Microplastic pollution of water and fish from Lake Victoria and the potential water decontamination methods

Abstract

Microplastic pollution is one of the most challenging environmental challenges of our times, but it is still an under-studied topic in Uganda. This study aimed to fill the knowledge gap by assessing the occurrence and extent of microplastic contamination of water and fish caught from the Inner Murchison Bay (IMB) of Lake Victoria in Uganda, as well as to evaluate potential microplastic decontamination methods of water. A total of 414 water samples and 45 fish samples (21 Nile Perch Lates niloticus and 24 Nile Tilapia Oreochromis niloticus) were taken weekly from the IMB. The water as well as the gut and gills from the fish were examined for microplastics (MPs), which were then identified using microscopy and the hot needle test. Additionally, distilled water was dosed with varying concentrations of a PE, PET, and PVC mixture and then filtered using a biosand filter, a ceramic filter, 1 layer, 3 layers, and 6 layers of cheesecloth. MP were found in water samples from IMB in varying amounts. The concentration of MP decreased significantly (p˂0.05) as the depth of water sample collection from the IMB increased from 0.5 to 1.5m, but increased non-significantly (p˃0.05) as the depth of water sample collection further increased from 1.5m to 3.0m. MP concentration decreased from an average of 1.13 particles per liter to 0.88 particles per liter as the distance from the shore increased to 1 km. MP concentration also increased from 1.27 particles per liter in October to 1.33 particles per liter in November and then reduced to 1.01 particles per liter in December. Microplastics were identified in 71.42% of the Nile Perch and 66.67% of Nile Tilapia. In the gut, particles ranged from 0 to 0.27 particles per gram of fish part in Nile Tilapia and 0 to 0.5 particles per gram in Nile Perch, while in gills, values ranged from 0 to 1.19 particles per gram of fish part in Nile tilapia and 0 to 0.43 particles in Nile Perch. The number of microplastics in Nile Perch also increased with an increase in MPs in water, while the number of MPs in Nile Tilapia decreased when those in water increased. 81.47% of the MPs identified in fish were fibers, while the rest were pellets. The Biosand filter and ceramic filters were more effective (p˂0.05) in removing microplastics than the 1 layer, 3 layers, and 6 layers of cheesecloth. This study unveiled evidence of the presence of a high concentration of microplastics in the IMB fish and water.