Written by Joyce Smith, BS. This study calculated the daily dose of benzene and formaldehyde being inhaled by drivers with commutes of at least 20 minutes per day.
Although we are aware of the indoor risk associated with Prop65 tested chemicals 1, we do not know the risk imposed by these chemicals within a commuting vehicle. Previous studies have found that concentrations of toxic chemicals in vehicle interiors were 2- to 3-fold higher compared to indoor concentrations 2, suggesting that vehicle interiors may pose a health risk to commuters. Phallates such as DBP (dibutyl phthalate), and DEHP (di (2-ethylhexyl) phthalate) are plastic-derived endocrine disruptors that along with the flame retardant, TDCIPP (tris(1,3-dichloro-2-propyl)phosphate), are chemically bound to foam and other materials in vehicle interiors 3 and are eventually adsorbed onto the surfaces of dust particles which are then inhaled 1. Benzene and formaldehyde are found in the air inside vehicles, suggesting both are very volatile organic chemicals (VOCs) that exist almost exclusively in a gaseous state. Benzene is derived from exhaust-related emissions 4 while both formaldehyde and benzene gas off, releasing gas as a byproduct of the interior vehicle materials into the air we breathe 5. According to the US Census Bureau, American adults spend an average of 6% of their time commuting in enclosed vehicles 6 of which 53 minutes per day are spent commuting to work 7, thus increasing their exposure to higher concentrations of VOCs such as carbon monoxide, benzene, formaldehyde, ozone, and TDCIPP.
A current study by Reddam et al 2021 8 calculated the potential health risk of five Prop 65-listed chemicals: benzene, formaldehyde, phthalates DEHP and DBP, and TDCIPP. These chemicals were detected by the research team in vehicle interiors and were inhaled by drivers who commuted at least 20 minutes per day. Study participants included 90 students, each of whom had commute times that varied from less than 15 minutes to more than two hours round trip. They all wore silicone wristbands continuously for five days. (The molecular structure of silicone is ideal for capturing airborne contaminants.)
In both 24-hour and daily exposure scenarios, interior vehicle air contained up to five times more benzene and formaldehyde when compared to the amount of TDCIPP, DEHP and DBP found in the vehicle interior dust. TDCIPP was the only organophosphate that was positively association with commute time. It also has the lowest safe harbor level out of all five tested Prop 65-listed chemicals. TDCIPP has the potential to cause cancer as well as developmental and reproductive toxicity. Studies have shown that 24 months of daily dietary exposure to TDCIPP increased, in a dose-dependent manner, liver, kidney and testicular tumors 9.
Benzene and formaldehyde were the only two chemicals with an estimated percent reference dose (%RfD) > 100 across any of the commute times. Even a short 20 minute commute produces benzene and formaldehyde concentrations that are predicted to exceed safe levels. Researchers found that in California the cancer risks associated with exposure to benzene and formaldehyde are substantially higher than the risk associated with reproductive and developmental effects caused by benzene exposure. The percentage of California commuters with a 10% probability of exceeding cancer risk associated with benzene or formaldehyde exposure was 78% and 63%, respectively, whereas the percent of commuters with a 10% probability of exceeding the risk of reproductive and developmental toxicity associated with benzene exposure was 11%. Concentrations of in-vehicle formaldehyde were about twice as high in California communities than in the states of New Jersey and Texas 10. These results reinforce an urgent need for additional research to study the association between benzene and formaldehyde exposure and the potentially higher occurrence of cancer in commuters such as truck drivers who commute long distances or commuters who travel in traffic-congested areas.
Source: Reddam, Aalekhya, and David C. Volz. “Inhalation of two Prop 65-listed chemicals within vehicles may be associated with increased cancer risk.” Environment International 149 (2021): 106402.
© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
Click here to read the full text study.
Posted March 9, 2021.
Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.
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- U.S. Census Bureau. American Community Survey. 2017; https://www.census.gov/acs/www/data/data-tables-and-tools/data-profiles/2017. Accessed March 4, 2021.
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- Reddam A, Volz DC. Inhalation of two Prop 65-listed chemicals within vehicles may be associated with increased cancer risk. Environ Int. 2021;149:106402.
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