Occurrence, sources, and impact mechanisms of soil microplastics and adsorbed heavy metals in the Ebinur Lake Basin, northwest China

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.