RAPID: Heavy Metals in Urban Soils After the 2025 Los Angeles Wildland-Urban Interface Fires

Wildfires are becoming more common in locations where cities and human development meet natural areas or unoccupied land, also known as the wildland-urban interface (WUI). In addition to burning vegetation, these fires cause the combustion of buildings and cars, releasing potentially harmful heavy metal(loid)s like lead and arsenic into the air. The produced ash and soot can travel downwind and settle onto nearby neighborhoods, where people live, work, play, and attend school.

Once heavy metals deposit onto soil, the metal particulates can be transported by rain or irrigation deeper into the soil, taken up by plants, transported to another location by wind or water, and potentially ingested by humans. This raises important questions about the safety of nearby soils after a WUI fire, how these metals move through the environment, and what risks they might pose to human and environmental health and safety over time.

This project investigates both burned and unburned residential lots resulting from the recent 2025 Los Angeles WUI Fires to assess heavy metal distribution, concentration, and bioaccessibility in ash-impacted soils over the course of 12 months after the fires. It will produce new knowledge that is highly relevant to Americans’ public and environmental health and will be transferable to future WUI fire sites in the American West and beyond.

This research examines how heavy metals from WUI fire ash are deposited into urban soils and how their concentrations and bioaccessibility change over space, depth, and time. Following the 2025 Los Angeles WUI Fires, soils will be sampled at burned and unburned residential properties to measure concentrations of metals such as lead (Pb), arsenic (As), cadmium (Cd), mercury (Hg), and chromium (Cr).

This study will track how these metals move through the soil profile and assess whether rain and time affect their mobility and bioaccessibility to humans. Using in situ portable X-ray fluorescence (XRF) measurements and laboratory assays, this work will study both the total amounts of metals present and how bioaccessible they are to humans. This work will provide data for residents, government agencies, and local organizations working to protect communities from toxic exposure after WUI fires.

The project will also engage undergraduate students in hands-on research and connect with community groups to share findings and safety information.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.