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Occurrence of microplastics in surface water, superficial sediments and Nile tilapia (Oreochromis niloticus) from fish breeding areas of Lake Victoria
Summary
Microplastics were detected in 100% of water samples, 83% of sediment samples, and 56% of Nile tilapia from four breeding sites in Lake Victoria, with urban sites showing higher contamination. Filaments were the dominant microplastic form, and microplastics found in fish gills raise concerns about direct human exposure through consumption.
Lake Victoria, the largest African Great Lake and the world’s second largest freshwater lake by surface area has several bays and inlets along its shoreline, which serve as breeding grounds for fish. The ecological and economic importance of these bays are now under threat due to rapid urbanization and agricultural expansion that have introduced pollutants into them. Using stereomicroscopy and micro-Fourier transform infrared (µ-FTIR) imaging, we investigated the occurrence of microplastics (MPs) in surface water (n = 12), superficial sediments (n = 12) and Nile tilapia (Oreochromis niloticus, n = 66) from four fish breeding areas (Port Bell, Masese, Kigaya and Nabulugo) on the northern shores of Lake Victoria. The frequency of MPs detection was 100%, 83.3% and 56.1% in surface water, sediments and fish samples, respectively. The corresponding microplastic counts were 22–60 particles/L, 2–10 items/kg and 1–16 items/fish. Port Bell and Masese that are in close proximity to urban areas had higher microplastic contamination than Kigaya and Nabulugo, which are in less disturbed sites (P > 0.05). Across all the samples, filaments were the most dominant form of MPs (43.1–100%), followed by fragments (7.8–55.6%), fibers (2.2–21.4%), foams (5.3–31.1%) and pellets (1.7–6.7%). The particles were confirmed by µ-FTIR to contain mainly polyethylene, polypropylene and polystyrene. Total length of fish from Nabulugo showed a strong and significant negative correlation (ρ = – 0.753, P = 0.01) with the number of MPs ingested, indicating that larger fish are associated with lower microplastic loads. Branchial intrusion of MPs in Oreochromis niloticus provide evidence of potential direct human exposure to MPs through consumption of this fish species. These results indicate that there is a growing threat of MPs to fishery sustainability and food safety in Lake Victoria, emphasizing the need for targeted policy interventions to mitigate plastic pollution in catchments of fish breeding habitats. Microplastics were found in water, sediments and Nile tilapia, with smaller fish having more pieces. Fish breeding areas near urban settings are more polluted with microplastics than remote locations. The presence of microplastics in tilapia gills indicate a possibility of low level microplastic exposure for individuals who consume the fish with its gills intact.