7 million LA residents hit by high lead levels

During the 2025 Los Angeles fires, a wildfire in Altadena and the Pacific Palisades killed at least 31 people and destroyed more than 16,000 homes. Scientists measured fine particulate matter every hour and found that about 7 million residents were exposed for 24 hours to lead levels over 80 times the normal background concentration.

Composition of the Smoke

The researchers compared the chemical makeup of the urban plume with that of a 2024 Riverside fire that burned mostly vegetation. The LA smoke contained about 50 times more lead, three times more arsenic, and seven times more halogens such as chlorine and bromine.

Lead is a neurotoxin that can stunt children’s development, lower IQ scores, and raise blood pressure in adults. Arsenic exposure is linked to various cancers. Because the exposures were brief but intense, scientists still do not know how short‑term, high levels of lead affect human health.

Nga Lee "Sally" Ng and Haroula Baliaka said the study shows wildfire smoke is fundamentally different from urban smoke. Ed Avol noted the surprising magnitude of the exposure. Yaguang Wei said the findings have important policy implications and urged governments to invest in more wildfire monitoring and public alerts.

The study highlights the need for monitoring and emergency response to adapt to an evolving climate that makes wildfires larger, faster, and more frequent, and as fires move into cities, monitoring must adapt.