February 19, 2025
Could wildfire smoke affect reproductive health?

When Jasper Kehoe’s flight from Denver landed in Southern California on Jan. 7, he quickly realized the Pacific Palisades blaze had ignited while he was in the air.

A Colorado State University junior in biomedical sciences, Kehoe works part-time as a wildland firefighter with the Larimer County Sheriff’s Office. During the next few days, he received multiple messages asking if he could join units deploying to Los Angeles, but he’d already committed to helping family on their ranch for the week, a promise he intended to keep. What’s more, he had to get back to Fort Collins for the start of the spring semester. “If I didn’t have school I would be fighting those fires right now,” Kehoe said.

Unable to assist on the ground, Kehoe decided to help wildland firefighters in another way — by recruiting subjects for research into the impact of wildfire smoke on male reproductive health. Kehoe is assisting CSU’s Luke Montrose, an associate professor of environmental toxicology in the College of Veterinary Medicine and Biomedical Sciences, who is leading the research. “We’re working now on reaching out to contacts in LA to push out our study and hopefully get some of these guys to be involved,” Kehoe said.

Luke Montrose

Currently, Montrose’s working hypothesis is that smoke-related impacts to reproductive health correspond to the effects smoke can have on the brain. “The brain is the master hormone regulator for the body, sending the signal to start, stop or speed up spermatogenesis,” Montrose said. “We think that breathing in air pollution causes neuroinflammation that can disrupt hormone regulation.”

Funded through a two-year grant from the Centers for Disease Control and National Institute for Occupational Safety, Montrose launched the study in the fall and is recruiting firefighters to participate. Already, the study has about 40 participants, and Montrose hopes to enroll 60 more. His lab previously found that simulated wildfire smoke altered the sperm DNA of adult mice in ways that could impair sperm function or reduce fertility. Montrose is interested in studying whether similar changes happen in humans.

“Our work is based on the premise that wildfire activity — duration, frequency and intensity — is increasing, and this new exposure paradigm means that organs other than the lungs may be impacted,” Montrose said. “Unfortunately, the LA fires bolster this premise; we need to consider both the short- and long-term impacts to our bodies.”

What wildfire season?

Although the devastating fires spreading through LA have presented Montrose and Kehoe with an opportunity to connect with additional firefighters, Montrose said the disaster has also highlighted a challenge: The increasingly clear reality that there is no “fire season,” that these kinds of events can occur year-round.

Montrose had considered analyzing samples from firefighters before, during and after the fire season. But there may no longer be a pre-season. “We may not have a period where some of these firefighters are unexposed,” Montrose said. “If these firefighters in LA provide data from a sample within the next 72 days, then this fire activity will be captured in that sample data.” (The human biological process that produces sperm cells, spermatogenesis, happens on a 72-day cycle.)

However, Montrose said, researchers are making it easy for firefighters to participate. Those who volunteer will use at-home test kits that can be analyzed using a Bluetooth device and can send the data directly to Montrose’s lab.

Jasper Kehoe

In addition to mice, Montrose has investigated the reproductive effects of wildfire smoke on cattle by analyzing sperm samples from bulls. He is finalizing data from a study conducted in partnership with a bull breeding facility on the Front Range. Samples from bulls showed “significant” impact related to wildfire events, he said. What’s more, the effects varied by breed. “That could mean that among human populations there may be sub-populations that are more or less sensitive to this,” said Montrose, who plans to publish the full results of the study later this year.

For his part, Kehoe is glad to be able to help better understand the risks associated with wildland firefighting. “I am incredibly concerned about their health,” he said. “I know there are environmental health implications — I’ll be hacking up black soot from my lungs for the next week after I fight a fire — but I want to keep learning more about those effects.”

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