| Abstract |
The Okavango River runs through 3 countries; Angola, Namibia and Botswana and is a major source of water for drinking and other domestic uses for the basin communities in the riparian states. Developments in the 3 countries, e.g. agriculture, tourism, mining, power generation industries, etc., are putting pressure on the river’s water quality which threatens both human and overall ecosystem health. Data is therefore needed to monitor changes of water quality as a result of both natural and anthropogenic sources. The objective of this study was to quantify the concentration levels of aluminium (Al) and beryllium (Be) at three sites (Mohembo East, Sepopa and Guma) of the Okavango Delta’s panhandle, study the influence of water discharge and pH on concentration of these metals and evaluate the human health risks associated with their occurrence. Surface water samples were collected in triplicates every three weeks from 3 sampling sites between July 2014 and October 2015. Samples were preserved with nitric acid and stored in the laboratory before analysis. Direct analysis with ICP-OES was used to determine their concentrations. Al values ranged from 0.032 – 0.305mg/L at Mohembo East; 0.005 – 0.333 mg/L at Sepopa and 0 – 0.151mg/L for Guma. Be concentrations ranged between 0 – 0.008mg/L at all three sites. There were no significant differences (P>0.05) between the three sites in concentrations of these metals. Seasonal variations in metal concentrations were observed for both metals, with the highest concentrations occurring around October, coinciding with lowest water levels. In accordance with the WHO regulatory limits for drinking water, the mean concentrations of both Al and Be, and the calculated hazard quotient(HQ) which was less than 1, do not pose any long term human health threats. However, both metals need to be monitored because concentrations above 200μg/L for Al and 4μg/L for Be (WHO acceptable limits) were exceeded at times at these sampling sites, which may cause acute toxicity to humans and aquatic organisms. From this study, we concluded that both aluminium and beryllium exist in the Okavango River at concentrations comparable to world river values. We recommend a more comprehensive monitoring programme for toxic metals in the Okavango River to ensure protection of both human and ecosystem health. |
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