Page - 92 - in Freshwater Microplastics - Emerging Environmental Contaminants?

mightdifferconsiderably indifferent regions.Fibersappeared tobemoreabundant inmore populated areas. 3.2.2 ParticleSize Size isanotherparameterusuallymeasuredformicroplastics,butnounifiedcriteria are currently available. Different size classes were reported by different authors, whichmake it difficult to compare the data fromdifferentworks [50].Due to the restriction of the samplingmethods used, usually onlymicroplastics>0.333mm (mesh size of themanta trawl net) are assessed in neustonic samples collected by trawling.Smallermicroplasticscanbeexaminedfor sedimentandbiota samplesas density separation combined with filtration is used.Whereas the examination of microplastics<0.05mmwill get increasinglydifficult, advanced instruments such asRamanmicroscopy,micro-Fourier transforminfraredspectroscopy(μ-FTIR),or scanning electronmicroscope (SEM)with energy dispersive spectroscopy (EDS) should be used [36].Generally,microplastic abundance increaseswith decreasing size[51–53]. InlakeHovsgol,0.355–0.999,1.00–4.749,and>4.75mmsizeclasses accounted for 41, 40, and 19% of the total plastics, respectively [30]. In the freshwaters of Wuhan, 0.05–0.5, 0.5–1, and 1–2 mm size classes together accounted for over 80%of the totalmicroplastics, and0.05–0.5mmmicroplastics were themost abundant in most of the studied waters [32]. In Yangtze Estuary, 0.5–1,1–2.5,2.5–5,and>5mmsizeclassesmadeup67,28.4,4.4,and0.2%of the total plastics, respectively [33]. In the estuaryofMinjiang,Oujiang, and Jiaojiang, thesmallest sizeclass (0.5–1.0mm)wasalso found themostabundant followedby the 1.0–2.0mmsize class, and these two size classes together accounted for over 70% of the total plastics [34]. However, among the four size classes (0.112–0.3, 0.3–0.5, 0.5–1.6, 1.6–5mm), 0.5–1.6 mmmicroplastics were themost abundant fromthemajorityof site in theThreeGorgesReservoir,whichmadeup30–57%of the total microplastics [22]. While for microplastic samples from the lakeshore sediment of the SilingCobasin, different size distribution patternswere observed fromdifferentsamplingsites[23].Thepatternsofmicroplasticsizedistributioncan be related to the sources of microplastics and might also reflect the degree of weathering.A higher degree ofweatheringmight result in a higher abundance of smaller particles. Biofouling and hydrodynamic conditions were also believed to affect the size distributionofmicroplastics [54–56]. 3.2.3 Color In some studies, colors of the microplastics were described. Microplastics can inherit their colors from their parent plastic products, but their colors can change due to weathering. Previous research infers that predators may preferably ingest microplasticswith colors resembling their prey [57–59].Therefore, color informa- tion of microplastics may be used to indicate their potential to be ingested by 92 C.Wuet al.