Seite - 80 - in Freshwater Microplastics - Emerging Environmental Contaminants?

fibers flow in 1 year in this site corresponding to an estimatedmass of synthetic fibers between 0.01 and 0.34metric tons flowper year. The evolution of this flux toward the estuary has to be determined in order to be able to determine the input from freshwater to themarine environment in termsofMPs. 4.3 Comparisonwith theFragments There isa largedifference in theconcentration levelsbetweenfibersandfragments. Themeanfiber concentration is around45fibersm 3 (n¼95 samples),while the mean fragment concentrations considering both methods is around 0.54 frag- ments m 3 (n¼ 17 samples). As a consequence, using two different sampling methods for fibers and fragments seems really pertinent. While analyzing fibers needs theuseofasmallmeshsize,samplinghighervolumesismandatorytocollect other shapes ofMPs. By assuming amean fiber length (973 μm) and diameter (25 μm) and for the fragments the mean area (168,000 μm [2]) and roughly estimated thickness (35 μm), the volumes of a typical particle for each shape can be approximated. CombiningMPproportionsandpolymerdensitieshypotheses (1and1.45gcm 3), themass concentrationswere approached. Itwas estimated that themean concentration for syntheticfibers is of 2 10 5 gm 3,while it isof3 10 6gm 3 for fragments.Becauseof thesmall amountof data, the fragmentmassfluxwasnot estimated.However, it seemswith this result that even if a fragment is bigger than afiber on average, the fragmentmassfluxes wouldbeoneorder ofmagnitude smaller thanfibermassfluxes. 5 ConclusionsandPerspectives Although information onMPs in freshwater increased dramatically over the very recent years, there is, until now,neither a systematicoverviewof the sources, fate, andsinksonacatchmentscalenora linkbetweenthecatchmentcharacteristicsand the concentrationofMPs in receiving systems. Afirst attemptwasmadeon theurbancatchmentofParisMegacityand itsmain drainage system: the Seine and theMarneRivers.During almost 3 years, samples havebeen collected fromatmospheric fallouts andurban runoff, fromupstream to downstreamof the sewage system, and in the rivers. Thekey results are: • The importanceof thefiber category (near urbanareas at least),which includes notonlyplasticfibersbutalsoothersyntheticfibers likerayon,whichmightalso have an environmental impact. 80 R.Dris et al.