Fish inhabiting freshwater environments are susceptible to the ingestion of microplastics (MPs). Knowledge regarding MPs in freshwater biota in Africa is limited. This study represents the first investigation of microplastic presence in the River Nile in Khartoum, using Nile Tilapia as a bio-indicator.
The prevalence (percentage of burdened fish), abundance (MPs/kg) and intensity (MPs/fish) are calculated. The examined fish showed 100% prevalence. A total of 567 particles were recovered from the digestive tracts of the fish, with intensity ranging from 5 to 45 particles/individual fish, and an average abundance of 72.07 ± 62.06 particles/kg.
The examination of the physical characteristics of MPs revealed a predominance on fibers (85.19%), small-sized particles of < 0.5 mm (30.51%), and (83.60%) coloured MPs. However, MPs of other shapes and sizes were also present in considerable percentages, for instance, 25.93% of MPs were detected in the size range of 0.5-1 mm, and 27.69% were in the range of 1-2 mm. In terms of shape, fragments accounted for 9.52% of the total MPs, while other shapes were present in very small quantities. The chemical characterization of MPs in this study showed two types of polymers, polyethylene (PE) and polypropylene (PP).
The high prevalence of fibers and fragments indicates that MPs pollution in the River Nile is originating from secondary sources. These shapes are formed by the fragmentation of macro- plastics. Their potential sources include domestic and industrial effluent, recreational activities, and surface run-off from urban centres. To the best of our knowledge, this is the first study to report microplastics in the River Nile in Sudan; the findings revealed concerning levels of MP pollution. However, the study provides a benchmark for guiding future monitoring studies and identifying research gaps.