Potential risk of microplastics in plateau karst lakes: Insights from metagenomic analysis

Microplastic (MP) pollution has become one of global concern. While MP pollution in lakes has been well studied, research on MP sources, distribution, and ecological risks in the Tibetan Plateau is limited. We systematically investigated the MP abundance and distribution in alpine travertine lakes in Jiuzhai nature reserve located in east edge of Qinghai-Tibetan Plateau and assessed the distributions of microbiomes, antibiotic resistance genes (ARGs), and virulence factor genes (VFGs) in water, sediments, and MPs, using macrogenomics. MP abundance was 20.27-58.80 n/L in water and 583.33-996.67 n/kg in sediments. MPs were dominantly fibrous and transparent. The particle size distribution was 0.1-0.5 mm for MPs in water, and 0.5-1 mm in sediments. MPs were mainly composed of polyethylene and polyethylene terephthalate. The microbial community of MP biofilms differed from that in the surrounding environmental medium, and Proteobacteria were more abundant in biofilm than in water and sediment. MP biofilms exhibited more cooperative behavior with microorganisms in water than with those in sediments. MPs were selectively enriched for ARGs and VFGs, and MP biofilms had a higher diversity of ARGs, the most abundant isoform being msbA, which is a multidrug resistance gene. VFGs were more abundant in MP biofilms than in water and sediment. The study results are useful for understanding MP sources and ecological risks in plateau karst lakes and provide a valuable dataset and theoretical basis for studies on MP pollution in other alpine calcareous lakes.