Seite - 90 - in Freshwater Microplastics - Emerging Environmental Contaminants?

China. Lake Hovsgol, a remote mountain lake in Mongolia, was surveyed for pelagic microplastics [30]. Results showed that microplastic abundance ranged from 997 to 44,435 items/km2. Microplastic abundance decreased with distance from the southwestern shorewhich had the highest human impact andwas distri- buted by the prevailingwinds. Zhang et al. [22] investigatedmicroplastic occur- rence in the surface waters of the Three Gorges Reservoir in China and found microplasticabundanceupto136,175 106items/km2,whichis thehighestmicro- plastic abundance ever reported in the literature. The authors suggested that the highaccumulationofmicroplastics isrelatedtothedamming,andreservoirscanact as potential hot spots for microplastics. In another study by Zhang et al. [23], microplasticswere sampled from the shorelines of four lakeswithin theSilingCo basin in northernTibet.Microplasticswere detected in six out of seven sampling sites, and the site with the highest microplastic abundance was related to the riverine input. Su et al. [31] reportedmicroplastic pollution inTaihuLake,which is the third largest freshwater lake inChina located in awell-developedareaunder extensive human influence. Microplastics were detected in plankton net, surface water, sediment, andAsian clams samples.More recently, microplastic pollution was studied in inland freshwaters in Wuhan, the largest city in Central China [32].Microplasticswere detectedwith concentrations ranged from1,660 639.1 to 8,925 1,591 items/m3 in surface water, and microplastic abundance was negatively correlatedwith the distance from the city center. Another two studies have also investigated the occurrence of microplastics in surface water from the estuaries ofYangtze, Jiaojiang, Oujiang, andMinjiang inChina [33, 34]. Results demonstrated that microplastics were present in high abundance in these transi- tional zones between rivers and the sea and suggested that rivers are important sources ofmicroplastics tomarine environment. The literature reporting the occurrence ofmicroplastics in inlandwaters from other geographical regions is also summarized in Table 1. A comparison of data fromdifferent regionscanbechallengingduetothedifferenceinsamplingmethods used,sizeranges investigated,andthereportingunits thatareemployed.Therefore, it is urgently needed to adopt universal criteria for sampling and reporting microplastics occurrence data to facilitate a comparison [49]. Additionally, the abundance of microplastics from different regions differs by several orders of magnitude. Even within the same region, the abundance of microplastics varies considerably.Thisunevendistributionpatterncanbe related to their relatively low density, which means that they can be transported easily with the current and accumulation in areas with weaker hydrodynamic conditions. In addition, the loadingrateofplasticwastecandiffer significantly indifferent regions.Previously, Yonkoset al. [45]demonstrated that theabundanceofmicroplasticswaspositively correlatedwith population density andproportion of urban/suburbandevelopment within the watersheds. However, researches also demonstrated that microplastics werealsofoundatrelativelyhighconcentrationsininlandwatersfromremoteareas with limited humanactivities [23, 30]. This is likely due to a lackof properwaste management measures in those areas. In many Asian countries, high population densityandunsoundwastemanagement systems lead toahigh riskof inlandwater 90 C.Wuet al.