Study: 'Thirdhand smoke' poses danger to young children, pregnant women

(April 20, 2011)—

April 19, 2011

An often odorless residue left behind long after smokers extinguish their cigarette is perhaps more harmful to young children and pregnant women than even secondhand smoke, local researchers say.

A study to be published this month in the American Journal of Physiology found that the heavier molecules of "thirdhand smoke," a term coined in the last two years or so, pose a serious threat to fragile developing lungs.

Thirdhand smoke is a "stealth toxin" that lingers on all kinds of surfaces in cars, hotels, homes, casinos and other places where children and others may be exposed to these toxins, said Dr. Virender Rehan, a researcher at Los Angeles Biomedical Research Institute near Torrance who conducted the study.

"It essentially means that even when you are not directly facing the smoke, there is still a risk," he said.

In the study, rats were exposed to two types of toxins present in thirdhand smoke, which is essentially aged and condensed secondhand smoke. The exposed rats had a far higher prevalence of asthma, and the effects were lifelong, researchers reported.

"This doesn't go away or dissipate," Rehan said.

The recent local study, released Tuesday, builds on prior studies over the past two years at the University of California, Berkeley, and MassGeneral Hospital for Children in Boston. Researchers in the Boston study found that nicotine in the residue from thirdhand smoke contains heavy metals, carcinogens and radioactive materials that children can easily ingest through their skin.

The residue can be found in clothing, upholstery, carpet and other materials, researchers have found. If the residue is recent, it could have a stale cigarette smell; but even when the smell has dissipated, the toxins are still present, researchers found.

In the Berkeley study, published in September, researchers at the Lawrence Berkeley National Laboratory's Indoor Environment Department found that nicotine from thirdhand smoke reacts with nitrous acid, an indoor pollutant commonly found in homes with gas-burning appliances, to form carcinogens called tobacco-specific nitrosamines.

"These are among the most broadly acting potent carcinogens present in unburned tobacco and tobacco smoke," Hugo Destaillats, a chemist at the Berkeley lab, said in the study.

While previous studies had documented the danger of nicotine in thirdhand smoke, Rehan's study looked at the effect of two other toxins in thirdhand smoke.

The researchers found prenatal exposure to these components plays a much greater role in altered lung function than childhood exposures.

That means pregnant women should be especially cautious when visiting the home of a smoker, or riding in a car with a smoker - even if the smoker does not light up in the women's presence, Rehan said.

"This is not an issue many people are aware of," he said. "It is a new issue being actively studied by a number researchers. Until now, we've only speculated that these toxins might be harmful."

The American Lung Association is sponsoring California legislation that would prohibit day-care workers from smoking in homes where they care for children - regardless of whether the children are present, said Paul Knepprath, vice president of advocacy and health initiatives for the association in California.

"There is definitely a concern over these lingering effects of tobacco smoke," he said. "We know that it can have significant consequences for people, especially children."