Study finds dangers in ‘thirdhand smoke’

WALNUT CREEK, Calif. — A common indoor air chemical reacts with residues of tobacco smoke clinging to clothing, skin and surfaces to form potent carcinogens, researchers at Lawrence Berkeley Laboratory reported in a study published Monday.

A few years ago, researchers began paying closer attention to the potential health effects of “thirdhand smoke,” which is a thin layer of toxic substances from tobacco smoke that settles on surfaces long after cigarettes have been extinguished.

The Berkeley scientists, however, are the first to find that nitrous acid, an indoor air pollutant created by gas appliances, vehicle engines and tobacco smoke, reacts with nicotine found on surfaces.

“We want to make people aware that there’s a potential hazard from thirdhand smoke that has not been recognized before,” said Lara Gundel, one of the authors of the study, which was published in the Proceedings of the National Academy of Sciences.

“This is a new finding that a common pollutant can react with nicotine to form carcinogens right in our own homes,” Gundel said.

Researchers found that when nitrous acid in the air reacts with nicotine, tobacco-specific nitrosamines, or TSNAs, are created. Unburned tobacco and tobacco smoke already contain TSNAs, which in 1989 the U.S. Surgeon General listed among the carcinogens found in tobacco.

What’s new is how many more of them are created when nicotine reacts with nitrous acid. After exposing surfaces to tobacco smoke, the Berkeley lab researchers found levels of TSNAs increased 10 times after exposure to nitrous acid.

The term “thirdhand smoke” was coined in 2009 in a study in the journal Pediatrics, which found that 65 percent of nonsmokers thought that the residue of tobacco smoke found on furniture and drapes, in rugs and dust, and on skin and clothing, can harm children and infants. Only 43 percent of smokers believed that it posed a health risk.

This thirdhand smoke enters the body via skin exposure, dust inhalation or ingestion.

Smoking outside does not eliminate exposure because nicotine from smoke adheres to clothing and skin, and can be carried back inside. Nor does opening windows or using a fan help much, since nicotine, a sticky molecule, readily clings to surfaces.