Potential for high toxicity of polystyrene nanoplastics to the European Daphnia longispina

Abstract Background Current regulatory discussions about microplastics are often questioned based on a lack of data indicating high ecotoxic hazards of these particles within standard and recognized definitions. Moreover, there is scientific debate on what metrics to report the micro-nanoplastics toxicity (i.e. mass or particle counts-based exposure). We present here the high potential sensitivity of three genotypically different clones of the European Daphnia longispina species complex exposed to non-functionalized polystyrene nanobeads of 50 nm and 100 nm in diameter according to adapted OECD 202 test protocol. Results EC 50 s 48 h varied from 0.2 to 8.9 mg L −1 (mean 2.49 mg L −1 ) for 50 nm beads, and from 32.7 to 90.3 mg L −1 (mean 59.39 mg L − 1) for the 100 nm. EC 10 s 48 h varied from 0.0007 to 7.5 mg L −1 (mean 0.28 mg L −1 ) for 50 nm beads, and from 25.5 to 69.1 mg L −1 (mean 47.51 mg L −1 ) for the 100 nm. Inter-clonal variability was about tenfold. Therefore, several 1000 s-fold variations in mass-based ecotoxicity for these polystyrene beads was observed if particle size and Daphnia genotype are considered jointly. Conclusions Such ecotoxicity potential is comparable to highly toxic chemicals in global and EU-based regulatory classification and labelling. Ecotoxicity based on particle counts suggested convergence of EC50s, with effects generally observed around 10 11 to10 15 particles L −1 . The present results highlight the potential high hazard of these particles and the relevance of particle size and exposure metrics on hazard conclusion. Graphical Abstract