Microplastics in aquatic environments: A review on occurrence, distribution, toxic effects, and implications for human health

Microplastics (MPs) are fragments, fibers, granules, flakes and spheres with a diameter or length of less than 5 mm. These may eventually end up in the aquatic environment by the progressive breakdown of larger plastics or via domestic and industrial sewage spillage. In order to better understand the current knowledge in this field, we carried out and extensive literature research to retrieve articles mainly focusing on the occurrence and distribution of MPs in aquatic matrix as well as their impacts on aquatic organisms and human derived cells. Once in the environment, MPs may be transported via wind and water movement, affecting their spatial distribution. Furthermore, density may also affect the buoyancy and vertical distribution of these pollutants. Consequently, MPs are ubiquitously distributed in fresh- and marine- water systems, posing a real threat to aquatic organisms. Furthermore, trophic transfer and biomagnification processes represent a viable route for the input of MPs to humans. This paper focuses on (1) Outline the occurrence of MPs in worldwide aquatic ecosystems; (2) Investigate the factors affecting the abundance and distribution of MPs in aquatic ecosystems; (3) Provide an in-depth discussion about the harmful effects that MPs poses to aquatic organisms; (4) Summarizes the possible mechanisms by which MPs may induce toxic effects on humans.