Seite - 257 - in Freshwater Microplastics - Emerging Environmental Contaminants?

obtained.Thus, thesestandardsare fundamental for regulationpurposesandshould preferablybe elaborated scientifically. The debate about reasonable standards has to face some paradoxical points of discussion: On one hand, a lower limit for particle size would promote the stan- dardization of sampling methods (see Sect. 3.5) and, thus, the elaboration of regulation standards. On the other hand, a lower size limit would exclude small particles fromregulation.AsMPparticlesareexpected tocontinuouslydisintegrate intosmaller fragmentsonsub-micrometer tonanometer scale,presentMPparticles are future nanoplastic particles, and thus, present regulatorymeasures onMPwill also impact the future concentrations of nanoplastics. Additionally, sources and entry pathways are similar for particles with a wide size range. Therefore, it is questionable towhat extent a further differentiation ofmicro- and nanoplastics is advantageous for the development of regulatorymeasures. The same plastic item mightbedocumentedandassessedasoneMPparticle inacurrentmonitoringbutas many nanoparticles in a futuremonitoring. Froman ecotoxicological perspective, there is also no lower size limit: The smaller the particles are, the more species might potentially ingest those (see [50]). Furthermore, smaller particles can per- meate through membranes and, hence, pose a higher risk for adverse effects in organisms.Against this background, it seemsunreasonable to exclude small parti- cles from regulation by defining a lower size limit. However, at the same time, generaldefinitionsareessential tobringregulatorymeasuresforward.Measuresare based onmonitoring data, andmonitoring again requires standardized and gener- ally acceptedmethods.Clear guidelines formaximumandminimumparticle sizes considered in sampling and analysis are required to generate reliable and legally validmonitoringdata.Furthermore, regulationneeds toassess thecurrent environ- mental status with knowledge on the ecotoxicological impacts on organisms. As described, ecotoxicological effects are strongly related to particle size, which determine ingestion,membranepermeation, etc.Apart fromsize limits, regulators should think about an appropriate categorization of particle size classes. To con- clude,finaldefinitionsofcertain standardsare fundamental for regulationpurposes and shouldpreferablybe elaborated scientifically. Afirst attempt topave theway for future standardshasbeendonebyanadhoc group (AHG) “Microplastics” under the InternationalOrganization for Standardi- zation (ISO) Technical Committee (TC) 61 “Plastics.” ISO decided to join all forces concerningenvironmental standardson theplastic issueunder this technical committee inorder toavoidduplicatework.Thescopeof thisTCisstandardization of nomenclature, methods of test, and specifications applicable to materials and products in thefieldofplastics.TheAHGrecommendedtostartapreliminarywork itemfor an ISO technical report “Plastics:Recommendations for theDevelopment of Standards for Investigations of Plastics in the Environment and Biota.” It is generally agreed that a global environmental problemneeds globally agreed stan- dardization approaches covering thewhole range from sampling to effect assess- ment in order to provide abasis for risk assessment and regulatory options. FreshwaterMicroplastics:Challenges forRegulation andManagement 257