Toxic Metals Linger in Maui Residents’ Bodies Long After the 2023 Wildfires

More than a year after flames tore through Lahaina, scientists are discovering that the most dangerous legacy of the 2023 Maui wildfires may not be what burned, but what remained behind. A new study from the University of Hawaiʻi at Mānoa’s Maui Wildfire Exposure Study, known as MauiWES, has found substantially elevated concentrations of toxic metals in the urine of Maui residents measured six to eighteen months after the disaster. The research, published on September 28 in the Proceedings of the National Academy of Sciences, also links greater accumulated metal burdens in the body to abnormal lung function, suggesting that the health consequences of urban wildfire catastrophes can persist long after the smoke has visibly cleared.

The study examined 1,400 Maui adults, measuring concentrations of 24 different metals in urine samples while simultaneously assessing pulmonary function through standardized breathing tests conducted at the same visit. When researchers compared the results against national biomonitoring reference data from the United States, the disparities were striking. Participants showed antimony concentrations nearly 40 times higher than U.S. reference values, manganese at 3.8 times, barium at 2.3 times and arsenic at 2.2 times the national benchmarks. These are not trace deviations; they represent a population carrying a metal burden far beyond what typical American residents experience.

The pulmonary findings may prove even more consequential. Across three complementary statistical approaches, higher combined metal exposure was consistently associated with several measures of abnormal lung function. Arsenic, cadmium, copper and antimony emerged as the metals contributing most strongly to those patterns. Each of these substances has well-documented toxicological profiles: arsenic and cadmium are established carcinogens, antimony is a metalloid used in flame retardants and electronics, and copper in excess can damage respiratory tissue. The convergence of elevated body burdens and measurable respiratory impairment in the same individuals points to a public health problem that outlasts the emergency phase of a disaster by many months.

The researchers are careful, however, not to attribute the entire burden to the fires alone. Because no pre-wildfire biomonitoring data exist for these residents, the study cannot determine precisely how much of the measured metal load came directly from the August 2023 disaster versus chronic, persistent or other ongoing exposures. Hawaiʻi’s geology, a long history of agricultural and industrial land use, diet and other environmental factors may all have contributed to exposures that predated the fires. The disaster may then have introduced entirely new contaminants while simultaneously disturbing and remobilizing pollutants already locked in soil, dust and the built environment. Disentangling those pathways, the team says, will require longitudinal biomonitoring and environmental sampling over years.

What makes the Maui situation scientifically distinct is the nature of the fire itself. Much of the existing knowledge about wildfire health effects derives from studies of smoke generated by burning vegetation. But the Lahaina fire belonged to a different and increasingly common category: the wildland–urban interface disaster, in which flames sweep through neighborhoods rather than forests. Such fires consume homes, vehicles, electronics, treated lumber and electrical systems, generating complex chemical mixtures that bear little resemblance to wood smoke. At the same time, they disturb pollutants accumulated in soil from decades of earlier agricultural, industrial or other land uses, redistributing them across the landscape during cleanup and recovery.

Those materials can remain in ash, settled dust, soil and debris long after the flames are extinguished, creating continued exposure pathways that include resuspended fine particles, direct contact with contaminated dust and debris, and indirect environmental exposure even when the air looks clear. This is the mechanism the MauiWES team believes explains why metal burdens remained elevated in residents’ bodies many months after the disaster. When a fire burns through an entire community, it can fundamentally alter how contaminants move through the environment, transforming a static contamination landscape into a dynamic and prolonged source of human exposure.

The geographic patterns uncovered by the study add another layer of complexity. Exposure was not confined to Lahaina, the town most closely associated with the disaster. Lahaina residents did show a distinct metal profile, including relatively elevated concentrations of arsenic and cadmium, but Wailuku and Kahului residents recorded the highest median concentrations of copper, iron and molybdenum. Kula and Kihei displayed different metal profiles as well, underscoring that no single uniform exposure pattern existed across the island. Pulmonary impairment varied in parallel: among interpretable breathing test results, Wailuku and Kahului exhibited some of the highest prevalence of abnormal lung-function measures, while Lahaina also showed substantial impairment and Kula generally showed the lowest burden.

These spatial differences suggest that the post-disaster exposure landscape is far more complicated than a simple comparison between people inside and outside a burn zone. The researchers believe the measured metal mixtures 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 central focus of the research program, and the answer will shape how communities recovering from urban fires should be monitored and protected.

The implications extend well beyond Hawaiʻi. As destructive fires increasingly reach developed communities across the American West, Australia, the Mediterranean and elsewhere, the Maui findings suggest that disaster-response systems may need to look beyond short-term measurements of smoke and particulate matter. Future responses, the researchers argue, 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. In September 2026, the National Institute of Environmental Health Sciences awarded the team a five-year, $3.6 million grant to investigate pollutants left behind by decades of agricultural and industrial activity in Hawaiʻi and to examine whether wildfires and other disasters can remobilize those contaminants into new pathways of human exposure.

That new project, led by MauiWES co-directors Alika Maunakea and Ruben Juarez together with Alison Lee of the Icahn School of Medicine at Mount Sinai, will follow approximately 1,000 Hawaiʻi residents over five years, combining environmental measurements, biological samples and cardiopulmonary assessments. Its goal is to distinguish persistent background exposures, legacy contamination and disaster-related exposures while examining how each contributes to heart and lung health over time. Together, the studies shift the scientific question from simply asking what a wildfire released to a broader and more consequential one: how a disaster transforms an existing environmental contamination landscape and changes what people are exposed to in the months and years that follow.

The research team has also emphasized that the study was designed not merely to document harm but to connect participants with information and care. MauiWES participants receive access to their individual health results, opportunities to discuss those findings with the research team, and referrals when screening identifies potential health concerns. The study will continue following families over time to understand how health evolves during Maui’s recovery. Juarez acknowledged that the findings may be difficult for families who have already endured so much, but stressed that the team’s responsibility extends beyond publishing the science to returning information to the community, connecting people with care when they need it, and continuing to learn alongside Maui as the island rebuilds. For now, the central lesson stands: exposure may not end when the smoke clears, and the next scientific challenge is to understand which exposures persist, where they come from and what they mean for long-term health.

Subject of Research: Persistent toxic metal exposure and pulmonary impairment among residents affected by the 2023 Maui wildfires

Article Title: EMBARGOED: Toxic metals found in Maui residents months after 2023 wildfires, UH study finds

Article References: EMBARGOED: Toxic metals found in Maui residents months after 2023 wildfires, UH study finds. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Maui wildfires, Lahaina, toxic metals, biomonitoring, lung function, arsenic, cadmium, antimony, wildland-urban interface, environmental health, University of Hawaii, PNAS