SPATIO-TEMPORAL VARIATION OF HEAVY METAL CONCENTRATIONS IN WATER, SEDIMENT AND IN SELECTED FISH SPECIES IN SHIRORO LAKE

ABSTRACT

Anthropogenic activities contribute the most to heavy metals pollution of water bodies around the world. This study was conducted to determine the spatial and temporal variation of heavy metal concentrations in sediment, water and in selected fish muscle from Shiroro Lake Niger State, Nigeria. Sediments and water samples were collected from three different stations across the lake for a period of eight (8) months between February and September 2019. Heavy metals that were analyzed were chromium Cr, cadmium Cd, lead Pb, zinc Zn and copper Cu. Analysis of heavy metals was carried out on the muscles of three commercially important fish species in the lakes, which were Alestes   macrolepidotus,   Bagrus   bayad   and   Clarias   gariepinus.   Water   quality parameters showed that dissolved oxygen ranged from 2.20 – 4.10 mg/L, temperature, 26.60 – 30.20 oC, biological oxygen demand, 1.20 – 3.00 mg/L, conductivity 49 – 120 µS/cm, alkalinity 18 – 36 mg/L, phosphate 0.16 – 2.28 mg/L, sodium 7.56 – 14.00 mg/L, pH 6.56 – 7.96, total dissolved solids 75 – 99 mg/L, total hardness 30 – 48 mg/L and potassium 1.16 – 2.42 mg/L. Analysis of the concentration of heavy metals of sediment samples collected across the three stations showed that zinc ranged 0.095 – 0.25 mg/l, copper 0.015 – 0.905 mg/L, lead 0.00 – 0.15 mg/L, chromium 0-0.03 mg/L and cadmium 0  –  0.015  mg/L.  Analysis  of  the  concentration  of  heavy  metals  of  water  samples collected across the three stations showed that zinc ranged 0.01 – 0.18 mg/L, copper 0.01 – 0.165 mg/L, lead 0 – 0.2 mg/L, chromium 0.00 – 0.01 mg/L and cadmium 0 – 0.01 mg/L. Cadmium exceeded the toxicity threshold in the water sample in line with World Health Organization (WHO) standard in drinking water. The result also showed higher levels of Zn 1.47 ± 0.50 mg/g and Cu 0.73 ± 0.31 in fish in comparison to other heavy metals examined. All the heavy metals in fish samples were below WHO maximum stipulated limit. The results of the mean values of potential ecological risk index (PERI) across all stations showed that Zn 0.083, Cu 0.29, Pb 2.06, Cr 0.03 and Cd 0.48 while the comprehensive PERI value ranged between 0.617-6.902, therefore the PERI value obtained showed that the ecological risk level is slight. The results of the mean values of the Geo-accumulation index reported that Zn -2.42, Cu -2.06, Pb -1.56, Cr – 0.92, and Cr -0.75, therefore the geo-accumulation index values of the five heavy metals analyzed for  across  all  three  stations  obtained  from  this  study  were  negative  i.e.  (<0),  this indicates an unpolluted state of the sampling stations. The results of the mean values of the enrichment factor (EF) reported that Zn 0.08, Cu 0.05, Pb 0.41, Cr 0.02, and Cr 0.02. Enrichment factor (EF) values of the five heavy metals analyzed for across all three stations obtained from this study were below one (<1), this indicates crustal enrichment origin of the sampling stations. The result of physicochemical parameters obtained from this research indicates a low level of pollution because all the water quality parameters recorded were either slightly below or within WHO permissible limit. The water in Shiroro Lake is not safe for human consumption as it can lead to Cd exposure.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Aquatic  ecosystem  is  the  ultimate  recipient  of  almost  everything  including  heavy metals. This has long been recognized as a serious pollution problem (Farombi et al.,

2007). The importance of freshwater ecosystems to human survival and sustenance can never be discounted. However, there is now persistent increase in pollution of water bodies that is directly or indirectly related to increasing urbanization and indiscriminate disposal of agrochemical and industrial effluents into aquatic systems (Dua and Gupta,

2005). Anthropogenic sources of heavy metal pollution in aquatic environments include industrial discharge, domestic sewage; non – point source runoff and atmospheric precipitation. However, metals also occur in small amounts naturally and enter aquatic systems through ore-bearing rocks, wind-blown dust, forest fires and vegetation (Fernandez-Leborans and Olalla-Herrero, 2000).

In developing countries, heavy metal analysis in freshwater is very important because these ecosystems provide drinking water and are habitats for flora and fauna (Asare et al., 2018). Fish is considered as one of the most significant indicators of heavy metal pollution in aquatic environment (Rashed, 2001). Fish are well known for their major role in the aquatic food-web and they can take up and accumulate high metal concentrations from surrounding water and food (Mansour and Sidky, 2002). The concentrations of heavy metals in fish depend on body size and age of the individuals, ecological needs, their life cycle and life history, feeding habits, season of capture, some abiotic factors like temperature, dissolved oxygen, pH, conductivity of water (Shrivastava et al., 2003) and other factors that influence the metabolic rate of fish

(Canpolat and Çalta, 2003).   Abiotic factors change from season to season. And this affects the accumulation of heavy metals in tissues of fish (Canpolat and Çalta, 2003; Eastwood and Couture, 2002).

The results of many reported studies underlined that heavy metals in fish inhabiting polluted waters can be considerably accumulated by these organisms without causing mortality. Principally, fish assimilate the metals by three possible ways (body surface, gills or digestive tract) (Dallinger et al., 1987; Pourang, 1995). The body surface is generally assumed to play a minor role in heavy metal uptake of fish (Dallinger et al.,

1987; Pourang, 1995). For these reasons, the estimation of risk potential for human consumption of fish accumulating high quantities of heavy metals in their tissues is very important (Oglu et al., 2015). Some edible species of fish have been widely investigated for those hazardous effects of heavy metals on human health (Begum et al., 2005).

Sediments are important sinks for heavy metals in aquatic ecosystem. These metals are non-biodegradable and once discharged into water bodies, they can either be adsorbed on sediment particles or accumulated in aquatic organisms. Heavy metal pollution may increase the susceptibility of aquatic animals to various diseases by interfering with the normal functioning of their immune, reproductive and developmental processes (US Environmental Protection Agency 2010).

Heavy metals could be found in water at the trace levels. Nonetheless, these constituents are very toxic and tend to accumulate in a long period of time. Heavy metals such as Pb, Cd and Cr are micro-pollutants and of special interest as they have both health and environmental significance due to their persistence, high toxic and bio-accumulation characteristics in water (World Health Organization 2008). Heavy metals in human body can cause serious health risks, hence the need to know the concentration of heavy

metals in water, sediment and selected fishes in Shiroro lake because of its daily usage by man and proximity to urban pollution. In this study muscle was chosen as the target organ for accessing heavy metal accumulation because of its importance for human consumption and as a primary site of metal accumulation (Kotze et al., 2012).

1.2       Statement of Research Problem

Pollution by heavy metals has been of great concern in the last decades because of their health  hazards  to  man  and  other  organisms  when  accumulated  within  a  biological system. In most Nigerian reports, heavy metals contamination results from absorption in contaminated water or via associated food (Aransiola et al., 2013). Over the last decades the freshwater environment has been polluted by different pollutants which originate from agricultural and industrial activities (Kalay and Canli, 2000). Heavy metals contamination in aquatic environment is of critical concern, due to toxicity of metals and their accumulation in aquatic habitats. Trace metals in contrast to most pollutants, are not bio-degradable, and they undergo a global ecological cycle in which natural water are the main pathways in which they are accumulated. Heavy metal being non- biodegradable, they can be concentrated along the food chain, producing their toxic effect at points after far removed from the source of pollution (Tilzer and Khondker, 1993).

All metals are virtually toxic if the exposure level is sufficiently high to exceed the tolerance limit. Specifically, some metals like (Cd, Pb, and Zn) have been reported to be extremely dangerous to human health even at low level of concentration (Ubalua et al.,

2007). Aquatic sediments can act both as a source and a sink for pollutants, whereby contaminants can lead to sediment concentrations that can exceed water concentrations (Barron, 1995). Sediment associated metals pose a direct risk to deposit feeding and

detrital benthic organisms and may also represent long-term sources of contamination to higher trophic level (Eimers et al., 2001). Fish are at the higher levels of the food chain and may concentrate large amounts of some heavy metals from the water and also metals can accumulate in human tissues via food chain (Eimers et al., 2001).

Shiroro Lake is a very important water body. It was majorly constructed for the purpose of hydro electrical power supply, which has now for so many years served as a good source of many fish species. With increase in human activities such as industrialization and urbanization around Shiroro Lake and its tributaries, activities such as washing of clothes and the use of detergents introduces pollutant into the water body daily in all the stations. Farming and application of fertilizers, herbicides and insecticides along the banks of the lake during rainy season frequently lead to pollution of the water body. All these human activities are quite rapidly increasing, and is threatening the sustainability and integrity of biodiversity and water quality. Thus there is need to assess the current status of the water quality and concentration of heavy metals in water, sediment, and some selected fish in the lake which will serve and provide baseline information on bio- monitoring guide of Shiroro Lake.

1.3       Justification for the Study

Shiroro Lake is an important source of drinking water for humans and animals. It serves as a means of irrigation of crops by both the rural and commercials rice farmers in the environ. The lake is a source of diverse species of fish for human consumption and commercial activities of the area generating income for young and old fish farmers in the area.  Apart from being a source of fish, it provides a means of transportation for rural dwellers and serves as a lake for generating electricity.

Arimoro et al., (2018) carried out a study on mouthpart deformities in chironomid larvae as bioindicators of heavy metals pollution in Shiroro Lake. The study was carried out in relation to only sediment contamination. Auta et al. (2016) carried out a study on seasonal changes in environmental variables and how the changes affect the chironomid distribution and diversity in Shiroro Lake. Kolo and Oladimeji (2004) carried out a study on water quality and some nutrient levels in Shiroro Lake. So far, no research has been carried out on the lake to assess heavy metal pollution of the lake using fish as a bio-indicator.  Assessment of the physicochemical parameters of the lake will provide a base line data and reference point for assessing periodic (short and long term) changes in the lake caused by anthropogenic activities of man over time. These data may be of high importance in environmental impact assessment for the water body and fisheries management. Monitoring water quality of Shiroro Lake would provide information and measures of improving and sustaining the aquatic ecosystem. This could also serve as bio-indication for monitoring changes in chemical condition and toxicity of the lake which could help to initiate policy for overall management of the ecosystem health and its productivity.

Information from the research would help in the improvement of sustainable fishing and other aquatic organisms without reducing their population density over a long period of time.  This  may  help  in  the  conservation,  effective  utilization,  and  sustainable exploitation of the vast aquatic resources that are available in the lake which is the mainstay of all the riparian communities around the lake.

1.4       Aim and Objectives of the Study

The aim of this study was to evaluate the spatio-temporal variation of heavy metal concentrations in sediment, water and in selected fish muscles in Shiroro Lake, Niger state.

The specific objectives of the study were to determine the:

i.    Physicochemical   parameters   (pH,   Alkalinity,   Dissolved   Oxygen   (DO), Temperature, Total dissolved solid (TDS), Conductivity, and Biochemical Oxygen demand (BOD) of the lake

ii.  Seasonal variations of heavy metal (Pb, Zn, Cr, Cu and Cd) concentrations in water, sediment and in the fish muscle

iii. Relationships between the metal levels in water, sediment and fish muscle

iv. Health status of the lake using ecological risk indices (Potential Ecological Risk

Index (PERI), the Geo-accumulation index, and Enrichment Factor (EF)).

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