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

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.