Nanoparticles Conspire with Free Radicals: Dose of Carcinogens Could Be Comparable to Smoking

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PHILADELPHIA -- The daily exposure to free radicals from car exhaust, smokestacks and even your neighbors' barbecue could be as harmful as smoking, according to a new study. Many combustion processes, such as those in a car engine, create tiny particles that may act as brewing pots and carriers for free radicals--chemicals believed to cause lung cancer and cardiovascular diseases.

Whether the exposure equates to smoking one cigarette or as many as two packs a day remains difficult to determine, said Barry Dellinger of Louisiana State University in Baton Rouge, who reported the findings August 17 in Philadelphia during a meeting of the American Chemical Society.

His team's experiments, also reported in the July 1 Environmental Science & Technology, suggest that noxious chemicals form on soot nanoparticles in the still-hot combustion residue in, for example, car exhaust pipes and catalytic converters.

The chemicals are hydrocarbon-based free radicals. Similar chemicals usually degrade quickly if they float solo. But in this case, the chemicals attach to the nanoparticles and linger in the air far longer than previously thought. "To our enormous surprise, the free radicals survive hours, days, even indefinitely," Dellinger said in an interview.

To mimic the conditions in car exhaust as it cools, Dellinger's team used silica particles 100 nanometers wide and coated with copper oxide. The team then exposed the particles to a hot gas--experimenting with a range of temperatures--containing hydrocarbons typically produced in flames. All are common ingredients in the exhaust of motor vehicles and factories.

The researchers examined the nano-particles with magnetic fields tuned to identify unpaired electrons, the feature that makes free radicals highly reactive and potentially dangerous to living cells. …