Research progresses and prospects of microplastics in the environment

The term “microplastics” (MPs) refers to fine plastics less than 5 mm in size and includes primary sources from the original production of small-sized particles and secondary sources from the degradation or fragmentation of large plastics. MPs have been widely detected in marine (estuaries, bays, coastal zones, deep seas, ocean waters and sediments), soils (farmlands, urban soils, wetlands, landfill and polar areas), freshwater (lakes, rivers, reservoirs, snow and ice, and sewage treatment plants) and sediments, atmosphere (outdoor and indoor airs), living organisms (plants, animals, microorganisms, human and pet faeces), and foods (table salts, drinking waters, beers, vegetables and pet foods). Besides, MPs could be acted as the vector for many environmental pollutants, pathogens and even antibiotic resistance genes (ARGs). Moreover, MPs can be taken up by various terrestrial and aquatic organisms and transfer along the food chain at various trophic levels. Thus, environmental MP pollution is becoming one of the most serious threats to the Earth’s surface ecosystems which has attracted serious concern and extensive research by many governments and the scientific community worldwide. Up to now, comprehensive studies and reports on the latest multidisciplinary research progress on microplastics in multiple environmental media remain limited. From the perspectives of earth sciences, chemistry, biology, and management, this article systematically reviews the research progress on the abundance, distribution and sources of microplastics in the waters, soils, atmosphere, sediments and organisms; the separation and analytical methods of microplastics in multiple environmental media; the migration and prediction of microplastics in terrestrial, marine and atmospheric environments; the surface changes and biofilm formation on microplastics and their adsorption characterization of environmental pollutants, pathogens and ARGs; the biological uptake, accumulation and ecological risks of MPs; the food chain transfer and health risks of MPs; the physico-chemical fragmentation and biodegradation of MPs in the environment and their risk reduction strategies and techniques. Finally, the key scientific issues and future research directions of environmental microplastics are also proposed in this review, such as methdology breakthroughs in separation and identification of submicron and nanoscale microplastics; comprehensive study on the distribution, migration, transport and flux of microplastics in environmental multi-media at cross-reginal and global scale; comprehensive monitoring, quantitative characterization and long-term evaluating the impacts of environmental microplastics on ecosystems; and the systematic assessment of human health risks of microplastics to different populations.