Improving micro-/nanoplastics (MNPs) ecotoxicity assessment: A harmonised ecotoxicity testing approach with Daphnia magna

Micro- and nanoplastics (MNPs) are emerging contaminants of global concern, yet their ecological risks remain poorly defined due to limitations in current toxicity testing. Standard assays with Daphnia magna, a keystone grazer and regulatory model species, typically employ pristine, monodisperse polystyrene MNPs and focus on endpoints such as immobilisation or reproduction. This simplified approach neglects the freshwater cladoceran Daphnia magna's' ecological function, fails to capture the diversity and weathering of environmental plastics, and generates fragmented datasets that hinder meta-analysis and robust risk evaluation. To address these shortcomings, a tiered framework for MNP ecotoxicological assessment using D. magna that integrates ecological relevance, mechanistic insight, and systematic data harmonization is proposed. The framework progresses from acute endpoints (mobility, behaviour) to chronic assays (growth, reproduction, population dynamics), multigenerational studies (offspring quality, ephippial investment, sex ratio, transgenerational resilience), and mechanistic investigations employing omics and epigenetics. A central principle across all tiers is environmental realism, operationalised through the inclusion of MNP characterization, heterogeneous and weathered MNPs, diverse polymer chemistries, MNP physicochemical heterogeneity, and co-occurring environmental stressors. By systematically linking life-history traits with molecular and transgenerational endpoints under realistic exposure scenarios, the framework provides a more comprehensive understanding of MNP effects at both organismal and population levels. Importantly, it establishes protocols for endpoint selection, exposure duration, and test material characterisation, thereby improving comparability and reproducibility across studies. Adoption of this approach will help bridge the gap between laboratory testing and ecological risk assessment, enhancing predictive capacity on plastic pollution risks.