LA fire smoke contained lead levels 80 times normal for millions
A new study reveals that urban fire plumes release far more toxic heavy metals than typical wildfires, exposing roughly 7 million people to hazardous levels during the 2025 Los Angeles fires.
By Andrew Kovalenko ·
Millions of Los Angeles residents breathed in smoke containing lead levels 80 times higher than typical background concentrations during the peak of the 2025 fires, according to a study published Wednesday in Science Advances.
The research, conducted by scientists at the California Institute of Technology, compares the chemical makeup of smoke from the Eaton Fire with that of a standard wildfire. The urban plume contained significantly higher amounts of lead, arsenic, and halogens, which include chlorine and bromine.
Nga Lee “Sally” Ng, an author of the study, stated that the primary finding is that wildfire smoke is fundamentally different from urban smoke. The team utilized a new measurement network to observe the detailed components of particles being inhaled by the population.
The Eaton Fire and the Pacific Palisades fire, which started on January 7, 2025, killed at least 31 people and destroyed more than 16,000 structures. These buildings housed cars, paint, furniture, and other materials that release toxic chemicals when burned.
Researchers 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 the chemical composition of airborne particles in real time.
By comparing data from the Eaton Fire to a 2024 wildfire in Riverside County that burned mostly vegetation, the team found the urban smoke had 50 times more lead, three times more arsenic, and seven times more halogens. At the height of the burning, approximately 7 million people were exposed to lead levels more than 80 times the norm for a 24-hour period.
Lead is a neurotoxin that can hinder children's development and lower IQ scores. It also raises blood pressure in adults. While scientists understand the long-term effects of lead, the impact of short-term, high-level exposure remains unclear. Arsenic exposure is linked to various cancers.
Ed Avol, a professor emeritus at the University of Southern California, noted that the high levels of heavy metals are consistent with his expectations but surprising because previous research lacked the technology to document them hour by hour.
Yaguang Wei, an assistant professor at Mount Sinai, said the findings reinforce earlier research showing that particulate matter from wildfire smoke is more toxic than particles from other sources. He explained that burning properties releases toxic materials such as lead paint, plastics, and electronics.
Experts suggest that monitoring and emergency response strategies must adapt as urban growth and climate change push fires into cities. Wei recommended that governments invest in more monitoring and public alerts, while Avol emphasized the need to protect people from materials containing metals and halogens in their homes.
