<p>The widespread applications of plastics in diverse human activities have dramatically increased their production and consumption, making plastic waste a pressing environmental issue worldwide. Ineffective management and disposal practices have led to plastic debris accumulation in aquatic environments across various global regions, from coastal marine systems to inland freshwater bodies. In these environments, plastics can act as sediment-like particles, accumulating on the seabed, being transported by currents, and interacting with natural sediments. This synthetic sedimentation process integrates plastics into sedimentary systems, influencing their dynamics and evolution. In these ecosystems, microbial biofilms have been observed forming on plastic surfaces, creating what is now termed the “plastisphere”. This review delivers a global overview of the plastisphere, focusing on its structural characteristics, ecological functions, and potential toxic effects. It further explores the role of plastics as synthetic sediments, examining how they contribute to sedimentary deposition, erosion, and transport processes. It also underscores the role of resident microorganisms in accumulating contaminants within this unique ecosystem. Drawing from recent studies, we analyze the distribution of key microbial species within the plastisphere across marine and freshwater environments, providing critical insights into their ecological and health implications. The role of plastics in sedimentary environments is also highlighted, discussing how they alter sediment structure, biogeochemistry, and ecological interactions. This study underlines the novelty of understanding plastisphere dynamics, offering recommendations for future research directions and potential mitigation strategies. Ultimately, our review emphasizes that a deeper understanding of plastisphere ecology is essential for addressing the far-reaching impacts of plastic pollutants on both aquatic ecosystems and human health. By positioning plastics as synthetic sediments, this work also contributes to advancing sedimentological research.</p> Graphical Abstract <p></p>