Seite - 108 - in Freshwater Microplastics - Emerging Environmental Contaminants?

3 Presence, Sources, andFate ofMPs in InlandAfrican Freshwaters 3.1 Presence ofMPs inFreshwaters ThepresenceofMPshasbeenextensivelyreportedin themarineenvironment [38– 40], including thatofSouthAfrica’scoast (asdescribed in theprevious section). In comparison,describingMPsinfreshwaters isstill in its infancywith themajorityof research only arriving in the last 5 years [9]. Thus, only a few studies have investigated the occurrence ofMPs in freshwaterswith research conducted in the vicinity of urbanization and industrialization, such as Laurentian Great Lakes in North America [10] and Lake Geneva in Switzerland [11], as well as in more remote locations, such asLakeHovsgol inMongolia [25] andLakeGarda in Italy [12].Not only do these studies show thatMPs are present in freshwaters, but also relate the typeof plastics found to their likely sources. In theLaurentianLakes (LakesSuperior,Huron, andErie),MPswere found in 20out of21 surface samples, and inmanyof the tows, themostnotableMPswere multicolored spherical beads thatwere determined to bepolyethylene in composi- tion. Shape, size, and composition were comparable to the microbeads used in exfoliatingfacialcleansersandcosmeticproductsandwere likely tooriginate from nearby urban effluents [10]. Although there have been efforts to raise scientific, regulatory,andpublicawareness tobantheuseofmicrobeads[41–43],successfully in some countries, the Canadian Great Lake study demonstrated that they are already abundant in the environment, and in the Laurentian lakes, “hot spots” were found where lake currents converge. Logically, it would be expected that remote lakeswith lowerpopulationdensitieswouldhave lessplasticpollution than freshwaters near urban centers, but in case ofLakeHovsgol, the remotemountain lake innorthwestMongolianear theRussianborder, theoppositewas true.AnMP density of 20,264particles km2was averaged fromnine transactsmaking the lake more polluted than Lakes Huron and Superior. Nomicrobeads were found with fragmentsandfilms insteadbeing themostabundantMPshapes.Theshorelinewas dominated by discarded household waste (bottles, plastic bags) and fishing gear, andthelikelysourceof thepelagicMPswasthedegradationof thisshorelinedebris [25]. Thus even low population densities can cause significant levels of MP pollution in the absence of waste management infrastructures. Taken together it appears that plastics recovered from freshwaters in different parts of the world closely reflect the anthropogenic activities and waste generated by the local populations. Although this would seem obvious, further research is required to verify this link with the aim of more specific waste management relating to the nature of plastic pollutionwithin a given location. To date only two studies have attempted to document the presence of plastic debris inAfrican freshwaters [16, 17], and only one specifically focused onMPs [17].Bothstudieswereconducted in theTanzanianwatersofLakeVictoria, and in the following sections,we describe themas case studies. In addition to providing 108 F.R.Khanet al.