After the historic fires that burned for nearly a month in January 2025, researchers from Harvard and universities in California and Texas are studying the toxic hazards that the fires left behind in homes that remain standing.
The Eaton and Palisades fires killed at least 20 people, making them one of the deadliest fires in California’s history. The fires also destroyed more than 16,000 structures, primarily in Altadena and Pacific Palisades, and exposed millions to particulate matter, gases, chemicals, heavy metals, asbestos, PFAS, microplastics, and other toxic pollutants.
Inside Climate News reports that researchers gather water samples, conduct mobile air and surface water testing, monitor firefighters’ health, and assess combustible “fuel stocks” from trees and brush to homes, vehicles, fencing, decks, and anything plastic in urban and wooded areas. Using a computer model, they can also estimate the amount of smoke that entered people’s homes in Southern California.
The project, the LA Fire Health Study Consortium, is a collaboration between three universities led by health, environmental, data and wildfire risk assessment researchers at Harvard’s T.H. Chan School of Public Health, the UCLA Fielding School of Public Health, the University of California, Davis and the University of Texas at Austin and supported by led by the Spiegel Family Fund—the consortium pledge to conduct a 10-year study and provide real-time health information.
Apart from studying toxic hazards from the burn zone, researchers are sweeping 50 undamaged homes enrolled in the environmental exposure study, some of which are located as far away as nearly two miles, but are situated downwind of the burned areas.
Residents were surprised to learn that they could receive their water test results within minutes, rather than days. In one household where the water quality was tested, the results indicated that the water was free of hydrogen sulfide (H₂S), which is used to detect fecal bacteria in water.
Additionally, some homes showed high levels of both free and total chlorine. Chlorine is applied to disinfect fire remnants in water, including organic carbon, ash, and sediments.
Samples of ash and water collected from numerous homes in the study reveal significantly lower levels of benzene and other volatile organic compounds (VOCs) than researchers had anticipated. This finding is encouraging and reflects lessons learned following the 2018 Paradise Fire. That fire, one of California’s most destructive and deadliest, blazed for two weeks, burning over 150,000 acres and claiming 85 lives.
After the fire was extinguished, residents complained for months about a foul odor coming from the tap water. Eventually, when the water company conducted tests, they found toxic levels of benzene throughout the entire water system.
To prevent a similar situation from happening again, water infrastructure and supply companies flushed water lines for an entire week, as soon as both the Palisades and Altadena fires were contained.
According to the Colorado Department of Public Health and Environment, smoke, ash, and soot from a fire can leave harmful chemicals, such as benzene, on surfaces throughout the home.
Homes heavily impacted by smoke may have higher levels of these pollutants, which can linger in the air for weeks. Cleaning carefully and taking health precautions can help reduce exposure.
Colorado’s Department of Public Health and Environment recommends taking certain precautions to protect one’s health and offers tips for cleaning an affected home.
This includes wearing a mask or respirator, such as an N95 mask or a P100 particulate respirator, wearing gloves and clothing that can prevent skin contact with ash or debris, airing your house when possible, and using air filters or cleaners until the odors dissipate.
The aftermath of the Eaton and Palisades fires has made it clear that the dangers of wildfire extend well beyond the flames.
The work of the LA Fire Health Study Consortium is bringing the long-term health risks posed by lingering toxins into focus, presenting a crucial step toward understanding and mitigating those risks.
Sources:
Dietz, N. (2025, May 25). After the LA Fires, Scientists Study the Toxic Hazards Left Behind. Inside Climate News. https://insideclimatenews.org/news/25052025/scientists-study-la-fire-toxins/
Vigliotti, J. (2024, June 11). 6 years after California’s deadly Camp Fire, some residents are returning to Paradise. CBS News. Retrieved from https://www.cbsnews.com/news/camp-fire-paradise-california-rebuild/
Colorado Department of Public Health and Environment. (2025). Retrieved from https://cdphe.colorado.gov/iaq-fires
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