Embryotoxicity of the alkylphenol degradation product 4-nonylphenol to thecrustacean Daphnia magna

Laboratory studies have suggested that some alkylphenols and pesticides eli cit developmental toxicity to crustaceans. The purpose of the present study was to evaluate the possibility that the alkylphenol degradation product 4 -nonylphenol is embryotoxic to the crustacean Daphnia magna through its kno wn ability to interfere with the metabolic elimination of testosterone. Dir ect exposure of maternal daphnids to testosterone caused developmental abno rmalities in neonates that consisted of partial arrest of early embryonic d evelopment and abnormalities in shell spine and first antennae development. Exposure of maternal daphnids to concentrations of 4-nonylphenol also prod uced developmental abnormalities though the profile of abnormalities was di stinct from that observed throughout the testosterone concentration-respons e curve. Thus, 4-nonylphenol is a developmental toxicant in daphnids, but i ts toxicity is not consistent with that elicited by elevated testosterone a ccumulation. Further experiments demonstrated that testosterone was directl y toxic to developing embryos, and the maternal organism can serve as the v ector for this toxicity. In contrast, neither direct embryo exposure nor ea rly maternal exposure to 4-nonylphenol elicited embryotoxicity consistent w ith that observed during continuous maternal and gestational exposure. Thus , 4-nonylphenol is not directly embryotoxic at these exposure levels, but r ather toxicity is mediated by maternal influences during gestation. The thr eshold concentration for the occurrence of developmental abnormalities (sim ilar to 44 mug/L) indicates that typical environmental concentrations of 4- nonylphenol pose no imminent hazard with respect to developmental toxicity. However, these effects do occur at sufficiently low levels to warrant eval uation of the relative susceptibility of other crustacean species to this p reviously uncharacterized mode of toxicity.