hu, a University of Southern California Keck Professor, told CBS News that health impacts depend heavily on exposure dose. He noted that while a single day of exposure usually resolves without violent illness, chronic exposure spanning weeks or months remains the primary concern. A separate University of California study from June also found that over 3 million people downwind of the Palisades and Eaton fires may have been exposed to chromium-6, a toxic carcinogen.
