Firefighters have a higher risk of cancer – but why?

Every night around 8, the air quality sensor inside Fire Station 3 registered an alarming spike.

The late evening timing provided a major clue: firefighters craving their after-dinner snack of popcorn. Popcorn burning on the stove would trigger the air quality monitor. Cooking can release harmful gases, particles and chemicals, a major source of indoor air pollution.

Firefighters are already exposed to smoke and other toxins during a firefight. They may inhale, ingest or touch known and suspected carcinogens such as benzene, phenols and heavy metals. The effects on their health include a 9% higher risk of a cancer diagnosis and 14% higher risk of dying from cancer, compared with the general population.

But less is known about the hazards inside the fire station. Cooking is likely not the only one. Fire trucks emit diesel fumes. At Fire Station 3, traffic exhaust can seep in from two overhead freeways.

It was the station’s captain, Jeffrey Kimura of the Los Angeles County Fire Department (LACoFD), who directed researchers’ attention to another possible source: turnout gear, the personal protective equipment that keeps them safe on the job.

The heavy-duty jackets and pants must be washed in specialty machines that are typically off-site, so they are worn multiple times before laundering. The dirt and debris from firefights accumulate on the clothing. The gear is stored in the station between calls, adjacent to living quarters, and may be a significant source of toxicity.

In cooperation with LACoFD, a multidisciplinary team at UCLA, led by Brigitte Gomperts, MD, and Kimura, will isolate the contaminants on the clothing, and assess their effects on human cells. The study will help determine if PPE contributes to firefighters’ cancer risk.

The concept is similar to thirdhand smoke, the residue that settles on surfaces after a cigarette is extinguished, continuing the exposure to hazardous chemicals.

“Nobody's ever tracked firefighter gear serially over the course of a year,” said Dr. Gomperts, associate director of translational research at the UCLA Broad Stem Cell Research Center and co-director of cancer stem cell biology at the UCLA Health Jonsson Comprehensive Cancer Center.

“We hypothesize that PPE carcinogens will induce changes in cells that are probably not good for cell health, and this could influence cancer risk in firefighters.”

The group is one of eight across the University of California awarded state funding from the California Firefighter Cancer Prevention and Research Program.

Extracting chemicals

The UCLA team will purchase five new firefighter jackets. Before sending them out to the station, they will perform baseline testing. The material of the PPE may itself be carcinogenic. Its textiles contain PFAS, known as “forever chemicals,” which are linked to cancer.

Firefighters at Station 3 will wear the jackets in rotation for two months, then send them back to researchers, unwashed and coated with debris from their firefights.

“Materials and surfaces act like sponges for chemicals that slowly get re-released into the air, and we think the same is going to be true for PPE,” said Victoria Barber, PhD, an assistant professor in the department of chemistry and biochemistry who studies indoor air. “There's a potential that things are evaporating from that gear over long timescales and resulting in exposures for the firefighters.”

Dr. Barber will use a technique called “off-gassing” to analyze what’s on the jackets. A sealed, heated container encourages evaporation. She will then use a mass spectrometer to determine the composition and concentration of what’s in the air.

“Materials and surfaces act like sponges for chemicals that slowly get re-released into the air, and we think the same is going to be true for PPE.”

Dr. Barber theorized what she might find on the surface of the jackets: most likely are semi-volatile organic compounds that deposit on surfaces and are also found in fire retardants. She believed that off-gassing would also reveal volatile organic compounds, including the highly toxic BTEX (benzene, toluene, ethyl, xylene) compounds formed in fires.

But gases are not the only contaminants on the jackets. Particulate matter (PM) refers to mixtures of solids and liquids, made up of hundreds of different chemicals. They are large enough to be seen (smoke, soot) or tiny (30 times smaller than a human hair). When the microscopic PM are inhaled, they can lodge deep in the lungs and cause serious health problems.

The research team includes David Gonzalez, PhD, an atmospheric chemist and postdoctoral fellow, with expertise in particulate matter. He has studied what happens post-inhalation, including how PM generate free radicals – unstable, chemically reactive molecules -- in the lung and lung fluid leading to toxicity.

“Particulates can settle and get stuck onto PPE,” said Dr. Gonzalez. “It's not necessarily just inhalation that leads to exposure. Dermal exposure, if any of this is touching their skin, or maybe they're touching their eyes, their mouth, can deliver a variety of carcinogenic compounds.”

Effects on human cells 

Once the chemists isolate the gases and PM from the jackets, Dr. Gomperts will test their effects on human cells. This is done in her laboratory where mini airway systems – replicas of human lungs – nestle in petri dishes. These three-dimensional organoids are grown from human stem cells and mimic the architecture of human lungs down to its different cell types. They include the tiny, hair-like cilia that line the airways of the lungs and beat to draw mucus, debris and pathogens out of the respiratory system.

The solids and liquids isolated from the jackets can be applied directly to the cells. But it will take a bit of engineering to expose the gases. Dr. Barber will place the jackets in an incubator, heat them up and use a pump to draw that air over the mini lungs. It’s “a pretty good proxy for what inhalation looks like,” she said.

“We think it's a really novel approach,” Dr. Barber said. “As far as we know, it's never been done before.”

Dr. Brigitte Gomperts (left, with former lab member and undergraduate student Carla Pantoja) co-leads a multidisciplinary team of UCLA researchers to determine if PPE contributes to firefighters’ cancer risk. (Photo by Ann Johansson/UCLA Broad Stem Cell Research Center)

Dr. Gomperts will then examine the cells for any changes that may reflect a reaction to toxicity: “Do they divide more? Do they die more? Do they make more mucus? Do the cilia beat or not beat?”

The final step of the study is to examine what changes inside the organoid cells at a molecular level.

Mehdi Bouhaddou, PhD, uses mass spectrometry-based phosphoproteomics to study phosphorylation, a small chemical modification that gets added to proteins. This can alter how proteins communicate with each other and could result in dysregulation of biochemical signaling pathways, which is tied to the development of cancer.

In previous experiments, Dr. Gomperts and Dr. Bouhaddou exposed lung organoids to wildfire smoke. The smoke activated specific signaling pathways known to be important in cancer. The same may occur because of the jacket’s contaminants.

“If you inhibit these pathways you can actually prevent some of the disease pathology associated with wildfire smoke exposure,” said Dr. Bouhaddou, an assistant professor in the department of microbiology, immunology and molecular genetics at the David Geffen School of Medicine at UCLA.

Future policy?

The two-year study will further understanding not only of the toxins that firefighters are exposed to and how they may be contributing to cancer risk, but the means of that exposure. If PPE is found to be a significant source, the results of the study may also serve to recommend new policies.

“If we can show that firefighter uniforms are not being handled appropriately, they're not being washed appropriately, and firefighters need more and better gear, then we can hopefully make some policy changes that will then protect firefighters,” said Dr. Gomperts.

For now, the air quality sensor at Fire Station 3 no longer spikes at 8 p.m. After discovering the source of the emissions, the research team bought the firefighters a popcorn maker.