Preliminary Assessment of Some Heavy Metals Pollution Status of Lisikili River Water in Zambezi Region, Namibia (Published)
Good water quality is fundamental to human health and sustenance of aquatic ecosystems. The Lisikili river in Zambezi region, Namibia is a major perennial river which serves diverse economic purposes in the host community. However, it is now receiving pollution threat from effluents discharge and surface run-off from large agricultural lands. Eight (8) water samples were collected at 8 random points within a stretch of approximately 2km on each extremity and median parts of the river. Two major economic fish from the river, tilapia fish (Oreochromis niloticus) and cat fish (Siluriformes) (8 samples of each) were collected using fish net at the points of water sampling. The samples were transported to analytical laboratory in ice boxes for processing and analyses for the levels of Pb, As, Cr, Cd, Cu, Zn, Mn and Fe using Inductively Coupled Plasma-Optical Emission Spectrophotometer (ICP: Perkin Elmer Optima 7000 DV). The results obtained showed wide mean concentrations of the heavy metals in the river water; iron recorded the highest level of 2.375 mg/l and arsenic (0.047 mg/l) recorded the lowest level. Apart from Zn (0.259 mg/l) and Cu (0.073 mg/l) with the present concentrations lower than their guideline permissible limits, the mean concentrations of the other heavy metals exceeded their maximum permissible guideline values for the protection of human and aquatic health. Based on the classification of metal pollution index (PI) for water, apart from Cu (PI = 0.03) and Zn (PI = 0.04); all the other heavy metals recorded pollution indices which suggest moderate to strong effect on the river water quality. In both the catfish and tilapia fish (wet weight whole sample), iron (4.926 mg/kg and 3.323 mg/kg) recorded the highest mean concentration while Cd (0.136 mg/kg and 0.078mg/kg) recorded the lowest level respectively. Generally, the present levels of the heavy metals were below their regulatory limits for the protection of human health. However, the fish’s bio-accumulation factors of the metals suggest that they have high potentials to bio-accumulate some of the heavy metals to high levels and this has adverse implication for human consumption. Because heavy metals are non-biodegradable and bio-accumulative in nature which therefore, make their presence in human foods even at very minute levels potential toxins, it is important to monitor their accumulations in the river and fish and advice precautionary measures to limit excessive human exposures to the heavy metals content.