Seite - 81 - in Freshwater Microplastics - Emerging Environmental Contaminants?

• The necessity to split MPs in two categories: fibers and fragments. Sampling protocolsoftendonotallowthesamplingoffibers.Thisstudyshowsthatmicro- plastic fibers are numerous in the catchment and in the receiving system and cannot be neglected. Of course the impact of such fibers is still unknown and mustbe investigated.Fragmentsare twoordersofmagnitude lessabundant than fibers, butwith different environmental impacts andmust also be analyzed. • Atmosphericfalloutsconstituteasignificantfluxoffibersat thescaleofanurban catchment. Up to now, the dynamics of these fibers in the atmosphere, its interaction with the catchment surface, the alternatingmechanisms of fallout/ re-suspension,and the lengthscaleof themovementofafiber in theatmosphere remain unknown. Moreover, while studies point out at the rivers as a major introductionwayof thefibers fromthecontinental into themarineenvironment, this study suggests that the atmospheric compartment and thewind should be further investigated as a potentiallymajor contributor. • Washing machines seem to be a major source of fibers, includingMP fibers. However,wastewater treatmentplantsplayamajorrole inthereductionoffibers andmicroplastic fragments, which are probably transferred to sludge. Investi- gation of sludges and, when sludge spreading takes place, of agricultural land has still to be reinforced. • Samplingprotocoloffragments inrivershastobeimproved, inorder todecrease theuncertainty indownstreamflowestimates. • Concerningfibers,surprisinglynoobvious increaseof theupstream-downstream flowhasbeenobserved.Various in-river phenomenamayexplain this, but both in situmeasurements and lab experiments have to be conducted to clarify this point. Actually, this study is only the starting point of a more comprehensive work related to the dynamics of (micro)plastics at a catchment and especially urban catchment scale.Otherplaceshave tobe investigatedandconsistent interdisciplin- ary researchprogramsconducted.This study showedmainly that the identification of the sources and the fate ofmicroplastic in freshwater is complicated and that a systematic andholistic approach is required. Acknowledgments Theauthorsacknowledgeall thepartnerswhocollaboratedduring thiswork. We thank the technical teams of SIAAP; those of the Val-de-Marne General Council; Anne Chabas of the Interuniversity Laboratory of Atmospheric Systems (LISA); Emmanuel Rinner andKadaBoukermaof the IFREMERDetection,Sensors, andMeasurementsLaboratory;and the Bruker demonstrating laboratory inChamps-sur-Marne and its staff. Thiswork is part of a thesis fundedby theParis researchnetworkon sustainable development (R2DS Ile-de-France). Sources andFate ofMicroplastics inUrbanAreas:AFocusonParisMegacity 81