There is a lack of research on soil microplastics in arid oases considering the rapid economic development of northwestern China. Here, we studied the occurrence and sources of microplastics in soil, as well as the relationships between microplastics and adsorbed heavy metals in the Ebinur Lake Basin, a typical arid oasis in China. Results showed that (1) the average microplastic content in all soil samples was 36.15 (±3.27) mg/kg. The contents of microplastics at different sampling sites ranged from 3.89 (±1.64) to 89.25 (±2.98) mg/kg. Overall, the proportions of various microplastic shapes decreased in the following order: film (54.25%)>fiber (18.56%)>particle (15.07%)>fragment (8.66%)>foam (3.46%); (2) among all microplastic particles, white particles accounted for the largest proportion (52.93%), followed by green (24.15%), black (12.17%), transparent (7.16%), and yellow particles (3.59%). The proportions of microplastic particle size ranges across all soil samples decreased in the following order: 1000-2000 µm (40.88%)>500-1000 µm (26.75%)>2000-5000 µm (12.30%)>100-500 µm (12.92%)>0-100 µm (7.15%). FTIR (Fourier transform infrared) analyses showed that polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC), polyethylene (PE), and polystyrene (PS) occurred in the studied soil; (3) random forest predictions showed that industrial and agricultural production activities and the discharge of domestic plastic waste were related to soil microplastic pollution, in which agricultural plastic film was the most important factor in soil pollution in the study area; and (4) seven heavy metals extracted from microplastics in the soil samples showed significant positive correlations with soil pH, EC, total salt, N, P, and K contents (P<0.01), indicating that these soil factors could significantly affect the contents of heavy metals carried by soil microplastics. This research demonstrated that the contents of soil microplastics are lower than other areas of the world, and they mainly come from industrial and agricultural activities of the Ebinur Lake Basin.

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Effective selenium is an important indicator for evaluating the supply capacity of selenium to plants in soil. The chemical extraction method and soil solution method have been applied to determine available selenium in soil, but it is not clear whether they can be applied to evaluate selenium bioavailability in natural selenium-rich soil. To explore the feasibility of using gradient diffusion film technology to evaluate the bioavailability of selenium in natural selenium-rich soil, the natural selenium-rich soil distributed in the Yanqi Basin of Xinjiang was taken as the research object, and the chemical extraction method, soil solution method, and DGT technology were employed to evaluate the bioavailability of selenium in the soil. The results showed that: ① The average content of CDGT measured by Fe-oxide DGT was 0.19 ± 0.083 µg/L, and the average content measured by Zr-oxide DGT was 0.25 ± 0.11 µg/L. The difference in available selenium content measured by the two types of DGT was not significant, however, because Zr-oxide DGT had specific adsorption characteristics for Se4+, Zr-oxide DGT could not effectively reflect the selenium content level in plants. For the determination of soil selenium bioavailability, Fe-oxide DGT was better than Zr-oxide DGT; ② The selenium content in plants Cplant-Se and the effective selenium content measured by the three methods were significantly positively correlated, but the correlation coefficient (r = 0.6805) of the effective selenium content measured by Cplant-Se and Fe-oxide DGT was greater than that measured by the other two methods; ③ The R-value (the ability of soil particles to supplement selenium to soil solution) and Kd value (the distribution coefficient between soil solid and liquid phases) calculated based on the DGT technology indicated that the soil selenium in the Hejing County research area had stronger mobility than that in the Heshuo County research area, however, the rate of the supplement of selenium ion to soil solution by soil solid phase was smaller than that of Heshuo County research area. In summary, the DGT method was superior to the chemical extraction and soil solution methods in terms of the evaluation of selenium bioavailability in natural selenium-rich soil, and had more advantages in testing the performance and reflecting the information of the soil dynamics process.

Due to the lack of research on organic pollutants in snow water and the rapid economic growth of oasis cities in dry areas, this study looked at the pollution characteristics and sources of organophosphorus flame retardants in the urban snow of Urumqi, a typical oasis city. The results showed that: (1) The average (mean) values of 10 organophosphorus flame retardants detected in the snow of Urumqi from 2019 to 2022 were TMP-50.09(45.52) ng/L, TEP-41.79(39.75) ng/L, TnBP - 41.48(43.32) ng/L, TEHP - 69.19(65.64) ng/L, TCEP - 64.64 (61.21)ng/L, TCPP-78.20(72.32) ng/L, TDCPP-140.62(132.22) ng/L, TCP-28.61(25.67) ng/L, TPhP - 29.83(31.22) ng/L, and EHDPP-6.21(8.65) ng/L, respectively. (2) According to an analysis of the single factor pollution index and comprehensive pollution index, the single factor pollution index values for TCEP, TCPP, and TDCPP in 2020, TCPP and TDCPP in 2021, and TCEP, TCPP, and TDCPP in 2022 are all larger than 1, which results in pollution. 10 organophosphorus flame retardants' complete pollution index values were found in the snow in Urumqi. The composite index value for January, February, and December of 2019 was 4.56, which is considered to be extremely high pollution. The overall index value of 3.16 in January, February, and December of 2022 indicated severe pollution, whereas other years belonged to low to moderate pollution levels. (3) The health risk assessment of organophosphorus flame retardants in snow showed that the ADDs of 10 OPEs ranged from 29.87 to 34.22 ng/(kg·d) under the average exposure level, and from 30.92 to 48.39 ng/(kg·d) under the high exposure level. The ADDs of 10 OPEs were much below the threshold for carcinogenic and non-carcinogenic risk computation, falling between 1.00×10-2 and 10-6 range. (4) Based on PCA and correlation analysis, we know that PC1 (TBOEP, TCPP, TCEP, TDCPP and EHDPP) is primarily from atmospheric migration and dry and wet deposition; PC2 (TMP, TEP and TPhP) mainly comes from VC materials and thermoplastic synthetic rubber; PC3 (TnBP and TCP) largely comes from atmospheric transport and dry and wet deposition.

There is a lack of research on soil microplastics in arid oases considering the rapid economic development of northwest China and Central Asia. Here, we studied the occurrence forms, pollution status, and sources of microplastics in soils, as well as the relationship between microplastics and adsorbed heavy metals in the Ebinur Lake Basin, a typical oasis in an arid area. Results showed that (1) the average microplastic content in all soil samples was 36.15 ± 3.27 mg/kg. The contents of microplastics at different sampling points ranged between 3.89 ± 1.64 and 89.25 ± 2.98 mg/kg. Overall, the proportions of various microplastic shapes diminished in the order: film (54.25%) > fiber (18.56%) > particle (15.07%) > fragment (8.66%) > foam (3.46%). (2) Among all microplastic particles, white particles accounted for the largest proportion (52.93%), followed by green (24.15%), black (12.17%), transparent (7.16%), and yellow particles (3.59%). The proportions of microplastic particle size ranges across all soil samples diminished in the order: 1000–2000 µm (40.88%) > 500–1000 µm (26.75%) > 2000–5000 µm (12.30%) > 100–500 µm (12.92%) > 0–100 µm (7.15%). FTIR analyses showed that PET, PP, PC, PE, and PS occurred in the studied soils. (3) Random forest predictions showed that industrial and agricultural production activities and the discharge of domestic plastic waste were related to soil microplastic pollution. Agricultural plastic film was the most important factor in soil pollution in the study area. (4) Seven heavy metals extracted from microplastics in soil samples showed significant positive correlations with soil pH, EC, and total salt, N, P, and K contents (p < 0.01), indicating that these soil factors could significantly affect the contents of heavy metals carried by microplastics.