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Residual nicotine from cigarette smoke reacts with nitrous acid on indoor surfaces to form carcinogenic tobacco-specific nitrosamines (TSNAs). This is one finding of a potentially seminal new article published recently in Proceedings of the National Academy of Sciences of the United States of America (2010;107:6576-6581).

“We've identified a new risk from tobacco smoke,” Lara Gundel, PhD, tells CA. “People are at risk from this in a way that's never been recognized before. Thirdhand smoke can get more dangerous over time as it reacts with a common indoor pollutant, nitrous acid,” says Dr. Gundel, a staff scientist at Lawrence Berkeley Laboratory in San Francisco, California and a lead researcher of the study.

“This is the first study that's been conducted by a well-respected group of researchers who've shown beyond the fact that thirdhand smoke exists, that it actually may present a health hazard,” says Thomas J. Glynn, PhD, director of Cancer Science and Trends as well as International Cancer Control for the American Cancer Society.

According to Mohamad Sleiman, PhD, first author of the article and a colleague of Dr. Gundel, “The main finding here is that we've discovered that nicotine…can be converted to some potent and carcinogenic substances after it's dissolved on indoor surfaces.”

Methods

  1. Top of page
  2. Methods
  3. Children at Greatest Risk
  4. Tobacco-Specific Nitrosamines
  5. The Public Health Message

To evaluate the presence of TSNAs, the researchers conducted both laboratory and field testing. In the laboratory, cellulose was used as a model surface. “Cellulose substrates were exposed to vaporized nicotine in a tubular-flow reactor,” the authors write. In the field, the researchers examined the cabins of trucks belonging to 2 smokers. In both contexts, the researchers were able to detect nicotine residue and TSNAs on surfaces exposed to tobacco smoke.

Sleiman et al also examined nicotine and TSNA residues on hair, skin, and cotton; on dust in the trucks and in homes; and on furniture. In all examined contexts, they found elevated levels of nicotine and of 3 carcinogenic TSNAs–NNN, NNA, and NNK–ranging from nanograms per square meter to micrograms per square meter.

“Substantial levels of TSNAs were measured on surfaces inside a smoker's vehicle. Laboratory experiments using cellulose as a model indoor material yielded a greater than 10-fold increase of surface-bound TSNAs when sorbed secondhand smoke was exposed to 60 ppbv [parts per billion by volume] HONO [nitrous acid] for 3 hours,” write Sleiman et al.

Children at Greatest Risk

  1. Top of page
  2. Methods
  3. Children at Greatest Risk
  4. Tobacco-Specific Nitrosamines
  5. The Public Health Message

Studies have shown that adult exposure to primary and secondary smoke has declined recently in the United States. However, according to a 2006 report from the Office of the US Surgeon General, progress in protecting children from tobacco smoke has lagged. The Surgeon General report suggests children's most important exposure occurs in the home. Infants, children, and other nonsmokers are at risk via dermal contact and by inhaling nicotine-contaminated dust and smoke residue. The findings by Sleiman et al add to the concern that children are exposed to nicotine-related carcinogens from a variety of sources in a variety of contexts.

Dr. Gundel posed the following example: A person smokes in the home when children are not present. The smoke may soon dissipate, but the carcinogenic TSNAs cling to the smoker's skin and hair; to dust; and to fabrics, furniture, and other surfaces in the room or rooms in which the smoking takes place. If a child or other nonsmoker then enters that room in which TSNA-contaminated dust settles or has contact with a carpet that's permeated with nicotine and resultant TSNAs (a toddler on the floor, for example), he or she is directly exposed to potent carcinogens.

“The closer the person is to the floor,” explains Dr. Gundel, “the more house dust would contain these compounds. The more the inhalation route would be important because the bigger dust stays close to the floor where the kids would be playing. House dust would pick up nicotine just like these other surfaces do.”

Tobacco-Specific Nitrosamines

  1. Top of page
  2. Methods
  3. Children at Greatest Risk
  4. Tobacco-Specific Nitrosamines
  5. The Public Health Message

One of the most alarming characteristics of TSNAs is their longevity. “[TSNAs] are among the most broadly acting and potent carcinogens present in burned tobacco and tobacco smoke,” write Sleiman et al.

Smokers may have long believed that they were not exposing nonsmokers to their carcinogens if they smoked in an enclosed space without others being present. In fact, the findings of Sleiman at al clearly demonstrate that anyone who smokes in a home, car, or other enclosed area in which nonsmokers later are present is exposing those nonsmokers to potent carcinogens.

“We know that these compounds are quite stable under indoor relevant conditions, so the levels can build up with time, the levels can be higher and higher if someone keeps smoking at a regular pace in the home,” Dr. Sleiman says. The more a person smokes in the home or car, the more TSNAs are formed and sorbed onto environmental surfaces, and into materials such as cotton, cellulose, upholstery, and carpeting.

The Public Health Message

  1. Top of page
  2. Methods
  3. Children at Greatest Risk
  4. Tobacco-Specific Nitrosamines
  5. The Public Health Message

Complicating this public health picture is the finding that the removal of TSNAs from real-world contaminated contexts (including hair, skin, homes, cars, bars, and hotel rooms) may be more difficult than simply dry cleaning or washing with soap and water. In fact, cleansers that dissolve nicotine into water must be acidic. “We can wash a marble countertop with vinegar and the nicotine will go away,” notes Dr. Gundel. Most soaps, however, are alkaline and will not effectively remove nicotine residue, even from smooth stone or metallic surfaces.

Removing thirdhand smoke in the form of nicotine residue from carpet, for example, especially carpet with long-term exposure, would be nearly impossible. “When we consider the carpet,” continues Dr. Gundel, “we don't see how to get rid of the nicotine and the TSNAs. Carpet will continue to uptake nicotine continually. We can't see the end of the nicotine off-gassing. There's so much nicotine coming to the surface from the years of deposition that I couldn't say how to remediate it.”

Dr. Gundel offers this solution: “We should keep public places 100% smoke free and smokers should not smoke in or near their homes if they have children.” 1