Assessing the impact of carrier solvent and solid phase extraction blank toxicity on fish embryo testing

Bioassays are powerful tools to comprehensively understand the effects of complex environmental mixtures on humans and other animal species. In particular, the fish embryo test (FET) with zebrafish (Danio rerio) is one of the most used bioanalytical tools to test in vivo the effect of environmental extract. However, it is well known that the preparation technique of complex environmental samples for bioanalytical testing could have huge impact on the composition of exposure solutions and hence the corresponding toxicity Considering this, it is important to develop reliable environmental sample preparation procedures to obtain accurate and reproducible results in the zebrafish embryo toxicity studies. In the present study, we aimed to investigate how different experimental set-ups using a Solid Phase Extraction (SPE) extract of a complex water sample might influence the toxicity assessment using embryos of Danio rerio. Firstly, we assess the influence of two typical carrier solvents (methanol and dimethyl sulfoxide) for dosing environmental extracts. We further investigated the effect of increasing exposure media pH. Finally, we studied the effect of the SPE blank on lethal and sublethal effects in embryos of Danio rerio. Although no significant differences were observed for different solvents, we observed an adverse effect on hatching rate when testing the blank. This indicates the potential impact of background contamination in experimental setups, highlighting the need for appropriate blank correction methods. Furthermore, the differential effects observed with different pH correction methods highlight the importance of carefully selecting the appropriate pH adjustment strategy to accurately assess toxicity levels. Overall, our study enhances the knowledge base and methodology for accurate and comprehensive ecotoxicological assessments in aquatic ecosystems, aiding in the protection and conservation of these fragile environments.