Page - 170 - in Freshwater Microplastics - Emerging Environmental Contaminants?

chemicals from personal care products). Many of these compounds are pseudo- persistentandbiologicallyhighlyactivebutdonotoccur inmarineecosystems(due to dilution or degradation). Accordingly, freshwaterMPs will sorb a completely different set of chemicals thanmarineones. In addition, being closer to the source of plastic litter and thus “younger,” freshwaterMPsmight contain higher concen- trations of plastic additives.With regard to desorption, physical water properties will affect the transfer of pollutants. The adsorption equilibrium of chemicals to organic materials is highly dependent on water temperature, quantity of organic matter, and the content of inorganic salts [83].Therefore, thepartition equilibrium will be different in salt- and freshwater. Besides thecapacityofMPsto influence thebioavailabilityof toxiccompounds, Besseling et al. [41] suggested thatMPs can interferewith intra- and interspecies signaling (e.g., phero- and kairomones) as an integral component of aquatic bio- coenosisregulatingpredator-preyinteractionsaswellaspopulationandcommunity structures [84]. Although they found significant interactions between kairomones andnano-PSwhen investigating thegrowthof thewater fleaD.magna, it remains unclearwhether the nano-PSbeads increased the bioavailability of kairomones or theyobservedanadditiveeffectofbothstressors[41].Anydisturbanceofthis inter- and intraspeciescommunicationcan lead tomaladaptive responses inbothsignaler and receiver [85]. So far, it is unclearwhetherMPs act as info-disruptors as is the case for severalmetalsandpesticides (reviewedin[85]), especiallywhenconsider- ing the abundance of additional particulate organic and inorganic matter in aquatic ecosystems. 3.3 Biofilm-Related Impacts Apart from thepotential ofMPs to act as carriers for chemicals,MPs can serve as substrates for microorganisms. The formation of biofilms [86] can affect the interaction ofMPswith biota onmultiple levels. For example, the colonization of MPswithmicrobesandtheadsorptionofbiopolymers increase thenutritionalvalue and improve the “taste” making themmore attractive for biota. In contrast, the colonization of MPs with pathogens [87] and toxic algae/bacteria might induce infections/chemical toxicity or avoidance of “bad tasting” MPs. Additionally, biofoulingwas shown to affect the fate ofMPsbychanging theparticle properties (e.g., density). The formation of biofilms increases the density of floating or buoyantMPs and leads to sedimentation of these low-density particles (reviewed in [88]). Furthermore, in the environment, MPs are most likely incorporated in so-calledhetero-aggregates.Theseaggregatesconsistofparticulatematter (MPsas well as other suspended solids) and microbes (e.g., protozoans, algae) with bio- polymers acting as binders. A laboratory study by Lagarde et al. [89] confirmed 170 C.Scherer et al.