In vitro transforming effect of the fungicides metalaxyl and zineb.

The cytotoxic effects and the transforming properties of two fungicides, metalaxyl and zineb, whose mutagenic or carcinogenic activity has not been clarified yet, were analyzed in the in vitro BALB/c 3T3 cell transformation test both in the presence and in the absence of an exogenous metabolizing system. Zineb was completely detoxified when the exogenous metabolizing system was added to the target cells to increase their inherent metabolic capacity. Metalaxyl induced cell transformation at any assayed dosage, i.e., 500, 250, and 50 micrograms/ml, in the presence of bioactivation, and at the highest dosage (500 micrograms/ml) in the absence of bioactivation. The transforming effect was detectable only in the level-II transformation cultures and it was likely linked to the induction of additional cell proliferation which allowed obtaining the transformation amplification in these experimental conditions.