The health effects of the Maui wildfires may have continued long after the flames were extinguished, with new research finding elevated levels of several metals in residents more than six months after the disaster.
Researchers from the University of Hawaiʻi at Mānoa analysed biological and lung-function data from 1,400 Maui adults between six and 18 months after the August 2023 fires.
The study found substantially higher concentrations of several metals in participants compared with US biomonitoring reference data, while greater overall metal exposure was associated with abnormal measures of lung function.
The findings suggest that exposure following a major wildfire can be more complicated than smoke inhalation alone.
Fires that destroy developed areas can burn buildings, vehicles, electronics, treated timber and infrastructure, while also disturbing contaminants already present in soil and the wider environment.
Metal exposure remained months after Maui wildfires
The study, conducted through the University of Hawaiʻi at Mānoa’s Maui Wildfire Exposure Study (MauiWES), measured 24 metals in participants’ urine alongside standardised pulmonary function tests.
Several metals were present at markedly higher concentrations than US reference values. Antimony levels were almost 40 times higher, while manganese was 3.8 times higher, barium was 2.3 times higher, and arsenic was 2.2 times higher.
The researchers used three complementary statistical methods to examine the relationship between metal exposure and lung function. Each identified associations between higher combined metal exposure and several measures of abnormal pulmonary function.
Arsenic, cadmium, copper, and antimony made particularly strong contributions to these patterns.
Wildfire exposure is not the only possible source
The researchers caution against attributing the measured metal burden entirely to the wildfire.
Maui’s residents may already have been exposed to some contaminants through the island’s geology, historical agricultural and industrial activity, diet and other environmental sources.
The Maui wildfires could then have introduced additional contaminants or disturbed material that had previously remained in soil, dust and the built environment.
This makes it difficult to establish exactly where the metals detected in residents came from.
There were no biomonitoring measurements from before the fires available for comparison, meaning the study cannot determine how much of the measured exposure was directly caused by the disaster and how much reflected longer-term or continuing exposure.
Long-term monitoring of both people and the environment will therefore be needed to separate these different sources.
Lahaina and other areas showed different exposure patterns
The research also found that exposure was not consistent across Maui.
Lahaina residents had a distinct metal profile, including relatively high concentrations of arsenic and cadmium. Wailuku and Kahului residents recorded the highest median concentrations of copper, iron, and molybdenum, while Kula and Kihei showed different patterns again.
Pulmonary health also varied geographically. Among participants with interpretable breathing test results, Wailuku and Kahului had some of the highest prevalence of abnormal lung-function measures. Lahaina also showed substantial pulmonary impairment, while Kula generally recorded the lowest burden.
The differences indicate that living in or near an area affected by the fires does not necessarily result in a single, uniform pattern of exposure.
Instead, the researchers say the results may reflect several overlapping factors, including wildfire-generated contaminants, material disturbed by the disaster, historically contaminated soil, local land use, geology, and other environmental sources.
From smoke exposure to a wider environmental picture
Much of the existing understanding of wildfire-related health effects has focused on smoke from burning vegetation.
The Maui disaster presents a more complex scenario because the fires moved through developed areas. Burning homes and infrastructure can create mixtures of contaminants that would not necessarily be present in a wildfire affecting vegetation alone.
After the fire, those materials can remain in ash, soil, dust and debris. They can also be redistributed during cleanup and recovery.
Potential exposure can therefore continue through fine particles that become airborne again, direct contact with contaminated dust or debris and other environmental pathways after visible smoke has disappeared.
This is particularly important where a wildfire occurs in areas that already contain pollutants from previous agricultural or industrial activity.
Research to investigate contamination sources
The latest findings are now feeding into further research in Hawaiʻi.
In September 2026, the University of Hawaiʻi announced a five-year, $3.6m National Institute of Environmental Health Sciences grant to investigate pollutants left behind by decades of agricultural and industrial activity and examine whether disasters such as wildfires can bring those contaminants back into the environment and into people’s bodies.
The project is being led by researchers from the University of Hawaiʻi at Mānoa and the Icahn School of Medicine at Mount Sinai. It will follow approximately 1,000 Hawaiʻi residents over five years, combining environmental measurements, biological samples and assessments of heart and lung health.
The work will examine the differences between persistent background exposure, historical contamination and exposure associated with disasters.
That could help researchers determine which contaminants remain in the environment, how they reach people and how different exposure pathways relate to longer-term health.
Long-term monitoring will remain important
The findings add to the broader work of MauiWES, which was established to follow the health consequences of the 2023 Maui wildfires over time.
The study has already expanded beyond its initial focus, with further funding supporting continued monitoring of affected adults and the inclusion of children in longer-term research.
For the researchers, the latest study highlights the need to consider what remains in the environment after a wildfire rather than focusing solely on conditions during the fire itself.
The central issue is no longer simply what contaminants a wildfire produces. It is also how a disaster changes the movement of contaminants already present, how long those exposures persist, and how they may affect people during the recovery period.
