Study: third-hand smoke may increase lung cancer risks
2018-03-09 17:25:00

The knowledge that active smoking and second-hand smoke can do harms to human, especially to lung, has been well-established, but that’s not all about the story. Have you ever heard of third-hand smoke?

A recently published article on “Clinical Science” shows that short-term early exposure to third-hand smoke increases lung cancer incidence in mice. Third-hand smoke refers to the toxic residues that linger on indoor surfaces and in dust long after a cigarette is extinguished. According to field studies in the U.S. and China, exposure to third-hand smoke occurs via inhalation, ingestion, or uptake through the skin, and moreover, traditional cleaning methods can’t remove such pollution effectively.

Photo shows Mao Jianhua (R2), Hang Bo (L1) and Wang Pin (R1) with other Berkeley Lab researchers. (Photo source: Lawrence Berkeley National Laboratory)

Five scientists from Jiangsu, namely Mao Jianhua, Hang Bo, Wang Pin, Bi Lei, Xia Yankai, are among the research team, mainly from Lawrence Berkeley National Laboratory (Berkeley Lab), UC San Francisco and Nanjing Medical University. Scientists in Berkeley Lab, Mao Jianhua, together with Hang Bo and Antoine Snijders and other lab researchers, found in 2017 that brief exposure of third-hand smoke was associated with low body weight and immune changes in young mice.

In the follow-up study, which involves many of the same researchers, 24 experimental A/J mice from the age of 4 to 7 weeks were housed with fabric impregnated with third-hand smoke. Comparing with the 19 control mice, the experimental ones were found to have an increased incidence of lung cancer, larger tumors, and greater number of tumors forty weeks after the last exposure. The dose the mice received, 77 micrograms per kilogram of body weight per day, was equal to a published estimate data of ingestion exposure of a human toddler living in a house with smokers. Further in vitro experiment using cultured human lung cancer cells indicates that third-hand smoke exposure induced DNA double-strand breaks, increased cell proliferation and colony formation, and activated p53 (tumor suppressor) signaling.

The study is sure to raise concerns of moms, since little kids who often crawl and put objects in their mouths are the most vulnerable targets for third-hand smoke. “I hope our research can raise people’s awareness of indoor-smoking risk,” said Hang Bo, who is currently working on biomarkers to detect and prevent third-hand smoke pollution in the future.

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