UH study: Toxic metals found in Maui residents months after 2023 wildfires

The health consequences of catastrophic wildfires that burn through towns and cities may extend far beyond the period when flames are extinguished and smoke disappears, according to new research from the University of Hawaiʻi at Mānoa’s Maui Wildfire Exposure Study (MauiWES).

A study of 1,400 Maui adults 6–18 months after the August 2023 wildfires found substantially elevated concentrations of several metals in participants’ urine, and also discovered that greater amounts of metals accumulated in the body was associated with abnormal lung function. Researchers measured 24 metals while assessing pulmonary function through standardized breathing tests at the same visit. The findings were published on September 28 in the Proceedings of the National Academy of Sciences.

Compared with US biomonitoring data, Maui participants had markedly higher concentrations of several metals, including antimony at nearly 40 times, manganese at 3.8 times, barium at 2.3 times and arsenic at 2.2 times US reference values.

“Our study suggests that months after the fires, many residents were still carrying elevated mixtures of metals in their bodies, meaning that exposure did not necessarily end when the smoke cleared. Urban wildfires can create a much longer lasting contamination problem involving ash, dust, soil, debris, homes, cars, and other burned materials,” said Alika Maunakea, MauiWES co-director and professor at the UH Mānoa John A. Burns School of Medicine.

Across three complementary statistical approaches, higher combined metal exposure was associated with several measures of abnormal lung function. Arsenic, cadmium, copper and antimony were among the metals that contributed most strongly to those patterns.

The researchers emphasize, however, that the elevated metal burden likely reflects a complex mixture of exposures rather than a single source. Some exposures may have existed before the wildfire because of Hawaiʻi’s geology, historic agricultural and industrial land use, diet and other environmental factors. The disaster may then have introduced new contaminants while also disturbing and remobilizing pollutants already present in soil, dust and the built environment.

Because pre-fire biomonitoring data are not available, the current study cannot determine precisely how much of the measured burden came directly from the wildfire versus chronic, persistent or other ongoing exposures. Longitudinal biomonitoring and environmental sampling will be critical to disentangling those pathways.

“The biggest message is that exposure may not end when the smoke clears,” said Ruben Juarez, MauiWES co-director and UHERO–HMSA Distinguished Endowed Professor of Health Economics at UH Mānoa. “What we are likely seeing is a complex combination of exposures—some that may have been present for years and others that may have been generated or remobilized by the wildfire. When a disaster burns through a community, it can fundamentally change how contaminants move through the environment. The next scientific challenge is to disentangle those sources and understand which exposures persist, where they come from and what they mean for long-term health.”

A different kind of wildfire

Much of what is known about wildfire health effects comes from studying smoke generated by burning vegetation. But fires such as those that devastated Lahaina represent a fundamentally different type of disaster.

Wildland-urban interface fires can burn homes, vehicles, electronics, treated lumber, electrical systems and other infrastructure, generating complex mixtures of contaminants while simultaneously disturbing pollutants accumulated in soil from earlier agricultural, industrial or other land uses. Those materials may remain in ash, settled dust, soil and debris or be redistributed across the landscape during cleanup and recovery. Potential pathways of continued exposure include resuspended fine particles, contact with contaminated dust and debris and indirect environmental exposure even after visible smoke has dissipated.

“We have traditionally thought about wildfire exposure primarily through the lens of smoke,” said Alika Maunakea, MauiWES co-director and professor at the UH Mānoa John A. Burns School of Medicine. “But when an entire community burns, we are dealing with a much more complicated exposure environment. The biology is telling us that we need to understand not only what was in the air during the fire, but what was already present in the landscape, what the disaster may have mobilized, and what is actually getting into people’s bodies during the months and years that follow.”

Exposure was not confined to Lahaina

The study also identified substantial geographic differences in both metal exposure and pulmonary health across Maui.

Lahaina residents showed a distinct metal profile, including relatively elevated concentrations of arsenic and cadmium, while Wailuku/Kahului residents had the highest median concentrations of copper, iron and molybdenum. Kula and Kihei showed different metal profiles as well, underscoring that there was no single uniform exposure pattern across the island.

Pulmonary impairment also varied across Maui. Among interpretable breathing test results, Wailuku/Kahului exhibited some of the highest prevalence of abnormal lung-function measures, while Lahaina also showed substantial pulmonary impairment and Kula generally showed the lowest burden.

Those patterns suggest that the exposure landscape after a major disaster may be more complicated than simply comparing people inside and outside a burn zone. Researchers believe the measured metal mixtures may reflect overlapping contributions from wildfire-generated material, contaminants remobilized by the disaster, historically contaminated soils, local land use, geology and other ongoing environmental sources. Determining the relative contribution of each pathway is now a major focus of the research.

Implications far beyond Maui

The findings from Maui have implications beyond Hawaiʻi. As destructive fires increasingly reach developed communities, researchers say disaster-response systems may need to look beyond short-term measurements of smoke and particulate matter. Future responses could include longer-term environmental monitoring, human biomonitoring, respiratory surveillance and targeted assessment of soil, ash and settled dust, particularly in places with histories of agricultural or industrial contamination.

New NIH study will disentangle legacy and disaster-related exposures

The next phase of research will investigate the sources of the metal contaminants. In September 2026, UH announced a five-year, $3.6 million grant from the National Institute of Environmental Health Sciences to investigate pollutants left behind by decades of agricultural and industrial activity in Hawaiʻi and examine whether wildfires and other disasters can remobilize those contaminants, creating new pathways of human exposure.

The project is led by Maunakea, Juarez and Alison Lee of the Icahn School of Medicine at Mount Sinai. It will follow approximately 1,000 Hawaiʻi residents over five years and combine environmental measurements, biological samples and cardiopulmonary assessments. The research will help distinguish persistent background exposures, legacy contamination and disaster-related exposures, while examining how those different sources contribute to heart and lung health over time.

Together, the studies shift the scientific question from simply “What did the wildfire release?” to a broader one: “How does a disaster transform an existing environmental contamination landscape and change what people are exposed to?”

Connecting participants with information, care

Researchers emphasized that the study is designed not only to document health effects, but also to connect participants with information and care. MauiWES participants receive access to their individual health results, opportunities to discuss those findings and referrals when screening identifies potential health concerns. The study will continue following families over time to understand how health changes during Maui’s recovery.

“We know these findings may be difficult for families who have already been through so much,” Juarez said. “Our responsibility is not simply to publish the science. It is to help people understand what we are finding, return information to the community, connect people with care when they need it, and continue learning alongside Maui as the community recovers.”

Resources for Maui residents

Research about the wildfires may raise health questions or bring back difficult memories. Maui residents can access the following resources:

• Current environmental conditions and advisories: The Hawaiʻi Department of Health maintains a Maui Wildfire Environmental Monitoring Data Portal with current information on air, soil, ash and debris, coastal waters and other environmental monitoring.
• Medical and behavioral health resources: The Hawaiʻi Department of Health Maui Wildfire Response site provides medical, mental health and recovery resources, including materials in multiple languages.
• Emotional or crisis support: Hawaiʻi CARES 988 provides free, confidential support 24 hours a day. Call or text 988. Local counselors can assist with mental health, crisis and substance-use concerns.
• Help finding community service s: Aloha United Way 211 connects Hawaiʻi residents with health care, housing, food, financial assistance, mental health services and other local resources. Dial 211 or visit the statewide resource directory.
• MauiWES participants: Participants can access individual health results through the MauiWES participant portal. Send questions about the study to mauiwes@hawaii.edu.