Systematic assessment of the mechanisms and risks of micro- and nanoplastic particle exposure in marine invertebrates

Marine invertebrates are among the most vulnerable organism groups to micro- and nanoplastic (MNP) exposure, yet understanding of their interspecies sensitivity and mechanistic responses remains limited. This study provides a systematic evaluation of MNP toxicity across diverse marine invertebrate taxa by (i) evaluating the effects of MNP exposure on key biological endpoints as a function of key particle characteristics, and (ii) constructing species sensitivity distributions (SSDs) to derive ecologically relevant hazard thresholds. Data were extracted from the Toxicity of Microplastic Explorer (ToMEx) for Aquatic Organisms database (version 2.0), with quality evaluated using the Technical and Risk Assessment "Red" Criteria framework to ensure the inclusion of essential experimental parameters. Chronic no-observed-effect concentration (NOEC) values, derived from mortality, fitness, and functional-related endpoints, were analyzed as a function of particle size (nanoplastics: <1 µm; microplastics: 1-5000 µm), shape (spherical vs. non-spherical), and exposure medium (water vs. sediment) to identify particle-specific toxicity trends. To translate reported biological effects into ecologically relevant risk estimates, SSDs were constructed using chronic fitness-related endpoints, accounting for two distinct exposure mechanisms: food dilution via ingestion and tissue translocation. Psedechinus huttoni (Echinoderm) emerged as the most sensitive, while Paracentrotus lividus (Echinoderm) were the least sensitive across both models. Preliminary Safe Standards (PSS), calculated using SSD-derived HC₅ values, offer provisional thresholds for protecting marine invertebrate communities. These findings provide insights into MNP toxicity and aid in identifying sensitive taxa and endpoints, while highlighting key knowledge gaps to advance risk assessment frameworks for MNPs in marine ecosystems.