Smoking has been banned in most public indoor spaces within the US for years now—and for the better—but that doesn’t necessarily mean nonsmokers are free from toxic cigarette chemicals. New research published Wednesday in Science Advances suggests that not only can the chemical residue left behind by cigarette smoking find its way into “smoke-free” buildings, but it can then attach itself to aerosol particles suspended in the air that are easily inhaled by our lungs.
In 2014, as part of a completely unrelated project funded by the US National Science Foundation, researchers at Drexel University in Pennsylvania analyzed the air of an unoccupied classroom that had long since banned smoking. Over a period of weeks, they discovered that just under a third of the room’s indoor aerosol mass contained toxic chemicals you normally wouldn’t expect to find there, such as nicotine, myosine, and pyridine.
“Once we identified the unique indoor chemical signature and realized it was linked to residual tobacco smoke, we really started to get interested in the whole process of thirdhand smoke uptake,” lead author Peter DeCarlo, an associate professor at Drexel’s Department of Chemistry, told Gizmodo via email.
It’s well known that the gaseous residue of cigarette smoke eventually becomes tiny solidified particles that contaminate indoor surfaces and our clothing—a form of exposure commonly referred to as thirdhand smoke.
But DeCarlo and his team’s initial findings from the classroom indicated that this residue, which had likely come from a nearby balcony where smokers hung out, as well as from smokers themselves, can turn back into something that lingers in the air. So they decided to test their theory in the lab.
The team blew smoke into a glass container, allowing enough time for chemicals like nicotine to attach themselves to the walls. Then they pumped out that air and pumped in clean air to clear out any secondhand smoke. A day later, they again pumped fresh air into the container, measuring its contents before and after it left the container. The air had 13 percent more of these same chemicals once it passed through, they found.
That suggests, DeCarlo believes, that the classroom discovery was no fluke. And it seems that thirdhand smoke residue can shapeshift into early-inhaled particles under certain common conditions.
As DeCarlo explains, the chemicals found in thirdhand smoke often include nitrogen. Nitrogen acts as a weak base, and can easily take on protons, becoming positively charged. When this happens, the molecules from these nitrogen-containing chemicals can’t leave their solid state in the residue. But when a stronger base, like, say, the ammonia found in everyday cleaning products and even our own breath, is around, it can strip the positive charge from the nitrogen, allowing these molecules to evaporate into the room’s air again.
“Once in the room air, the molecules can be absorbed into particles in the room, and again react to become positively charged if there is associated water with the particle,” DeCarlo said. Once the molecules are absorbed into aerosol particles loaded with water, they again become positively charged, trapping them inside. That’s especially likely to happen during a hot summer, when warm humid air from outside mixes with air that’s been cooled by a typical heating, ventilation, and air conditioning (HVAC) system. The HVAC system can then easily circulate the thirdhand smoke to other rooms.
DeCarlo’s lab doesn’t focus on the health side of things, but he notes there’s been some research, mostly in animals, that suggests that thirdhand smoke has the potential to cause many of the same risks as smoking and secondhand smoke, such as worsening asthma and cancer.
Given the broader implications of their finding, the authors hope their study can serve as a wake-up call for other researchers to begin looking closer at thirdhand smoke. Even as smoking has become less popular, they noted, there are some shared spaces left where indoor smoking is allowed, including rental cars and certain hotels. DeCarlo and his team plan to keep studying thirdhand smoke themselves, as well as how newer trends, namely e-cigarettes, can contribute to its presence.
“We are excited to continue this research, and are currently looking at e-cigarettes as another source of nicotine indoors,” he said. “Since e-cigarettes are more commonly used indoors, this can be a potentially large indoor source.”