Effects of long-term inhalation of N-nitrosodimethylamine in rats.

The toxicological evaluation and histopathological findings of a long-term inhalation study in progress with N-nitrosodimethylamine (NDMA) are presented. Exposure was to three concentrations of NDMA: 0.04, 0.2 and 1.0 ppm (corresponding to 120, 600 and 3000 micrograms/m3). A significant reduction in median survival time (nine months) was seen in animals treated with the highest concentration of NDMA. Tumours occurred mainly in the nasal cavity, with the highest incidences in the groups receiving 1.0 and 0.2 ppm NDMA (19/36 and 31/36 tumour-bearing animals); in the lowest exposure group, 13/36 nasal tumours have been observed. The survival time of this treatment group, however, was about two months longer than that of the controls.