For this study, researchers recruited 101 U.S. citizens owning a car with a model year of 2015 or newer to hang a silicone passive sampler on their rearview mirror for seven days.

A silicon passive sampler can be used to measure different types of pollutants in the air, including brominated and organophosphate flame retardants.

Scientists reported that organophosphate esters (OPEs) were the most frequently detected fire retardant collected by the silicone passive samplers.

“OPEs are increasingly used as both flame retardants and plasticizers — i.e. chemicals that change the properties of plastics — in various materials,” said Heather M. Stapleton, PhD, Ronie-Richele Garcia-Johnson Distinguished Professor in the Nicholas School of the Environment at Duke University and corresponding author of this study.

“Car interiors often contain a large proportion of plastic components that are likely sources of these OPEs, such as the foam in the interior roof lining, the seats, the electronics in the dashboards, etc,” Stapleton explained to Medical News Today.

“The more plastics we surround ourselves with in our daily lives, the more exposure we will have to these chemicals, particularly inside a car interior where the space is relatively small compared to a home or building,” she added.

Of OPEs, tris(1-chloro-isopropyl) phosphate (TCIPP) had a 99% detection frequency with in-cabin air measurements ranging from 0.2 to 11,600 ng/g of sampler.

Stapleton and her team also found that TCIPP was the dominant fire retardant discovered in car seat foam.

“TCIPP is a chlorinated organophosphate flame retardant that has been used extensively in some textiles, building insulation, and furniture,” Stapleton said. “It has been increasingly used following the phase-out of its close chemical cousin, TDCIPP, which is considered a probable human carcinogen.”

“New data suggest that TCIPP may also be carcinogenic. Some recent epidemiology and toxicology studies also suggest TCIPP may be neurotoxic at high exposures, and impact thyroid hormone regulation.”

– Heather M. Stapleton, PhD

About half of the cars included in the study were tested both during the summer and winter.

Researchers reported that sampler fire retardant concentrations within vehicle cabins were two to five times higher in the summer than in the winter.

They also found that the presence of TCIPP in foam resulted in about four times higher average air sampler concentrations in winter and almost nine times higher during the summer months.

Stapleton explained:

“Chemicals are emitted from plastics at higher rates with higher temperatures. Therefore, levels of these chemicals in the cabin air of a vehicle will be higher in cars parked or residing in warm areas of the country vs cars in colder parts of the country. And people entering these cars will be breathing in this air with higher concentrations of flame retardants and receiving higher exposures.”

“We hope this research brings more attention to the use of these chemicals in personal vehicles and the risks they potentially pose to human health,” she continued. “There are no research studies that prove the use of these chemicals in car seats helps to save lives. In contrast, there (is) data showing that the presence of flame retardant chemicals in seat foam leads to the generation of more smoke and toxic chemicals like carbon monoxide and hydrogen cyanide when they burn during a fire.”

“It’s also important to note that these chemicals do not stop materials from burning, they only slow the rate at which they burn, and while they burn they are creating dangerous conditions — i.e. more smoke and toxic chemicals,” Stapleton added. “We need to address fire safety with different technologies and approaches, such as using inherently non-flammable materials, or redesigning flame retardants so they do not escape from materials over time.”

To help protect drivers and passengers from the potential of flame retardant exposure in vehicle cabins, Stapleton said ventilating your car, particularly during hot summer months, is very important.

“And if possible, park your car in the shade or use a sun visor to minimize the car interior temperature during the day,” she continued. “I also recommend that people open the car windows and ventilate the air before getting into the car to drive. If you have an automatic starter, it would be best to start the car for a few minutes before driving and put the air conditioner on to cool the interior temperature.”

MNT also spoke with Douglas A. Miller, MD, radiation oncologist and medical director of the Department of Radiation Oncology at Hackensack Meridian Jersey Shore University Medical Center in New Jersey, about this study.

“Many vehicles also allow the ability to recirculate air within or utilize outside air when heating/cooling,” Miller offered as another tip. “For people wishing to maximally reduce potential exposure, consider avoiding use of the recirculating air feature.”

“(This) research … raises awareness of potential environmental exposures of compounds that may be harmful to humans,” he continued. “In clinical practice, environmental exposures and their absolute risks for cancer development remain challenging to sharply define for the entire population, but this study is an important first step to identify potential exposures and mitigate risk.”

“Given the millions of people (who) drive or travel in vehicles across the country on a daily basis, we statistically may find cases where environmental exposure from chemical retardants may induce a malignancy,” Miller added. “Moving forward, I would like to see research into (the) modernization of the regulations regarding the material requirements in vehicles and develop alternative materials which do not contain (potentially) harmful compounds.”