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: EC₅₀s _{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. EC₁₀s _{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 10¹¹ to10¹⁵ 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. [ABSTRACT FROM AUTHOR]