Co-occurrence of microplastics and heavy metals in sediments of the Lanzhou section of the Yellow River: Distribution characterizations and comprehensive ecological risk assessment

Microplastics (MPs) and heavy metals (HMs) are significant pollutants in river ecosystems. Their coexistence can lead to synergistic toxic effects and increase environmental risks. Therefore, a risk assessment was carried out, involving optimization of the two-dimensional comprehensive index (TPI) model for MPs-HMs co-contamination and analysis of their distribution characteristics in sediments from the Yellow River's Lanzhou section. The results showed that the highest pollution levels were observed for Cu and Cd. The abundance of MPs in the sediments ranged from 243.00 ± 9.92-4289.33 ± 215.22 items/kg, with the dominant forms being fragmented, white/translucent, and <100 μm. Additionally, risk assessment revealed substantial ecological threats, evidenced by an elevated shape risk index (SRI) of MPs at 1122.54 and a potential risk index (MRI) of HMs at 241.45. The mean value and risk level of the integrated TPI model were 344.08 ± 14.58 and 6 respectively, confirming severe composite pollution. The results of this study enhance the methodological framework for assessing combined pollutant toxicity and provide critical insights for ecological risk management in urban river systems.