Thirdhand smoke is the term for leftover nicotine as well as other harmful chemicals contaminating an indoor environment after cigarettes have been smoked. Consider the lingering odor you’ve most likely experienced when handling the garments of a smoker, or when staying in cigarette-friendly accommodation.1✅ JOURNAL REFERENCE
DOI: 10.1021/acs.est.2c02559
Researchers first determined thirdhand smoke as a likely health hazard ten years ago. This study presents more extensive insights into the long-term health risks of thirdhand smoke. It was discovered that toxic chemical concentrations that linger in indoor environments where cigarette smoking has taken place surpass risk guidelines, which means non-smokers are potentially exposed to health risks just by residing in contaminated spaces.
It was previously found that aerosolized nicotine that’s released when vaping and smoking accumulates on indoor surfaces and can interact with a compound found in indoor air known as nitrous acid to create highly carcinogenic compounds known as tobacco-specific nitrosamines. Nicotine accumulated on household surfaces can generate tobacco-specific nitrosamines continuously, long after the smoke has left the space.
Since this chemistry was first described in 2010, other research has also shown the presence of tobacco-specific nitrosamines on indoor surfaces and dust that has settled. For this study, researchers integrated the information provided over the past 10 years with these results, to determine the daily dosages to which individuals may be exposed when residing in thirdhand smoke contaminated homes.
Tobacco-specific nitrosamines go into the body through multiple pathways. The study determined dosages from inhaling and dust ingestion by measuring tobacco-specific nitrosamine indoor concentrations. The focus was also on harder to measure dermal exposures, for which there’s a lot less available data. These dermal exposures can take place by direct skin contact, from polluted air or from a contaminated surface that contains tobacco-specific nitrosamines, for instance, while asleep on smoky bed sheets. This can also happen through epidermal chemistry which is when nicotine that has already settled on the skin reacts with environmental nitrous acid to create tobacco-specific nitrosamines directly on the body’s surface.
Nicotine is released in considerable quantities when smoking, coating all indoor surfaces, which includes human skin. The researchers identified that the presence of sweat and skin oils on model surfaces led to a greater tobacco-specific nitrosamine yield in the presence of nitrous acid, in comparison to surfaces that were clean.
Three different tobacco-specific nitrosamines were produced in this reaction, 2 of which are known carcinogens (known by the acronyms NNN and NNK). There’s less toxicological data for the 3rd one, NNA, which isn’t found in tobacco smoke. Because of this, the study included an in vitro evaluation.
The researchers provide more evidence of NNA’s genotoxicity by assessing its impact on cultured human lung cells. NNA contact resulted in DNA damage, which included double-strand breaks, the most harmful genotoxic outcome.
To understand dermal exposures better, researchers assessed how nicotine and NNK penetrate through mice’s skin. The assessment of the metabolites in the urine of the mice revealed that direct dermal contact led to the circulation and accumulation in the body for both compounds for 7 days after dermal exposure had ended.
It was revealed that exposure via all 3 pathways, dermal absorption, dust ingestion, and inhalation, under normal indoor conditions can lead to NNK dosages that surpass health guidelines. These cumulative exposures can lead to an increased risk of cancer. Routes of dermal exposure contribute to tobacco-specific nitrosamine intake at significant levels that are equal to to or even greater than inhalation.
These results demonstrate the harmful health effects of thirdhand smoke, which contains not just tobacco-specific nitrosamines but many other chemicals, of which several are known carcinogens.
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