Driving Factors of Macroplastic Dynamics in Rivers: A Global Review

Abstract

Understanding riverine macroplastic dynamics is critical, as rivers are the main pathways transferring land-based plastics to the ocean, contributing to global marine pollution. This review synthesizes current research on the environmental factors controlling macroplastic dynamics in rivers, including hydrometeorological (e.g., rainfall, discharge), anthropogenic (e.g., mismanaged plastic waste, population density), and river characteristics (geographical features, e.g., riparian vegetation, slope, and man-made, e.g., dam, weir). A systematic literature search identified 193 studies, which were classified into ten relationship types for cross-study comparison. Our analysis reveals a strong research bias toward hydrometeorological drivers (53.7%), with fewer studies addressing anthropogenic or river characteristics (23.1% each). Environmental drivers are investigated unevenly across macroplastic transport phases, with hydrometeorological variables primarily linked to movement, anthropogenic factors to input, and river characteristics to both movement and accumulation. However, these relationships remain inconsistent across studies due to methodological and environmental differences. Importantly, a large proportion of studies rely on qualitative or descriptive approaches, with limited use of statistical testing to quantitatively evaluate driver–transport relationships. Geographic imbalances were also evident, with most research focused on Europe and Asia. This review highlights the need for more quantitative, evidence-based research to establish globally applicable links between environmental factors and riverine macroplastic pollution.