First came the warnings of the doctors about cigarettes. Then came discoveries about the danger of passive smoking. Now more and more scientists are raising the fear of third smoke – residual chemicals left behind by tobacco smoke on the inner surfaces.
Increasing research has shown that such potentially hazardous residues can be absorbed and inhaled over months and even over the skin after the smoke has dissolved.
A study this year showed that the risk of lung cancer in mice was increased by third-party smoking. 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 the ban on smoking, heavy smoke remained on the walls and carpets.
The latest study, published Wednesday in the Science Advances journal, shows how tobacco smoke from the outside air can seep into a non-smoking classroom and coat its surfaces, and how these dangerous chemicals often get back into the air and over central Air conditioners circulate in buildings.
"It shows that just because you're in a non-smoking environment, which means you're not exposed to tobacco," said Peter DeCarlo, a chemist at Drexel University in Philadelphia, who is considered the lead author of the study , "Into that Uber-car you jump into, into the hotel room you sleep in, even in a classroom that has not smoked for decades: these are places where you're exposed to much more than you expected."
The Latest Findings were in some ways an accident.
DeCarlo, who studies outside air, had teamed up with an interior air expert at Drexel, Michael Waring, to examine how the two interacted. A PhD student working with them examined chemicals in a classroom about 20 meters from DeCarlo's office and came across a mysterious chemical signature they could not explain.
First, they suspected residues of coffee, which is ubiquitous in universities. But after a series of tests, they were surprised to find signs of nicotine and tobacco smoke. To replicate the chemical signature, they performed a series of experiments, blowing cigarette smoke into a Pyrex glass jar, extinguishing the smoke, and leaving the glass to rest for a week. The residues were exactly the same, they found.
So they turned their investigative efforts toward the classroom and ran a series of tests pumping outside air into and out of the room.
They found that tobacco smoke can enter interior spaces and adhere to surfaces. Especially in the summer, when rooms are blown up by air conditioning systems, the chemicals are not only released back into the air, but can also easily spread through the ventilation system of buildings.
"This is giving a new twist to what we are now discovering about the third smoke," said Hugo Destaillats, a chemist at the Lawrence Berkeley National Laboratory in California, who carried out similar research but was not involved in the Drexel study. "It shows how much we still need to know about the mechanisms of this type of exposure."
Public health experts have gathered mountains of data on how life-threatening smoking is. And they have extensive data on the consequences of passive smoking. But the idea of third-hand smoking only began to emerge in the last ten years.
Previous research on its health implications suggests that it may be harmful, but data remain scarce and are mostly limited to studies with mice. However, researchers are confident that tobacco smoke chemicals often dwell on clothing, surfaces and even skin.
Public health advocates fear that those most at risk will also come into contact with the harmful effects of passive smoking. For example, a baby crawling on the floor has much more contact with carpets that often contain cigarette fragments. And due to increasing socio-economic disparities in smoking, low-income families are more likely to live in homes and neighborhoods where decades of smoking have led to third-hand smoking accumulation.
"I do not think we have any idea how big the problem is," said Matthew L. Myers, president of the campaign for tobacco-free children. "So far, science has not been able to say how widespread and serious the risk is, but what we've already seen only adds to the reasons that should be banned in public places."
Growing research on such residues has led lawmakers to consider legislation prohibiting smoking in rooms such as daycare, even outside the hours when there are no children present.
The American Academy of Pediatricians has issued recommendations to limit the exposure of children to secondhand smoke. And in recent years, California has established a new consortium of scientists funded by state cigarette taxes to study the mechanics and potential dangers of tobacco smoke.
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