Homogenization of microplastics in alpine rivers: Analysis of microplastic abundance and characteristics in rivers of Qilian Mountain, China.

Microplastics in remote areas has received increasing concern in recent years. However, studies on microplastics in alpine rivers and their affecting factors are still limited. In this study, we investigate the abundance and characteristics of microplastic in the surface water of five alpine rivers in Qilian Mountain, China. Utilizing sieve collection, digestion and density separation, along with microscopy and Raman spectroscopy analyses, microplastics were observed in all the water samples and the average abundance of microplastics was 0.48 ± 0.28 items/L, which was lower than in other freshwaters. Transparent (37.3%) and fibrous (72.1%) microplastics were predominant. Polypropylene (53.8%) was the most frequently identified polymer type. Analysis of similarities (ANOSIM) and linear discriminant analysis (LDA) based on microplastic shape, color, and polymer type showed that there was no significant difference in the microplastic characteristics among rivers of Qilian Mountain. The distance decay models revealed that the similarity in microplastics characteristics was not affected by changes in watershed characteristics, such as geographical distance, elevation, water quality, and land use. This finding suggests that the primary source of microplastics in Qilian Mountain rivers could be from dispersed origins. The results of this study indicated that despite remote alpine rivers suffering limited anthropogenic impacts, they were not immune to microplastics. However, in watersheds with lower intensity of human activity, the abundance and characteristics of microplastics in water bodies may be more uniformly distributed and controlled by diffusion conditions such as atmospheric transport or riverine transport. Our investigation unveils novel understanding of microplastic dispersion in secluded alpine territories, emphasizing the crucial need for managing atmospheric transport of microplastics within conservation areas.