Genotoxicity studies on mice after short term inhalation exposure to methyl isocyanate

Mutagenicity testing is an important aspect of the toxicological evaluation of environmental chemicals for safety. Methyl isocyanate (MIC), a very hazardous chemical used for the manufacture of insecticides, was studied for its genotoxic effects on the somatic cells of mice after inhalation exposure by means of an in vivo micronucleus test and chromosomal analysis of bone marrow cells. Animals were exposed for 10 min to different concentrations (2.40, 4.80 or 7.20 microliters) of MIC in a 22 litre chamber at 0 and 24 h. Bone marrow smears prepared 6 h after the second treatment were examined for the occurrence of micronuclei (MN) in polychromatic (P) and normochromatic (N) erythrocytes. The frequencies of cells with MN and the P/N ratio did not differ significantly from those of the control at all the exposure levels. Chromosomal preparations revealed few structural and numerical abnormalities. Aberrations encountered were of the chromatid type only. Quantitative analyses failed to exhibit any significant increase in aberration rates in the three treated groups. Numerical abnormalities were within the control range.