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micrometersizerange[40,41],andtheterm ‘mesoplastic’ introducedtoaccountfor itemsbetween1 and2,500mm. Lambert et al.  describedmacroplastics as >5mm,mesoplastics as 5 to>1mm,microplastics as 1mmto>0.1μm, and nanoplastics as 0.1μm.However, the upper limit of 5mm is generally accepted because this size is able to include a range of small particles that can be readily ingestedbyorganisms . Generally,MPsaredivided into categories of either primaryor secondaryMPs. Primary MPs are manufactured as such and are used either as resin pellets to produce larger items or directly in cosmetic products such as facial scrubs and toothpastesor inabrasiveblasting (e.g. to remove lacquers).Compared to thisdeli- berate use, secondary MPs are formed from the disintegration of larger plastic debris. MPs have undoubtedly been present in the environment for many years. For instance, Carpenter et al. , Colton et al. , and Gregory  reported on marineplastics in the1970s,but theyhavenotbeenextensivelystudiedparticularly in the context of freshwater systems.As research focusedon the issuemore inten- sivelysincetheearly2000s,MPsareconsideredcontaminantsofemergingconcern [8, 10, 46]. 3 SourcesofPlasticsandMicroplastics intotheFreshwater Environment Plastics will enter freshwater environments from various sources through various routes.Onlandlitteringisanimportantenvironmentalandpublic issue[47,48]and is amatter of increasing concern in protected areaswhere volumes are influenced byvisitor density; consequently,measures are nowneeded to reduce andmitigate for damage to the environment . In addition, wastemanagement practices in different regionsof theworldalsovary,andthismaybeamore important source in onegeographical region compared to another .Aswithbulkplastic items,MPs canenter theenvironmentbyanumberofpathways, andan important route inone geographical regionmay be less important in another. For example, primaryMPs used in consumer cosmetics are probably more important in affluent regions . MPs have several potential environmental release pathways: (1) passage throughWWTPs, either fromMPuse inpersonal careproductsor releaseoffibres from textiles during the washing of clothes, to surface waters, (2) application of biosolids fromWWTPs toagricultural lands , (3) stormwateroverflowevents, (4) incidental release (e.g.during tyrewear), (5) release fromindustrialproductsor processes, and (6) atmospheric depositionoffibres (discussed further inDris et al. ). Plastic films used for crop production are considered an important agricul- tural emission, and their use is thought to be one of themost important sources of plastic contamination of agricultural soils [52–54]. There advantages include con- serve of moisture, thereby reducing irrigation; reduce weed growth and increase MicroplasticsAreContaminants ofEmergingConcern inFreshwater. . . 5
Freshwater Microplastics Emerging Environmental Contaminants?