Walters C L
Oncology. 1980;37(4):289-96. doi: 10.1159/000225455.
Although nitrate is more abundant than nitrite in food and the environment in general, it requires reduction by, for instance, bacterial or plant enzymes before it is involved in the nitrosation of amines or amides. Part of the exposure of humans to nitrite arises from its use as a food additive where it performs a very useful function in protecting the consumer from pathogenic micro-organisms such as Clostridium botulinum. Some untreated foodstuffs, such as potatoes, tomatoes and beets, also contain low levels of nitrite. Nevertheless, the main source of human contact is that produced in vivo from nitrate ingested in foods in general and in vegetables in particular. Nitrate also occurs widely in drinking water supplies and this source can also contribute in some measure to human exposure. As yet, it is not possible to compute with accuracy the contribution from any endogenous synthesis within the gastrointestinal tract. Since the rate of nitrosation of an amine is dependent on the nitrite concentration to a power of greater than unity, it is probable that nitrite ingested in one application over a short period will be more active in the synthesis of N-nitroso compounds than a continuous supply at lower concentrations over long periods.
尽管硝酸盐在食物和一般环境中比亚硝酸盐更为丰富，但在其参与胺类或酰胺类的亚硝化反应之前，需要先通过细菌或植物酶等进行还原。人类接触亚硝酸盐的部分来源是其作为食品添加剂的用途，它在保护消费者免受诸如肉毒杆菌等致病微生物侵害方面发挥着非常有用的作用。一些未经处理的食品，如土豆、西红柿和甜菜，也含有少量的亚硝酸盐。然而，人类接触亚硝酸盐的主要来源是一般食物尤其是蔬菜中摄入的硝酸盐在体内产生的亚硝酸盐。硝酸盐在饮用水供应中也广泛存在，这一来源在一定程度上也会导致人类接触亚硝酸盐。目前，尚无法准确计算胃肠道内任何内源性合成的贡献。由于胺类的亚硝化速率取决于亚硝酸盐浓度的幂次且大于1，因此短期内一次性摄入的亚硝酸盐在N-亚硝基化合物合成中可能比长期低浓度持续供应的亚硝酸盐更具活性。
