Seite - 33 - in Freshwater Microplastics - Emerging Environmental Contaminants?

microplastics the processes of ad- and absorption may both be relevant to their potential role as pollutant vectors. Manyengineerednanomaterialsaremanufactured frominorganicmaterials–or inorganiccarboninthecaseofC60fullerenesandCNTs. Inthesecases, thesorption of co-pollutants is governed by adsorption to the particle surface, rather than absorption into the particlematrix. Hence, the sorption capacity is determined by available adsorption sites on the surface of the nanomaterial. The differences in sorption processes between polymer particles and inorganic nanomaterials are illustrated inFig. 2. Nano- andmicroplastics aswell as engineerednanomaterials have thepotential to act as vectors for co-pollutants in the environment. The process will always dependon thespecificchemicalpollutant (e.g.Kow), the specificparticleproperties (e.g. composition and size) and the properties of the surroundingmedia (e.g. pH), influencing theparticle surfacepropertiesand thespeciationanddissociationof the chemical pollutant. It hasbeenproposed that thevector effect ofparticle-mediated transport of co-pollutants can be divided into three groups: (1) an environmental vector effect, whereby the co-pollutant is transported through the environment; (2) anorganismalvector effect,whereby theco-pollutant is transported intoorgan- isms; and (3) a cellular vector effectwhereby the co-pollutant is transportedwith theparticle into cells [9].Combining thiswith aproposed framework for different pollutant-particle interaction mechanisms, originally developed for engineered nanomaterials [37], the vector function of particle pollutants can be summarised as illustrated inFig. 3. Another type of vector function relates to leaching of substances that were originally part of the particlematrix. In the case of engineered nanomaterials, this is primarilymetal ions (frommetal andmetal oxide nanomaterials) or release of coating materials. Similarly, polymer additives can leach from plastic particles. From the field of ecotoxicology of nanomaterials, the importance of properly quantifying ion release is becoming increasingly clear, as observed biological effects can often be directly linked to the concentration of freemetal ions [8]. In the same way, the release of plastic additives should be examined when A B C Fig. 2 Illustration of the difference between adsorption (a) (more pronounced for inorganic engineered nanomaterials) and absorption (b) (more pronounced for polymer particles). In the caseofpolymerparticles, thesorptionmayalsobeacombinationofab-andadsorptionprocesses(c) AquaticEcotoxicity ofMicroplastics andNanoplastics: LessonsLearned from. . . 33