Heavy metal contamination in water, sediments and fish from selected wetlands in the Lake Victoria basin of Uganda

Abstract

In Uganda, there is increased industrial and municipal waste disposal into wetlands around Lake Victoria which pose a great threat to different wetland components. A number of studies have been carried out to ascertain the impact of heavy metals in wetlands. Due to the increase in population near the wetlands, there is a higher possibility of receiving more pollutants and effluents hence the necessity of this study. This study assessed the physicochemical parameters and heavy metal concentration in water, sediments and fish from Gabba, Nabugabo, Nakivubo and Lwera wetlands. This study undertook a quantitative research approach with data collected from twelve random sample sites over a period of six months from August 2021 to January 2022. Some parameters were measured in-situ whereas others were analysed at the National Water Quality Laboratory in Entebbe. All water quality analysis was performed according to Standards methods for the Examination of waters and Wastewaters. Heavy metals analysis was done using the inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES) following the American Public Health Association – 23rd Edition. The physicochemical parameters and heavy metals of water analysed were within the recommended limits of the East African Standards (2018) except for Nakivubo wetland which had a higher Chemical Oxygen Demand result of 60mg/L. In all the sediment samples, there were considerable concentrations of Chromium (22.97 mg/Kg - 39.34 mg/Kg), Lead (9.34 mg/Kg-19.32 mg/Kg), Cobalt (2.68 mg/Kg- 3.87 mg/Kg) and Nickel (7.67 mg/Kg-11.43 mg/Kg). In particular, Nakivubo and Gabba wetlands had the highest levels of heavy metal concentrations compared to Lwera and Nabugabo wetlands in as much as there was no significant difference in concentrations across the wetlands. The fish species analysed; Clarias Galiepinus, Clarius Liocephalus and Protopterus are mainly consumed by the local population. Chromium and Nickel concentrations in the fish muscles were observed to exceed the WHO maximum permissible limits in all the wetlands. Gabba and Nakivubo wetlands had cadmium results of 0.189 mg/Kg and 0.116 mg/Kg respectively which is beyond the recommended WHO limits. It is therefore recommended that collaborative engagement with the respective stakeholders be pursued to create awareness in communities on the apparent health risks from consuming this fish but also improve the regulatory framework of catchment-based water quality goals that would aim at reducing heavy metal loads. Continuation of regular monitoring by relevant authorities’ guidance for proper wetland management, conservation policies implementation and further research on the pollutant retention ability of these wetlands to be urgently undertaken.