Bioaccumulation of Trace Elements in Fish From Lake Kivu and Its Potential Risk to Consumers in Rwanda

Lake Kivu, located between Rwanda and the Democratic Republic of the Congo, is subject to trace element contamination primarily due to the geological composition of its bedrock, watershed soils, and anthropogenic activities. In this study, we investigated the accumulation of trace elements in 13 fish species from Lake Kivu, with samples obtained from fishermen in Rubavu, Karongi, and Rusizi. The fish samples were digested and analyzed for selected trace element concentrations using atomic absorption spectrophotometry (AAS). The concentrations of trace elements in the fish ranged from 0.07 to 2.53 mg/kg for mercury (Hg), 0.69 to 1.16 mg/kg for cadmium (Cd), 0.28 to 0.76 mg/kg for copper (Cu), 2.58 to 3.83 mg/kg for chromium (Cr), and 0.22 to 0.68 mg/kg for manganese (Mn). The highest bio-concentration factor (BCF) was observed for mercury. Oreochromis niloticus exhibited significantly higher BCFs for mercury compared to other species, with a value of 16,867 L/kg. Haplochromis scheffersi also displayed a high BCF for mercury at 3533 L/kg, followed by Labeo victorianus with a BCF of 2867 L/kg. Mercury (Hg) posed a potential risk for adults in 77% of the fish species analyzed, as indicated by target hazard quotient (THQ) values exceeding 1. Additionally, Cd, Cr, and Hg posed potential risks for children in over 75% of the fish species analyzed. Continuous monitoring of trace element sources and concentrations in the water column and fish of Lake Kivu is urgently needed to assess contamination sources and exposure levels.