More than a year after two massive wildfires swept through Los Angeles, thousands of families are still wondering whether their backyards and nearby beaches are safe. Now, a team of scientists from the University of Southern California is offering some of the clearest answers yet.
The researchers, part of a project called CLEAN (that stands for Contaminant Level Evaluation and Analysis for Neighborhoods), have spent the last 18 months testing soil from more than 3,000 households and collecting over 6,000 soil samples across the county. They also gathered more than 900 seawater samples along the Southern California coast to check for pollution that might have washed into the ocean from the ash and debris.
The Palisades and Eaton fires burned through more than 37,000 acres in January 2025, destroying thousands of homes and sending huge clouds of smoke and ash across the region. When wildfires burn through buildings and everyday objects, they can release chemicals and heavy metals into the soil and water. That has left many residents worried about long-term health risks, especially for children who play in the dirt.
The CLEAN team found that the fires did release lead into the environment. But here's the surprise: researchers say it was hard to tell exactly how much lead came from the fires versus how much was already there from older homes and past pollution. Lead-based paint, used in homes built before the 1970s, breaks down into tiny flakes over time and can accumulate in soil. The scientists also found no widespread evidence of dangerous levels of other metals like arsenic, mercury, or hexavalent chromium in the soil across the county.
One key finding: lead levels can vary dramatically even within a single yard. On average, one soil sample from a property had about twice as much lead as another sample just a few feet away. That variation can be even more extreme in areas that burned. The message from researchers: every property is different, and the only way to know for sure is to test your own soil.
For coastal waters, the news was more reassuring. While the fires did leave a measurable chemical fingerprint in the ocean, it was largely temporary. Nutrients, metals, and hundreds of fire-related compounds increased in the weeks right after the fires but returned to normal levels within a few months. "The fires left a clear signal in the ocean, but it wasn't a permanent one," said Noelle Held, an assistant professor of biological sciences at USC who led the coastal water research.
For families still grappling with what to do, a new coalition called CONSORTIUM has released practical guidance on the CLEAN website to help residents evaluate and reduce contamination where they live. Researchers say they will keep monitoring and expanding their work in response to what communities need most.
"Communities deserve clear, science-based information about their environment after the L.A. fires," said Erika Garcia, an associate professor at the Keck School of Medicine of USC. "With clear data about what is in their soil, L.A. residents can make more informed decisions about possible risk-reduction strategies, or perhaps their minds will be put at ease knowing that lead in their soil is not at a level of high public health concern."