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Bacon was fried in the normal UK domestic manner, and the rashers, the cooked-out fat and the vapour were analysed for N-nitrosopyrrolidine and N-nitrosodimethylamine. Quantitative results were based on high resolution mass spectral measurements, and it was found that for both of the nitrosamines by far the greatest proportion occurred in the vapour.

The assessment of the potential carcinogenic risk to human health of the small quantities of N-nitrosamines formed in some foodstuffs depends on the availability of information on the routes by which they can be formed and of analytical methods having adequate sensitivity and selectivity for their determination. The present state of knowledge on these two aspects is reviewed in this paper.Demonstrations that a large number of N-nitrosamines are carcinogenic when fed to experimental animals1 have prompted investigations into their potential significance in human cancer. Chemical aspects of these studies have centred on attempts to ascertain which N-nitrosamines are likely to be present in food and the environment and upon the development of analytical methods for their determination. This paper reviews progress made in elucidating the parameters involved in the formation of N-nitrosamines, with particular reference to their possible presence in food and their formation in vivo, and the development of analytical methods of sufficient sensitivity and specificity to permit determination of them at the very low concentrations at which they are likely to be found. Formation of N-nitrosaminesThe principal chemical reaction involved in the formation of N-nitrosamines in circumstances relevant to human cancer is that of secondary amines with nitrous acid. The former are present at low concentrations in proteinaceous foods and the latter can arise from sodium nitrite used as a preservative or from enzymic reduction of nitrate which is commonly present in small quantities in water and foods and is also used in conjunction with nitrite in food preservation.Mirvishz studied the nitrosation of dimethylamine in aqueous solution as a function of pH. Figure 1 shows the pH dependence; the extent of reaction is a maximum at pH 3.4 and falls off at both higher and lower pH values. The nitrosating species is Nz03, derived from non-ionised nitrous acid and the reaction is therefore second order with respect to nitrous acid concentration. The Nz03 reacts with unprotonated amine and the reaction is first order with respect to the latter. Thus the reaction rate can be expressed as Rate= kl[R2NH][HN02l2 (1) a Presented at the SCI/IFST Symposium "The Role of Nitrate/Nitrite in Food", London, March 1975.

Nitrosamines have been found in spice-curing salt premixes which were used in meat products. A number of premixes were analysed using gas chromatography and high resolution mass spectrometry and the presence of N-nitrosopiperidine was confirmed in the majority of the premixes. After storage for 6 months levels of N-nitrosopiperidine had increased in most instances, and N-nitrosopyrrolidine was detected in several samples.

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