Microplastic and Nanoplastic Pollution in Zooplankton: A Systematic Literature Review and Bibliometric Analysis of Ingestion, Ecotoxicological Effects, and Research Gaps

Microplastic pollution is a pervasive and ecologically significant threat to aquatic systems. Zooplankton, as key mediators of energy transfer and carbon cycling, are particularly vulnerable to microplastic ingestion due to size overlap with natural prey. This systematic literature review synthesises 250 peer-reviewed studies on zooplankton–microplastic and nanoplastic interactions, identified through a Web of Science search (403 initial records, 2012–2026) and screened using Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria. Bibliometric and narrative thematic analyses were conducted to evaluate publication trends, taxonomic coverage, biological endpoints, experimental design, particle characteristics, and geographic distribution. Publication output increased rapidly after 2019, with nanoplastics emerging as a major research focus. The literature is strongly biassed toward model organisms such as Daphnia magna and Artemia salina, with limited representation of marine taxa. Ingestion and oxidative stress are the most studied endpoints, while trophic transfer, carbon flux, and multi-stressor interactions remain underexplored. Reported experimental designs are predominantly laboratory-based and frequently employ supra-environmental concentrations and simplified particle types. A major geographic gap is identified for the Black Sea, with minimal coverage and no data for dominant regional species. Future research should prioritise ecologically realistic conditions, broader taxonomic and geographic representation, and integrated multi-stressor approaches to support ecosystem-based management. This review characterises publication patterns and knowledge gaps; it does not constitute a formal evidence synthesis, and frequency distributions reflect research coverage rather than strength of evidence.