Page - 12 - in Freshwater Microplastics - Emerging Environmental Contaminants?

particles mL 1 after 21 days, which is 0.027% of the concentration fed to the mussels.Another studyhas demonstrated the potential ofMP transfer frommeso- tomacro-zooplankton, using PSmicrospheres (10 μm) atmuch lower concentra- tions of 1,000, 2,000, and10,000particlesmL 1 [28].Because excretion rates are unavailableandMPuptakeisoftendefinedasparticlespresent in thedigestive tract (i.e. theoutsideandnot the tissuesofanorganism), it is so farnotclearwhether the trophic transfer of MP also results in a bioaccumulation or biomagnification. However, it is clear that MP will certainly be transferred from the prey to the predator and that this can– in certain situations–be retained for longer periods in the bodyof the latter. Anopen question is towhat extent the organisms consumenaturally occurring microparticlesandhowtheeffects compare toMPs(foramore in-depthdiscussion on this topic seeScherer et al. [26]).This is important becausenaturally occurring particlesarean importantcomponentofaquaticecosystemsandparticleproperties, such as concentration, particle size distribution, shape, and chemical composition, aswell asdurationofexposureplaysa strong role indetermining their interactions with aquatic communities [95]. Overall, an understanding of the relationships between cellular level responses and population level impacts will be important in order to determine the broader implications for ecosystem functioning. Points to be assessed concern both the biological aspects (molecular target, affected endpoints) and the particle aspects such asMPphysical and chemical characteristics. The bioavailability of theMPs and the penetration of submicron MPs into the cells are factors to take into consideration. 6.2 Effects ofLeachingChemicals The environmental effects of residual starting substances and monomers, non-intentionally added substances (impurities, polymerisation byproducts, break- down products), catalysts, solvents, and additives leaching from plasticmaterials arenoteasy toassess [96].Themixturecompositionandconcentrationof leachable compoundsdependon thephysical, chemical, andbiological conditions of receiv- ingenvironments.The leachingofwater-solubleconstituents fromplasticproducts using deionised water is considered a useful method for profiling environmental hazards posed by plastics [97, 98]. Lithner et al. used such leachates in a direct toxicity testing approach to assess their acute toxicity toD.magna [97, 98]. For instance,with a liquid to solid (L/S) ratio of 10 and 24 h leaching time, leachates frompolyvinyl chloride (PVC),polyurethane (PUR), andpolycarbonate (PC)were themost toxicwithEC50 values of 5–69gplasticL 1 [98].HigherL/S ratios and longer leaching times resulted in leachates fromplasticised PVCand epoxy resin products to be themost toxic at (EC50 of 2–235 g plastic L 1) [99]. In a recent study,Bejgarnetal. [99] investigated the leachates fromplastic thatweregroundto 12 S.Lambert andM.Wagner