Comparison of Microplastics between Lung Tissues and Intestinal Contents in Finless Porpoises (Neophocaena asiaeorientalis)

Microplastics are ubiquitous environmental pollutants in terrestrial, marine, and atmospheric ecosystems. Plastic inputs into the atmosphere occur through weathering or abrasion, dispersing microplastics globally, which can enter the animals' respiratory systems through inhalation. We analyzed the lung tissues for the first time and the intestinal contents of 11 dead finless porpoises (Neophocaena asiaeorientalis) to assess the intake of microplastics from prey and atmospheric sources. The lung tissues and intestinal contents contained average concentrations of 0.14 ± 0.11 MPs/g and 0.35 ± 0.36 MPs/g, respectively. Microplastics found in the lung tissues and intestinal contents were similar in physical characteristics (e.g., fragment shape, transparent to white color, and size <100 μm). On the other hand, they differed in the polymer types, with a higher proportion of epoxy-type microplastics in the lungs. Epoxy is a highly hazardous polymer according to the polymer hazard index, and in the present study, the lung tissues had a higher plastic hazard index than the intestinal contents. Hence, the respiratory system is more vulnerable to microplastic pollution from atmospheric sources than the digestive system is from water and food intake. These findings underscore the growing threat of airborne microplastics to lung-breathing animals including marine mammals.