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(Oreochromis variabilis) and Singidia tilapia (Oreochromis esculentus), which
subsequently disappeared from parts of the lake [49, 50]. Thus Nile perch and
Nile tilapia have established themselves as dominant commercial and ecological
speciesandtherefore represent logicalchoicesbywhichtomonitorMPpollutionin
the area.Moreover, their differing feeding habits could provide additional infor-
mation bywhich to contextualize plastic ingestion. Nile perch are predatory fish
feeding on haplochromine cichlids and gastropod snails, whereas Nile tilapia are
omnivorouswith a diet consistingof plankton andfish.
InMarch 2015, 20 fish of each species were purchased fromMwanza harbor
market,wherefish are caught and solddaily. Thefishing territory for both species
extends to Ukerewe Island (the largest island in Lake Victoria) to the North of
Mwanza and across the Mwanza Gulf to the neighboring district of Sengerema
(Fig. 2). Nile perch andNile tilapia were 46–50 cm and 25–30 cm in length and
500–800 g and 500–700 g inweight, respectively. For each fish, the dissection of
the entire gastrointestinal tract (buccal cavity to anus)was conducted on site. All
efforts were made to eliminate sample contamination with separate clean dishes
used for eachfishand thoroughcleaningofdissectionutensils betweensamples.A
preliminaryexaminationwasmadeofeachgastrointestinal tract, and in thecaseof
Nile perch, undigested gastropods and cichlids were removed. Gastrointestinal
tracts and their contents were then individually preserved in 96% ethanol and
transported to laboratory facilities at the University of Dar es Salaam (Dar es
Salaam, Tanzania), a journey of approximately 1,150 km. In the laboratory,
NaOHdigestion (10MNaOH at 60 C for 24 h) was used to isolate plastic litter
fromtheorganic tissue.TheNaOHmethodhasbeenshowntodigestorganicmatter
with an efficacy of>90% [51], and the tests of this protocol prior to its use
confirmedsuchhighefficiencies(96.6 0.9%,n¼5,datanotshown). Importantly,
NaOH digestion has a minimal impact on the chemical and physical states of
plastics, especially when compared to strong acid digestion which, while also
Fig.2 Mapof theLakeVictoria studyarea showing theMwanza region. (a)NileperchandNile
tilapiawerepurchasedfromtheharbormarketatMwanza(regionalcapital).Thelocalfishingarea
extends across theMwanzaGulf and toUkerewe Island. Inset LakeVictoria (LV) bordered by
Uganda,Kenya,andTanzania.TheMwanzaregionlocatedonthesouthernshoreofLakeVictoria
is highlighted. (b)Urbanwaste inMwanza, including plastic debris, collects in drainage ditches
whichareapotentialsourceofplasticpollutioninLakeVictoria. (c)NileTilapiausedinthisstudy
(photographedprior to dissection)were purchased from themarket
Microplastics in InlandAfricanWaters: Presence, Sources, andFate 111
Freshwater Microplastics
Emerging Environmental Contaminants?
- Titel
- Freshwater Microplastics
- Untertitel
- Emerging Environmental Contaminants?
- Autoren
- Martin Wagner
- Scott Lambert
- Verlag
- Springer Open
- Datum
- 2018
- Sprache
- englisch
- Lizenz
- CC BY 4.0
- ISBN
- 978-3-319-61615-5
- Abmessungen
- 15.5 x 24.1 cm
- Seiten
- 316
- Kategorien
- Naturwissenschaften Chemie