New York, Nov 17 (IANS): While simply sitting in cars with people who smoke, non-smokers breathe in a host of potentially dangerous compounds that are associated with cancer, heart disease and lung disease, says a new research.

In a small yet significant study, 14 non-smokers sat for one hour in the passenger seat of a parked sport utility vehicle behind a smoker in the driver's seat.

The non-smokers showed elevated levels of butadiene, acrylonitrile, benzene, methylating agents and ethylene oxide (carcinogens and other toxins) in their urine.

This group of toxic chemicals is "thought to be the most important among the thousands in tobacco smoke that cause smoking-related disease", said senior investigator Neal Benowitz, professor at the University of California, San Francisco (UCSF) in the US.

"This is the first study to measure exposure to these particular chemicals in people exposed to second-hand smoke," Benowitz added.

"This tells us that people, especially children and adults with pre-existing health conditions such as asthma or a history of heart disease, should be protected from second-hand smoke exposure in cars," lead author Gideon St. Helen from UCSF said.

The study appeared in the journal Cancer, Epidemiology, Biomarkers & Prevention.