Page - 78 - in Freshwater Microplastics - Emerging Environmental Contaminants?

addition,fiberscomingfromdryweatheratmosphericfalloutcouldbere-suspended bywindorwashedduring the roadsandstreets cleaning, limiting theaccumulation between two rain events. While only fibers were detected in atmospheric fallout, runoff contained also fragments. It suggests that fibers can be transported by air, while the larger fragments seem to fall directly on surfaces and wait to be transported by the urban runoff, if not cleaned by road cleaning services.We can suppose that the fragmentsstemfromthedegradationof largerdebris,but thishypothesisstillneeds verification. WWTPs were also studied as potential sources ofMPs. Fibers were found in washing machine effluents and consequently in wastewater. Mechanisms and dynamics thatfibersundergo insideof a sewage systemareup tonownot reported in the literature. The roughly estimated flux of fibers enteringWWTPs lies in the same range as the amounts supposedly discharged by washing machines. The estimation range is however large and fluxes could be potentially lower. Because the transport duration in the sewer systems is probably short (max. 48–72 h), it is considered that no fragmentation occurs. On the other hand, a sedimentation process during dry weather periods in the sewage network is possible. WWTP effluentsareperhaps themost investigatedsources to thereceivingsystems.For the differentParisianWWTPs, theestimatednumberofMPfibersevenwitharemoval of fibers between 80 and 95% is higher than the fibers coming from atmospheric fallout.TheWWTPeffluentsseemtobethemajorsourceoffibers incomparisonto otherMPs. In contrast, CSOs contain both high fragments and fiber concentrations. It appears that CSOs are themain andmajor input ofMP fragments into the fresh- water.Moreover, the fact that it presentsconcentrationsoffibers sometimeshigher than wastewater tends to confirm a re-suspension of sewer deposits during wet weather periods. The knowledge on the various dynamics and mechanisms of MPs in urban catchments is still very coarse. For instance, conditions driving the fibers suspen- sion, the aerial transport, and the fallout processes are unknown. If some sources andfluxes have been identified, it is necessary to compare the results obtained on theParisMegacity onother case studies all over theworld. 4 MonitoringMicroplastics in theRiverSeine 4.1 Overviewof theApproach Inapreliminarystudypublishedatearlystagesof thiswork,wetested twodifferent meshsizenets tosample theriverSeine[18]. Ithighlighted thedifferencesbetween asmall (80μm)andalargermeshsize(330μm).Fibersarehighlyconcentratedand 78 R.Dris et al.