Ecotoxicological interactions between triclosan and 17α-ethinylestradiol: chronic assessment in Ceriodaphnia dubia and mixture effects

The chronic effects of triclosan (TCS) and 17α-ethinylestradiol (EE2) were assessed individually in Ceriodaphnia dubia. The joint effect of triclosan (TCS) and 17α-ethinylestradiol (EE2) in Ceriodaphnia dubia was determined using the concentration addition (CA) and independent action (IA) mathematical models. The effects of synergy and antagonism resulting from binary mixtures of these compounds, and the deviations related to dose-level and dose-ratio dependence were investigated. Both compounds are endocrine disruptors, present in hygiene and pharmaceutical products, potentially causing environmental and wildlife issues. The results of the chronic bioassay with Ceriodaphnia dubia demonstrated that TCS with an EC50 (median effective concentration) = 93 ± 1.41µg L-1 was more toxic than EE2 with an EC50 = 589 ± 2.12 µg L-1 for the microcrustaceans. The CA model better predicted the mixture toxicity. The results revealed interactions between the compounds, mainly showing synergism, but also dose level deviations with synergism at low dose levels and antagonism at high dose levels. The mixture interactions identified in this study underscore the significance of enhancing chemical screenings of environmental samples with mixture toxicity data, especially when dealing with combinations whose joint effects are not well understood.