Formation of Tobacco Specific Nitrosamines in Mainstream Cigarette Smoke; Part 1, FTC Smoking

This report evaluates the formation of nitrosonornicotine (NNN) and of 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) from nicotine, and of NNN from nornicotine in the mainstream smoke of a burning cigarette. The cigarettes analyzed in the study were Kentucky reference cigarettes 1R4F and 2R4F, and five other cigarettes, three of them having tobaccos with low levels of tobacco specific nitrosamines (TSNAs). All cigarettes had ‘tar’ levels around 10 mg [where ‘tar’ is defined as the weight of total wet particulate matter (TPM) minus the weight of nicotine and water]. Cigarettes were smoked according to the U.S. Federal Trade Commission (FTC) puffing regimen, using a 35 mL puff volume, 2 sec puff duration and 60 sec puff intervals. Three separate experiments were performed in this study to evaluate the proportion of TSNAs transferred from preexistent tobacco TSNAs and the proportion formed during smoking (pyrosynthesized). In one experiment, the results were obtained by GC/MS analysis of ¹³C₃-TSNAs formed in smoke when ¹³C₃-nicotine was intentionally added to cigarettes. Another experiment used GC analysis with chemiluminescence detection of TSNAs from smoke before and after an excess of nornicotine was intentionally added to cigarettes, and another experiment consisted of LC/MS/MS analysis of ²H₄-TSNAs formed in the smoke when ²H₄-nicotine and when ²H₄-nornicotine were intentionally added to cigarettes. The use of different analytical methods for the study of TSNA formation conveyed an additional level of confidence regarding the reliability of the results obtained. It was found that NNK was generated during smoking from nicotine with 3 × 10^-5% to 8 × 10^-5% conversion (0.3 ppm to 0.8 ppm conversion of the nicotine) while the result for NNN generation was not conclusive. One experiment demonstrated the formation of NNN from nicotine between 4 × 10^-5% and 1.5 × 10^-4% (0.4 ppm to 1.5 ppm reported to nicotine), but another experiment did not provide proof of NNN formation, with a limit of quantitation LOQ for NNN corresponding to 5 × 10^-5% (or 0.5 ppm). Nornicotine was proven to generate NNN, and the results for the 2R4F cigarette showed 3.3 × 10^-3% yield (33 ppm reported to nornicotine) in one experiment and 4.6 × 10^-3% (46 ppm reported to nornicotine) in a different experiment, the agreement being very good. Using the results from this study, it was concluded that pyrosynthesis may account for about 5% to 10% of the NNK in mainstream smoke for a filter cigarette with the FTC ‘tar’ level around 10 mg. Pyrosynthesis may account for higher proportions of smoke TSNAs when the cigarette tobacco is low in TSNAs, since the mainstream smoke TSNAs yield from direct transfer from tobacco is small in this case. The contribution of pyrosynthesis may account for 5% to 25% of NNN in mainstream cigarette smoke, or potentially an even higher proportion when the tobacco blend is both low in TSNAs and high in nornicotine. Anabasine is typically present at low levels in tobacco and therefore the formation of nitrosoanabasine(NAB) is of less interest. Anatabine is present in different tobaccos in a range similar to that of nornicotine and being a secondary amine has the potential to act similarly to nornicotine. However, the pyrosynthesis of nitrosoanatabine (NAT) from anatabine was not evaluated in the present study. The study indicated that complete elimination of TSNAs from tobacco is unlikely to completely eliminate the TSNAs from cigarette smoke, and that high nornicotine tobaccos should be avoided in order to minimize the levels of NNN in cigarette smoke.