Tissue-specific microplastic burden in cetacean non-digestive organs

Revealing the microplastic (MPs) pollution characteristics and influencing factors in multiple tissues of cetaceans is an essential and fundamental effort and significant research gap to alleviate the pollution pressure on marine mammals. This study investigated MPs pollution in non-digestive tissues of nearshore (Neophocaena phocaenoides) and offshore (Peponocephala electra) cetaceans. The results revealed widespread MPs accumulation across various non-digestive tissues, with an average detection rate >75 % in both species, and the dose-response model showed low abundance but widespread pollution. The MPs feature-based analysis indicated no significant separation of inter-species MPs. And the Simpson index revealed that the tissue-specific diversity difference (0.32) was higher than that of species-specific (0.01), highlighting the impact of tissues on MPs features. The clustering analysis results indicated that the characteristics of MPs between tissues with similar physiological functions are more similar, like the heart and liver. Differential correlation between the diversity (affected by pollution source) and abundance of MPs in nearshore and offshore species, indicating the potential effectiveness of pollution source control in reducing MPs in nearshore rather than offshore species. This study emphasizes the importance of non-digestive tissue-specific MPs accumulation patterns and the necessity of multi-tissue investigation to reveal the true MPs pollution in cetaceans.