Abstract
Human activities can have dramatic effects on animal populations around urban areas with heavy metal contamination being a primary cause of harm. Amphibians, as residents of aquatic systems and with their semi-permeable skin are especially susceptible to heavy metal contamination. To better understand the effect of heavy metals on Wild African Tiger frogs (Hoplobatrachus occipitalis) and the resulting production of oxidative stress enzymes, the concentrations of the heavy metals, cadmium (Cd), copper (Cu), iron (Fe), zinc (Zn), lead (Pb) and nickel (Ni) were investigated in the tissues of H. occipitalis as well as in water and sediment samples collected from five different locations in Lagos State, Nigeria. The activities of superoxide dismutase (SOD), reduced glutathione (GSH) and level of lipid peroxidation product, malondialdehyde (MDA) were analyzed in the liver of the sampled frogs. Most measured physicochemical characteristics of the water varied significantly across the sampling locations (P<0.05). The levels of metals (mg/kg dry weight) in muscle tissues also varied significantly across the locations (P<0.05) and ranged as follows: Cd: 0.21-5.03, Cu: 0.74-13.40, Fe: 3.19-109.10, Zn: 3.70-120.20, Pb: 0.12-18.24 and Ni: 3.20-7.28. Zn was the most accumulated metal, followed by Fe, Cu and Ni, while Pb was the least. The mean of SOD and reduced GSH in the frogs indicate some responses to oxidative stress which varied significantly among sampling areas (P<0.05). MDA values however did not consistently correlate with either oxidative stress or heavy metal concentrations in the frogs. The water-sediment-tissue analysis for heavy metals demonstrated that the sediment concentrated more heavy metals than water, while the frog tissues accumulated these metals particularly in more polluted areas. Key words: Heavy metal pollution, bioaccumulation, Hoplobatrachus occipitalis, biomarkers, oxidative stress.
Highlights
Heavy metal pollution is ubiquitous in our environment (Don-Pedro et al, 2004) and results from diverse activities such as industrial effluents, foundry wastes, wearing of metal parts and equipments, paints, automobiles, mining and rock weathering
This trend was reflected in the high acidity, Chemical oxygen demand (COD), sulphate and low pH recorded in most areas around the industrial town of Amuwo
total suspended solids (TSS) was above the Nigerian Federal Environmental Protection Agency (FEPA) acceptable limit of 30 mg/l at the three most polluted sites (Amuwo-Odofin, Ojo and Yaba)
Summary
Heavy metal pollution is ubiquitous in our environment (Don-Pedro et al, 2004) and results from diverse activities such as industrial effluents, foundry wastes, wearing of metal parts and equipments, paints, automobiles, mining and rock weathering. It is commonly speculated that amphibian species may be globally on decline (Wake and Vredenburg, 2008) Their decline and loss of viable populations has been attributed to habitat destruction, introduction of invasive species, over exploitation, emerging diseases, pathogens, climate change and environmental contamination (Becker et al, 2007; Smith et al, 2009; Hayes et al, 2010). A number of pollutants including heavy metals have been linked with the presence of free radicals which may induce oxidative stress in biological systems (Osuala, 2012) Certain biosynthetic mechanisms, such as induction of low molecular weight proteins exists which have been attributed to the ability to inhibit metal activity and possibly their absorption into the bloodstream of Rana ridibunda (Loumbourdis et al, 2007). The presence of these proteins can be a protective mechanism for managing oxidative stress and can confer tolerance to heavy metal pollution
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