Are we underestimating the sources of microplastic pollution in terrestrial environment?

Microplastics (MPs, plastic particles < 5 mm) are an ever-increasing global issue due to their widespread occurrence in the environment and negative effects on organisms. Currently, more than 96 % of MPs studies are related to marine systems. However, the majority of marine MPs pollution has been confirmed to originate from land-based sources, evidence of MPs in the terrestrial system cannot be overlooked. In this manuscript, up-to-date knowledge regarding the sources and occurrence of MPs from the terrestrial system is comprehensively reviewed. According to the different studies both in China and abroad, microfibers derived from textile washing attributed approximately 35 % of the MPs identified in the aquatic system. Additionally, personal care and cosmetic products, tires, agricultural plastic films, artificial turfs and road paints, landfill, littering, packaging and construction industry can also release MPs to the environment. The aquatic system plays an important role in MPs transport. By using a one-way ANOVA test, polypropylene (PP) and polyethylene (PE) accounted for significantly higher percentages than other polymer compositions in surface water. Polyamide (PA) and PP accounted for the majority of polymers in soils. PP, PE, and polystyrene (PS) presented an overwhelming proportion in sediment. Atmospheric deposition presents a new vehicle for entering into the wider environment. More research is urgently required on the topic of exposure risk of atmospheric MPs via inhalation. Morphological characteristics including shapes, sizes, and colors have been discussed among waters, soils, sediments and airborne. These source-occurrence implications continuum summaries can bring us new insights that we cannot underestimate the severity of MPs from land-based sources and should pay more attention to MPs contamination in the terrestrial ecosystem.