Risk from toxic metals can persist months after wildfires, Maui study finds

Metal mixtures left in smoke, ash, and debris after the deadly August 2023 Maui wildfires were harmful to nearby residents' lung health long after burning ended, according to a new study. The work indicates major wildfires, which are worsening as the planet warms, can have lasting effects beyond immediate exposure, and it argues post-wildfire air quality needs longer-term monitoring, with recovery efforts accounting for what remains in contaminated soot, residue, and dirt.

The fires were caused by wind spreading a brushfire spurred by downed power lines; they burned on Maui in August 2023, destroyed the town of Lāhainā, killed more than 100 people, and were among the deadliest in U.S. history. As part of the Maui Wildfire Exposure Study (MauiWES), one of the largest postfire investigations in the country, University of Hawai‘i researchers studied urine from 1,400 adults. The PNAS study published Monday found higher metal levels associated with respiratory harm in nearby residents up to a year and a half after the fires, including substantially elevated arsenic, cadmium, copper, and antimony.

The researchers say these metals could come from burned buildings, vehicles, electronics, and other materials lost in the wildfires, producing a different human impact than the burned vegetation typically studied after fires of that magnitude. They found antimony nearly 40 times higher in Maui participants than U.S. biomonitoring data, manganese 3.8 times higher, barium 2.3 times higher, and arsenic 2.2 times higher. Having more metals in the body was more likely to be associated with abnormal lung function, such as less breathing capacity and difficulty moving air in and out of the lungs during standard breathing tests. Those lung effects aligned with the geographic distribution of smoke and ash, with people nearest Lāhainā, Wailuku, and Kahului experiencing a different impact than those near Kula.

Alika Maunakea, co-principal investigator of MauiWES and a professor at the University of Hawai‘i, Mānoa, said the aftermath involved 'a much more complicated mixture of these chemical exposures' than typical wildfire studies. He added that consequences of fire 'can unfold over many years' and stressed the importance of identifying potential sources of exposure and mitigating or reducing risks of re-exposure. 'What happens to the land and environment can shape what people breathe, take into their bodies, and develop over time,' Maunakea said. The excerpt also notes that a warming planet can worsen wildfires.