Microplastics have been found to adhere to the surface of specific tissues or organs other than being
ingested by the organisms. To further test the hypothesis that microplastics might get into specific body
parts of organisms, mussel byssus was chosen as a target subject in the present study. In the field
investigation, microplastics were found in mussel byssus, and the abundance of microplastics was 0.85
e1.02 items/individual mussel and 3.69e9.16 items/g byssus, but the location of microplastics in byssus
was not easily determined. Therefore, we simulated environmental conditions in the laboratory for
mussels to form fresh byssus in the presence of microplastics. Three types of man-made microplastics
(Polystyrene beads, Polyamide fragments, and Polyester fibers) were found in newly formed byssus of
mussels after exposure to these test materials. We observed that microplastics not only adhered to the
surface but also fused into the byssus of mussels. Since byssus is important for the well-being of mussels,
the incorporation of microplastics into the byssus might impair the function of byssus. To the authors’
best knowledge, this is the first study to show that microplastics can contact and fuse with the byssus of
mussels during their formation, suggesting possible alternations for mussels to grip and interact with
microplastics in the aquatic environments.