Microplastic is an umbrella term that covers particles with various physical and chemical properties.
However, microplastics with a consistent shape, polymer type and size are generally used in exposure
studies (e.g., spherical polyethylene or polystyrene beads 1e100 mm in size). In the present study, we
exposed freshwater Asian clams (Corbicula fluminea) to microfibers with different physicochemical
properties at concentrations of 100 and 1000 fibers/L. The first experiment in this study exposed clams to
microfibers made from six different polymers, demonstrating that Asian clams uptake more polyester
(PET) (4.1 items/g) relevant to other polymers. The next experiment exposed clams to PET fibers of
different size classes, demonstrating that uptake in the size range 100e250 mm (1.7 items/g) was greater
than other size classes. These results suggest that physicochemical properties such as polymer and size
play important roles in the uptake of microfibers by organisms. Thus, we strongly suggest that the
properties of microplastics used in future laboratory exposure experiments be considered, with the aim
of being “environmentally relevant”, i.e., similar to what is found in nature.