Seite - 159 - in Freshwater Microplastics - Emerging Environmental Contaminants?

between themaximumingestibleparticle sizeand theoverall sizeof several clado- ceran and protozoan species. Studies with the aquatic larvae of the dipteran C. ripariusconfirm thispattern for abenthicdeposit feeder.Here, only individuals with a head capsule width larger than 400 μm ingested 90 μmPS spheres ([16], Table 1). Fine-meshfilter feeders (size range0.2–75μm;e.g.,Daphniamagna)arehighly efficient bacteria feeders, whereas coarsemeshfilter feeders (macrofiltrators, size range >2 μm; e.g., Holopedium gibberum) feed mainly on larger particles [28]. Results from feeding studies with polymer spheres illustrate that several protozoans feed effectively on 0.5μmparticles [9]; several rotifers on 0.5, 3, and 6 μmparticles [19]; and cladocerans on 0.5, 3, 6, 10, and 20 μmparticles ([13], Table1). Incomparison, calanoidcopepodsaremacrofiltrators and ingestparticles >2.1μmbutnot0.5μmparticles(e.g., [10],Fig.1a). Inaddition,somespecieswith a broad feeding size rangehavebeen shown to selectively forageon specific sizes when exposed tomultiple size fractions. For instance,Bosmina sp. ingested large algae cells (Cosmarium sp.) six times faster than a small algae species (Chlorella sp.) [29,30].Furthermore,AgasildandNõges[12]observedhigherfilteringratesof Daphnia cucullata on 3 and 6 μmcompared to 0.5 μmMPs, whereas the rotifer Conochilus unicornis exhibited an increased filtering rate on 3 μm compared to 0.5μmMPs. Particle shape is another important propertydeterminingMP-biota interactions. Currently, the majority of the available literature focuses on MP beads, and it remains unclear whether the investigated species have similar feeding rates on non-sphericalMPs(e.g.,fibers, fragments).Somespecies(e.g.,G.pulex,D.magna, Notodromasmonacha) feed readilyon secondary, irregularly shapedMPs [17, 31] with different toxicological profiles (see Sect. 3.1). Asmost of theMPs found in aquatic ecosystems are not spherical, more research is needed on irregularly shapedMPs. Fig. 1 Estimated feeding size ranges on microplastic particles (a).Dotted lines and question marks indicate the lackofmin tomax limitsbasedon ingestedsizeclasses.An increasing feeding selectivity decreases theprobability to directly ingestmicroplastics (b) Interactions ofMicroplasticswithFreshwaterBiota 159