Target particle size will depend on the aim of individual studies. Aims may include potential health effects on individuals, their populations or consumers such as humans. Observations from the natural environment suggest that microplastics are ingested by bivalves beyond the size of their natural prey particles. Particle retention of M. gigas is highest between 4 and 12 μm and reported absent for particles of 15 μm. Van Cauwenberghe and Janssen (2014) found mainly microplastics <25 μm in M. gigas, but larger items were also present. Rochman et al(2015) found fibres between 2300 and 15,800 μm in length in M. gigas. Fibre length may not be crucial for microplastic size determination as the particle could be present compacted or knotted up. However, diameters of those fibres were 20 to 50 μm. In addition, Courtene-Jones et al(2017) found fragments and film >52 μm in M. edulis., a species with a particles retention range of 2–12 μm . In a laboratory setting, the ribbed mash mussel Geukensia demissa ingested microbeads of 250–300 μm in size, which is beyond their usual feeding range.