Heavy Metal Levels in Water, Sediment and Tissues of Sarotherodon melanotheron from the Upper Bonny Estuary, Nigeria and Their Human Health Implications

Abstract

Heavy metals in small amounts or in excess of permissible limits in aquatic organisms may pose a health risk to their consumers. The aim of this study was to investigate the levels of heavy metal in water, sediment and tissues of Sarotherodon melanotheron , from the Upper Bonny Estuary in the Niger Delta and to evaluate their human health implications. Water, sediment and S. melanotheron samples were collected from 5 different stations namely; Okochiri Creek (S1), Ekerekana Creek (S2) - Point of industrial effluent discharge (POD), Okari-Ama Creek (S3), Ogoloma Creek (S4) and Bonny Estuary (Control). The levels of Cr, Ni, Zn, V, Cd, Pb, Hg, and As were analysed following Standard Procedures using Atomic Absorption Spectrophotometer (AAS). Metals analysed were below detectable limit (0.001 mg/L) in water while metals such as Pb, Cr, Ni, Zn and V were below permissible limit in sediment. Ecological indices indicated that the sediment of the study area was unpolluted. The levels in the tissues (gill, muscle and liver) showed varying concentrations. Ni concentration in the tissues exceeded FAO/WHO permissible limits, Cr was above permissible limit in most tissues, while Pb was only detected in the muscle of S. melanotheron from Okari-ama Creek (S3). Zn and V were below the FAO/WHO permissible limit. Cd, As, and Hg were not detected in all samples. BSAF showed bio-accumulative potentials in the tissues. Further calculations on the risk associated with consumption of S. melanotheron showed that HQ and HI were <1 which showed no threat to public health. However, more studies on heavy metals and proper monitoring of the creeks should be encouraged by regulatory agencies in Nigeria to give informed decisions from risk assessments.