Effects of mixtures of azole fungicides in postimplantation rat whole-embryo cultures

The effect of mixtures of azole fungicides on development of postimplantation rat whole-embryos cultured in vitro has been tested. On the basis of bench mark dose (BMD) modeling of the in vitro effect in rat embryo, the potency of 7 azoles was determined and compared. Then, relative potency factors have been derived based on either the NOAEL or on the BMD curve. Alternatively, each compound was used as index compound (IC), and IC-equivalent concentrations have been calculated for each mixture. Expected effects of such IC-equivalent concentrations of the mixture were derived from the appropriate BMD curve. Test mixture includes the agrochemicals triadimefon and imazalil (MIX2) or triadimefon, imazalil, and the clinically used fluconazole (MIX3) at their previously determined no-effect concentration, corresponding to approximately a benchmark response of 5-10 %. Subsequently, we tested the effect of a mixture of the agrochemicals triadimefon, imazalil, triadimenol, cyproconazole, tebuconazole, and flusilazole (MIX6) at concentration levels derived from their established human acceptable daily intake. MIX6 was also added with fluconazole at concentration levels indicated as the minimum therapeutically effective plasmatic concentration (MIX7A) or ten times this level (MIX7B). Generally, the experimental response was higher than the estimated one, by a factor of 2-6. Our data suggest that it is in principle correct to assume that azoles act as teratogens via a common mode of action and therefore should be grouped together for risk assessment. The synergistic effect needs to be confirmed with more combinations of concentrations/compounds in vitro and with specific in vivo experiments.