Experimental methods for assessing the effects of microplastics on Caenorhabditis elegans: a scoping review

Microplastics (MPs) are ubiquitous environmental contaminants of growing toxicological concern. Although the nematode Caenorhabditis elegans has emerged as a robust, genetically tractable model for evaluating MP toxicity, experimental methodologies remain highly fragmented, limiting cross-study comparability and hindering the development of reproducible risk assessment frameworks. This scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines to systematically evaluate methodological trends in C. elegans MP toxicology research. Searches across Scopus, PubMed, and Web of Science identified 59 peer-reviewed studies that evaluated individual-level biological effects after exposure to MPs or their leachates. Data on polymer characteristics, exposure conditions, and concentration metrics were extracted and synthesized. The current methodological landscape remains heavily skewed toward simplified experimental designs, with pristine particles (44%) and spherical shapes (73%) most frequently reported and polystyrene the most common polymer. Most studies with reported sizes included at least one size or size range classified as ingestible within 1-3 µm (74%). Exposure conditions most frequently involved durations of ≤ 24 hr (42%), aqueous media (45%), and the L4 developmental stage (47%). Critically, although evidence indicates that chemical additives, leachates, and environmental weathering substantially influence MP toxicity, experimental designs still rely predominantly on virgin polymers. In addition, a substantial proportion of studies use single-concentration exposure designs (24%), while mass per volume is the dominant dosing metric (80%). Overall, a gap exists between conventional laboratory exposures and the complexity of real-world environmental contamination. To improve ecological validity and environmental relevance, future C. elegans research should build on existing protocols, prioritize standardized multi-dose frameworks with environmentally realistic concentrations, include environmentally weathered and irregularly shaped particles from diverse polymers, and expand longer-duration and stage-specific exposure assessments.