Microplastics in freshwater systems: Occurrence and effects

Micro(nano)plastics (MNPs) have been detected in every environmental compartment, yet most research still focused on marine systems. Although freshwater environments are key pathways for the transport of plastics from land to sea, they remained comparatively underexplored. This Virtual Special Issue (VSI) of Journal of Contaminant Hydrology, titled "Microplastics in freshwater systems: occurrence and effects", partly fills this gap by gathering 45 contributions (30 research articles and 15 reviews) from across the globe. Together, the VSI provides a comprehensive view of MNP occurrence, transport, fate, and ecotoxicological effects in various freshwater habitats, including estuary ecosystems. The collected manuscripts highlight advances in analytical methods, modeling, and mitigation strategies, while identifying major knowledge gaps such as limited long-term data sets, methodological inconsistencies, and scarce field-based ecotoxicological studies. This VSI underscores the need for standardized quantification methods, interdisciplinary approaches, and stronger links between science and policy to support effective management of plastic pollution in freshwater systems.