Carcinogenic heavy metal found in air samples taken after LA fires. What you need to know

Hexavalent chromium nanoparticles were found in air samples gathered by researchers over the course of several days in the spring as they drove through and around the Eaton and Palisades fire burn areas.

The heavy metal — also known as chromium-6 and brought to public consciousness by environmentalist Erin Brockovich in the 1990s — is a known carcinogen. But researchers aren’t yet sure what the public health implications are.

“ We think that there's hotspots in the cities, but we don't have a way to quantify that yet with what we've measured so far,” said Michael Kleeman, professor of civil and environmental engineering at UC Davis.

Kleeman was the lead author of a paper that’s been submitted to the journal Nature’s Communications Earth and Environment for peer review and published online as a preprint. The researchers are part of the L.A. Fire Health Study, a group of universities working together to investigate the health effects of the January fires.

The high temperatures produced by wildfires can transform chromium — which is both naturally occurring and found in consumer products — into chromium-6. It’s a known hazard. A 2023 study found chromium-6 present in soil 10 months after the Hennessy Fire in Northern California. The persistence was likely in part due to a lack of precipitation.

Kleeman said it’s unclear where the nanoparticles they detected may have come from.

Tires could be a source, as could solar panels, electronics, or even fire retardant, which LAist found contains chromium.

To gather the samples, the team drove through the Altadena and Palisades burn areas on eight separate occasions with air samplers mounted to their roof. The trips occurred while lots still were being cleared, raising the possibility that now, with that activity dying down, less dust may be kicked up and chromium-6 levels in the air will be lower.

They’ll be gathering additional samples from the burn areas next week.

Health effects

The levels of chromium-6 detected were below Occupational Health and Safety Administration workplace limits but above the U.S. Environmental Protection Agency screening levels for workplace and home air, according to the study.

“It would be important to follow up with more recent measures to make sure that the problem is gone,” said Dr. Ana Navas-Acien, the chair of environmental health sciences at Columbia University’s Mailman School of Public Health who wasn’t involved in the research.

That’s because chronic exposure to hexavalent chromium can increase a person’s risk of lung cancer and nasal cancer, as well as lead to eye, kidney, and lung damage. Asthma and respiratory irritation are the primary concern with short-term, low-level exposure.

When inhaled, the tiny chromium-6 particles are absorbed rapidly and fully through the respiratory tract, entering the blood stream, penetrating cells, and traveling to major organs, including the liver and the brain.

Navas-Acien said it would be reassuring to know that levels of chromium-6 in the air have come down, as that would indicate this was a temporary phenomenon.

“But if you still detected it today, then I think that’s when we need to be more careful because there could be a real issue that’s more chronic,” she said. “Was it because of the fires, the cleaning? Was something going undetected?"

It will take a few weeks for Kleeman’s team to process the results of new tests.

Questions to be answered

Kleeman said the researchers’ work is not done. They hope additional study in the burn areas can answer some of the following questions:

• Have levels of hexavalent chromium returned to normal background levels? This will help determine if there’s an ongoing threat to public health.
• What's the source of the hexavalent chromium nanoparticles? Determining a source is critical to figuring out where the hotspots may be, who has been exposed, and to what degree their health may be compromised.
• Given all of the information gathered, should we change how we approach fighting and cleaning up after fires going forward? Can this problem be mitigated? If the problem is due to naturally occurring chromium in the soil, not much can be done. If it’s related to a product, then maybe that product can be removed from high fire areas.

How to stay safe and learn more

Both Kleeman and Navas-Acien recommended that you follow the same procedures you might for responding to lead contamination: run air purifiers, use a vacuum with HEPA filters, wipe down dusty areas with a wet cloth, all in an effort to prevent particles from becoming airborne in your home. It helps to leave your shoes at the door to keep dust out of the home and to wear a mask when you do cleanup work as well.

“The important message that we want to get across is: Get air filters in your house if you haven't done it yet,” said Jane Lawton Potelle with Eaton Fire Residents United, which has been working with L.A. Fire Health Study researchers.

Your HVAC system should have MERV-13 or higher HEPA filters; and standalone air purifiers should have HEPA and carbon filters, according to a Q&A on the L.A. Fire Health Study website.

In collaboration with Eaton Fire Residents United and Resilient Palisades, experts held an online Q&A at 6 p.m. Thursday. Public health specialists from UCLA, Harvard and other universities answered questions and explained their research. Find a summary and a video of the webinar on the PostFire website.

LAist senior editor Jared Bennett contributed to this report.