Microplastic concentrations in water and four commercially important fish species in Kisumu Bay, Lake Victoria, Kenya

Abstract

Microplastics (MPs) are fragments of any type of plastic formed through processes such as abrasion and photodegradation and are considered emerging pollutants in aquatic ecosystems. They can be mistakenly ingested by aquatic organisms. Despite the high plastic pollution within Kisumu City, there is inadequate data and infonnation on the levels of microplastic concentrations in water and fish within Kisumu Bay of Lake Victoria. This study aimed to determine levels of microplastics in water and identify polymers of microplastics in water and fish as Well as evaluate the impact they have on fish. The study was conducted at four sites with different anthropogenic impacts; the Airpofl area (close to the shore with minimal anthropogenic activities), Kichinjio (a near shore site characterized by anthropogenic disturbance), River Nyalenda mouth (a site preceded by a wetland and a tourist beach adjacent), and the Open water (the site was situated several kilometres off shore, representing the pelagic zone) within Kisumu Bay of Lake Victoria. Water quality parameters were measured in situ at each sampling site. Sampling was conducted monthly between March and May 2022. A plexiglass water sampler was used to collect composite water samples. Bulk water samples were filtered through a series of stacked sieves (45 - 300 pm mesh sizes) in the field. Deionized water was added to the residue collected in 250 mL glass bottles. Samples of fish species were caught using 3 and 6-inch gill nets set overnight. Microplastics concentrations in the water ranged between 0.85 i 0.04 - 2.41 i 0.15 particles/L at different sites. The concentration of microplastics differed significantly among the sites (Mood’s median test, X2 = 18,22, df=3, p < 0.05). Fish gastrointestinal tracts were examined, and 62 out of 95 (FO = 65.26%) contained MPs. The sampled fish had consumed MPs with different proportions among the species, 75% (Clarias gariepinus), 71.43% (Lates niloticus), 59.26% (Oreochromis niloticus) and 75% (Synodontis victoriae). Poly (perfluorobutadiene) and poly (vinylidene fluoride-co-hexafluoropropylene) were the main plastic polymers found in water. Polystyrene and poly (perfluorobutadiene) were the main plastic polymers found in fish as analyzed by ATR-FTIR spectroscopy. Condition factors for O. niloticus, S. victoriae and L. niloticus were > 1 and below l for C. gariepinus. Positive correlations were observed between microplastic numbers and fish length and weight. However, the low R2 values obtained implied a weak relationship between these parameters. These findings reveal that Kisumu Bay, Lake Victoria is experiencing escalating plastic pollution, with quantitative evidence underscoring the urgent need for targeted environmental interventions and comprehensive plastic waste management strategies.