[Effect of Polyethylene Microplastics on the Microbial Community of Saline Soils].

Mulching to conserve moisture has become an important agronomic practice in saline soil cultivation, and the effects of the dual stress of salinity and microplastics on soil microbes are receiving increasing attention. In order to investigate the effect of polyethylene microplastics on the microbial community of salinized soils, this study investigated the effects of different types (chloride and sulphate) and concentrations (weak, medium, and strong) of polyethylene (PE) microplastics (1% and 4% of the dry weight mass of the soil sample) on the soil microbial community by simulating microplastic contamination in salinized soil environments indoors. The results showed that:PE microplastics reduced the diversity and abundance of microbial communities in salinized soils and were more strongly affected by sulphate saline soil treatments. The relative abundance of each group of bacteria was more strongly changed in the sulphate saline soil treatment than in the chloride saline soil treatment. At the phylum level, the relative abundance of Proteobacteria was positively correlated with the abundance of fugitive PE microplastics, whereas the relative abundances of Bacteroidota, Actinobacteriota, and Acidobacteria were negatively correlated with the abundance of fugitive PE microplastics. At the family level, the relative abundances of Flavobacteriaceae, Alcanivoracaceae, Halomonadaceae, and Sphingomonasceae increased with increasing abundance of PE microplastics. The KEGG metabolic pathway prediction showed that the relative abundance of microbial metabolism and genetic information functions were reduced by the presence of PE microplastics, and the inhibition of metabolic functions was stronger in sulphate saline soils than in chloride saline soils, whereas the inhibition of genetic information functions was weaker than that in chloride saline soils. The secondary metabolic pathways of amino acid metabolism, carbohydrate metabolism, and energy metabolism were inhibited. It was hypothesized that the reduction in metabolic functions may have been caused by the reduced relative abundance of the above-mentioned secondary metabolic pathways. This study may provide a theoretical basis for the study of the effects of microplastics and salinization on the soil environment under the dual pollution conditions.

[Effect of Microplastics on Soil Water Infiltration and Evaporation].

In order to explore the influences of microplastics with different abundances (0.5%, 1%, and 2% of the dry weight of the soil) and different types (PP, PVC, and PE) on the moisture infiltration and evaporation of the soil, we adopted the method of indoor soil column simulation to elaborate the influences of the microplastics with different abundances and different types on the moisture accumulated infiltration time, moisture containing rate, wetting front, and evaporation characteristics, among which the A1, A2, and A3; Q1, Q2, and Q3; and Z1, Z2, and Z3 respectively represented the experimental number of PE, PVC, and PP under the abundances of 0.5%, 1%, and 2%. The influences of the microplastics with different types and different abundances on the moisture infiltration and evaporation of the soil showed obvious differentiation. Under the same types of conditions, when the abundances of the microplastics increased, the accumulated infiltration time also increased significantly. However, under the occurrence condition of the microplastics of different types but the same abundances, the accumulated infiltration time of the PP experiment group>that of the PVC experiment group>that of the PE experiment group>that of the blank experiment group. Under the occurrence condition of microplastics, the maximum moisture rate of the soil basically appeared at the depth from 10 to 25 cm, and the CK of the blank group appeared at the depth from 20-25 cm. Within the same infiltration time, when the abundances of the microplastics increased, the moving distance and the moving rate of wetting front of the soil decreased accordingly. When the infiltration time was 60 minutes, the wetting moving distances of A1, A2, and A3; Q1, Q2, and Q3; and Z1, Z2, and Z3, respectively, decreased 4.38%, 8.76%, and 10.58%; 7.30%, 10.22%, and 14.60%; and 10.95%, 13.14%, and 15.33% compared to those of the CK groups, among which the influence of PP microplastics was the most significant. The occurrence of the microplastics had a prohibition function to the moisture evaporation of the soil; when the microplastics had the same types, the accumulated amount of the soil decreased with the increase in abundance. When evaporating for 27 hours, the accumulated evaporation amount of the experiment soil column of PP, PVC, and PE microplastics with the added abundances of 2% respectively decreased 22.9%, 19.4%, and 13.3% compared to that in the CK. The Rose evaporation model relatively truly reflected the changing situation of the soil accumulated evaporation amount with time under the occurrence situation of the microplastics. This research can provide a theoretical basis for the changing study of the soil moisture movement under the occurrence condition of microplastics.

[Distribution Characteristics of Microplastics in Ice Sheets and Its Response to Salinity and Chlorophyll a in the Lake Wuliangsuhai].

There are sparse reports on the distribution of microplastics in the ice sheets of freshwater lakes. In this study, the abundance, color, shape, and species of microplastics in the ice sheet of Lake Wuliangsuhai were characterized using field sampling and microscope observations. Fourier-transform infrared spectroscopy (FTIR) and correlation analysis were used to examine the distribution of microplastics contained in the lake and its relationships with salinity and chlorophyll a. The results show that the average abundance of microplastics in the Lake Wuliangsuhai ice sheet is 56.75-141 n·L-1, which is approximately 10-100 times higher than in the surface water of the Lake Wuliangsuhai. Fibers were the most common type of microplastics followed by fragments. Overall abundance showed a decreasing trend in the downstream horizontal direction and was positively correlated with salinity in the vertical direction. The abundance of microplastic in the surface ice and bottom ice was greater than in the middle of the ice and near bottom of the ice. There was no correlation between the abundance of microplastic and the concentration of chlorophyll a. In addition, due to the capturing effect of the ice, microplastic particles are temporarily stored in the ice sheet in winter, which are released into water in spring. This study provides baseline information to inform microplastic pollution control measures in Lake Wuliangsuhai.

[Occurrence Characteristics and Quality Estimation of Microplastics in Drainage Ditches in Hetao Irrigation District of Inner Mongolia].

Microplastic pollution due to land runoff has gained increasing attention as it is closely associated with human beings. In this study, we analyzed the occurrence characteristics of microplastics in drainage channel and main drainage channel in Hetao irrigation district of Inner Mongolia and estimated its quality. Through field sampling, the density separation of suspension method and microscope observation, Fourier infrared spectrum measurement, and proportional flow method, the abundance distribution, shape, color, particle size, and chemical composition of microplastics in the water body and sediment of the drainage channel and main drainage channel in the Hetao irrigation district were identified. The mass of microplastics transported in the main drainage channel was also estimated. The results showed that the value range of microplastic abundance in the water body of the drainage channel and the main drainage channel in Hetao irrigation district was 2880-11200 n ·m-3, and the value range of microplastic abundance in the sediment was 100-292 n ·kg-1. Fiber was the most common microplastic form, occupying 34.98%-70.39% and 42.24%-58.56% in the water and sediment, respectively. The color of microplastics was mainly transparent, which occupied 46.43%-61.51% and 40.41%-57.44% in the water and sediment, respectively. The largest particle size of microplastics was<0.5 mm, accounting for 46.43%-61.51% and 43.27%-54.79% in the water and sediment microplastics, respectively. It was concluded that polyethylene was the most common type (43%), followed by polystyrene (34%) and polypropylene (16%) using Fourier infrared spectroscopy. It was estimated that the main drainage channel in the Hetao irrigation district could transport 116.06 kg of microplastics into Lake Ulansuhai every day, and a serious microplastic pollution effect was generated due to the accumulation of microplastics in Lake Wulangsuhai. This study can provide reference for the pollution of microplastics in Hetao irrigation district of Inner Mongolia.