A study of 1,400 adults enrolled after the August 2023 Maui wildfires found several urinary metals above U.S. reference levels and an association between higher combined metal burden and abnormal spirometry. The results do not establish that the fires caused the measured metal levels or lung-function differences: participants had no pre-fire biomonitoring, and the measurements describe a cohort rather than diagnosing or predicting outcomes for individuals.
What the Maui study measured
The community-engaged Maui Wildfire Exposure Study (MauiWES) enrolled 1,400 adults between six and 18 months after the August 2023 fires. Researchers measured 24 metals in urine and performed standardized spirometry at the same visit, according to the University of Hawaiʻi Economic Research Organization (UHERO), whose summary was published September 30, 2026.
Urinary biomarkers reflect metals present in the body; spirometry measures aspects of lung function. Because both were measured at one visit, the analysis can test whether they were associated, but it cannot show that an individual’s lung function changed after the fires or establish cause and effect.
Which urinary metals were elevated?
UHERO compared participants’ urinary metal measurements with U.S. reference levels. Its September 2026 summary reported the following ratios:
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| Metal | Comparison with U.S. reference levels |
|---|---|
| Antimony | 40-fold higher — UHERO, 2026 |
| Manganese | 3.8-fold higher — UHERO, 2026 |
| Barium | 2.3-fold higher — UHERO, 2026 |
| Arsenic | 2.2-fold higher — UHERO, 2026 |
These are comparisons with reference levels, not clinical safety thresholds or a measure of how much metal came from the fires. The report also identifies elevated urinary levels of several metals in the cohort; the four figures above are the specific comparisons provided in the summary.
How the metal mixture was associated with spirometry
Across three complementary mixture-modeling approaches, higher cumulative metal burden was consistently associated with greater odds of an abnormal spirometry measure. In weighted quantile sum models, a one-quantile increase in the positive mixture index was associated with these odds ratios for results below the lower limit of normal, as reported by UHERO in 2026:
| Spirometry measure below its lower limit of normal | Modeled odds ratio per one-quantile increase |
|---|---|
| FVC | 1.71 |
| FEV₁ | 1.53 |
| FEV₁/FVC | 1.83 |
| FEF25–75 | 1.84 |
These are modeled associations in odds, not absolute probabilities, estimates of how many people were affected, or causal effects. They do not mean every participant with higher metal levels had abnormal lung function, nor that a given person’s result can be inferred from the cohort pattern.
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Patterns differed across Maui
The Columbia University Mailman School of Public Health account, published September 29, 2026, describes variation in both metal profiles and lung-function findings by location. Lahaina participants showed relatively elevated arsenic and cadmium. Wailuku/Kahului had the highest median copper, iron, and molybdenum, and some of the highest prevalence of abnormal lung-function measures. Kula generally had the lowest prevalence of abnormal lung-function measures; Kihei had a different metal profile from the other areas.
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These differences argue against treating Maui as if it had one uniform exposure pattern or one island-wide risk estimate. The account describes geographic variation, not proof that location alone explains an individual’s measurements.
Why the study cannot assign the metals to the fires
There were no pre-fire biomonitoring measurements for participants, so researchers cannot determine precisely how much of the urinary metal burden was caused by the wildfires. The Columbia account notes that Hawaiʻi’s geology, historic agricultural and industrial land use, diet, and other environmental factors could also contribute.
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Fires through built environments may generate contaminants or disturb pollutants already present in soil, dust, and infrastructure. Researchers also describe resuspended fine particles and contact with dust or debris as possible continuing exposure pathways. Those are plausible explanations, not source apportionment for any participant.
Kathrin Schilling, PhD, assistant professor of Environmental Health Sciences at Columbia Mailman School of Public Health, said: “The elevated metal burden likely reflects a complex mixture of exposures rather than a single source,”
Ruben Juarez, MauiWES co-director and UHERO–HMSA Distinguished Endowed Professor of Health Economics at UH Mānoa, said: “The biggest message is that exposure may not end when the smoke clears.”
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How state air monitoring fits—and what it does not show
Hawaiʻi Department of Health (DOH) community air sampling is a separate line of evidence from the study’s urine tests. The Hawaiʻi DOH Maui Data Portal says community sampling ran from January 15, 2024, before debris removal began, through February 19, 2025, after Lahaina property debris removal was complete.
For antimony, arsenic, cobalt, copper, and lead, the portal says more than 1,000 air samples collected since the fires found amounts extremely low and not harmful to health. It notes two exceptions on August 25, 2024: manganese and nickel exceeded protective levels at Opukea Townhomes, and manganese exceeded the level at the Lahaina wastewater pump station. The cause was unclear; possible local contributors included windy conditions, metal grinding or cutting, and fertilizer use.
Air samples measure metals in the air at particular places and times; urinary tests measure internal biomarkers in people. Different measurement types, locations, and time windows mean the DOH results neither negate nor confirm the cohort’s urinary biomarker findings.
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What residents can take from the findings
The study adds evidence that urinary metal levels and lung-function measurements were associated in the adults enrolled, with patterns that differed across Maui. It does not identify the source of each person’s metals, prove that wildfire exposure caused lung impairment, or provide an individual diagnosis. The lack of measurements before the fires is central to interpreting the results.
For a separate, practical precaution around ash, DOH advises: “If you are near a location where there is visible dust or if the ash will be disturbed, you can limit the amount of metals you might breathe in by either temporarily leaving the area or by wearing a snug-fitting dust mask or N95 mask—look for the words ‘NIOSH Approved’ printed on the mask.” This advice concerns limiting inhalation of disturbed dust; it is not a treatment for the lung-function findings in the study.
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