Seite - 59 - in Freshwater Microplastics - Emerging Environmental Contaminants?

In freshwater environments of lakesand rivers, studiesalso report highlyhetero- geneous concentrations comparable to those reported for the marine environment. Highwithin-site variabilities, aswell asdifferent units used formicroplastic quanti- tation, complicate thecomparisonofmicroplastic concentrations inaquatic systems. Microplastics in riverine systemswere reported for large European rivers, e.g., the river Rhine and the riverDanube, aswell as for tributaries such as the riverMain. Plasticparticles in the riverDanubeweredeterminedwithhighabundanceandeven exceededthenumberoffishlarvae.Lechneretal. statedthat therivermight transport high loadsofplasticparticles into theBlackSea [44].Studies investigating the river Rhineshowedhighabundancesofmicroplastics,especially in theGermansectionof the river. Average concentrations amounted to approx. 900,000 particles km 2 for surfacewater andup to4000particleskg 1 for shore sediments. In theSwisspartof the riversRhoˆne,Aubonne,Venoge, andVuachie`re,microplasticswere detected in concentrations between 0.10 and 64 particles m3 (mean, 7 particles m 3; median, 0.36 particlesm 3) [45].Distinctly higher concentrationswere detected inChinese riverestuaries.Theestuariesof theriversJiaojiang,Oujiang,andMinjiang,whichall are located in an urban region, contained microplastics in the range of 100–- 4100particlesm 3 [46]. A study conductedwith lakeshore sediments collected fromLakeGarda (Italy) showed high abundances of polyethylene (PE) and polystyrene (PS)microplastics, indicating the importanceofbuoyantmicroplastics for shore sediments. In addition, polymerparticles of a higherdensity, suchasPVCandPET,werealso identified in this study underlining the variety of microplastics present in shore sediments [8].Microplasticsweredetectedinconcentrationsbetween108and1,108particlesm 2with notable spatial variation between the south and the north shore of the lake. Faure et al. reportedmicroplastics in the Swiss parts of LakeGeneva, Lake Con- stance, LakeNeucha^tel, LakeMaggiore, Lake Zurich, and LakeBrienz. The con- centrations of microplastics in lakeshore sediments varied between 20 and 7,200 particles m 2 (mean, 1,300 particles m 2; median, 270 particles m 2) and are comparablewith concentrations reported for LakeGarda. Between 11,000 and 220,000particleskm 2ofmicroplasticsweredetected in thesurfacewaterof thesix lakesmentioned.Microplasticswere alsodetected in theLaurentianGreatLakes in North America with concentrations ranging between 0 and 466,305 particles m 2 (mean, 42,533 particlesm 2; median, 5,704 particlesm 2). Higher abundances of microplasticshavebeendetectedinproximity tourbanareas[32].Thedetermination ofmicroplastics ingastrointestinal tractoffishfromLakeVictoria (Tanzania) shows firstevidenceforthemicroplasticpollutionofAfricanlakes[47](microplasticuptake biological interactions are discussed in Scherer et al. [48] of this volume). A monitoring study of LakeTaihu in China detected up to 6,000,000 particles km 2 in surface water samples. In bulk water samples, microplastics were present in concentrations between 3 and 26 particles L 1, while the sediments of LakeTaihu containedmicroplastics in the rangeof11–235particleskg 1.The reportedconcen- trationsofmicroplastics in thesedimentsofLakeTaihuare lowercompared to those detected in the sediments of theEuropean lakes.However, it needs tobe taken into account that lake-bottom sediments were sampled in Lake Taihu, whereas shore Analysis,Occurrence, andDegradation ofMicroplastics in theAqueous. . . 59