If ever there was a time to reconsider how you get to work every day, it’s now.

A study found that those who commute with their car in California are likely exposed to dangerous chemicals that increase the risk for cancer and birth defects — way over the threshold for exposure established by state government legislation.

Bad for you, bad for the planet

US adults spend an average of 6% of their time within an enclosed vehicle, a large amount of which is spent commuting. In the US, a person spends an average of 52.8 min per day commuting to work. This isn’t just bad for the planet (by producing more pollution and greenhouse gas emissions), it’s also bad for you: longer commute times are strongly associated with negative health outcomes such as shorter sleep, obesity, and poor physical/mental health

People who spend a longer amount of time in vehicles are also exposed to higher concentrations of particulate matter, carbon monoxide, VOCs, ozone, and flame retardants. This effect is so pronounced that people experiencing long commutes over years and decades likely represent a sub-population vulnerable to excess exposure to vehicle-borne chemicals. Now, a new study adds even more weight to those concerns.

A group of researchers at the University of California Riverside wanted to better understand the potential risk associated with exposure to vehicle-specific chemicals as a function of commute time. They focused on five Prop 65-listed chemicals detected within vehicle interiors: benzene, formaldehyde, di phthalate, dibutyl phthalate, and trisphosphate.

California’s Proposition 65 (Prop 65) requires businesses to inform people about exposure to chemicals known to cause cancer, birth defects, or other reproductive harm. Prop 65-listed chemicals represent a wide range of naturally occurring and synthetic chemicals that include additives or ingredients in pesticide formulations, common household products, food, drugs, dyes, or solvents. In some cases, Prop 65-listed chemicals that are used in indoor products have the potential to migrate, abrade, or off-gas from end-use products and accumulate in indoor environments. The presence of Prop 65-listed chemicals in indoor air and dust has been well documented, suggesting that people may be exposed to these chemicals through inhalation of air and ingestion of dust.

While several studies have evaluated the potential risk to Prop 65-listed chemicals detected within indoor environments, we don’t know all that much about the risk of these chemicals in regards to exposure within personal vehicles. Due to the small size of a car, chemicals emitted from its interior have the potential to be concentrated.

Chemicals such as phthalates, volatile organic compounds (VOCs), flame retardants, and hydrocarbons — several of which are Prop 65-listed — are commonly detected within interior vehicle dust. Prior studies have demonstrated that the concentration of certain chemicals within vehicle interiors were 2- to 3-fold higher compared to indoor concentrations. In their new study, the researchers at UC Riverside found that the average commuter in California is breathing unsustainably high levels of benzene and formaldehyde, both of which are used in automobile manufacturing. These are highly carcinogenic substances, with benzene carrying the additional risk of reproductive and developmental toxicity. The levels at which these substances are inhaled by many commuters is considered unsafe.

The study calculated the daily dose of benzene and formaldehyde being inhaled by drivers with commutes of at least 20 minutes per day. This showed that up to 90% of the population in Los Angeles, San Diego, Orange, Santa Clara, and Alameda counties have at least a 10% chance of exceeding cancer risk from inhaling the chemicals, based on having 30-minute average commute times.

The presence of these compounds within vehicles can be attributed to extensive use in different vehicle parts. Formaldehyde is used in carpets, leather, and paints within vehicles, resulting in off-gassing and high concentrations within indoor air. Meanwhile, benzene is linked to fuel- and exhaust-related emissions that accumulate in the cabin of operating vehicles. It’s also used to produce styrene, nylon, and phenol

“These chemicals are very volatile, moving easily from plastics and textiles to the air that you breathe,” David Volz, UCR professor of environmental toxicology and co-author of the study, said in a statement. Volz suggested keeping the windows open during car rides if possible so to reduce the concentration of these chemicals thanks to the airflow.

The study was published in the journal Environmental International.