USC Scientists Trace the Hidden Environmental Legacy of Los Angeles Wildfires
More than a year after the devastating Pacific Palisades and Eaton wildfires, Los Angeles residents are still asking questions that cannot be answered by a single inspection or a quick visual survey: Is the soil around my home contaminated? Did wildfire smoke and ash carry toxic metals into neighborhoods? Are coastal waters safe for swimming and marine life? New findings from University of Southern California researchers offer the most detailed picture yet of how the fires altered the region’s environment, while also revealing why the health risks cannot be explained by wildfire exposure alone.
The Contaminant Level Evaluation and Analysis for Neighborhoods, or CLEAN, project has analyzed more than 6,000 soil samples collected throughout Los Angeles County, alongside more than 900 seawater samples obtained along the Southern California coast. The research indicates that the fires released lead into the environment, but distinguishing that wildfire-related contribution from older, persistent sources of contamination is difficult. Aging homes, deteriorating lead-based paint and decades of urban activity may already have deposited lead in residential soil before the fires occurred.
Lead is particularly challenging to assess because it does not break down into harmless substances in the environment. Instead, it can persist in soil and become a potential exposure risk when contaminated dust is inhaled or soil particles are accidentally swallowed, especially by children. The researchers found that lead concentrations could differ sharply across the same property. On average, one soil sample contained approximately twice as much lead as another collected only a few feet away. In areas directly affected by the fires, the variation was sometimes even greater, showing why a single sample may fail to represent conditions across an entire yard.
“Every property is different,” said Josh West, a professor of earth sciences at the USC Dornsife College of Letters, Arts and Sciences and a principal investigator on the project. He emphasized that testing individual properties remains the most reliable way for residents to understand possible exposure because lead distribution is highly uneven. Wind, ash deposition, building materials, soil composition, drainage and landscaping can all influence where contaminants accumulate. A burned structure may therefore leave behind a patchwork of contamination rather than a uniform layer across an entire neighborhood.
The soil findings also provide important reassurance. Although the fires appear to have added lead to the environment, the researchers found no evidence of countywide post-fire contamination from several other metals that generated widespread concern, including arsenic, mercury and hexavalent chromium. That result does not mean every location is free of risk, but it suggests that broad regional contamination by those substances was not detected in the project’s sampling. The distinction between countywide trends and individual properties is crucial: a community may show no overall increase while isolated yards or burn sites still contain elevated concentrations.
The environmental investigation extended from residential neighborhoods to the ocean. Led by Noelle Held, an assistant professor of biological sciences at USC Dornsife, the CLEAN Waters team monitored coastal pollution for 18 months, examining the movement of wildfire-related chemicals through beaches and seawater. Their analysis detected a measurable chemical signature from the fires. Nutrients, metals and hundreds of compounds associated with combustion increased in coastal waters during the weeks after the blazes, when rain, wind and runoff could transport ash and debris from burned areas toward the shoreline.
That chemical signal, however, was largely temporary. Many of the substances detected soon after the fires declined toward more typical levels within several months. The pattern suggests that the coastal ecosystem experienced an acute pulse of pollution rather than a permanent transformation of seawater chemistry. Such short-lived contamination can still matter: sudden increases in nutrients and metals may stress marine organisms, alter microbial activity or interact with other pollutants already present in coastal waters. But the timeline also demonstrates why repeated sampling is more informative than a single post-disaster measurement.
“The fires left a clear signal in the ocean, but it wasn’t a permanent one,” Held said. Continued monitoring allowed researchers to follow how fire-derived chemicals moved through coastal waters and declined over time. That approach helps scientists separate the environmental effects of a single disaster from chronic pollution generated by urban runoff, wastewater, transportation and other ongoing sources. It also creates a baseline that may help researchers respond more quickly when future wildfires affect densely populated coastal regions.
To help residents reduce exposure regardless of whether contamination originated from wildfire debris, old paint or another source, the newly established CONSORTIUM has released practical guidance for homes and yards. The collaboration brings together USC CLEAN, partner universities and community organizations. Its recommendations focus on everyday measures that can limit contact with contaminated soil and dust, including controlling the movement of soil into homes and making informed decisions about testing and cleanup. The guidance is intended to complement, rather than replace, professional environmental assessments when elevated contamination is identified.
The CLEAN project is continuing to expand as new environmental emergencies emerge. Researchers have recently adapted their sampling strategy to investigate lead concerns associated with the June warehouse fire in Boyle Heights. The broader lesson from the project is that wildfire recovery does not end when flames are extinguished or smoke clears. Contaminants can remain in soil, move through waterways and interact with pollution that existed long before the disaster. By combining large-scale sampling, laboratory analysis and sustained coastal monitoring, USC scientists are building a data-driven framework for understanding those overlapping risks—and giving communities evidence they can use to make decisions about testing, exposure reduction and recovery.
Subject of Research: Environmental contamination following the January 2025 Los Angeles wildfires, including lead in residential soil and fire-related pollutants in Southern California coastal waters.
Article Title: USC Scientists Trace the Hidden Environmental Legacy of Los Angeles Wildfires
Web References: CLEAN soil research: https://public-exchange.org/usc/project/soil-testing/clean-issue-brief-aug-26/; CLEAN Waters research: https://public-exchange.org/usc/project/clean_waters/clean-waters-brief-jul-26/; CLEAN project: https://public-exchange.org/usc/project/soil-testing/; CONSORTIUM guidance: https://www.consortium-science.com/
Image Credits: Photos/Courtesy of USC Dornsife Earth Sciences and USC Public Exchange
Keywords: Los Angeles wildfires, Pacific Palisades fire, Eaton fire, wildfire contamination, lead in soil, environmental health, seawater pollution, coastal ecosystems, USC CLEAN project, CLEAN Waters, wildfire recovery, environmental monitoring
