Dynamics of interaction and effects of microplastics on planarian tissue regeneration and cellular homeostasis.

• Planarians belonging to Dugesia japonica species were exposed to differently shaped and sized plastic microparticles via the diet. • Planarian feeding activity was not altered by the presence of microplastic mixed in food, irrespectively to the size, shape and chemistry. • The time of persistence of ingested microplastic was affected by size and shape; microplastic with a size below 6 μm were engulfed by enterocytes. • Chronic alimentary exposure to microplastics did not affect regeneration but induced apoptosis and growth delay. Increasing microplastics pollution of marine and terrestrial water is a concerning issue for ecosystems and human health. Nevertheless, the interaction of microplastics with freshwater biota is still a poorly explored field. In order to achieve information concerning the uptake, distribution and effect of microplastics in planarians, Dugesia japonica specimens have been fed with mixtures of food and differently shaped and sized plastic particles. Feeding activity and food intake were non-altered by the presence of high concentrations of different types of plastic particles. However, the persistence of microplastic within the planarian body was a function of size/shape, being small spheres (<10 μm in diameter) and short fibers (14 μm large and 5/6 μm length) more persisting than larger spheres and longer fibers which were eliminated almost entirely by ejection in a few hours. Transmission electron microscopy analysis demonstrated that at least part of microplastics was phagocytized by the enterocytes. Chronic exposure to small plastic did not alter the regenerative ability but caused a significant reduction of the gut epithelium thickness and lipid content of enterocytes, together with the induction of apoptotic cell death, modulation of Djgata 4/5/6 expression and reduced growth rate. The ability of microplastic to perturb planarian homeostasis is concerning being them extremely resilient against mechanical and chemical insults and suggests possible harmful effects upon other more susceptible species in freshwater ecosystems. [ABSTRACT FROM AUTHOR]