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In tests at Berkeley Lab of celluose surfaces contaminated with nicotine residues from third-hand smoke, levels of newly formed TSNAs rose 10 times following a three hour exposure to nitrous acid. TSNAs are potent carcinogens.

Nicotine in third-hand smoke, the residue from tobacco smoke that clings to virtually all surfaces long after a cigarette has been extinguished, reacts with the common indoor air pollutant nitrous acid to produce dangerous carcinogens. This new potential health hazard was revealed in a multi-institutional study led by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab).

“The burning of tobacco releases nicotine in the form of a vapor that adsorbs strongly onto indoor surfaces, such as walls, floors, carpeting, drapes and furniture. Nicotine can persist on those materials for days, weeks and even months. Our study shows that when this residual nicotine reacts with ambient nitrous acid it forms carcinogenic tobacco-specific nitrosamines or TSNAs,” says Hugo Destaillats, a chemist with the Indoor Environment Department of Berkeley Lab’s Environmental Energy Technologies Division. “TSNAs are among the most broadly acting and potent carcinogens present in unburned tobacco and tobacco smoke.”

Destaillats is the corresponding author of a paper published in the Proceedings of the National Academy of Sciences (PNAS). Co-authoring the PNAS paper with Destaillats were Mohamad Sleiman, Lara Gundel and Brett Singer, all with Berkeley Lab’s Indoor Environment Department, plus James Pankow with Portland State University, and Peyton Jacob with the University of California, San Francisco.

The authors report that in laboratory tests using cellulose as a model indoor material exposed to smoke, levels of newly formed TSNAs detected on cellulose surfaces were 10 times higher than those originally present in the sample following exposure for three hours to a “high but reasonable” concentration of nitrous acid (60 parts per billion by volume). Unvented gas appliances are the main source of nitrous acid indoors. Since most vehicle engines emit some nitrous acid that can infiltrate the passenger compartments, tests were also conducted on surfaces inside the truck of a heavy smoker, including the surface of a stainless steel glove compartment. These measurements also showed substantial levels of TSNAs. In both cases, one of the major products found was a TSNA that is absent in freshly emitted tobacco smoke — the nitrosamine known as NNA. The potent carcinogens NNN and NNK were also formed in this reaction.

“Time-course measurements revealed fast TSNA formation, up to 0.4 percent conversion of nicotine within the first hour,” says lead author Sleiman. “Given the rapid sorption and persistence of high levels of nicotine on indoor surfaces, including clothing and human skin, our findings indicate that third-hand smoke represents an unappreciated health hazard through dermal exposure, dust inhalation and ingestion.”

Since the most likely human exposure to these TSNAs is through either inhalation of dust or the contact of skin with carpet or clothes, third-hand smoke would seem to pose the greatest hazard to infants and toddlers. The study’s findings indicate that opening a window or deploying a fan to ventilate the room while a cigarette burns does not eliminate the hazard of third-hand smoke. Smoking outdoors is not much of an improvement, as co-author Gundel explains.

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“Smoking outside is better than smoking indoors but nicotine residues will stick to a smoker’s skin and clothing,” she says. “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 dangers of mainstream and secondhand tobacco smoke have been well documented as a cause of cancer, cardiovascular disease and stroke, pulmonary disease and birth defects. Only recently, however, has the general public been made aware of the threats posed by third-hand smoke. The term was coined in a study that appeared in the January 2009 edition of the journal “Pediatrics,” in which it was reported that only 65 percent of non-smokers and 43 percent of smokers surveyed agreed with the statement that “Breathing air in a room today where people smoked yesterday can harm the health of infants and children.”

Anyone who has entered a confined space — a room, an elevator, a vehicle, etc. — where someone recently smoked, knows that the scent lingers for an extended period of time. Scientists have been aware for several years that tobacco smoke is adsorbed on surfaces where semi-volatile and non-volatile chemical constituents can undergo reactions, but reactions of residual smoke constituents with atmospheric molecules such as nitrous acid have been overlooked as a source of harmful pollutants. This is the first study to quantify the reactions of third-hand smoke with nitrous acid, according to the authors.

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