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Study finds longer commutes associated with increased human exposure to TDCIPP, a known carcinogen

Researchers at the University of California, Riverside, with colleagues from Duke University, report that longer commutes are associated with increased human exposure to TDCIPP (tris(1,3-dichloro-2-propyl) phosphate)—a chemical flame retardant that is a known carcinogen and that was phased out of furniture use because it required a Proposition 65 warning label in California.

The paper is published in the journal Environment International.


Organophosphate esters (OPEs) are a class of semi-volatile organic compounds (SVOCs) used as flame retardants, plasticizers, and anti-foaming agents. Due to stringent flammability standards in vehicles and the ability of OPEs to migrate out of end-use products, elevated concentrations of OPEs have been found in car dust samples around the world. As many residents of Southern California spend a significant amount of time in their vehicles, there is potential for increased exposure to OPEs associated with longer commute times.

As approximately 70% of the University of California, Riverside’s undergraduate population commutes, the objective of this study was to use silicone wristbands to monitor personal exposure to OPEs and determine if exposure was associated with commute time in a subset of these students. Participants were asked to wear wristbands for five continuous days and complete daily surveys about the amount of time spent commuting. Data were then used to calculate a participant-specific total commute score.

—Reddam et al.

Some scientists assumed that humans stopped being exposed to TDCIPP after it was placed on California’s Proposition 65 list in 2013. However, it is still widely used in automobile seat foam. The study shows that not only is your car a source of TDCIPP exposure, but that less than a week of commuting results in elevated exposure to it.

David Volz, associate professor of environmental toxicology at UCR, said the results were unexpected.

I went into this rather skeptical because I didn’t think we’d pick up a significant concentration in that short a time frame, let alone pick up an association with commute time. We did both, which was really surprising.

—David Volz

Over the past decade, Volz has studied how various chemicals affect the trajectory of early development. Using zebrafish and human cells as models, the Volz laboratory has been studying the toxicity of a newer class of flame retardants called organophosphate esters since 2011.

Little is known about the toxicity of these organophosphate esters—TDCIPP is one of them—but they’ve replaced older flame-retardant chemicals that lasted longer in the environment and took longer to metabolize.

Using zebrafish as a model, Volz found TDCIPP prevents an embryo from developing normally. Other studies have reported a strong association between TDCIPP and infertility among women undergoing fertility treatments.

Knowing its use is still widespread in cars, Volz wondered whether a person’s exposure is elevated based on their commute. UC Riverside undergraduates made for excellent study subjects, as a majority of them have a daily commute.

The research team was funded by the National Institutes of Health as well as the USDA National Institute of Food and Agriculture.

Participants included around 90 students, each of whom had commute times that varied from less than 15 minutes to more than two hours round trip. All of them were given silicone wristbands to wear continuously for five days.

The molecular structure of silicone makes it ideal for capturing airborne contaminants. Since TDCIPP isn’t chemically bound to the foam, Aalekyha Reddam, a graduate student in the Volz laboratory, said it gets forced out over time and ends up in dust that gets inhaled.

Multiple organophosphate esters were tested, but TDCIPP was the only one that showed a strong positive association with commute time.

Components of Firemaster 550 (triphenyl phosphate, or TPHP, and isopropylated triaryl phosphate isomers) and Firemaster 600 (TPHP and tert-butylated triaryl phosphate isomers)—both widely used commercial flame retardant formulations—were strongly correlated with other OPEs detected within participant wristbands. Moreover, the concentration of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) was significantly correlated with the concentration of several Firemaster 500 components and tris(2-chloroisopropyl) phosphate (TCIPP).

Finally, out of all OPEs measured, TDCIPP was significantly and positively correlated with total commute score, indicating that longer commutes are associated with increased human exposure to TDCIPP. Overall, our findings raise concerns about the potential for chronic TDCIPP exposure within vehicles and other forms of transportation, particularly within densely populated and traffic-congested areas such as Southern California.

—Reddam et al.

While Volz and his team did not collect urine samples to verify that the chemical migrated into the bodies of the participants, they believe that’s what happened.

Going forward, the research team would like to repeat the study with a larger group of people whose ages are more varied. They would also like to study ways to protect commuters from this and other toxic compounds.

Until more specific reduction methods can be identified, the team encourages frequently dusting the inside of vehicles, and following US Environmental Protection Agency guidelines for reducing exposure to contaminants.

Until safer alternatives are identified, more research is needed to fully understand the effects of TDCIPP on commuters.

If we picked up this relationship in five days, what does that mean for chronic, long-term exposure, for people who commute most weeks out of the year, year over year for decades?

—David Volz


  • Aalekhya Reddam, George Tait, Nicholas Herkert, Stephanie C. Hammel, Heather M. Stapleton, David C. Volz (2020) “Longer commutes are associated with increased human exposure to tris(1,3-dichloro-2-propyl) phosphate,” Environment International, doi: 10.1016/j.envint.2020.105499



Better set your A/C to change the air more frequently or drive with the windows open more.

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