How Indoor Pollution
Reacts With Third-Hand Smoke
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
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
"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
February 9, 2010