DETERMINATION OF HEAVY METAL CONCENTRATIONS IN FISH AND WATER OF IKPOBA RIVER
This study determined the concentrations of Copper (Cu), Iron (Fe), Lead (Pb) and Zinc (Zn) in four fish species (i.e Brycinus nurse, Chrysichthys nigrodigitatus, Hemichromis fasiatus, and Tillapia zilli). This was evaluated in whole fish and water collected from two locations (Okhoro and Bridge) of Ikpoba River, Benin City, Nigeria, in order to ascertain the magnitude of impact by these heavy metals on the resources of the investigated ecosystem. Heavy metal concentrations in water and fish were analysed using an atomic absorption spectrophotometer. The mean concentrations of the heavy metals in water were Cu (0.047-0.063mg/l), Fe (0.067-0.167mg/l), Pb (0.0137-0.0185mg/l) and Zn (0.47-0.53). The mean concentrations of the heavy metals in fish were Cu (B. nurse 1.100mg/kg, C. nigrodigitatus 2.106mg/kg, H. fasiatus 2.060mg/kg, T. zilli 1.480mg/kg,), Fe (B. nurse 78.20mg/kg, C. nigrodigitatus 85.80mg/kg, H. fasiatus 83.30mg/kg, T. zilli 84.64mg/kg), Pb (B. nurse 0.040mg/kg, C. nigodigitatus 0.1408mg/kg, H. fasiatus 0.296mg/kg, T. zilli 0.0452mg/kg), Zn (B. nurse 36.40mg/kg, C. nigrodigitatus 54.54mg/kg, H. fasiatus 88.80mg/kg, T. zilli 37.92mg/kg). The mean concentrations of metals in fish species were not significantly different (P > 0.05), the mean concentrations of metals in water were also not significantly different (P > 0.05) between stations. Metals were bioaccumulated by the fish species at various stations with higher values of Cu and Fe at station 2 and Pb and Zn at station 1. Heavy metal concentrations in fish and water were discussed with reference to the World Health Organisation (WHO) limits for food fish and water, the mean levels of Fe, Pb and Zn in fish exceeded the WHO limits for fish and fishery products. Therefore it was advocated that regular monitoring of heavy metals in fish and water in the River be carried out in order to curtail further negative impacts.
Africa is blessed with a lot of inland water bodies. These aquatic ecosystems could be lagoons, creeks, rivers, streams e.t.c. which play important role in the socio-economic lives of the riverine populace. The inhabitant of these areas depends on these water bodies as a source of livelihood, recreation among other things (Ndimele et al., 2011a). Apart from this, some of these aquatic ecosystems are major nursery grounds for fish species, so they are also important for their continuous existence (Kumolu-johnson, 2004). Fish constitutes an important and cheap source of animal protein to human beings and a large number of people depend on fish and fishing activities for their livelihood. All these benefits are threatened by industrialization in a bid to meet the growing demands of the world population. Nations are investing massively in industrialization, industrial, agricultural and domestic activities have led to the pollution of the Nigerian environment and subsequently increased the problem of waste disposals, however they are not committing enough funds to develop processes that will treat the waste generated by these industries as well as mitigate their effects on the environment and man (Ndimele et al., 2011b). A lot of industrial effluents are emptied into the aquatic environment untreated, in few cases where they are treated, the products of the treatment plants are still potentially harmful to aquatic flora, fauna and even man. One of the common components of industrial effluents is heavy metals (Kumolu-johnson et al., 2005), among environmental pollutants, metals are of particular concern, due to their potential toxic effect and ability to bioaccumulate in aquatic ecosystems (Censi et al., 2006). Therefore, knowledge of the changing concentration and distribution of heavy metals and their compounds in various compartments of the environment is a priority for good environmental management programmes all over the world (Don-Pedro et al., 2004).
Over the last few decades there has been growing interest in determining heavy metals levels in aquatic environment and attention was drawn to the measurement of contamination levels in public food supplies particularly fish. Increasing human influences through heavy metal pollution have however led to the depletion of our fish resources and substantial reduction in the nutritive values (Srivastava and Srivastava, 2008). As a result of these heavy metals pollution several endemic fish species have become threatened. Heavy metal pollution is a serious and wide spread problem due to the toxic, persistent, biodegradable and bio-accumulation properties of these contaminants (Yuan et al., 2009), they are considered as major environmental pollutants causing cytotoxic, mutagenic, and carcinogenic effects in animals (Rauf et al., 2009).
Heavy metals are general collective term which applies to the group of metals and metalloids with a specific gravity or density greater than 4g/cm3 (Duffus, 2002), they are chemical elements with a specific gravity that is at least five times the specific gravity of water. The specific gravity of water is 1 at 4°C (39°F). Simply stated, specific gravity is a measure of density of a given amount of a solid substance when it is compared to an equal amount of water. Heavy metals including both essential and non-essential elements have a particular significance in ecotoxicology, since they are highly persistent and all have the potential to be toxic to living organisms (Storelli et al., 2005). Heavy metals such as copper, iron, chromium and nickel are essential metals since their play an important role in biological systems, whereas cadmium and lead are non-essential metals, as they are toxic, even in trace amounts (Fernandes et al., 2008).
1.1 SOURCES OF HEAVY METAL POLLUTION IN THE AQUATIC ECOSYSTEM