Sources, distribution, and environmental effects of microplastics: a systematic review

Microplastics (MPs) are receiving increasing attention from researchers. They are environmental pollutants that do not degrade easily, are retained for prolonged periods in environmental media such as water and sediments, and are known to accumulate in aquatic organisms. The aim of this review is to show and discuss the transport and effects of microplastics in the environment. We systematically and critically review 91 articles in the field of sources, distribution, and environmental behavior of microplastics. We conclude that the spread of plastic pollution is related to a myriad of processes and that both primary and secondary MPs are prevalent in the environment. Rivers have been indicated as major pathways for the transport of MPs from terrestrial areas into the ocean, and atmospheric circulation may be an important avenue for transporting MPs between environmental compartments. Additionally, the vector effect of MPs can change the original environmental behavior of other pollutants, leading to severe compound toxicity. Further in-depth studies on the distribution and chemical and biological interactions of MPs are highly suggested to improve our understanding of how MPs behave in the environment.