Mixtures of organic micropollutants exacerbated in vitro neurotoxicity of prymnesins and contributed to aquatic toxicity during a toxic algal bloom

Prymnesins produced by an algal bloom of Prymnesium parvum led to the death of several hundred tons of freshwater fish in the Oder River in summer 2022. We investigated effects on aquatic life and human cell lines from exposure to extracts of contaminated water collected during the fish kill. We detected B-type prymnesins and >120 organic micropollutants. The micropollutants occurred at concentrations that would cause the predicted mixture risk quotient for aquatic life to exceed the acceptable threshold. Extracts of water and filters (biomass and particulates) induced moderate effects in vivo in algae, daphnids and zebrafish embryos but caused high effects in a human neuronal cell line indicating the presence of neurotoxicants. Mixture toxicity modelling demonstrated that the in vitro neurotoxic effects were mainly caused by the detected B-type prymnesins with minor contributions by organic micropollutants. Complex interactions between natural and anthropogenic toxicants may underestimate threats to aquatic ecosystems. In summer 2022 an enormous fish kill was observed in the Oder River as a consequence of prymnesins produced by an algal bloom. An investigation of the exposure of aquatic life and human cells to the contaminated Oder water revealed the presence of neurotoxicants, which are attributed to B-type prymnesins, with minor contributions by organic micropollutants.