Aquatic biotests are important tools targeting various effects in ecotoxicology, including endocrine disruption. Unintentional exposure of bioassay organisms to endocrine disruptors during cultivation or testing may interfere with assessed endpoints. We illustrate this issue on the example of laboratory phytoplankton cultivation, where possible sources of estrogenic compounds have been revealed. Fifty-four blank samples (water and fresh or cultivated growth media) were assessed by in vitro biotests for their estrogenicity, and major known estrogens originating from plastic materials, bisphenol A and alkylphenols, were analyzed in selected samples. The samples of freshly prepared growth medium elicited weak estrogenic response in bioassays and some samples of the aerated media caused responses even above the 50% of maximum of the reference compound (17β-estradiol, E2), while the samples from diverse laboratory water sources did not show significant estrogenic activity. The results identified substances contained in the growth medium as minor but reproducible contributors to estrogenicity in the cultivations. Sporadic but significant effects (up to 4.9 ng E2 equivalent/L) can be ascribed to compounds released from the used plastic materials during aeration of the cultivations. The potential sources of unintentional exposure to estrogenic compounds need to be considered in aquatic cultivations and biotests, since they could impact their outcomes, especially in arrangements assessing reproduction or whole life cycle biotests, or production of bioactive compounds by phytoplankton. The findings emphasize the necessity to assess all relevant blanks, ideally by sensitive high throughput in vitro assays that reflect also unknown pollutants and minimize all potential sources of background contamination. In vitro assays show very good applicability for this purpose since they enable to screen for any background estrogenicity of the used media and materials without the need of analyzing individual compounds, which often might not be known.

RECETOX Faculty of Science Masaryk University Kotlarska 2 CZ 62500 Brno Czech Republic

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