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disposal ofwashingmachines . Therefore, based on both scenarios (5 and 60%of synthetic fibers), between 2 1013 and 1 1015 annualMPfibers are discharged into the wastewater at the Paris agglomeration scale. This corre- sponds to amass between6and437metric tons/year. • Wastewater. As 2.3 million m3 wastewater are treated daily for the Paris agglomeration, between 6 1013 and 4 1014 fibers flow annually in the wastewater. Assuming that the proportion of synthetic fibers remains constant betweenthewashingmachinedisposalandtheentryof thewastewater treatment plant, itwas considered that between5and60%of thefibers inwastewater are synthetic. Therefore, between 3 1012 and 3 1014 synthetic fibers, i.e., between 2 and 225metric tons of fibrousMPs, flow annually on wastewater. Byapplying the removal ratesofWWTPSeineCentre (between80and95%) to theglobal estimationmadeabove for thewastewater,weestimate that theParis agglomeration releases annually between 2 1011 and 5 1013 plastic fibers into thesurfacewaters, corresponding toamassbetween0.1and45metric tons. • Combined sewer overflows. CSO discharges in the Paris combined sewage system are approximated about 21 million m3 year 1, corresponding to a potential introduction into the freshwater of between 4 and 5 1012 fibers annually. It is hard to provide an accurate estimation of the proportion of plastic polymers among thosefibers. 3.4 ComparisonofMicroplastic Sources inFreshwater Among the various sources investigated, fibers were always present, while frag- ments weremainly detected in the urban runoff and the CSOs. The atmospheric compartmentwasconfirmedasasourceoffibers includingMPs.Thesefiberscould havedifferent sources including syntheticfibers fromclothes andhouses, degrada- tionofmacroplastics, landfills,orwaste incineration.Thecharacterizationindicates that thehypothesisof theclothingbeing themain sourceof thesefibers is themost plausible (proportion of polymers close to the uses on the textile industry). These fibers intheatmosphere, includingMPs,couldbetransportedbywindtotheaquatic environment or deposited on surfaces of cities or agrosystems. After deposition, they could impact terrestrial organisms or be transported into the aquatic systems through runoff. Future work is needed in order to investigate these atmospheric fibers and understand where they come from, where they end up, and which mechanisms and factors lead to their transport and their fallout. The distance over which a fiber could be transported is also still unknown. In this study, it was not possible to assesswhether theobservedfibers come fromveryclose sources in the proximity or from distant places. MPs found in isolated lakes suggest that the transport could occur over long distances . It seems that atmospheric fallout is a significant sourceofMPsandshouldbeconsideredwhen investigatingMPs in freshwater. In addition to atmospheric fallout, other sources have tobe considered likefibers thatcandepositdirectly fromtheclothesofpeoplewalkingonstreets. In Sources andFate ofMicroplastics inUrbanAreas:AFocusonParisMegacity 77
Freshwater Microplastics Emerging Environmental Contaminants?