Maui adults carrying the most toxic metals were more likely to have abnormal breathing tests, and the pattern extended beyond Lahaina.
Once the flames are out and the smoke drifts off, a wildfire seems to be over. A fire that burns through a town is different.
Houses, cars, wiring and treated lumber burn along with the brush, and what’s left of them may remain in ash, soil and dust long after.
Adults on Maui tested 6 to 18 months after the August 2023 wildfires had far higher levels of several metals in their urine than a national sample of U.S. adults.
The people with the highest mix of metals were also more likely to score below normal on a breathing test.
If that pattern holds, checking the air during and after a fire may miss how much of a disaster’s pollution ends up inside people.
Researchers at the University of Hawaiʻi at Mānoa drew on the Maui Wildfire Exposure Study, or MauiWES, which tracks residents’ health after the fires.
Alika Maunakea of UH Mānoa’s John A. Burns School of Medicine led the research with health economist Ruben Juarez, and the two co-direct MauiWES.
Each person was tested once, so the study can show a link between metals and breathing problems but can’t prove the metals did the damage.
In all, 1,400 adults from across Maui County took part. Each one gave a urine sample and took a breathing test at the same visit. The team measured 24 metals in every sample.
Urine shows what a body has absorbed, something an air monitor can’t measure. The researchers compared their results with national survey data from U.S. adults.
The typical participant had nearly 40 times as much antimony in their urine as the national figure. Manganese was 3.8 times higher, and barium was 2.3 times higher. Arsenic came in at 2.2 times.
Those four metals stand out for another reason. The metals most elevated in people’s bodies match those found in ash, soil and settled dust collected around Maui after the fires.
Not every metal was elevated. Lead was 1.8 times the national figure, and cadmium showed no real difference at all.
The breathing test measures how much air a person can blow out and how fast. A result counts as abnormal when it falls below the normal range expected for that person.
Depending on the measure, between 18% and 31% of participants with usable tests scored below normal.
Metals rarely show up one at a time, so the team scored each person’s combined load and analyzed that score three different ways.
Each time, a higher combined load went with greater odds of an abnormal breathing test.
In the main analysis, each step up the scale was linked to roughly 50% to 85% higher odds of an abnormal result. Single metals showed a less consistent pattern than the mix.
Among people who don’t smoke, the results were similar. They stayed similar after accounting for time since the fire.
“The mixture itself, particularly metals such as arsenic, cadmium, copper, and antimony, appeared to matter the most,” Juarez said.
Lung problems showed up across Maui
Lahaina, the coastal town the fires devastated, had the highest share of people reporting frequent contact with ash. More than 40% said they came into contact with it daily or weekly.
Lahaina residents also had relatively high arsenic and cadmium.
But the worst lung results came from the towns of Wailuku and Kahului, where about 37% scored below normal on one key measure.
Residents there also had the highest copper, iron and molybdenum. Kula, a community at higher elevation, had the lowest rate on that same measure, about 21%.
“That tells us that the health footprint of a disaster like this can extend beyond the places where the buildings actually burned,” said Maunakea.
The fire may have stirred up old pollution
Most of what’s known about the health effects of wildfire smoke comes from fires that burn plants.
“We have traditionally thought about wildfire exposure primarily through the lens of smoke,” Maunakea said.
“But when an entire community burns, we are dealing with a much more complicated exposure environment.”
On Maui, arsenic-treated materials, farm chemical residues and contaminated soil remain from the plantation era. Parts of Hawaiʻi’s volcanic ground are also naturally higher in arsenic and manganese.
The authors suggest the fire did two things at once. It created new ash rich in toxic metals, and it disturbed older contamination already in the soil.
After the 2025 Los Angeles fires, other researchers measured elevated airborne lead and chromium particles near cleanup zones.
As destructive fires reach more built-up places, the researchers say disaster response should go beyond short-term air quality checks.
They call for testing people’s bodies, screening lungs over time and cleaning up contaminated soil and dust.
What remains unknown
There are no measurements of these residents’ metal levels from before the fire. Without them, the study can’t say how much of the metal came from the fire and how much was there already.
Some arsenic in urine can come from food. The national data used for comparison date from 2011 and 2012, and background exposure across the country has fallen since then.
Participants signed up through community outreach rather than being picked at random, and each gave one urine sample.
“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,” Juarez said.
The university has also won a $3.6 million grant from the National Institute of Environmental Health Sciences to pull those sources apart. Maunakea, Juarez and Alison Lee of the Icahn School of Medicine at Mount Sinai will lead it.
Over five years, the team will follow about 1,000 Hawaiʻi residents, measuring their surroundings and checking their hearts and lungs.
The goal is to learn which exposures came from the fire and which were already in the ground.
The full study was published in the journal Proceedings of the National Academy of Sciences.
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