Dimethylnitrosamine--formation in fish meal and toxic effects in pigs.

The production of fish meal from fresh and from formaldehyde- and sodium benzoate-preserved catches results in the formation of considerable dimethylnitrosamine (DMNA). This is in contrast to the prevailing opinion that only nitrite preservatives can be incriminated in producing this toxin. With capelin fish preserved in a mixture of 920 g of sodium benzoate and 920 ml of formaldehyde/hectoliter for 11 days, 7.5 mgs of DMNA/kg fish meal were produced. Pigs exposed to different daily levels of DMNA, of commercial source, proved to be rather resistant to intoxication compared with other domestic animals. Doses of 100, 200 and 500 ppm of DMNA added to a commercial pig diet, with a cumulative ingestion of 8.1 to 13.9 g pig or from 282 to 583 mg DMNA/kg body weight, resulted in extensive vasoobstructive disease over a period of 64 to 105 days. These lesions are most severe in the liver where they produce a diffuse form of cirrhosis. Additional findings include anaplastic changes in the tubules of the kidneys. A DMNA level of 15 ppm in the feed, in this experiment from fish meal, did not result in pathologic lesions over an observation period of up to 525 days.