Seite - 264 - in Freshwater Microplastics - Emerging Environmental Contaminants?

representative sampling inwastewater streamsandriversunderdifferenthydrolog- ical conditions ismissing. The picture is similar for sample processing, chemical analysis, sample throughput, and biological effect methods. Crucial criteria like waterdepthfor samplingormeshsizeofsamplingnetsneed tobestandardized.As mentionedabove, suchcriteriacansignificantly influence themonitoring results.A marine study conducted in Swedish coastal waters revealed 105-fold higher con- centrations ofMPusing80μmnets compared to 450μmnets [71]. Besides a lack of sampling guidelines, no standardizedmethods for chemical analysisofMPparticles in environmental samples exist, so far.Theproblemstarts with sample processing which is a precondition for a precise analysis of plastic particles. Severalmethods are under development (as summarized in [58]). Some of them are time and work intensive; others are suspected to corrode the plastic items. A generally accepted method for extensive application has still to be developed.However, the requiredsamplecleanupdependsontheanalysismethods applied.Currently, twomaindirectionsofanalyticalmethodsareappliedtoidentify MP: spectroscopy and thermogravimetry (see [58]). For both, several techniques exist for the identification of polymer types. However, the choice of a certain technique is determining the outcome less than the choice of the main direction of methods: Spectroscopic methods (e.g., IRmicroscopy or Raman) can lead to an exact definition of single particles regarding size, shape, color, and main polymer type but are not appropriate for exact mass balancing. In contrast, thermogravimetricmethods (e.g., TED-GC-MSorpyrolysisGC-MS)canquantify the exactmass of certain polymers in environmental samples –but thermal degra- dation of particles does not allow any further characterization of particles. Both directions are appropriate to answer specific questions. (Waste)watermanagement willbemoreinterestedinmassbalances,whileecologyandwaterconservationwill rather ask foranexactdescriptionofparticle sizedistribution inorder toassess the risk to organisms. 3.6 MassBalanceVersusParticleCharacterization asCriterion forRegulation Thechoiceofmassversusparticleconcentrationdependsontheaimsofregulation. Togive someexamples: TheEUMSFD[4]aims to regulate thecontributionofplasticwaste fromsingle member states to themarineenvironmentvia rivers.Here, it seemsobvious for the regulation to require information on mass balances instead of particle numbers because (1) the regulation aims to impose financial penalties depending on the contribution of each state to the overall plastic load and (2) plastic particlesmay disintegrate andbreak intomorepieceson theirway throughdifferent countries. If regulation should refer to the impact on freshwater ecosystems, it will ask about ecotoxicological effects of MP, for instance. Hence, such regulation requires 264 N.Brennholt et al.