Seite - 27 - in Freshwater Microplastics - Emerging Environmental Contaminants?

environment, andno studies havedemonstrated their presence [2].However, labo- ratory studies have shown the formation of nanoplastics down to sizes of 30 nm during artificialweathering of larger plasticmaterials, using nanoparticle tracking analysis [6]. This is a strong indication that this process can also take place in the environment.Particlesasemergingenvironmentalpollutantscall forabetterunder- standingof theirenvironmentalbehaviourandpotentiallyharmfuleffectsonorgan- isms.Ecotoxicity testingof particles represents a shift in test paradigmaway from testing of soluble chemicals anddemands reconsiderationof existing testmethods andprocedures, including the standardisedmethods developedbyOECDand ISO [7,8].On theonehand,parallels cangenerallybedrawnbetweenecotoxicological testing of particles, independent of whether those particles are engineered nano- materials or plastic particles [9]. On the other hand, it is important to understand where the similarities end, inorder toavoid redundant testing, useof inappropriate testmethods andgenerationofmeaningless data.Nano- andmicroplastics cover a wide range in terms of particle sizes. To illustrate this: If a 1mmparticle corre- sponded to the sizeof theEarth, thenananosizedparticlewouldcorrespond to the InternationalSpaceStation in theorbit around it, i.e. differing in sizebysixorders of magnitude. Resemblances, in terms of behaviour, fate and effects, are more likely to occur for particles that are similar in size. Therefore the similarities between engineered nanomaterials and nano- andmicroplastic particles aremore likely to apply for smaller microplastics of up to a few microns as well as the submicron-sizednanoplasticparticles,whichwillbe themainfocusof thischapter. Further noteworthydifferences exist in termsof their chemical properties, sources and their relatedmethodological challenges, as described in further detail below. 2 Sources,Emissions andRegulation Thepotential sources and routes bywhich engineerednanomaterials andnano- and microplasticsenter theenvironmentaresomewhatsimilar (seeFig.1).Astheirname suggests, engineered nanomaterials are intentionally designed and produced for specific applications, processes or products. Production can take place by synthesis (bottom-upapproach)orcomminutionof largermaterials (top-downapproach).This is comparable to the production of primary nano- andmicroplastics, for example, microbeads intentionally produced for cosmetic products or plastic pellets used as feedingmaterial inplasticproduction.Dependingonthedefinitionsapplied,primary nanoplasticswouldactuallyfallunder thedefinitionofengineerednanomaterials.An estimated amount ofmore than 4,000 t of primarymicroplastic beadswere used in cosmetics inEurope in2012[10].Nonetheless,primarymicroplasticsonly represent a small fraction of the estimated overall environmental microplastics load [11], a fraction, however,which can relatively easily be addressed and reduced. Themain sources of nano- and microplastic pollution, however, are uncontrolled processes such as abrasion and degradation of larger plastic products and fragments, i.e. secondary sources of anthropogenic origin [12]. These sources include AquaticEcotoxicity ofMicroplastics andNanoplastics: LessonsLearned from. . . 27