Eaton Fire Smoke Carried 80 Times Normal Lead Over 7 Million Angelenos

Smoke from the Eaton Fire carried lead at roughly 80 times normal atmospheric levels over about 7 million Los Angeles residents for 24 hours, according to a new study in Science Advances. ScienceAlert reported on the findings, which come from researchers at the California Institute of Technology, known as Caltech.

The health consequences for people who breathed the smoke remain unknown, and the authors are calling for studies of those outcomes, especially in children.

The key numbers

• About 7 million: Los Angeles residents covered by smoke plumes by Jan. 9, 2025, after the fire began Jan. 7, 2025.
• Roughly 80 times normal: the lead level in the air for 24 hours, according to ScienceAlert.
• 0.6 nanograms per cubic meter: the typical daily lead average at the Caltech monitoring site in Pico Rivera.
• Above 50 nanograms per cubic meter: the concentration experienced by approximately 7 million residents on Jan. 9.
• 50 times: how much more lead the Eaton plume contained than a 2024 wildfire in Riverside that burned almost entirely in vegetated wildlands.
• More than 9,000: structures burned in the area, along with electronics and vehicles.

What was in the smoke

The study was led by atmospheric chemists Haroula Baliaka and Nga Ng at Caltech. Besides lead, the smoke contained high concentrations of chlorine, bromine, zinc, copper and arsenic.

The researchers say the plume came mainly from burning homes, vehicles and infrastructure, a different fuel with a distinct chemical signature from the forests and grasslands that decades of smoke research have focused on.

Compared with the Riverside fire, which occurred about four months earlier, the Eaton plume held 7 times the chlorine and bromine, 4 times the zinc and 3 times the copper and arsenic.

Who was exposed, and when

A Caltech air monitoring facility in Pico Rivera, directly south of the fire, tracked the pollution in real time. Air quality was worst in the first two days. People in eastern Los Angeles and the San Gabriel Valley saw the highest 24-hour average lead concentrations.

As the fire shifted from burning structures to burning wildland, peak concentrations fell, but the total number of people exposed kept rising as the plume spread across the basin, the researchers wrote. ScienceAlert also noted that a team from the University of California, Los Angeles reported similar results, using monitoring stations in Westwood and Huntington Park.

Why it matters: an unanswered health question

Many homes in Altadena were built in the early to mid 20th century, when lead paint and brominated flame retardants were common. That could explain why the plumes were so toxic, according to the report.

The authors note that the harms of long-term exposure to single elements, such as lead's effects on the nervous system or arsenic's link to cancer, are well established. Far less is known about short, intense exposures to mixtures of many contaminants at once. The researchers also worry about the long-term effects of contaminants that settled across playgrounds, watersheds and farmlands.

The team wrote that there is an urgent call for epidemiological studies of these exposures. They also warned that as climate change and urban expansion push more fires into cities, another urban firestorm is a question of when, and that it remains to be seen whether monitoring and emergency response systems can adapt fast enough to measure such emissions and the risks they pose.

Around Prague, based on reporting by ScienceAlert