Microplastic Pathways: Investigating Vertical and Horizontal Movement from Riverine Environments to Oceans

Abstract Microplastics (MPs) contamination is a global and pervasive problem in the riverine ecosystem, where rivers serve as conduits, transporting microplastics from land-based sources to the ocean. MPs transport is influenced by physical characteristics and hydrodynamics, with high-density MPs likely to be near riverbeds, while low-density particles float over river surfaces. The transport of MPs occurs either due to settling (horizontal transport) or gravity-driven (vertical transport). This study investigates the intricate relationships between sediment transport, hydrological processes, and the behavior of various MPs, with a particular focus on their vertical and horizontal migration in riverine environments. Additionally, the study highlights how the physicochemical properties of MPs influence their transport within these systems. Several removal methods have been developed to mitigate microplastic pollution, including coagulation/sedimentation, adsorption, ultrafiltration, biodegradation, and photocatalytic degradation. These techniques have proven effective in eliminating microplastics composed of polymers such as polystyrene (PS), polyethylene (PE), and polyethylene terephthalate (PET). Among the solutions, biochar and microbial agents stand out as promising, eco-friendly alternatives. Therefore, this study also emphasizes the importance of the development of effective removal of MPs to protect aquatic ecosystems.Keywords: Microplastics; Riverine; Ocean pollution; Vertical; horizontal movement