Page - 29 - in Freshwater Microplastics - Emerging Environmental Contaminants?

unintentionally produced anthropogenic nanomaterials. For micro- and nano- plastics, upstreamregulationmaybeeffective in reducing theenvironmental emis- sions of primarymicroplastics. Examples are theUS ‘Microbead-FreeWatersAct of 2015’ [15] prohibiting plastic microbeads in rinse-off cosmetics including toothpaste aswell as the upcomingUKban onmicrobeads in cosmetics by 2017 [16].For secondarymicroplastics, on theother hand, reducing their environmental occurrence involves takinggeneralactionagainstplasticsentering theenvironment duringall stepsofplasticproduction,useandwastemanagement.Taxationof, ora ban on, single-use plastic shopping bags [17] and bottle return systems [18] are examples of regulatory measures aimed at reducing the general environmental plastic load.Once theplastic has entered theenvironment, the formationofmicro- plastics is governedby the inherent properties of theplastic and theenvironmental conditions [19] and thereby practically impossible tomitigate through regulatory measures. 3 Material Synthesis,ChemicalComposition andConsequences forEnvironmentalDetection Aclear difference between engineered nanomaterials andnano- andmicroplastics relates totheirchemicalcomposition. Inprinciple,engineerednanomaterialscanbe produced from any solid material. Higher production volume engineered nano- materials are typicallymade frommetals ormetal oxides (suchasTiO2,CeO2and Ag) or from carbon (such as carbon nanotubes (CNTs)) [20] although organic nanomaterials are also manufactured (from polymers, monomers and lipids) [21]. Nano- andmicroplastics, on the other hand, consist specifically of synthetic polymers, produced bypolymerisation of variousmonomers and covering a range ofmaterials such as polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyvinylchloride (PVC) [1, 22]. Synthetic polymers differ in properties such as density, porosityandcontentofnon-polymeric additives.Additivesmayconstitute up to 50%of the totalmass of plastics and can be composed of both organic and inorganic substances [23].Hence,whilenano-andmicroplastics consist of specific syntheticpolymers (e.g.PEorPP), thereareasmanyvariationsas therearecombi- nations and ratios of additives. These additives may alter the properties of the material in suchaway that itwill behavedifferently in the environment andcause differentenvironmentaleffects.Thesameis true forengineerednanomaterials:For engineerednanoparticleswith agivenchemical composition (e.g.TiO2), theprop- erties changewithdifferentcrystalline structuresandsurfacecoatings.At the same time,engineerednanomaterialscanbemadefromarangeofdifferentmaterialsand combinationsofmaterials.Anongoingdiscussionwithinengineerednanomaterials relates to ‘sameness’:Whencan twoparticlesbeconsidered thesameandwhenare they so different that they cannot? This has consequences for categorisation and AquaticEcotoxicity ofMicroplastics andNanoplastics: LessonsLearned from. . . 29