Third-hand Smoke can Cause DNA Damage in Human Cells, Study Finds

Third-hand cigarette smoke-residue that clings to surfaces even after the smoke has cleared out can damage DNA, according to a new study.

The study was conducted by researchers from Lawrence Berkeley National Laboratory and colleagues who found that chronic exposure to this toxic residue could severely affect cells.

Smoking causes many types of cancers including lung, bladder, kidneys, mouth and ovaries. Previous researches have revealed that second-hand smoke could just be as dangerous to human health as smoking. In the present study, researchers found that being exposed to third-hand smoke could also damage genetic material in cells.

"This is the very first study to find that third-hand smoke is mutagenic. Tobacco-specific nitrosamines, some of the chemical compounds in third-hand 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 Lara Gundel, a Berkeley Lab scientist and co-author of the study.

For the study, researchers used the Comet assay and the long amplicon-qPCR assay- two common in vitro assays to test the genotoxicity of third-hand smoke. They found that cigarette residue can cause oxidative DNA damage and also break the DNA strands, both of which could lead to gene mutation.  

"Until this study, the toxicity of third-hand smoke has not been well understood. Third-hand smoke has a smaller quantity of chemicals than secondhand smoke, so it's good to have experimental evidence to confirm its genotoxicity," Bo Hang, a biochemist in the Life Sciences Division of Berkeley Lab and lead author of the study.

For the study, researchers sampled paper strips that the experiment group had put in smoking chambers. Here the paper strips were exposed to five cigarettes smoked in 20 minutes. For chronic samples, researchers used paper strips that were exposed to cigarette smoke for 258 hours over 196 days. The chronic samples were generated at University of California, San Francisco, San Francisco.

Scientists found that the concentration of toxic substances were higher in samples of chronic smoke exposure than acute exposure. "The cumulative effect of third-hand smoke is quite significant," Gundel said in a news release. "The findings suggest the materials could be getting more toxic with time."

Third-hand smoke tends to linger on surfaces for long periods of time. Traditional cleaning methods such as dusting or vacuuming aren't effective in removing these residues. Previous research has shown that people who stay at hotels that have partial ban on smoking have high risk of third-hand smoke exposure.

The study "Third-hand smoke causes DNA damage in human cells," is published in the journal Mutagenesis.