Inhaling secondhand smoke or passive smoking has been well-documented as a health hazard for non-smokers. According to a new study published last week in the journal Science Advances, researchers at Drexel University in Philadelphia found that thirdhand smoke, or residual chemicals left on indoor surfaces by tobacco smoke, could be harmful. Research suggests that tobacco residue can be absorbed through the skin, ingested and inhaled months and even years after the smoke has dissipated.
One study this year showed thirdhand smoke increased risk of lung cancer in mice. Another study last year showed liver damage and diabetes in mice. A third study this year focused on casinos and showed that six months after smoking was banned, heavy smoke residue remained on the walls and carpet.
For the latest study, researchers measured the air composition in a non-smoking, unoccupied classroom over the course of a month using an aerosol mass spectrometer. They initially wanted to see what happens to outdoor air particles when they come inside. But they kept noticing a chemical signature that was only indoors and not outdoors. They discovered it consisted of chemicals from thirdhand smoke — and made up 29% of the air mass in the room.
Peter DeCarlo, associate professor of environmental engineering and chemistry at Drexel, was the lead author on the study. DeCarlo and his team looked into the mechanism that would allow compounds from tobacco smoke to end up in a classroom where smoking was not allowed in at least 20 to 25 years. They discovered that thirdhand smoke compounds were effectively hitching a ride on tiny particles in the air. The classroom they studied was 20m down the hall from a balcony where people would smoke. The room was also located near an office space where several smokers worked; that space shares the same central air conditioning system as the classroom in question.
Though they could not identify the exact source, the researchers suspect the thirdhand smoke from these smokers made its way into the classroom and stuck to surfaces there. The compounds were then exposed to another chemical — possibly ammonia from people’s breath or skin, or even cleaning products — and became gaseous again.
The Drexel researchers suggest that after becoming gaseous again, smoke residue compounds can attach themselves to tiny air particles that come inside through a building’s central air conditioning system, which in summer months pulls in outside air and chills it. That cooling process condenses water vapour in the air, which primes those outside particles to react with thirdhand smoke gasses. Once the chemicals attach themselves to the air particles, the building’s air distribution carries those chemicals throughout the building, including to the classroom researchers studied.
All this means people could be unwittingly exposed to thirdhand smoke in higher volumes than previously thought — even in locations where smoking is banned. Action is needed, considering that thirdhand smoke can create long-term, low-level exposure to chemicals that may constitute significant risks to human health, especially to children and other vulnerable people.
