UCLA and UC Davis researchers released a report that projected chromium may have traveled six to nine miles downwind from the Eaton and Palisades fire cleanup zones.
Researchers found airborne chromium in the carcinogenic oxidation state two months after the fire, according to the study, published in the Journal Nature Communications Earth & Environment.
The average concentrations were below the National Institute for Occupational Safety and Health workplace exposure limit but above the U.S. Environmental Protection Agency’s screening levels for indoor air.
“It shows that well after the wildfires were extinguished, nanoparticles, which are so small they can enter the circulatory system very quickly, were in the air around the burn zones,” said Dr. Michael Jerrett, UCLA professor in the Department of Environmental Health Sciences, in a statement. “These probably traveled far enough to give 3.3 million people doses that were hundreds of times the levels that are normally seen in the air in Los Angeles.”
The report used calculations based on models for wind-carried contaminants to project that chromium containing nanoparticles may have traveled six to nine miles in communities well away from the fire areas.
According to the researchers, hexavalent chromium or chromium-6 can impact the lungs and is associated with asthma, bronchitis and lung cancer.
“The source of the elevated chromium-6 nanoparticles observed two months after the fire remains an important question that warrants further investigation, given its known carcinogenicity,” UCLA Professor Dr. Yifang Zhu said in a statement. “Encouragingly, chromium-6 concentrations declined over time, through reduction to the less toxic chromium-3 form and returned to background levels approximately eight months after the fire. This highlights the importance of continued monitoring to track how environmental risks change during the recovery process.”
In April 2025 a Los Angeles County Public Health study found a higher percentage of soil samples with lead levels above health-based screening levels at parcels downwind of the Eaton fire.
A subsequent test of soil at Pasadena Unified School District sites found 18 locations with at least one area of harmful substances that included lead, arsenic, chromium, Polycyclic aromatic hydrocarbons (PAHs) and dioxins/furans.
Last week, PUSD announced a toxic-soil-removal project over the summer, which includes the removal of about 200 trees.
The researchers said modeling suggests airborne particles may have reached communities including Beverly Hills, West Hollywood and portions of the San Fernando Valley. They recommended continued monitoring around wildfire cleanup zones and advised nearby residents to use indoor air filtration and limit outdoor exercise until conditions return to normal.
The January 2025 Palisades and Eaton fires killed at least 31 people and damaged or destroyed more than 18,000 structures, according to Los Angeles County officials.
Researchers said the findings underscore growing concerns about health risks associated with wildland-urban interface fires as such events become more common.
City News Service contributed to this report.