Seite - 112 - in Freshwater Microplastics - Emerging Environmental Contaminants?

being an effective digestant of organic matter, can discolor or degrade plastics. Post-digestion, plastics, and a minimal amount of partially digested tissue were rinsed from theNaOH through 250 μmmesh stainless steel sieves under running waterandplacedonfilterpaper todry.Sampleswere thenbrought to the laboratory (RoskildeUniversity,Denmark), and suspectedplastic pieceswere separated from tissue residue under light dissectionmicroscope. The chemical composition of all suspected plastics was identified nondestructively by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, a standard analytical tech- nique for identifying the chemical composition of samples larger than 0.5 mm. Scanswere runat a resolutionof2cm 1between4,000and650cm 1onaBruker Alpha FT-IR instrument (Bruker, Billerica, MA, USA) fitted with a diamond internal reflectance element. Spectra were compared with standard references on the same instrument andprocessedusingOpus software suppliedbyBruker. In total, suspected plastics were recovered from the gastrointestinal tracts of 11 perch (55%) and 7 tilapia (35%).However, some plasticswere too small (i.e., <0.5mm) to have their chemical structure confirmed byATR-FTIR. In addition, spectroscopy of some suspected plastic samples showed that their compositions most closely resembled cellulose, suggesting these samples were likely plant material or paper originating fromperhaps newspaper, tissues, or cigarette filters. Thus 20% of each fish species (i.e., four individuals) contained confirmedMPs within their gastrointestinal tracts. The polymers recovered from the fish were polyethylene, polyurethane, polyester, copolymer (consisting of polyethylene and polypropylene), and silicone rubber (Fig. 3). The common use of suchmaterials includes packaging, clothing, food and drink containers, insulation, and industrial applications (Table 2).Given thedimensionsof the recoveredplastics (0.5–5mm, Fig. 3), it is likely that theMPs ingestedby thefishare secondaryMPswhichhave resulted fromthedegradationandbreakdownof largerplasticpieces [38].A likely sourceoftheinputofsuchmaterials intotheMwanzaGulfarea isfromthedrainage ditches thatarefilledwithurbanwaste, includingplasticproducts(Fig.2).Thismay beaparticular problemduringheavy rainwhen input into the lake is increased. In commonwithotherstudiesconductedat freshwatersites[10,25], itappears that the nature of theplastic pollution is related to theusage andwaste by the local human population. Thisworkprovided thefirst evidence thatMPsarepresent in theAfricanGreat Lakesandthat theyare ingestedbyeconomically importantfishspecies. Inaddition to confirming the ingestion ofMPs by freshwater fish species [48], the chemical compositionof theMPswasdetermined.However, this isonlyapreliminary study andonly limitedconclusionscanbedrawn.Withplasticsconfirmedinonly20%of both species, the study likelyunderestimates the true extent of plastic ingestionby Nile perch and Nile tilapia, especially when considering the constraints of ATR-FTIR analysis and the inability to confirm the identity of the smaller-sized suspected “MPs.” Similarly, it is not possible to determine whether the feeding preferences of the two species effected their ingestionof plastics. Thus,while this studyprovidesevidencefor theingestionofsecondaryMPsbyfishpopulations, it is clear that further researchneeds tobeundertaken inLakeVictoria to fully charac- terize the extent ofMPpollution. 112 F.R.Khanet al.