Thirdhand Smoke Forms Indoor Carcinogens,

Lawrence Berkeley lab scientists report

By Suzanne Bohan
Contra Costa Times

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. Contra Costa Times, 02/08/2010

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 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," said Gundel, who works in the lab's Indoor Environment Department.

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 thought that it posed a health risk.

That study focused on earlier research analyzing the potential harms to children and infants from ingesting or breathing any of the 250 toxic substances found in tobacco smoke, such as lead. Research also found that many children had detectable blood levels of cotinine, a chemical formed by exposure to nicotine.

However, the Berkeley lab researchers also 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 health hazards of tobacco smoking and secondhand smoke are well known, with research associating inhalation of the smoke with elevated risk of cancer and heart disease.

This thirdhand smoke, however, enters the body via a different route, either through skin exposure, dust inhalation and ingestion, and it poses an "unappreciated health risk," the Berkeley researchers wrote. Children and infants are of particular concern, since they have far more exposure to contaminated surfaces, and with their smaller sizes would absorb proportionately more TSNAs than adults.

The human health effects of thirdhand smoke have not been well-studied, Gundel said, and further work is needed to understand the extent of the threat they pose.

David Sutton, a spokesman with the Altria Group, parent company of Philip Morris USA, noted that no human exposure measurements were done as part of the Berkeley study.

"The study authors recommended more research on the topic," he said. Sutton said that Altria discourages adults from smoking when children are present.

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

As a precaution, Gundel advised replacing furniture and drapes that have been heavily exposed to nicotine, and she supports 100 percent smoke-free public places. In addition, smoking inside vehicles also leaves behind nicotine on surfaces, she noted.

The Berkeley researchers plan to continue their studies on thirdhand smoke, assessing how long TSNAs can remain on surfaces, and seeking reliable biomarkers for studying the uptake of them into the body.

The study was sponsored by the University of California's Tobacco-Related Disease Research Program.