The infernal blazes burning in Southern California are raising concerns about the potential airborne hazards they may be leaving behind.
Even once the fires are ultimately extinguished, experts warn, contaminants from the structures they’ve destroyed — some of them potentially containing toxic materials — could linger in the air and pose uncertain health hazards.
While just how many buildings have burned remains inconclusive, estimates indicate that at least 15,000 structures succumbed to the flames of the initial Palisades and Eaton fires. And some “will have experienced significant damage from smoke and toxic ash deposits,” noted Daniel Swain, a University of California, Los Angeles, climate scientist, at a webinar earlier this week.
“This is a growing concern in the wake of this highly urban fire that burned not just vegetation, but a whole lot of structures that contain things like lead paint, asbestos, various heavy metals contained in the batteries that burned in vehicles and in home system backups and solar panels,” he said.
Describing these losses as “a staggering toll,” Swain warned of indirect harm residents could endure from smoke and toxic ash exposures.
“The health harms, the illness and sometimes, the death that can result from large scale disasters and wildfires, is not limited only to the people who don’t make it out of the fire zone,” he added.
Heading into a likely rainy weekend, the Palisades Fire, which has ravaged the Pacific Palisades neighborhood, was 23,448 acres and 77 percent contained. The Eaton Fire, north of Pasadena, was 14,021 acres with 95 percent containment. But the new Hughes Fire, which began Wednesday near Castaic Lake, had grown to 10,396 acres and was only 56 percent contained.
Wildfire smoke contains a mixture of pollutants, although the most well-studied ingredient is fine particulate matter (PM 2.5). When inhaled, these tiny particles can invade the lungs and penetrate the bloodstream, noted Tarik Benmarhnia, a climate change epidemiologist at the University of San Diego’s Scripps Institution of Oceanography, in a recent explainer.
In addition to exacerbating existing conditions like asthma, repeat PM 2.5 exposure is also associated with future lung cancer, cardiovascular disease and dementia, Benmarhnia stated. He and his colleagues recently demonstrated how repeat exposures to PM 2.5 from wildfire smoke over multiple years can increase the risk of developing dementia and Alzheimer’s disease.
Shedding light on the wildfire smoke’s reach, Scripps Oceanography researchers announced Tuesday they identified ash and debris as far away as 100 miles offshore — prompting concern about potential impacts on fisheries and the broader food web.
“These fires are not only consuming vegetation but also massive amounts of urban infrastructure,” project leader Julie Dinasquet said in a statement. “This introduces a novel ‘urban ash’ component to the wildfire source, filled with exceptionally toxic materials.”
Among the materials she flagged were lead, arsenic, asbestos, microplastics and polycyclic aromatic hydrocarbons, organic compounds that occur naturally in fossil fuels.
“These fires pose a potential significant threat to both humans and ecosystems through the introduction of a large amount of toxic material in the system,” Dinasquet added.
Public health hazards riddled with uncertainty
Precisely just how big the public health threat of these wildfires will be, whom that threat will affect and when, remains uncertain.
Richard Castriotta, a pulmonologist at the University of Southern California’s Keck School of Medicine, noted the “big difference” between urban wildfires such as those burning in Los Angeles and those that impact trees alone.
Recognizing the dangers associated with forest fire smoke are real, Castriotta told The Hill they pale in comparison to the potential contaminants unleashed by a burning building.
He, too, described a smorgasbord of toxic substances involved in such exposures, including chlorine, lead, asbestos and oxides of nitrogen, as well as mystery materials — created as a high-intensity flame “turns the plastics and artificial materials into unknown substances.”
“The danger is there for everybody, but it’s worse, naturally, for people who have lung disease, heart disease, diabetes and impaired immunity,” Castriotta said, also noting pregnant and nursing individuals could be at risk.
Children, meanwhile, are particularly vulnerable and should not be involved in cleaning up houses burned in the blazes, he stressed.
Short-term effects of exposure to smoke tend to appear in both the upper and lower airways, with the nose screening out a lot of larger particles and then the lungs acting as “a first responder” to some of the smaller particles, Castriotta explained.
“This is our first immune response, and so if there are a lot of these toxic particles that get in, it can overwhelm the immune response system,” he said. “That would render the person, regardless of previous state of health, relatively immune deficient — unable to cope with additional burdens, much like the firefighters themselves.”
In the days and weeks to come, that immune impairment could lead to a greater chance of contracting respiratory ailments like pneumonia, influenza, COVID-19 and bronchitis, Castriotta added. As for people who are already ill, he said that the exposure could exacerbate conditions like asthma, chronic obstructive pulmonary disease, pulmonary fibrosis and heart disease.
Castriotta acknowledged, however, he doesn’t know what the long-term effects of exposure to these fires will be and that he’s “not sure if anybody does.” Referencing the 9/11 twin towers collapse, he noted how long it took to determine health impacts on first responders. And while he recognized the differences between these situations, he described similar uncertainties.
One potential problem in many of the homes that burned could be the presence of asbestos, which Castriotta described as “a durable, fireproof fiber that lasts forever.” If these fibers get into the lungs, the “first-responder” white blood cells “don’t have the ability to digest and destroy them,” he explained.
“That’s the reason why there is a long latent period from the exposure to asbestos and the adverse consequences that may be as long as 30 years,” he said.
At the same time, Castriotta noted that long-term impact depends on both the duration and extent of exposure — and that inhaling one single particle of asbestos wouldn’t lead to disease.
Things could have been worse
Although the air pollution levels in these dense, urban conditions might be dire, circumstances could have been even worse if the fires had occurred in the summer instead of the winter.
Alexei Khalizov, a professor of chemistry and environmental science at the New Jersey Institute of Technology, attributed this difference to the higher levels of ground ozone that are notorious on Los Angeles summer days.
Wildfires, he explained, produce high concentrations of chemicals that exhibit a range of volatilities, with low-volatile compounds condensing on soot particles quickly as smoke cools.
The more volatile chemicals are not able to condense as rapidly and instead travel in the air alongside the soot and interact with other pollutants, such as ozone, according to Khalizov. Only then do they become less volatile and begin to condense onto the soot — thereby increasing the toxicity of these particles, he noted.
Among the volatile compounds that alarmed Khalizov the most was polyvinyl chloride (PVC), a common ingredient in plastics. He referred to the 2023 train derailment in East Palestine, Ohio, after which officials made the controversial decision to burn tankers of vinyl chloride — a cancer-causing chemical used to produce PVC — to prevent an explosion.
“Polyvinyl chloride is not very different from the chemical which is used to make it,” he said.
In an urban wildfire scenario, Khalizov raised concerns about the compounding effects of multiple contaminants, or what he described as a “synergism between pollutants.”
“If you’re exposed to smoke and ozone together, they actually make a much worse effect,” he said.
Risks in returning home
As residents begin returning to their charred homes and cleaning up the remains, Castriotta recommended they do so only with N95 masks and goggles, while also warning that air quality indexes don’t account for the toxic materials he mentioned.
“People will look at the Air Quality Index and say, ‘Oh, it’s moderate, or it’s good, it’s the usual L.A. air,'” Castriotta said. “But that doesn’t measure the specific toxins that are released from these particular fires.”
Swain, from UCLA, likewise urged residents to wear particulate filtering masks and use HEPA filters indoors, citing county-wide health advisories of wind-borne ash that could be “falling from the sky.”
Taking such steps, he reiterated, could help minimize future repercussions impacts of such disasters, particularly since smoke and ash can persist even after a fire is largely extinguished.
“The health harms, the casualties and injuries in the days and weeks and months and even years that follow are indirect and they’re harder to count,” Swain added. “These sorts of large-scale disasters have a much greater toll than we’ve really been able to quantify easily in decades past.”
