Systemic distribution and transplacental transfer of micro- and nanoplastics in a filter-feeding marine predator

Micro- and nanoplastics (MNPs) are pollutants of global concern, yet their internal distribution and potential for maternal transfer in large marine vertebrates remain poorly understood. In this study, we assessed the presence and concentration of MNPs in the internal tissues of 13 North Atlantic fin whales ( Balaenoptera physalus ), a migratory filter-feeding marine predator. Using fluorescence-based nanocytometry with Nile Red staining, we detected MNPs in the kidney, liver, lung, and skeletal muscle of the whales, with the highest concentrations observed in the lung and skeletal muscle, in which we found a negative correlation with age. Thus, tissue type and age significantly influenced the MNP load in these tissues, while body size and reproductive state showed no detectable effect, considering our limited sample size. Furthermore, a subset analysis comparing five pregnant females and their foetuses revealed significantly lower MNP concentrations in foetal tissues, yet it confirmed the occurrence of transplacental transfer. These findings provide the first evidence of systemic distribution of nanoplastics in baleen whale tissues, while corroborating previous observations of microplastic presence, and indicate that even early developmental stages may be vulnerable to plastic exposure. Given the whales’ filter-feeding behaviour and seasonal movements across pollution gradients during their seasonal migration, these findings underscore the likelihood of persistent exposure to plastic particles and the need to better understand the drivers of tissue concentration as well as the toxicological effects of MNPs on marine megafauna. • Evidence of systemic micro- and nanoplastic (MNP) loads in fin whale tissues • Muscle and lung showed the highest MNP concentrations across tissues • MNP concentrations declined with age in muscle and lung, not in liver or kidney • Transplacental transfer of MNPs confirmed in fin whale foetal tissues