Good water quality is fundamental to human health and sustenance of aquatic ecosystems. The Lisikili river in Zambezi region, Namibia is a major perennial river which serves diverse economic purposes in the host community. However, it has been receiving pollution threat from effluents discharge and surface run-off from intensive agricultural lands, as well as cottage and hospitality industries and no research has been carried out on the pollution status of the river. Thus, the main aim of this study is to conduct preliminary assessment of some heavy metals pollution status of the river water. Eight (8) water samples were collected at 8 random points within a stretch of approximately 2km on each extremity and median parts of the river. Two major economic fish from the river, tilapia fish (Oreochromis niloticus) and cat fish (Siluriformes) (8 samples of each) were collected using fish net at the points of water sampling. The samples were transported to analytical laboratory in ice boxes for processing and analyses for the levels of Pb, As, Cr, Cd, Cu, Zn, Mn and Fe using Inductively Coupled Plasma-Optical Emission Spectrophotometer (ICP: Perkin Elmer Optima 7000 DV). The results obtained showed wide mean concentrations of the heavy metals in the river water; iron recorded the highest level of 2.375 mg/l and arsenic (0.047 mg/l) recorded the lowest level. Apart from Zn (0.259 mg/l) and Cu (0.073 mg/l) with the present concentrations lower than their guideline permissible limits, the mean concentrations of the other heavy metals exceeded their maximum permissible guideline values for the protection of human and aquatic health. Based on the classification of metal pollution index (PI) for water, apart from Cu (PI = 0.03) and Zn (PI = 0.04); all the other heavy metals recorded pollution indices which suggest moderate to strong effect on the river water quality. In both the catfish and tilapia fish (wet weight whole sample), iron (4.926 mg/kg and 3.323 mg/kg) recorded the highest mean concentration while Cd (0.136 mg/kg and 0.078mg/kg) recorded the lowest level respectively. Generally, the present levels of the heavy metals were below their regulatory limits for the protection of human health. However, the fish’s bio-accumulation factors of the metals suggest that they have high potentials to bioaccumulate some of the heavy metals to high levels and this has adverse implication for human consumption. Because heavy metals are non-biodegradable and bio-accumulative in nature which therefore, make their presence in human foods even at very minute levels potential toxins, it is important to monitor their accumulations in the river and fish and advice precautionary measures to limit excessive human exposures to the heavy metals content.
1.1 Background to the study
Heavy metals are natural components of the environment but they have become a matter of great concern because of the continuous increase in concentration of these metals in our environment (Abah et al, 2013). In particular, studies on heavy metals pollution of rivers, lakes, fish and sediments have become a major environmental focus in the recent decades (Ali and Fishar, 2005). The pollution of aquatic environment by chemical agents such as heavy metals poses adverse threat to aquatic organisms including fish, and this could yield extended effects on the human food chain. Heavy meals concentrations in the aquatic organism depict the past as well as the current pollution load in the environment in which the organism lives (Ravera et al., 2003).. Water pollution occurs when unwanted materials with potentials to threaten human and other natural systems find their ways into rivers, lakes, wells, streams, boreholes or even reserved fresh water in homes and industries (Aboyeji, 2013). According to this author, the effect of water pollution can be catastrophic, depending on the kind of chemical pollutants, concentration of the pollutants and where the pollution occurs. In aquatic ecosystem, the contamination by heavy metals is a serious threat because of their toxicity, and environmental persistence with possibilities for bio-accumulation and bio-magnification in the food chain. Aquatic organisms, including fish, accumulate pollutants directly from contaminated water and indirectly via the food chain (Hammer, 2004; Mohammed, 2009). In the aquatic environment, the trace elements are partitioned among various environmental components (water, suspended solids, sediments and biota) (Shakweer and Abbas, 2005).
Due to increased human population with the attendant anthropogenic activities, both surface and underground water supplies are now affected and deteriorating fast worldwide. Water pollution has been indicated to be the leading cause of death and diseases worldwide (Pink, 2006), and accounting for more than 14,000 deaths of people daily (West, 2006). A report by the Food and Agricultural Organization of the United Nation (FAO) revealed that in African countries, water related diseases had been interfering with basic human development (FAO, 2007). This scenario has raised serious concerns to World Health Organization, in an attempt to improve the cultural and socio-economic standards of people in the tropical region (Umeh et al., 2004). Research report has shown that in addition to the acute problems of water pollution in developing countries, the developed countries also continue to struggle with the same pollution problems (Aboyeji, 2013). For example, in the national report on water quality in the United States, 45 percent of assessed stream miles, 47 percent of assessed lake acres, and 32 percent of assessed bays and estuarine square miles were classified as polluted (EPA, 2007). A report by Hays (2013) indicated that the China government in summer of 2011 reported that 43 percent of state-monitored rivers are so polluted, and are unsuitable for human contact. It was further submitted that by one estimate, one-sixth of China’s population is threatened by seriously polluted water. Pyrbot and Laloo, (2015) in a study on the toxic elements of a river noted that water is the most important and precious natural resources that is essential for the survival of living organisms, and which man has exploited more than any other resources for the sustenance of life. River water pollution can be linked to the type of waste water produced by urban, industrial, and agricultural activities that flow into surface and subsurface waters (Vittori et al., 2010).
1.2 Statement Of The Problem
The increasing quantities and heterogeneity of effluents discharged into water bodies have greatly affected the natural processes of pollutants reduction. Thus, regular monitoring of the qualities of water resources is absolutely necessary to assess the quality of water for ecosystem health and hygiene, industrial use, agricultural use and domestic use (Poonam et al., 2013). It has been submitted that the protection of water and aquatic ecosystem from adverse effects of pollutants such as heavy metals is central to environmental risk management (Bere and Tundisi, 2011). The Lisikili river in Zambezi region of Namibia is a high economic resource which serves diverse human needs such as domestic utilization, fishing, and subsistence farm irrigation in the host community. Agricultural contaminations of many resources through fallout, drainage and run-off erosion is highly probable in rivers within the vicinity of intensive agricultural activities (Abah et al., 2013). Where this occurs, it constitutes threat to the sustainable use of the river resources. Even though, the Lisikili river – a major economic river in Zambezi region, is very prone to surface run-off from agricultural lands owing to intensive agricultural activities along the bank of the river, especially its proximity to Kalimbeza National Rice Research field, and effluent discharges from the cottage and hospitality industries within the vicinity of the river, there has not been any documented research on the pollution status of the river. This creates the need to carry out this baseline study with a view to determining the current heavy metals pollution status of the river and provide scientific data for future monitoring of the metals accumulation in the water body. Evaluation and understanding the sources and impact relationship of the effects of heavy metals in water bodies and biological species is important for effective water management, and the preservation of the aquatic ecosystem (Olatunji and Osibanjo, 2012). Thus, it becomes pertinent to carry out preliminary assessment of heavy metals pollution status of the Lisikili river water and its two economic fishes: tilapia fish (Oreochromis niloticus) and cat fish (Siluriformes) consumed in and around Zambezi region.
1.3 Aim and Objectives of the Research
The aim of this research study is to ascertain the level of concentration of heavy metals in freshwater fish in Lisikili river water, and the objectives are as follows: to
- a) Determine the concentrations of the heavy metals in the river water
- b) Concentrations of the heavy metals in the Fish (Catfish and Tilapia fish)
- c) Determine the Pollution index (PI) and metal index (MI) of the heavy metals in Lisikili river water
- d) Examine Inter-elemental correlation between paired mean concentrations of the heavy metals
1.4 Significance of the Study
Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution studies have been conducted in other areas downstream of River but none is yet conducted at the confluence of heavy metal on fresh fishes
- a) for the first time, provide baseline data on heavy metals (HM) and polycyclic aromatic hydrocarbons (PAHs) for this area of study.
- b) generate data to be used to assess the impact of these heavy metals (HM) and polycyclic aromatic hydrocarbons (PAHs) in water and fish consuming populace in the area of study.
- c) the result will be of use to Health management practitioners in the diagnoses of certain diseases prevalent in the area of study which could be caused by heavy metals.
1.5 Scope of the Study
The study was designed to assess and evaluate the level of Heavy Metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) contamination in the fresh fish and sediments of in Lisikili river water using atomic absorption spectrophotometer for the heavy metals determination and gas chromatography coupled with mass spectrometry (GC-MS) techniques for the determination of the polycyclic aromatic hydrocarbons (PAHs) respectively. The physico-chemical characteristics of the media were also measured using appropriate probes since they are the factors responsible for the environmental mobility and bioavailability of the pollutants. The work was limited to a dry and rainy season for HMs analysis and a rainy season for PAHs analysis and Lisikili river water and three kilometers (3 km) upstream and downstream of river.
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