Occurrence and formation of nitrosamines in animal feeds.

A total of 465 samples of ingredients of animal feeds (fish meal, antarctic krill meal, experimental silage containing 40% dried animal wastes) and complete mixed feeds and protein concentrates were analysed for nitrate and nitrite content in the period 1973-78. Over 62% of the samples contained nitrates in concentrations ranging from 1 to 1020 mg/kg, and 6% contained 1-15 mg/kg of nitrites. After a preliminary survey, the samples having the highest levels of nitrate, nitrite and amines were selected and analysed for volatile N-nitrosamines. Of 171 selected samples, 40% were found to contain N-nitrosodimethylamine in the range of 0.003 to 0.417 mg/kg. No statistically confirmed correlation between concentrations of nitrates or nitrites and nitrosamines could be demonstrated. Large amounts of dimethylamine, ranging from 110 to 1765 mg/kg, were found in all samples of krill meal. Incubation of krill meal and fish meal with nitrite, under conditions similar to those existing in the animal stomach, resulted in the formation of substantial amounts of NDMA. The occurrence of N-nitrosamines in feeds and their possible formation in vivo from precursors present in feeds seems to be an important problem from the hygienic standpoint, because of possible "carry-over" to tissues, milk and eggs.