Metal mixtures found in the leftover smoke, ash and debris from the deadly 2023 Maui wildfires were harmful to the lung health of people living nearby long after the burning ended, a new study says.
The work shows that major wildfires, which are worsening with the planet’s warming, could have lasting effects beyond immediate exposure.
Post-wildfire air quality needs to be monitored longer term, the research suggests, and recovery efforts need to consider what might remain in contaminated soot, residue and dirt well after burning stops.
The wildfires, caused by wind spreading a brushfire spurred by downed power lines, burned on the Hawaiian island of Maui in August 2023, destroyed the town of Lāhainā and killed more than 100 people. They were among the deadliest in U.S. history.
New research published in the journal Proceedings of the National Academy of Sciences on Monday found higher metal levels, associated with respiratory harm, in nearby residents up to a year and a half after the fires.
As part of the Maui Wildfire Exposure Study, one of the largest postfire investigations in the country, University of Hawai‘i researchers studied the urine of 1,400 adults. They found substantially elevated concentrations of metals such as arsenic, cadmium, copper and antimony.
Chemicals from burned buildings and electronics
These metals could be the result of burned buildings, vehicles, electronics and other materials lost in the wildfires, the researchers say. They can cause a different human impact than simply the burned vegetation that is typically studied after fires of this magnitude.
“What we’re dealing with, especially in the aftermath of what we experienced in Lāhainā, is a much more complicated mixture of these chemical exposures,” said Alika Maunakea, co-principal investigator of MauiWES and an anatomy, biochemistry, and physiology professor at the University of Hawai‘i, Mānoa.
The researchers found antimony nearly 40 times higher in the Maui participants than U.S. biomonitoring data. They found manganese 3.8 times higher, barium 2.3 times and arsenic 2.2 times.
Having more metals in the body was more likely to result in abnormal lung function, such as having less breathing capacity and difficulty moving air in and out of one’s lungs, during standard breathing tests, the study found.
Those lung effects aligned with the geographic distribution of smoke and ash; those nearest to Lāhainā, and Wailuku and Kahului, experienced a different impact than in those near Kula.
“It’s really important to identify potentialsks for re-exposures that might be contributing to these effects,” Maunakea said. “What happens to the land and environment can shape what people breathe, take into their bodies, and develop over time. The consequences of that can unfold over many years.”
Warming planet can worsen wildfires
Wildfires are getting larger, more intense, faster-moving and more frequent in certain parts of the globe, experts say, in part due to the warming and drier weather associated with climate change. Human-caused climate change has upped the likelihood of many major fires around the world in recent years and led to fires in regions that typically do not see them as often.
The researchers did note a limitation of the study in that it cannot assess exactly how much of the impact came directly from the wildfires versus chronic or other exposures — such as Hawai‘i’s geology, diet, historic agricultural and industrial activity and environmental3
However, previous studies have also found significant long-term human impacts from wildfires and other environmental crises. The impacts have included lung issues and mental health issues such as depression.
“This is bigger than wildfires. These climate-related disasters can change the environment in ways that continue after the immediate emergency is over,” said Ruben Juarez, co-principal investigator of MauiWES and professor of health economics at the university. “Floods, hurricanes, fires, and other disasters definitely can disturb soil, debris, buildings, and legacy contaminants that we have in Hawai‘i, creating these pathways for exposure. … Disaster response should not stop when visible danger is gone.”
Kekoa Taparra, a physician and assistant professor who studies chronic diseases at the University of California, Los Angeles, said the research expands our understanding of the health burden of the fires, particularly over an extended period.
“This type of work echoes that climate-related disasters affect human health well beyond the immediate injuries and deaths we see during the event itself,” said Taparra, who was not involved in the study released Monday but has studied the health impacts of disasters. “Historic wildfires in Lāhainā and even Los Angeles have highlighted how these disasters can produce longer-lasting consequences through displacement, disruption of healthcare and social networks, environmental exposures, and potentially increased mortality.
“As these events become more frequent and severe, understanding and measuring their full health impact will be essential to building more resilient communities and health systems.”
