Post-Fire Resuspension of Metal Toxins at the Wildland–Urban Interface

Alireza Namayandeh , Charlie Lamb, Frida Daniela Garcia Ledezma, Jonathon Howell, Catherine Erol, Dan Kubota, Raphael Kim, Charise Young, Katie Huy, Scott Fendorf

After wildland–urban interface (WUI) fires, the severe destruction leaves metal-containing materials on the ground. During post-fire recovery, wind, debris removal, vehicle movement, and reconstruction can disturb these residues and release these materials into the air. However, what toxic metals are released into the air from fire-altered materials and what controls their airborne release are only partly understood. Here, we designed and fabricated a windbox to resuspend and collect WUI fire-altered materials under controlled conditions from samples collected after the January 2025 Los Angeles fires. Bulk metal concentrations did not consistently predict the corresponding airborne metal concentrations. Instead, the amount of resuspendable particulate material and its rate of depletion from the air controlled the release of lead (Pb) and chromium (Cr). Vehicle-associated debris produced >50-fold Pb enrichment and >100-fold Cr enrichment in ultrafine particles (< 0.25 µm). Electron microscopy identified Pb-, Cr-, Fe-, Ti-, and Ni-bearing particles < 100 nm that can deposit deep in the lungs, cross the air–blood barrier, and reach other organs, including the brain. Our findings suggest that toxic metal-containing ultrafine particles can be resuspended into the air even at low wind speeds after WUI fires, threatening public health in local communities for extended periods post-fire.