Size-dependent elimination of ingested microplastics in the Mediterranean mussel Mytilus galloprovincialis.

Filter feeding organisms have been reported to ingest microplastics (MP) in marine environments. However, information regarding how long the ingested MPs are retained in their digestive tracts remains limited. Here, we report the gut retention time (GRT90) and the long-term egestion time of three different sized polystyrene microspheres (1, 10, and 90 μm) in the Mediterranean mussel Mytilus galloprovincialis. We found significant differences in GRT90 with respect to MP size. With respect to the long-term egestion of MPs, most of the smaller MPs were excreted immediately, although some were detected intermittently until day 40. In comparison, larger MPs were slowly excreted in bulk, after which they were not detected. The results indicate that different sized MPs are retained differently in the digestive tract of mussels. The size-dependent effects of MPs should thus be considered when evaluating the effects of MPs in mussels.