Tracing Microplastic Pollution Through Animals: A Narrative Review of Bioindicator Approaches

Monitoring microplastic pollution relies increasingly on bioindicators that integrate environmental exposure across habitats. This review presents animals explicitly proposed as microplastic bioindicators in recent literature and qualitatively evaluates their appropriateness using established biomonitoring criteria encompassing ecological, physiological, and methodological dimensions. In aquatic systems, bivalves (clams and mussels) demonstrate high suitability due to wide distribution, habitat-specific feeding, effective microplastic retention, and well-established analytical protocols. Fish exhibit intermediate suitability, as ecological representativeness and retention vary among species, and standardized methods often require multi-species approaches. Sessile organisms, including barnacles and sea anemones, align strongly with all three dimensions through spatial fidelity, effective retention, and methodological ease. Crustaceans and sponges also exhibit robust ecological relevance and high retention, with sponges uniquely integrating fine particles over time. Terrestrial and aerial indicators, such as carabid beetles and insectivorous birds, provide complementary coverage with moderate physiological integration and feasible ethical sampling. Sea turtles demonstrate exceptional physiological integration and methodological robustness at regional scales, despite non-sedentary behavior. Overall, taxa combining sedentary or spatially faithful ecology, effective microplastic retention, and standardized laboratory applicability, particularly bivalves, sponges, barnacles, sea anemones, and sediment-associated crustaceans, emerge as the most suitable bioindicators. Future research should prioritize harmonized, multi-taxa frameworks to improve standardization, cross-ecosystem comparability, and long-term microplastic monitoring.