Study: cancer-causing chromium-6 spread miles from fire zones Play

A carcinogen with potentially serious impacts on human health was found six to nine miles downwind from the fire zones. That is according to newly published work by University of California researchers.

The chemical is hexavalent chromium, or chromium-6. It is a toxic metal and carcinogen that can impact the lungs and is associated with asthma, bronchitis, and lung cancer.

After the wildfires were extinguished, nanoparticles were in the air around the burn zones. Nanoparticles are so small they can enter the circulatory system very quickly. The nanoparticles are less than 1/1000th the width of a human hair.

The particles 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.

And hex-6 is bad stuff. Researcher Michael Jerrett at UCLA:

“It can cause lung cancer, and some throat and nasal cancers if the exposure is over a long period of time. On a more acute basis you can see respiratory irritation, skin irritation and eye irritation.”

Researcher Michael Kleeman at UC Davis says there are two concerns: smoke and ash from the fire, and ash and airborne particles from hauling off the debris.

“It's more a cause for concern because we are moving into a more active fire season. And so if there is another fire that moves into an urban area, how do you treat that debris? That's more of the public health message from our study.”

Just how bad was the chromium-6 contamination in the air downwind from the fires? The researchers found the airborne particles were in the danger zone peaking at two months after the fires.

A UCLA study co-author says that, encouragingly, chromium-6 concentrations declined over time. They returned to background levels approximately eight months after the fire.

That's the good news. The bad news is that models for wind-carried contaminants suggest that chromium-containing nanoparticles may have traveled six to nine miles downwind from the cleanup zone.

The January 2025 blazes hit Los Angeles County in both the Pacific Palisades-Malibu area in western Los Angeles and the Altadena-Pasadena communities in the foothills of the San Gabriel Mountains. The fires directly killed 31 people and damaged or destroyed more than 18,000 structures, according to the County.