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Nonsmokers traveling in an automobile with a smoker for sixty minutes had markers of elevated levels of carcinogens and other toxins in their urine, a new study has found. 

The presence of toxins indicate that secondhand smoke in motor vehicles poses a potentially major health risk, the study said. 

The nonsmoking passengers showed increased levels of butadiene, acrylonitrile, benzene, methylating agents and ethylene oxide. "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 L. Benowitz, MD, a UCSF professor of medicine and bioengineering and therapeutic sciences and chief of the division of clinical pharmacology at San Francisco General Hospital and Trauma Center, in the press release.

"Ours is the first study to measure exposure to these particular chemicals in people exposed to secondhand smoke," said Benowitz. "This indicates that when simply sitting in cars with smokers, nonsmokers breathe in a host of potentially dangerous compounds from tobacco smoke that are associated with cancer, heart disease and lung disease."

"This tells us that people, especially children and adults with preexisting health conditions such as asthma or a history of heart disease should be protected from secondhand smoke exposure in cars," added lead author Gideon St. Helen, PhD, a postdoctoral researcher in the UCSF Department of Medicine, in the press release.

The study however cautioned that the findings might not represent smoking situations in most cars because the stationary vehicle used in the research would provide less ventilation than a moving car.

"Nonetheless, the air samples we took were similar in makeup to those seen in previous smoking studies that used closed cars and cars with different ventilation systems in operation," said St. Helen. "And so we believe that the general levels of risk to nonsmokers that we present is realistic."

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