Micronucleus frequency in sheep lymphocytes after in vitro exposure to fungicide tolylfluanid

The fungicide tolylfluanid (N-dichlorofluoromethylthio-N', N-dimethyl-N-p-tolylsulfamide), was investigated by cytokinesis-block micronucleus assay. Tolylfluanid at the lowest concentration (1 x 10(-6)mol L-1) did not influence significantly the frequency of micronuclei in sheep lymphocyte cultures in comparison with control (32.33 +/- 3.51/1000 binucleated cells versus 30.33 +/- 2.82/1000 binucleated cells in dimethylsulfoxide (DMSO) control, P = 0.44). Higher tolylfluanid concentrations (1 x 10(-4) and, 1 x 10(-5) mol L-1) resulted in a significant dose-dependent increase in the number of micronuclei in comparison with control (74.00 +/- 13.00/1000 binucleated cells and 52.67 +/- 10.12/1000 binucleated cells versus 30.33 +/- 2. 82/1000 binucleated cells in DMSO control, P = 0.005 and 0.02, respectively, ANOVA followed by Tukey test P < 0.05). Many of the treated cells also possessed multiple micronuclei. Tolylfluanid did not affect the nuclear division index at all treatment concentrations. Our in vitro results thus demonstrate that tolylfluanid had a significant genotoxic effect at only the highest concentration tested.