Abstract
An assessment of the fish health status and human health risk associated with consumption of fish from Itezhi-tezhi Dam, Kafue River, Zambia
The Kafue River in Zambia is the largest tributary of the Zambezi stretching across five provinces, sixteen districts and three national parks. The Itezhi-tezhi Dam is located on the Kafue River approximately mid-course from the river’s source. The Kafue River is both ecologically and economically important to Zambia. A lot of fishing is carried out in the Itezhi-tezhi Dam for commercial and subsistence purposes. The river is a major source of water for domestic and industrial purposes. It also provides drinking water and habitat to fish and other wildlife.
Despite the highlighted importance, the Kafue River is prone to mining pollution which risks the health of fish, other wildlife and humans. Copper mining is carried out in the upper Kafue River Basin and effluents from the mines are discharged into the river. Considering the highlighted pollution, the fish health status and human health risk associated with consumption of the fish from the Itezhi-tezhi Dam has not been studied. The aim of the present study was to determine the fish health status in the Itezhi-tezhi Dam and the human health risks arising from fish consumption using the commonly consumed native Three-spot Tilapia (Oreochromis andersonii) as a bioindicator.
Fish were sampled from the Itezhi-tezhi Dam and a near-pristine reference sited located upstream of the Dam near the source of the Kafue River before it enters the mining region. Sampling was carried out over a two-year period in both the high-flow and low-flow seasons. Sixty fish were sampled from each site. A necropsy-based qualitative and semi-quantitative histology assessment protocol was used to evaluate fish health. Condition factor was calculated from body measurements and used to evaluate possible effects on fish growth rate. Organosomatic indices calculated from organ mass measurements were used to assess possible effects on organ size. Visceral organs comprising the gills, gonads (ovary and testes), heart,
ix
kidneys and liver were examined for histological alterations. The alterations were quantified using a scoring method to establish an organ index for each organ. The organ indices were summed into a fish index for each individual fish. Pollution was evaluated by measuring the physicochemical water quality parameters and analysing for metal content in the water, sediment and fish muscle. Inductively coupled plasma mass spectrometry was used in the metal analysis. The physicochemical water quality parameters measured were total dissolved solids (TDS), pH, electrical conductivity (EC) and temperature. The biota sediment accumulation factor (BSAF) was used to assess metal bioaccumulation in fish. The hazard quotient (HQ) derived from a standard procedure adapted from the United States Environmental Protection Agency (USEPA) was used to evaluate human health risk. All quantitative variables were compared between the Itezhi-tezhi Dam and the reference site using R statistical software (version 3.6.3).
Mean TDS, pH and EC were significantly higher at Itezhi-tezhi Dam compared with the reference site (p <0.05). There was an upward trend in mean metal concentration in water, sediment and fish muscle at Itezhi-tezhi Dam. The upward trend included arsenic (As), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), selenium (Se) and these metals are common in the copper ore. Mean Se and Cu concentrations were significantly higher in Itezhi-tezhi Dam sediment. Selenium at the reference site was below detection limit in water and sediment (<0.010 mg/L and <0.010 mg/kg respectively). Mean Cu, Mn and Se concentrations were significantly higher in fish muscle from Itezhi-tezhi Dam compared with the reference site (p < 0.05). The BSAF for Cu and Se was greater than 1 (BSAF > 1). There was an increase in histological alterations of mostly degenerative in nature in the gills, liver and kidney of fish from Itezhi-tezhi Dam compared with the reference site. The Itezhi-tezhi Dam had higher gill, kidney, liver and overall fish indices compared with the reference site. The gill and fish indices were significantly higher at the dam compared with the reference site (p < 0.05). The HQ was less than one for all metals with the value for Cu being much higher than that of other metals.
The findings strongly indicate that the Itezhi-tezhi Dam has elevated sediment metals concentration that can be traced to copper mining upstream. There is an increased metal bioaccumulation in fish at Itezhi-tezhi Dam with Cu and Se being
x
bioaccumulated in higher quantities. Fish health in Itezhi-tezhi Dam was adversely affected with the metal pollution being a contributing factor. Further, a daily consumption of 150g of O. andersonii (Kafue Bream) did not indicate any health risk to humans.
Keywords: Fish histopathology, fish health, human health risk, metal pollution, acid mine drainage, hazard quotient