Tobacco smoke contamination lingering on furniture, clothes and other surfaces, dubbed thirdhand smoke, may react with indoor air chemicals to form potential cancer-causing substances, a study found.
After exposing a piece of paper to smoke, researchers found the sheet had levels of newly formed carcinogens that were 10 times higher after three hours in the presence of an indoor air chemical called nitrous acid commonly emitted by household appliances or cigarette smoke. That means people may face a risk from indoor tobacco smoke in a way that's never been recognized before, said one of the study's authors, Lara Gundel.
Previous research has shown that secondhand smoke, which is inhaled by nonsmokers exposed to fumes from cigarettes, raises the risk of cancer and heart disease. More research is needed to identify the potential health hazards of thirdhand smoke, Gundel said. Overall, tobacco use causes 20 percent of all cancer deaths, according to the study published in today's Proceedings of the National Academy of Sciences.
"We have considered that nicotine on surfaces has been pretty benign up to this point. It turns out we shouldn't say that now," said Gundel, a staff scientist at Lawrence Berkeley National Laboratory in Berkeley, California, in a Feb. 5 telephone interview. "People can be exposed to toxins in tobacco smoke in a way that's never been recognized before."
A spokesman for Philip Morris USA, a unit of Altria Group Inc., did not return a telephone call for comment. Spokesmen for Reynolds American Inc. and Lorillard Inc. did not respond to telephone calls for comment.
A previous study, published in the journal Pediatrics in January 2009, found residual tobacco smoke is deposited on furniture, carpeting and clothing and coined the phrase "thirdhand smoke."
Today's study found that when the residue from tobacco smoke settled on indoor surfaces, it mixed with indoor air pollutants to form tobacco-specific nitrosamines, or TSNAs, which are potent cancer-causing substances found in unburned tobacco and tobacco smoke.
The researchers checked for nitrosamine levels by exposing paper to smoke and then to nitrous acid, which is produced by gas ovens and burners that aren't properly vented and by cars. They also tested the surfaces on the inside of a truck of a heavy smoker.
In both cases they found the reaction between the nicotine in thirdhand smoke and the nitrous acid produced two known and potent nitrosamines. They also found a tobacco-specific nitrosamine that is absent in freshly emitted tobacco smoke.
People, particularly infants and toddlers, are most likely exposed to these carcinogens by either inhaling dust or by skin contact, the authors said. Using fans and opening a window doesn't help eliminate the hazards because most of the nicotine and other substances from burning cigarettes aren't found in the air, but are absorbed by surfaces, Gundel said.
"Buildings, rooms, public places should be 100 percent smoke free," she said. "Replace nicotine-laden furniture, carpets and curtains. Nicotine absorbs into these materials. The stuff that's imbedded can continue to come to the surface."
The researchers are trying to determine how long these nitrosamines may last as a result of the interaction of thirdhand smoke and the indoor air pollutant, nitrous acid. They are also looking to develop ways to track exposure to nitrosamines.
"We know that these residual levels of nicotine may build up over time after several smoking cycles, and we know that through the process of aging, thirdhand smoke can become more toxic over time," said study co-author Hugo Destaillats, a chemist with the Indoor Environment Department of the Berkeley national lab's Environmental Energy Technologies Division, in a statement. "Our work highlights the importance of thirdhand smoke reactions at indoor interfaces, particularly the production of nitrosamines with potential health impacts."
The study was sponsored by the University of California's Tobacco-Related Disease Research Program.