Seite - 6 - in Freshwater Microplastics - Emerging Environmental Contaminants?

soil temperaturewhich reduces competition for soil nutrients and reduces fertiliser costs, thereby improving crop yields; and protect against adverse weather condi- tions [7, 55]. However, weathering canmake thembrittle and difficult to recover resulting indisintegrationof thematerial, andwhencoupledwith successivepreci- pitation events, the residues anddisintegratedparticles canbewashed into the soil where theyaccumulate [7, 55,56].Other sources exist and includeemissions from manufacturing and constructions sites. Automotive tyre wear particles may also release large volumes of synthetic particles. These tyre wear particles are recog- nised as a source ofZn to the environment,with anthropogenicZn concentrations thatarecloselycorrelatedto trafficdensity [57].Thesourcesandemissionroutesof nanoplastics are also discussed inRist andHartmann [58]. 4 Occurrence inFreshwaterSystems The isolation ofMPs in environmental matrices can be highly challenging parti- cularlywhen dealingwith samples high in organic content such as sediments and soils. Likewise, the spectroscopic identification of synthetic polymers is compli- catedbyhighpigment contents and theweatheringofparticles andfibres.Accord- ingly, the detection and analytical confirmation of MPs require access to sophisticated equipment (e.g.micro-FTIR andmicro-Raman; discussed further in Klein et al. [20]). Recent monitoring studies have established that – similar to marine environments – MPs are ubiquitously found in a variety of freshwater matrices.ReportedMPconcentrations in surfacewater samples of theRhine river (Germany)average892,777particleskm 2withapeakconcentrationof3.9million particles km 2 [15]. In river shore sediments the number of particles ranged from 228 to 3,763 and 786 to 1,368 particles kg 1 along the rivers Rhine andMain (Germany), respectively [19].Highsurfacewaterconcentrationsare reportedat the ThreeGorgesDam,China (192–13,617 particles km 2),which are attributed to a lack of wastewater treatment facilities in smaller towns, as well as infrastructure issues when dealing with recycling and waste disposal [14]. These studies may underestimate the actualMP concentrations because their separation and identifi- cation are based on visual observationmethods (e.g. Reddy et al. [59]) andmay exclude those in the submicron size ranges. The environmental occurrence and sources ofMPs in freshwatermatrices in anAfrican,Asian, andEuropean context arefurtherdiscussedinDrisetal. [51],Wuetal. [60],Khanetal. [61], respectively. 5 Fate andTransport inFreshwaterSystems OnceMPsare releasedor formed in the freshwaterenvironment, theywillundergo fate and transportation processes. In the following section, these processes are discussed. 6 S.Lambert andM.Wagner