Exposure pathway derived accumulation of microplastics in freshwater fish: A critical review

Microplastic (MP) pollution poses an emerging ecological threat to freshwater ecosystem and ichthyofauna. However, the understanding of tissue-specific MP accumulation in fish remains limited. To clarify the relationship between exposure pathways, target organs, and differential accumulation, this review synthesizes evidence from 78 peer-reviewed field and laboratory studies on MP distribution in freshwater fish tissues. By establishing an exposure-pathway framework based on receptor organs, we demonstrate that the gastrointestinal tract (GT) shows the highest MP accumulation, with a real-world mean abundance of 6.57 items/g and an artificial exposure BCF value of 37.7, highlighting oral ingestion as the dominant source for MP burden in freshwater fish. Key factors influencing exposure pathway-derived MP accumulation include MP characteristics (e.g., color, shape, and size), fish biology (e.g., feeding habits, gill structure, and reproductive strategies), and environmental conditions (e.g., water flow velocity, and turbidity). The influence weights of different factors vary significantly across exposure pathways. Uniquely, this review integrates exposure pathways with organ-specific accumulation patterns, providing quantitative data on MP accumulation in freshwater fish from both field and laboratory studies. The findings provide key guidance for predicting MP exposure levels in specific fish species, assessing trophic-level ingestion risks, and selecting sentinel species in different exposure scenarios. It also offers a framework for future study on tissue-specific toxic response, such as intestinal damage, respiratory dysfunction, and reproductive impacts. Overall, this work enhances understanding of MP-fish interactions, providing a foundation for future monitoring of freshwater ecosystems and predicting human health risks associated with freshwater fish consumption.