Persistent Internal Metal Mixtures Associated with Pulmonary Impairment

The health consequences of catastrophic wildfires may extend far beyond the period when flames are extinguished and smoke disappears, according to a new study by researchers at Columbia University Mailman School of Public Health, the University of Hawaii, and Icahn School of Medicine at Mount Sinai. Findings from the Maui Wildfire Exposure Study are published in the  Proceedings of the National Academy of Sciences.

Researchers assessed lung function in approximately 1,400 Maui adults and measured 24 metals in their urine. Compared with U.S. biomonitoring reference data, urinary antimony was nearly 40 times as high, manganese 3.8 times as high, barium 2.3 times as high, and arsenic 2.2 times as high. Across three statistical approaches, higher combined metal levels were associated with measures of reduced lung function. Arsenic, cadmium, copper, and antimony contributed most strongly to those associations.

“The elevated metal burden likely reflects a complex mixture of exposures rather than a single source,” said Kathrin Schilling, PhD, assistant professor of Environmental Health Sciences at Columbia Mailman School of Public Health. “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 disturbing 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, according to the researchers.

“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.”

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.

The researchers make the point that traditionally wildfire exposure was thought about primarily through the lens of smoke. But when an entire community burns, there is a much more complicated exposure environment.

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. Kula generally showed the lowest prevalence of abnormal lung-function measures while Wailuku/Kahului exhibited some of the highest prevalence of abnormal lung-function measures. “We need to understand which metals were present before the fire, which may have been released or redistributed by it, and whether people continue to be exposed in the months and years that follow,” said Schilling.

A total list of the co-authors can be found in the paper. 

The study was supported by the National Institute on Minority Health and Health Disparities, grant R33MD019793, the Maui Strong Fund, Kaiser Permanente, the National Institute for Occupational Safety and Health grant U01OH012782, and the National Heart, Lung, and Blood Institute, grant P01HL152953. 

The authors declare no competing interests.