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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.

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SUMMARY Following the report of the presence of nitrosamine-like substances in samples of homemade spirit from Zambia, which had been obtained from an area where cancer of the oesophagus is common, samples of distilled alcoholic drinks were collected throughout western Kenya and southern Uganda from areas where the frequency of cancer of the oesophagus varies from very common to very rare. The 44 samples of spirit were screened by polarography and substances giving a similar response to nitrosamines were indicated at levels as high as 21 ppm. Subsequent analysis by gas chromatography for selected individual nitrosamines showed no evidence for the occurrence of methylethylnitrosamine (MEN), diethylnitrosamine (DEN), dipropylnitrosamine (DPN), ethylbutylnitrosamine (EBN), dibutylnitrosamine (DBN), nor of N nitrosopiperidine (N Pipn), but traces of compounds having a similar retention time as dimethylnitrosamine (DMN) were observed. However, subsequent examination by mass spectrometry showed no evidence of dimethylnitrosamine. There was no apparent association between the levels of unknown constituents indicated by polarography and gas chromatography, nor between either of these levels and the frequency of cancer of the oesophagus. The results by gas chromatography and mass spectrometry confirm that polarography is too unspecific to be a useful indicator of nitrosamines.

although this does not exclude the possibility of in vivo adsorption. Preliminary experiments with class-specific anti-M lg suggest that the lg on any one cell belongs to a single class. This result is most easily reconciled with the third hypothesis. The question of whether the surface lg molecules function as antigen-specific receptors remains to be answered.We thank Mr R. Lucken, Mr A. Savill and Miss J.