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)
titled "Formation of carcinogens indoors by surface-mediated
reactions of nicotine with nitrous acid, leading to potential
third-hand smoke hazards."
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.
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"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.
"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.
"Whereas the sidestream smoke of one cigarette contains at least
100 nanograms equivalent total TSNAs, our results indicate that
several hundred nanograms per square meter of nitrosamines may be
formed on indoor surfaces in the presence of nitrous acid," says
lead-author Sleiman.
Co-author James Pankow points out that the results of this study
should raise concerns about the purported safety of electronic
cigarettes. Also known as "e-cigarettes," electronic cigarettes
claim to provide the "smoking experience," but without the risks of
cancer. A battery-powered vaporizer inside the tube of a plastic
cigarette turns a solution of nicotine into a smoky mist that can
be inhaled and exhaled like tobacco smoke. Since no flame is
required to ignite the e-cigarette and there is no tobacco or
combustion, e-cigarettes are not restricted by anti-smoking
laws.
"Nicotine, the addictive substance in tobacco smoke, has until
now been considered to be non-toxic in the strictest sense of the
term," says Kamlesh Asotra of the University of California's
Tobacco-Related Disease Research Program, which funded this study.
"What we see in this study is that the reactions of residual
nicotine with nitrous acid at surface interfaces are a potential
cancer hazard, and these results may be just the tip of the
iceberg."
The Berkeley Lab researchers are now investigating the long-term
stability in an indoor environment of the TSNAs produced as a
result of third-hand smoke interactions with nitrous acid. The
authors are also looking into the development of biomarkers to
track exposures to these TSNAs. In addition, they are conducting
studies to gain a better understanding of the chemistry behind the
formation of these TSNAs and to find out more about other chemicals
that are being produced when third-hand smoke reacts with nitrous
acid.
"We know that these residual levels of nicotine may build up
over time after several smoking cycles, and we know that through
the process of aging, third-hand smoke can become more toxic over
time," says Destaillats. "Our work highlights the importance of
third-hand smoke reactions at indoor interfaces, particularly the
production of nitrosamines with potential health impacts."
In the PNAS paper, Destaillats and his co-authors suggest
various ways to limit the impact of the third hand smoke health
hazard, starting with the implementation of 100 percent smoke-free
environments in public places and self-restrictions in residences
and automobiles. In buildings where substantial smoking has
occurred, replacing nicotine-laden furnishings, carpets and
wallboard can significantly reduce exposures.
SOURCE