US researchers found that potentially harmful chemicals from tobacco smoke get trapped in clothes, furniture and carpets but can become airborne again and be circulated through office blocks, schools or other nominally smoke-free buildings.
Unlike direct smoking, or passive “secondhand” smoke – from being in a room or vehicle while someone is smoking – the health risks of thirdhand smoke on surfaces and in the air are less well established.
Laboratory tests have shown indirect exposure with tobacco residues, common on skin, clothes or surfaces, can “detrimentally affect growth and immunity in mice”, the authors write.
Experts said they could also be a concern for babies in the homes of a smokers who are lying on furniture or carpets where these particles may have settled.
The problem is caused by nicotine residue sticking to indoor surfaces, this later interacts with nitrous acid formed from the gas nitrous oxide, which is released by car exhausts and gas appliances.
When these chemicals combine, they can form tobacco-specific nitrosamines (TSNAs) which can cause cancer, previous studies have shown
The latest results, published in the journal Science Advances today, warn that not only are these chemicals on surfaces, but they can get back into the air and spread further afield.
This could also occur in electronic cigarettes, which also contain nicotine and are used in indoor public spaces much more frequently than conventional cigarettes, the authors said.
“In an empty classroom, where smoking has not been allowed in some time, we found that 29 percent of the entire indoor aerosol mass [air particles] contained thirdhand smoke chemical species,” said Dr Anita Avery from Drexel University, Philadelphia.
“This was obviously quite startling and raised many questions about how that much thirdhand smoke could be lingering in a non-smoking, ventilated room.”
To investigate their findings further the researchers ran laboratory trials using sealed containers, one of which was filled with cigarette smoke, and then subsequently flushed with air from outdoors.
The following day they pumped in the filtered air to mimic a draft or ventilation system and measured the particle content and found it was 13 percent higher in the air that had passed through the smoking container.
They said the humid circulating air, as is common in communal buildings with air conditioning and heating, allows getting these potentially harmful chemicals to get airborne again instead of being fixed on the surfaces of the room where smoking took place.
“Many public areas have a restriction on smoking, including distance from doorways, non-smoking buildings and even full smoking bans on campus for some universities,” said Dr Michael Waring, associate professor at Drexel’s College of Engineering.
“These smoking limitations often only serve to protect non-smoking populations from exposure to secondhand smoke.
“This study shows that thirdhand smoke, which we are realising can be harmful to health as with secondhand smoke, is much more difficult to avoid.”
Neil Thomas, professor of epidemiology and research methods at the University of Birmingham said that earlier studies on these types of indoor toxic build-ups had suggested a small increase in cancer risk – around one extra case in 1,000 people exposed.
“This study is again providing similar evidence to what has already been published showing that this process takes place, and shows us how widely our exposure to these chemicals might be,” he said.
“Studies have shown children are exposed to thirdhand smoke, more so than adults, and can be found in surprising places, such as in neonatal intensive care incubators.
“We know that these chemicals can cause harm to the body and, although studies are not available, there is no reason not to assume that these chemicals are not damaging those who are exposed.
While he said this study couldn’t tell us more about health risks it did show these potentially harmful chemicals could be spread more widely.
The Independent
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