As quoted in an article by the French news agency AFP, a co-author of the recent study regarding the risks of "thirdhand smoke" has warned that smokers represent a health threat to their children even if they only smoke outdoors because the residue on their skin and clothing is deposited in the home and leads to the formation of harmful levels of tobacco-specific nitrosamines, some of which are recognized as carcinogens.
Apparently, study investigators told the news agency that smoking outside the home does not mitigate the significant risk posed by thirdhand smoke. According to the article, Dr. Lara Gundel, a co-author of the thirdhand smoke study which was published in the Proceedings of the National Academy of Sciences stated: "Smoking outside is better than smoking indoors but nicotine residues will stick to a smoker's skin and clothing. Those residues follow a smoker back inside and get spread everywhere. The biggest risk is to young children. Dermal uptake of the nicotine through a child's skin is likely to occur when the smoker returns and if nitrous acid is in the air, which it usually is, then TSNAs will be formed."
The study itself was a laboratory study which found that residual nicotine from tobacco smoke that deposits on indoor surfaces can react with ambient nitrous acid to form carcinogenic tobacco-specific nitrosamines (see: Sleiman M, Gundel LA, Pankow JF, Jacob P, Singer BC, Destaillats H. Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. Proceedings of the National Academy of Sciences 2010. Published online ahead of print).
The Rest of the Story
While the study documents that residual nicotine deposited on indoor surfaces is capable of reacting with ambient nitrous acid to form tobacco-specific nitrosamines that are carcinogenic, there is nothing in the study that allows one to conclude that substantial levels of nitrosamines are generated in the households of smokers who refrain from smoking inside the home.
The study cites evidence that nicotine surface concentrations ranging from 5 to 100 micrograms per square meter have been measured in cars and homes of smokers. The study itself documented the measurement of tobacco-specific nitrosamines in the truck of a driver who routinely smoked while commuting. However, the study does not cite evidence of nor measure the presence of tobacco-specific nitrosamines in environments that are documented to be smoke-free but which are frequented by smokers.
As I explained earlier, the key study - conducted by Matt et al. - failed to document the absence of smoking in households that were categorized as smoke-free by measuring ambient nicotine levels. Smokers are probably reluctant to admit that they smoke inside the home, so many of the reportedly smoke-free households were probably not actually smoke-free. Moreover, the study documented levels of nicotine that were not any higher than outdoor (background) levels in at least some households that were smoke-free, indicating that at least in some known cases, smokers who only smoke outdoors do not produce significant nicotine-laden residues in the home.
The study itself comes to a reasonable conclusion: that smokers should refrain from smoking inside the home in order to protect children in the home from exposure. However, the information provided by the co-investigator to the media is quite different. She is now suggesting that the study documents a risk to children even in smoke-free households if they live with a smoker. In other words, she is telling the public that if children live with a smoker, they are at risk from exposure to tobacco-specific nitrosamines even if that smoker smokes only outside of the household.
Moreover, she provides a detailed account of what she apparently knows to occur: "Those residues follow a smoker back inside and get spread everywhere. The biggest risk is to young children. Dermal uptake of the nicotine through a child's skin is likely to occur when the smoker returns and if nitrous acid is in the air, which it usually is, then TSNAs will be formed."
However, the study did not measure exposure to TSNAs among children at all. Nor did it measure the presence of nicotine in the households of smokers who only smoke outside of the home.
In other words, the study itself provides no evidence that "residues follow a smoker back inside and get spread everywhere" or that "dermal uptake of the nicotine" occurs in such situations or that "TSNAs will be formed."
The rest of the story, then, is that this researcher appears to be widely disseminating a conclusion that is not supported by any evidence. She appears to be misrepresenting the results of her own study to imply having demonstrated something that the study did not even measure.
If you are going to go to the extreme and tell the public that smoking outside the home still results in significant nicotine residues inside the home that then result in significant concentrations of TSNAs that are harmful to children, then you sure as heck better have some documentation that this is the case. At the very least, you ought to have evidence of substantial levels of nicotine on surfaces in homes where smoking has been clearly documented not to occur, but in which a smoker resides. Neither of these pieces of evidence have been provided in this case; thus, I view this investigator's apparent statements to the media to be not only unsupported by evidence, but also inappropriate and possibly damaging.
The damage is significant: smokers who believe that their smoking poses a risk to their children even if they smoke outside the home are much less likely to take the effort required to smoke outside the home. If I am a smoker and I find out that my efforts to protect my child from tobacco smoke are futile because I'm exposing them anyway by the nicotine that I'm dragging with me on my skin and clothing, then why bother going through the effort to refrain from smoking inside the home? And if I'm not able to quit (which 97% of smokers are not) and I decide to smoke inside the home, then the public's health is going to be harmed by this unsupported statement.
What's most problematic to me, however, is the fact that a conclusion would be drawn and disseminated to the public without any evidence and that the study is being misrepresented as having provided evidence for something that it did not even assess.
That is the real harm being done here. It is harm to science itself.
I think it sets a poor example to misrepresent research as having provided evidence for something that is not even assessed by that research. Why bother doing the research? If you are going to disseminate conclusions that were not tested in the research, then why not just disseminate those conclusions and save the expense of conducting the research?
If these researchers are interested in telling the public that smoking outside only does not mitigate the risks posed by TSNA exposure from thirdhand smoke, then do a study to determine whether or not when smokers smoke only outside the home, their homes are still contaminated with significant levels of nicotine residue.
If you're going to disseminate the conclusions without having even done the study, then what's the point of doing the research in the first place?