STUDIES ON THE RELATIONSHIP BETWEEN TREATMENT CONDITION AND MICRONUCLEUS INDUCTION IN V79 CELLS EXPOSED TO SILICA AND GLASS-FIBERS

Studies have been carried out to determine the relationship between tr eatment condition and frequencies of micronucleated cells (MNC) and mu ltinucleated cells (MTC) in Chinese hamster lung fibroblasts (V79 cell s) exposed to dusts and fibers. Cells were treated with Min-U-Sil 5 si lica or Owens Coming AAA-10 glass fibers under three different conditi ons: 24-h exposure (24E), 24-h exposure followed by 24-h post-incubati on in fresh medium (24E-24P), and 48-h exposure (48E). Results showed that the frequency of MNC increased in a concentration-related manner in silica-treated V79 cells only under the condition of 24E-24P. The i ncrease in MNC frequency after 24-h exposure was not concentration-rel ated. No significant increase in MNC was detected in cells sampled aft er 48-h treatment. The frequencies of MTC in the treatment groups were higher than that in the control group. However, the increase was not statistically significant. Compared with silica, glass fibers were mor e active for MTC and MNC induction on a mass basis. The highest respon se was also observed under the condition of 24E-24P. These results ind icate that 24-h exposure followed by 24-h post-incubation is a suitabl e treatment condition for the micronucleus assay on mineral dusts and fibers.