San Francisco, Feb 15 (IANS): A new study has revealed that California's commuters are likely inhaling chemicals at levels that increase the risk for cancer and birth defects. Even 20 minutes or longer in the car also raises risk of birth defects, said the study.

Benzene and formaldehyde -- both used in automobile manufacturing -- are known to cause cancer at or above certain levels of exposure.

New University of California-Riverside research shows that the average commuter in California is exceeding the threshold for exposure, breathing in unsustainably high levels of both chemicals.

Both benzene and formaldehyde are carcinogens, and benzene carries the additional risk of reproductive and developmental toxicity.

"These chemicals are very volatile, moving easily from plastics and textiles to the air that you breathe," said David Volz, a professor of environmental toxicology.

The study, published in the journal Environment International, calculated the daily dose of benzene and formaldehyde being inhaled by drivers with commutes of at least 20 minutes per day.

It found that up to 90 per cent of the population in Los Angeles, San Diego, Orange, Santa Clara, and Alameda counties have at least a 10 per cent chance of exceeding cancer risk from inhaling the chemicals, based on having 30-minute average commute times.

"Of course, there is a range of exposure that depends on how long you're in the car, and how much of the compounds your car is emitting," said Aalekhya Reddam, a graduate student in the Volz laboratory, and lead author.

Previously, Volz and Reddam studied commuter exposure to a flame retardant called TDCIPP or chlorinated tris and found that longer commute times increased exposure to that carcinogen as well.

They set out on this study wanting to understand the risk of that compound relative to other chemicals introduced during car manufacturing.

Reddam advises commuters to keep the windows open during their rides if possible.

"At least with some air flow, you'd be diluting the concentration of these chemicals inside your car," she said.

Benzene is used to produce synthetic fibres, and formaldehyde is a binder in plastics.

"There should be alternatives to these chemicals to achieve the same goals during vehicle manufacturing," Volz said. "If so, these should be used."