Microplastic source-sink coupling in water-sediment-fish intestine systems and its effects on fish reproductive...

Understanding the migration pathways of microplastics (MPs) in freshwater ecosystems and their associated risks to aquatic reproductive health is critically needed. This study investigated these processes in Baiyangdian, a typical large shallow lake. MPs were analyzed in water, sediment, and intestines from two habitat-differentiated fish species-the benthic Carassius auratus and the water column-dwelling Pseudorasbora parva. Across all compartments, 31 polymer types were identified, with 20 common to all media. Small particles (< 100 μm) were significantly more abundant than large ones (> 100 μm) in each compartment. Principal coordinates analysis (PCoA) and SourceTracker indicated that there was no significant difference between MPs in C. auratus intestines and those in sediment, and the proportion of intestinal MPs derived from sediment was significantly higher than that from the water column (P < 0.05). MPs in P. parva intestines differed significantly from both water and sediment, with the majority (> 80%) attributed to unassigned sources. Boosted Regression Trees (BRT) analyses revealed species-specific patterns: sediment and intestinal MPs showed higher relative importance for reproductive parameters in C. auratus, and water and intestinal MPs in P. parva. Multiple Linear Regression (MLR) identified specific polymers as key risk factors, with effect directions largely consistent with the overall medium-level associations identified by BRT. Integrating multivariate statistical and modeling approaches, this study characterizes MP transfer from environmental compartments to fish and assesses associations with reproductive parameters under field conditions. These findings underscore the necessity of incorporating pollutant sources and biological exposure pathways into ecological risk assessment frameworks.