Nitrosamines

Nitrosamines are a class of chemical compounds that were first described in the chemical literature over 100 years ago, but not until 1956 did they receive much attention. In that year two British scientists, John Barnes and Peter Magee, reported that dimethylnitrosamine produced liver tumors in rats. This discovery was made during a routine screening of chemicals that were being proposed for use as solvents in the dry cleaning industry. Magee and Barnes' landmark discovery caused scientists around the world to investigate the carcinogenic properties of other nitrosamines and N-nitroso compounds. Approximately 300 of these compounds have been tested, and 90% of them have been found to be carcinogenic in a wide variety of experimental animals. Most nitrosamines are mutagens and a number are transplacental carcinogens. Most are organ specific. For instance, dimethylnitrosamine causes liver cancer in experimental animals, whereas some of the tobacco specific nitrosamines cause lung cancer. Since nitrosamines are metabolized the same in human and animal tissues, it seems highly likely that humans are susceptible to the carcinogenic properties of nitrosamines.

Tobacco-specific nitrosamines (TSNAs) are widely considered to be among the most important carcinogens in smokeless tobacco products and cigarette smoke. Two of these tobacco-alkaloid derived compounds, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) N'-nitrosonor-nicotine (NNN), are consistently carcinogenic in labortaory animals, with NNK showing higher activity. The other two commonly measured TSNAs are N'-nitrosoanabasine (NAB) and N'-nitrosoanatabine (NAT). NAB is a weak carcinogen and NAT apparently lacks activity. NNK and NNN have been evaluated by the International Agency for Research on Cancer (2005)as carcinogenic to humans.

For the last 40 years, American farmers growing flue-cured tobacco have cured leaves through direct-fired systems that burn natural or LP gas. This method has been found to produce TSNA's, or tobacco specific nitrosamines. Nitrosamines are produced when nitrous oxides, a product of combustion, combine with nicotine in tobacco leaves. Tobacco specific nitrosamines have been shown to be carcinogenic. Research has shown that if such direct-fired systems are retrofitted with heat exchangers, tobacco specific nitrosamines can be dramatically reduced.

Formation of Tobacco Specific Nitrosamines

Origin of Tobacco-Specific Nitrosaminese
The importance of the tobacco curing process. The drying (curing) of green tobacco is an extremely delicate process, since tobacco must not be allowed to dry to the point that it crumbles. Incorrrect curing can result in the growth of bacteria in the tobacco leaves. The bacteria then form nitrite, which in turn reacts chemically with alkaloids to form nitrosamines. In an unfortune combination of circumstances, the nitrosamine content can become very high. Fire-cured tobacco, which contains other undesired components as well, such as benzopyrene. (Swedish Match - GothiaTek).