Micro- and nanoplastics (MNPs) are increasingly detected in soils, groundwater, rivers, lakes, wetlands, and sediments. Despite growing evidence of their widespread occurrence, the mechanisms controlling their mobilisation, transport, retention, transformation, and transfer between environmental compartments remain poorly constrained. MNP behaviour is influenced by particle properties and by the hydrological, physical, and biogeochemical characteristics of the surrounding environment. Processes such as runoff, infiltration, recharge, erosion, sediment transport, and groundwater–surface water exchange can govern their movement, while interactions with soil and sediment matrices, organic matter, minerals, microorganisms, and biofilms may promote retention, remobilisation, aggregation, or transformation. MNPs may also interact with co-occurring pollutants, including metals, pesticides, pharmaceuticals, PFAS, nutrients, and other emerging contaminants. These interactions can influence contaminant mobility, persistence, bioavailability, and exposure, raising important questions about the role of plastic particles within complex contaminant mixtures and their implications for ecosystem health.
We invite contributions examining MNP occurrence, transport and retention mechanisms, surface–subsurface connectivity, transformation and remobilisation, interactions and co-transport with other contaminants, biological interactions, exposure, and environmental risk. Field investigations, laboratory experiments, analytical advances, monitoring approaches, numerical and process-based modelling, and risk assessments are particularly encouraged. The session aims to connect researchers across hydrology, hydrogeology, soil and freshwater sciences, environmental chemistry, engineering, and ecotoxicology to advance a process-based understanding of MNP fate and risks across interconnected environmental systems.