Stagnant freshwaters can be affected by anthropogenic pollution and eutrophication that leads to massive growth of cyanobacteria and microalgae forming complex water blooms. These can produce various types of bioactive compounds, some of which may cause embryotoxicity, teratogenicity, endocrine disruption and impair animal or human health. This study focused on potential co-occurrence of estrogenic and retinoid-like activities in diverse stagnant freshwaters affected by phytoplankton blooms with varying taxonomic composition. Samples of phytoplankton bloom biomass and its surrounding water were collected from 17 independent stagnant water bodies in the Czech Republic and Hungary. Total estrogenic equivalents (EEQ) of the most potent samples reached up to 4.9 ng·g-1 dry mass (dm) of biomass extract and 2.99 ng·L-1 in surrounding water. Retinoic acid equivalent (REQ) measured by in vitro assay reached up to 3043 ng·g-1 dm in phytoplankton biomass and 1202 ng·L-1in surrounding water. Retinoid-like and estrogenic activities at some sites exceeded their PNEC and effect-based trigger values, respectively. The observed effects were not associated with any particular species of cyanobacteria or algae dominating the water blooms nor related to phytoplankton density. We found that taxonomically diverse phytoplankton communities can produce and release retinoid-like compounds to surrounding water, while estrogenic potency is likely related to estrogens of anthropogenic origin adsorbed to phytoplankton biomass. Retinoids occurring in water blooms are ubiquitous signalling molecules, which can affect development and neurogenesis. Selected water bloom samples (both water and biomass extracts) with retinoid-like activity caused effects on neurodifferentiation in vitro corresponding to those of equivalent all-trans-retinoic acid concentrations. Co-occurrence of estrogenic and retinoid-like activities in stagnant water bodies as well as the potential of compounds produced by water blooms to interfere with neural differentiation should be considered in the assessment of risks associated with water blooms, which can comprise complex mixtures of natural and anthropogenic bioactive compounds.

Department of Botany Faculty of Science University of South Bohemia Na Zlaté stoce 1 České Budějovice Czech Republic

RECETOX Faculty of Science Masaryk University Kotlarska 2 Brno Czech Republic

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