Embryolethality of new herbicides is not detected by the micromass teratogen tests

New herbicidal compounds (11 pyrimidine-diones, 3 benzoates and 1 sulfonamide) were found to be embryolethal but not teratogenic in rats. The range of the embryolethal dose varied from 0.2 to greater than 200 mg/kg. This broad range enabled us to validate whether proposed in vitro teratogen tests can detect the embryolethality of these herbicides. The IC50 values (inhibition concentration 50%) for both differentiation and proliferation of midbrain and limb bud cells of rat embryos were determined and found to be above 50 micrograms/ml in all cases, confirming that the herbicides were not teratogenic. No correlation, however, was observed between the embryolethality in vivo and the activities in these cells. In order to test whether the potential to cause embryolethality could be predicted and detected as a general cytotoxic effect, the inhibition of colony forming ability in V79 cells was determined. The results indicated that cytotoxicity in V79 cells may be useful for preliminary testing of the embryolethal effect of herbicides.