Microplastic migration and distribution in the terrestrial and aquatic environments: A threat to biotic safety.

Plastics production has been increasing over years, while their recycling rate is lower, resulting in huge amounts of microplastics (MP) accumulating in the environment. Although the environmental behaviors of MPs have been focused on in recent years, the migration, distribution and adverse effects of MPs in terrestrial and aquatic environments are still not systematically understood. In this review, based on the newest publications from the core database of the Web of Science, both the migration and distribution of MPs were summarized, as well as MPs transfer in biota and their biological effects were also focused on. Generally, the complicated and numerous pathways of MPs migration lead to their distribution throughout or nearly all environments on a global scale. However, the migration mechanisms of MPs with various sizes, shapes, and colors by physicochemical and biological processes, and the prediction models of MP migration and distribution, are deficient, despite these properties being highly related to MPs migration and bio-safety. Although MPs have already invaded microorganisms, plants, animals, and even human beings, the biological effects still need more study, so far as their sizes and shapes and also their composition and adsorption are concerned. Moreover, based on the highlights and deficiencies of current studies, further studies have also been proposed. This review aims to help people re-evaluate the uncertain behaviors of MPs in various environments, and could be helpful to fully understand their biological effects in different environmental conditions.

Microplastics change the leaching of nitrogen and potassium in Mollisols.

Nowadays, the dynamics of nutrients leaching from the soils and their driving mechanism have been focused on, however, it is still unclear how microplastics (MPs) influence the nutrients' leaching in soils. In this study, five concentrations (w/w, 0.0 %, 0.5 %, 1 %, 2 %, 3 %) and three sizes of MPs of polyethylene (PE) (0.15-0.36 mm, 0.36-0.60 mm and 0.60-1.00 mm) influencing the leaching of NO3--N and water-soluble potassium (WSK) was simulated by a column method in Mollisols, and both the pre-fertilization and post-fertilization were considered. The results showed that, before KNO3 addition, there was a negative power function relationship between the NO3--N concentration and the leaching solution volume/leaching time. The amount and concentration of NO3--N leaching was higher in the early leaching stage. Compared with the CK, PE0.5% significantly reduced the leaching amount of WSK, while increased the leaching amount of NO3--N but not significantly. The leaching amount of WSK decreased with the increasing size of PEMP when the PEMP concentration was the same, while NO3--N was opposite. PE0.60-1.00 increased the leaching amount of NO3--N, while reduced the leaching amount of WSK. After KNO3 addition, compared with CK, PE1% significantly reduced the leaching amount of NO3--N, and PE1% had the lowest leaching amount of WSK. However, when the PEMP concentration in the soil reached a certain threshold (w/w, >1 %), the leaching amount of NO3--N and WSK increased gradually with PEMP increasing. PE0.60-1.00 reduced the leaching amount of NO3--N and WSK most obviously. In general, low concentrations (w/w, <1 %) and large sizes (0.60-1.00 mm) of PEMP promoted NO3--N leaching and inhibited the WSK leaching from the soil before the addition of KNO3, however, they both inhibited the leaching of NO3--N and WSK from the soil after addition of KNO3.

Heterogeneity of plastic residue was determined by both mulch film and external plastic pollutants in the farmland of Northeast China.

Plastic pollution in farmland ecosystems has been widely concerned. However, the heterogeneity and driving mechanisms of plastic residue (PR) remain unclear in the farmland surrounded by complex pollution points. In this study, the abundance, mass, and accumulation areas of PR of mulch film (MF) and non-MF (NMF) were investigated in a large area of the vegetable field covered by plastic mulching in a long-term in Northeast China. Geostatistics combined with classical statistics were used to clarify how pollution source and migration factors change the PR heterogeneity in the farmlands. Results indicated that the MF type was only polyethylene (PE) (79.1 % of total PR), while NMF accounted for 20.9 % of total PR. As well, NMF-polypropylene (PP) and NMF-PE accounted for 45.3 % and 39.7 % of total NMF respectively, followed by polystyrene accounting for 7.5 %. In the 0-20 cm soil layer, the spatial autocorrelation of mass and accumulation areas of MF were significantly (p < 0.05) positive, and their spatial pattern tended to cluster. The accumulation areas of MF was predoniment in northwest and southeast near the roadside in all soil layers, while the accumulation areas of NMF was higher near the landfill in the 0-20 cm soil layer. Landfill and residential areas were critical sources of PR for the farmland. Southwest wind and southeast wind were the main driving force of PR migration and their annual migration rates were 23.7 and 19.8 m·year-1. The functional groups on the surface of plastics were different after degradation (including different types and different utilization methods), and PR was oxidized could release or adsorb toxic substances from the soils. Generally, in order to reduce PR pollution, in addition to source control and recycling, farmland tillage should be avoided in the weather when the wind speed is strong, especially near the PR pollution source.