The fungicide propiconazole interferes with embryonic development of the crustacean Daphnia magna

Propiconazole is a fungicide used in a variety of agricultural applications . Preliminary studies had suggested that embryos of the crustacean Daphnia magna are particularly susceptible to the toxicity of this chemical. The go als of the present study were to define endpoints of daphnid embryonic deve lopment that could be routinely used to assess the embryo toxicity of chemi cals and to characterize definitively the embryo toxicity of propiconazole to daphnids. Daphnid embryonic development was characterized into six readi ly distinguishable stages based on the degree of tissue differentiation. Em bryonic development could be monitored either in the brood chamber of the m aternal organism or using embryos removed from the brood chamber and incuba ted ex vivo. Standard toxicity assessment revealed that propiconazole elici ted no significant adverse effects on daphnid survival or fecundity during a 21-d exposure to concentrations as high as 0.25 mg/L. Exposure to 0.25 mg /L propiconazole, however, caused a significant incidence of developmental abnormalities and embryonic death. Abnormalities were consistent with devel opmental arrest at later stages of embryonic maturation. Propiconazole elic ited a steep concentration-response curve with respect to embryo toxicity, with a 10% and a 90% incidence of embryo toxicity measured at 0.50 and 0.82 mg/L, respectively. Direct exposure of embryos to propiconazole resulted i n toxicity, though the incidence and characteristics of developmental abnor malities were not consistent with that observed during chronic exposures. H owever, maternal exposure to propiconazole followed by transfer of early em bryos to prop icon azole-free media resulted in embryo toxicity consistent with that observed during chronic exposure. These results indicate that pro piconazole interferes with the later stages of daphnid embryonic developmen t, and that this toxicity is manifested largely via maternal exposure to th e fungicide.