Browsing by Author "Siwela, A.H."

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    Comparison of oxidative stress biomarkers in Oreochromis mossambicus in minimally and highly disturbed aquatic environments in the Matabeleland region, Zimbabwe
    (African Journal of Aquatic Science, 2022-09-06) Makuvara, Z.; Marumure, J.; Chapungu, L.; Machingura, J.; Siwela, A.H.
    Owing to their ability to provide a functional measure of organismal response to chemical stressors, oxidative biomarkers are useful in ecotoxicological studies to assess disturbance in aquatic environments. This study assessed the use of oxidative stress biomarkers in Oreochromis mossambicus (Peters, 1852) (Perciformes: Cichlidae) to distinguish between minimally and highly disturbed aquatic environments. A water quality index (WQI) and overall index of pollution (OIP) were used to characterize the target sites, namely the Mananda Dam (control, reference site) and Lower Mguza Dam (disturbed site). Forty male O. mossambicus samples were collected from each dam between April and August 2013. Values for the WQI and OIP indices were significantly higher for the Lower Mguza Dam than for the Mananda Dam (p < 0.05). Oxidative stress biomarker evaluation results showed that the activities of glutathione peroxidase (GPx), superoxide dismutase (SOD) and glutathione S-transferase (GST) as well as the malondialdehyde (MDA) concentration in the liver of O. mossambicus were significantly higher in fish collected from Lower Mguza Dam than those collected from Mananda Dam (p < 0.05). The activities of DT-diaphorase (DTD) and catalase (CAT) were significantly inhibited in fish from the Lower Mguza Dam, when compared to those collected from the Mananda Dam (p < 0.05). From these findings, it is evident that oxidative stress biomarkers, such as antioxidant enzyme activity and MDA accumulation, can be used to differentiate minimally and highly disturbed aquatic environments.
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    Effects of chronic exposures of selected heavy metals on the glutathione S-transferase activity of freshwater snails Lymnaea natalensis in Zimbabwe
    (Taylor & Francis, 2019) Mnkandla, S.M.; Siwela, A.H.; Basopo, N.
    The effect of the heavy metals (cadmium, copper, mercury and lead) on snail glutathione S-transferase (GST) was investigated in 2015. Groups of Lymnaea natalensis snails were exposed to heavy metals for 28 days at concentrations reportedly found in the Mguza Dam. Water and food were changed daily. Samples were collected at days 1, 7, 14, 21 and 28 post exposure. Inhibition of GST activity, following cadmium exposures, ranged between 58 and 60%, with a decrease of 30% on day 28. When snails were exposed to copper, inhibition significantly decreased by 16%, 29%, 49% and 72% inhibition when tested on days 1, 7, 14 and 21, respectively. Inhibition on day 28 was 44%. Mercury exposures resulted in significant increases in GST inhibition, namely, 47%, 62% and 79% inhibition on days 1, 7 and 14, respectively. Inhibition on day 21 was 82%, whereas on day 28 it was significantly lower, at 29%. Concerning lead exposures, inhibition levels on day 1, 7 and 21 had mean inhibition of 60%. Inhibition on days 14 and 28 was significantly lower, with a mean inhibition of 30%. These results suggest that chronic exposures could inhibit GST activity for a certain period, after which inhibition is reduced, possibly as a result of adaptation.