While remarkable progress has been made in several countries to prevent people inhaling toxic secondhand fumes from cigarettes, evidence shows the harmful chemicals linger in a room after the smokers have left, and many places have banned smoking altogether.
Now, significant chemical residues of this thirdhand smoke have been detected in a German movie theatre that has had a rigorous smoking ban for the past 15 years, exposing people to the equivalent of one to 10 cigarettes of secondhand smoke.
“Thirdhand smoke research has been ongoing for about a decade,” says senior author Drew Gentner, from Yale University in the US, but typically focussed on rooms where people have smoked.
“In the past, it has been described as the residual contamination from cigarette smoke stuck to walls, dust, and other surfaces in places where smoking has previously occurred, leaving an odour and a reactive surface that can produce other hazardous compounds.”
He notes that people spend around 90% of their time indoors, highlighting the importance of understanding the chemical composition and air quality of indoor environments.
His team’s research, published in the journal Science Advances, shows that off-gassing of chemicals from cigarette smoke is a prominent source of indoor air pollution; “one that is likely occurring regularly around us given that worldwide smoking rates are at 22%”.
Measuring the air conveniently exiting the theatre from an exhaust air duct in real-time, they found “sharp spikes” in 35 tobacco-related chemicals such as benzene, formaldehyde and acrolein when people entered the theatre over four days.
These spikes were considerably larger during R- than G-rated movies, even with smaller audiences, presumably because more smokers attended. And even though the chemicals peaked when audiences arrived then decreased, some still lingered.
“In many cases, they left a persistent contamination observable the following days in the unoccupied theatre,” says Gentner.
That’s because the chemicals don’t remain entirely in the air, but also adhere to various surfaces and furnishings from which they re-enter the air over time, he explains – which is a concern for air quality and public health.
“It is clear that the myriad of chemicals from secondhand smoke do not remain isolated to where they are smoked, and substantial amounts of thirdhand smoke can be transported to new environments by smokers or those exposed to tobacco smoke.
“These findings advance our understanding of the fate of chemicals from cigarette smoke and catalyse an important discussion about human exposure to thirdhand smoke off-gassing from people.”
Gentner hastens to say that the study shouldn’t deter people from going to the movies which are spacious, well-ventilated environments that would lower the chemical concentrations compared to smaller, less well-ventilated environments such as bars, public transport, offices and homes.
“The phenomenon is occurring around us all the time.”