MICROPLASTIC POLLUTION AND ITS ECOLOGICAL IMPACT ON FRESHWATER AND MARINE FAUNA

Abstract

Microplastics, defined as plastic particles less than 5 mm in their longest dimension, are now among the most widespread and persistent contaminants of aquatic ecosystems globally. Since the first formal mention of microplastics in the scientific literature in 2004, they have been reported in all major marine compartments and a growing proportion of freshwater systems, with global production of synthetic polymers now approaching 359 million tonnes per annum and a single synthetic garment able to release up to 1,900 fibres per wash cycle (Cauwenberghe et al., 2015; Osman et al., 2023). Riverine conduits are thought to transport 70–80% of marine plastics to the ocean, whereas land-based sources account for approximately 80–90% of the total microplastic load entering aquatic systems (Horton et al., 2017; Osman et al., 2023). This review follows a systematic literature-review approach broadly aligned with PRISMA principles to synthesise peer-reviewed evidence published between January 2004 and December 2024 from Scopus, Web of Science and PubMed. Quality appraisal and thematic narrative synthesis are used to characterise the evidence base. The results show that ingestion of microplastics occurs over virtually the entire spectrum of aquatic fauna. In the marine environment, 13 of 15 northeast-Atlantic zooplankton taxa have been shown to ingest polystyrene beads, including particles as small as 1.7 µm in Temora longicornis (Cole et al. 2013). In freshwater systems, 12% of gudgeon collected from 11 French streams were contaminated and invasive round gobies in the Laurentian Great Lakes carried tissue burdens averaging 20 particles per fish with body burden positively correlated with both the trophic fraction (r 2 = 0.050, P = 0.032) and body length (r 2 = 0.393, P = 0.010) (McNeish et al., 2018; Wagner et al., 2014). Trophic transfer is quantitatively significant: fish exposed via mysid prey consumed 8–11 times more polyethylene beads by number and 3–5 times more by mass than fish exposed directly via the water column; mussels transferred microplastics to shore crabs at haemolymph concentrations of up to 163,111 particles mL-1 (Hasegawa & Nakaoka, 2021; McNeish et al., 2018). Cell and organism-level effects include dose-dependent logarithmic reductions in copepod algal-ingestion rate at exposures of ≥4,000 beads mL -1 and zebrafish oxidative-stress responses with elevated TNF-α, IFN-γ and pro-inflammatory interleukins under combined microplastic and copper exposure (Cole et al., 2013; Subaramaniyam et al., 2023). There remain large gaps in the research. Research on freshwater plastic pollution only represents 13 per cent of all publications on plastic pollution, and is increasing at approximately one-fifth of the rate of marine research, despite freshwater systems being the primary land-to-sea transport pathway (Blettler et al., 2018). There is an urgent need for ecologically realistic chronic-exposure studies and population-level risk assessments, and for standardized sampling protocols (Blettler et al.,., 2018; Horton et al.,., 2017; Wagner et al.,., 2014). Closing these gaps is essential if the descriptive evidence base is to be converted into predictive, management-relevant understanding of the impacts of microplastics on freshwater and marine fauna.