[Nitrate and nitrite in prepared meals in relation to the nitrate concentration of drinking water (author's transl)].
The nitrate and nitrite content of prepared foods was investigated in four areas in Rhineland Palatinate. The nitrate content of the drinking water was different in each area, the first region always having less than 1 mg NO-3/litre, the second an average of 19.5 mg NO-3/litre, the third an average of 35.6 mg NO-3/litre and the fourth 130 mg NO-3/litre. The samples were restaurant food which had been served without previously informing the maker. They were separately analysed according to soup, meat and gravy, carbohydrate accompaniments, vegetables and salad. It was shown that, in the four areas (in the above order) an average of 46, 67, 45 and 65 mg NO-3/main meal was ingested, which corresponds to a ratio of 1:1.5:1:1.4. For nitrites, the figures were 1.4, 2.0, 1.5, and 2.8 mg NO-2/main meal, corresponding to a ratio of 1:1.4:1.1:2. The nitrate excess consumed by the population in the principal meals in areas with a drinking water concentration of 130 mg/1 is consequently only 1.4 times higher than in an area where the water supply is free from nitrate. Under the same conditions the nitrite content is doubled. However, the levels at 2 and 1 mg NO-2/kg are altogether very low and are not likely to be of any importance hygienically for the public at large. The concentrations of nitrate in potatoes and carbohydrate accompaniments (94 mg NO-3/kg), vegetables (99 mg NO-3/kg) and salads (109 mg NO-3/kg) show average levels which are double those of soups (50 mg NO-3/kg) and meat dishes (58 mg NO-3kg). An effect of the nitrate content of drinking water on these figures is only seen in soups and meat, an increase by a factor of 4 occurring between the area with nitrate-gree drinking water and the area with 130 mg NO-3/1). Contrary to expectation, the nitrite levels show the reverse relationship. They are highest in soups (4.7 mg NO-2/kg) and meat dishes (3.5 mg NO-2/kg) to salads (1.4 mg NO-3/kg). The values obtained may be considered representative for the average population, because the present day cooking habits of the private household is largely equivalent to that of the restaurant industry as a result of the use of tinned foods, ready-cooked soups and ready-made gravies.