Scientists have found for the first time that thirdhand smoke - the noxious residue that clings to virtually all surfaces long after the secondhand smoke from a cigarette has cleared out - causes significant genetic damage in human cells.
The study led by researchers from Lawrence Berkeley National Laboratory in US also found that chronic thirdhand smoke exposure is worse than acute exposure.
They found the chemical compounds in samples exposed to chronic thirdhand smoke existed in higher concentrations and caused more DNA damage than samples exposed to acute thirdhand smoke, suggesting that the residue becomes more harmful over time.
"This is the very first study to find that thirdhand smoke is mutagenic," said Lara Gundel, a Berkeley Lab scientist and co-author of the study.
"Tobacco-specific nitrosamines, some of the chemical compounds in thirdhand smoke, are among the most potent carcinogens there are. They stay on surfaces, and when those surfaces are clothing or carpets, the danger to children is especially serious," said Gundel.
The researchers used two common in vitro assays, the Comet assay and the long amplicon-qPCR assay, to test for genotoxicity and found that thirdhand smoke can cause both DNA strand breaks and oxidative DNA damage, which can lead to gene mutation.
Genotoxicity is associated with the development of diseases and is a critical mechanism responsible for many types of cancer caused by smoking and secondhand smoke exposure.
To generate the samples, the researchers put paper strips in smoking chambers. The acute samples, generated at Berkeley Lab, were exposed to five cigarettes smoked in about 20 minutes, and the chronic samples were exposed to cigarette smoke for 258 hours over 196 days. During that time, the chamber was also ventilated for about 35 hours.
The researchers found that the concentrations of more than half of the compounds studied were higher in the chronic samples than in the acute. They also found higher levels of DNA damage caused by the chronic samples.
"The cumulative effect of thirdhand smoke is quite significant. The findings suggest the materials could be getting more toxic with time," Gundel said.
The study was published in the journal Mutagenesis.