Seite - 161 - in Freshwater Microplastics - Emerging Environmental Contaminants?

However, the feeding type is not a reliable predictor ofMP ingestion as several studies on pelagic zooplankton communities highlight a far more complex MP-biota interaction than currently understood. Overall, the feeding on particulatematter is a sequential process involving the encounter, pursuit, capture, and ingestionofpotential prey [30].Every single stage is determined by species-specific abilities and preferences to distinguish between favored and non-favored food sources (e.g., size, shape, taste, motile, sessile). Additionally,many taxa can adapt their feeding habits (e.g., targeting a preferred sizeclassand/ornutritionalvalue) inresponsetoenvironmentalconditions(optimal foraging). Ingeneral, it appears that thecapability todirectly ingestMPsdecreases with an increasing selectivity in feeding (Fig. 1b). Generalist filter feeders will actively and directly ingestMPs from thewater column or sediments in the size range of their typical food, whereasmore specialized feeders (e.g., fluid feeders, raptorial carnivorous feeders)will indirectly ingestMPsassociatedwith theirprey. Thevariety of feeding types anddegreesof selective feedingpresent in aquatic faunacomplicatesgeneralizingpatternsofMPuptake.This is especially truewhen comparing experimental to the real exposure scenarios. In the laboratory, virgin sphericalmicrobeadsareused,whereas in theenvironment, irregularlyshapedMPs are colonized bymicrobes (see Sect. 3.2), adsorb extracellular proteins (biofilm), and formhetero-aggregates (increasingsize).WhileMP-biota interactionsarehard topredictbasedonthecurrentlyavailabledata, feedingselectivitymaybeadriving factor (seeFig. 1b for a conceptualmodel). 3 Effects onFreshwaterBiota Studies on the potential adverse effects caused byMP exposures are scarce for freshwatercompared tomarinespecies.Thefewavailablestudies (Table2) include the filter feederD. magna [34, 35, 41], the amphipodsHyalella azteca [18] and G. pulex [31], the freshwater snailP. antipodarum [38] as well as several fishes [37–39]. In this section, the outcomesof these studies are discussed. 3.1 Physical Impacts Theevaluationof feeding types (Sect. 2.1) suggests that nonselectivefilter feeders areespeciallyprone toMPexposures.BasedontheirhighratesofMPfiltrationand ingestion in laboratory studies, adverseeffects inducedby theparticle toxicitymay include blockages, reduceddietary intake, and internal injuries. Interactions ofMicroplasticswithFreshwaterBiota 161