Page - 169 - in Freshwater Microplastics - Emerging Environmental Contaminants?

(e.g., phthalates, bisphenolA) adversely affecting life-cycle parameters of a broad rangeofspecies [72,73].Friesetal. [74]extractedseveralorganic(e.g.,phthalates) and inorganic additives (e.g., metals) from MP samples in marine sediments highlighting the relevanceof thesecompounds.Besidesadditives, adsorbedpersis- tent organic pollutants have been found onMPs (e.g., [75, 76]). The capacity of plasticmaterials to accumulatehydrophobicorganic chemicals is thoroughly stud- ied and frequently applied in passive samplings/monitoring (e.g., [76, 77]). For MPs, the large surface-to-volume ratio supports an accumulation of dissolved pollutants (e.g., PAHs,PBTs,metals), andcomplexadsorption-desorptionpatterns havebeendemonstrated [77, 78]. Although adetailed reviewof the complexity in adsorption-desorption kinetics is beyond the focus of this chapter, the default hypothesis is thatMPs readily sorb hydrophobic compounds and therefore act as vectors transferringwaterborne con- taminants to aquatic organisms (vector hypothesis). However, this idea is contro- versially discussed. Several laboratory studies illustrate the capacity of MPs to modifyadverse effects of chemicalsbyaffecting thebioavailabilityor actingasan additional stressor. For instance, (1) the exposure to spikedMPs lead to an accu- mulation of pollutants to the tissues of lugworms (PVC, [6]),mussels (PEandPS, [59]), amphipods (PE, [79]), and fish (LDPE, [39]); (2) Besseling et al. [80] observed a decreased bioaccumulation of polychlorinated biphenyls in lugworms athigherdosesofPSparticles; (3)Oliveira et al. [40] confirmedadelayedpyrene- inducedmortalityof juvenilefishes(Pomatoschistusmicrops) in thepresenceofPE MPs;and(4)Karamietal. [37]aswellasPaul-Pontetal. [60]detectedmodulations of adverse effects by an exposure to phenanthrene-loadedLDPE fragments (Afri- can catfish) andPSbeads andfluoranthene (Mytilus spp.), respectively.However, Gouin et al. [81] andKoelmans et al. [82] highlight theminor influenceofMPsas vectors for thebioaccumulationofpollutants considering theyareoutcompetedby natural occurringmatter.Theseauthors emphasize the importanceof experimental design and chemical analysis in order to understand the relevance and underlying mechanisms ofMPs as vectors of bioaccumulative substances. For instance, the introduction of freshly spikedMPs in cleanwater can result in desorption, which increases dermal exposure [82]. Furthermore, desorbed chemicalsmight adsorb to foodorsedimentsanddecrease thepotential relevanceofMPsasvectors. Inprinci- ple,adsorptionanddesorptionpatternsfollowthepartitionequilibriumbetweenthe available compartments (e.g., biota, food,MPs, sediment, water). This may con- foundtheanalysisofsinglepathwaysparticularly ifanalytical informationisabsent (e.g., exposure via ingestionofMPs, foodor sediments vs. dermal uptake). While studies on the vector hypothesis were mostly performed with marine species andpersistent organic pollutants, the situation is likely tobeverydifferent infreshwaterecosystems.Firstandforemost, freshwatercompartmentsareexposed to a completely different and much larger spectrum of chemicals than marine systems. This is because they receive a constant input of chemicals from land- based sources (e.g., pesticides) and wastewater (e.g., pharmaceuticals and Interactions ofMicroplasticswithFreshwaterBiota 169