Comparative analysis of microplastics in aquatic environments: Matching thresholds, abundance versus mass...

Microplastic (MP) pollution assessment faces critical challenges from methodological inconsistencies in detection and risk evaluation frameworks. This study conducts a comparative analysis using water and sediment samples from a karst region in Southwest China to address three key aspects: quantification of MP characterization disparities under differing spectral matching thresholds (0.600 vs. 0.800); comparative assessment of abundance versus mass concentration metrics; and evaluation of five distinct ecological risk assessment methodologies. Results showed that lowering matching threshold significantly increased MP types and abundances, reshaping spatial patterns and polymer rankings and thereby indicating higher risk levels. Crucially, abundance and mass concentration metrics yielded conflicting assessments. Risk assessment comparisons revealed systematically higher risk categorizations by traditional indices: pollution load index, polymer hazard index, and ecological risk index classified >83.0 % of sites as high-risk, whereas ecotoxicity-based methods including risk quotient (RQ) and ecological risk quotient (ERQ) indicated only 25.0 % of sites posed high risk. This highlights the comparative advantage of RQ/ERQ frameworks incorporating species sensitivity distributions and probabilistic MP diversity adjustments. Consequently, this study provides a new standardized methodological framework, establishing that the 0.800 matching thresholds, dual metric reporting (abundance and mass), and ecotoxicity-based risk indices are essential for accurate MP pollution characterization and mitigation prioritization globally.