SECOLOGICAL RISK OF HEAVY METALS IN SURFACE WATER, SEDIMENT AND DOMINANT FISH SPECIES FROM TUNGAN KAWO RESERVOIR, KONTAGORA, NIGER STATE, NIGERIA

ABSTRACT

Developing countries like Nigeria are faced with increased in generation of domestic, industrial and agricultural wastes that found their way into the surrounding water bodies which are slowly contaminating the water. This study was aim to evaluate ecological risk of heavy metals in surface water, sediment and dominant fish species from Tungan Kawo Reservoir, Kontagora, Niger State, Nigeria. Physico-chemical parameters and heavy metals in surface water, sediment and three commercially important fishes were determined in the reservoir water using standard methods from July 2018 – February 2019 at four different sampling stations of human activities around the water.  A total of five heavy metals were selected [lead (Pb), copper (Cu), manganese (Mn), iron (Fe) and chromium, (Cr)]  in the surface water,  sediment and fish  species. The results from physio-chemical parameters showed that, nitrate (3.2 – 7.5 mg/L), temperature (27 – 32.4 0C), dissolved oxygen (2.4 – 5.2 mg/L), electrical conductivity (81 – 125 µS/cm), biochemical oxygen demand (1.9 – 4.4 mg/L), alkalinity (16 – 34 mg/L) and total dissolved solids (117 – 198 ppm) were within standard for drinking water and survival of fishes, however, the pH (6.3 – 9.8) and phosphate (0.4 – 2.5 mg/L) was above the standard for FEPA and NESREA for drinking water but can fairly support aquatic life. The results obtained from heavy metals showed that iron (Fe) and (Cr) had the highest concentration with mean of 6.18 mg/kg and 1.45 mg/kg in surface water and 7.08 mg/kg and 1.54 mg/kg in sediment respectively, followed by Mn with 1.36 mg/kg (sediment) and 0.09 mg/L (water) while Cu had the lowest concentration of 0.03 mg/kg in the Surface water and 0.99 mg/kg in the sediment respectively. Lead was detected in the sediment in low concentration with a mean value of 0.01 mg/kg in Stations 1, 2 and 4 respectively. However, Pb was not detected throughout the time of the study from surface water. In the three fish species examined, iron was the most highly concentrated value (0.64±0.072 mg/kg) in Synodontis clarias while lead (0.01±0.013 mg/kg) was the lowest found in Oreochromis niloticus and Coptidon zillii (formerly Tilapia zillii). The bottom feeders were found to accumulate more of these heavy metals. This indicates the good health status of the reservoir for aquatic biota. The values obtained from risk indices  were  very low  when  compared  with  the  background  values  and  target  for Hakanson risk index of a standard soil and have not constitute any risk to Tungan Kawo Reservoir. This current finding indicates that the water is safe for both aquatic life and domestic purpose but not suitable for direct human consumption without being properly treated. However, there is the need for regular monitoring of the heavy metals load in this water body and the aquatic organisms because of the long-term effects.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Ecological  risk  is  the  term  used  to  describe  a  perceived  threat  posed  by stressors (contaminants) to the survival and health of an aquatic ecosystem (MacFarlane, 2009). The pollution of the aquatic environment with heavy metals has become a world-wide problem during recent years, because they are indestructible and most of them have toxic effects on organisms (MacFarlane, 2009). This has long been recognized as a serious pollution problem (Farombi et al., 2007). There are various sources of heavy metals in the ecosystem such as anthropogenic activities like draining of sewage, dumping of domestic wastes, recreational activities and storm water runoff thereby rendering it environmentally unstable (Malik et al., 2010). Heavy metals find their way into aquatic systems through Agricultural practices like the use of fertilizers, herbicides and pesticides for the control of pests in the cultivation of crops. Other activities such as mining industry as well as growth of the human population have increased the discharge of wastes into lakes and rivers rendering it environmentally unstable (Malik et al., 2010). It may also occur in small amounts naturally through the leaching of rocks, airborne dust, forest fires and deforestation.

Heavy metals are defined as metallic elements with a high relative density compared to water (Duffus, 2002). With the assumption that heaviness and toxicity are inter-related, they include metalloids, such as arsenic, that are able to induce toxicity at low level of exposure. These heavy metals are categorized as potentially toxic agents such as cadmium, lead, and nickel even at low concentrations it can become harmful to human health when ingested over long period of time (Tuzen, 2009).

The toxicity of these chemicals is highly influenced by geochemical factors that influence their bioavailability (Fairbrother et al., 2007). Consequently, the discharge from slaughter houses near lakes as pointed out by Arimoro (2008), has the capacity to pose severe health risk to the populace, if not properly managed. However, World Health Organization, WHO (2008) investigation revealed that about 5 million people die every year from drinking contaminated water.

The family cyprinidae which has a widespread of distribution and widely consumed by human beings in the world today, due to their high protein supply and omega-3 fatty acids that help reduce the risk of certain types of cancer and cardiovascular diseases (Ayanwale et al., 2018). These fishes can as well accumulate heavy metals through the food chain (Mansour and Sidky, 2002).). Fishes are widely used as bio-indicators for the  determination  of  heavy metal  pollution  in  aquatic  ecosystems  (Alibabić,  2007; Ahmad and Shuhaimi, 2010). The concentrations of heavy metals in tissues and organs of fishes could indicate their concentrations in water (Ogbeibu et al., 2002). Fishes are notorious for their ability to concentrate heavy metals in their muscles and since they play important role in human nutrition, they need to be carefully screened to ensure that unnecessary high level of some toxic trace metals are not being transferred to man through fish consumption (Adeniyi and Yusuf, 2007).

Sediments are important sinks for heavy metals in aquatic ecosystem (WHO, 2008). These metals are non-biodegradable and once discharged into water bodies, they can either be adsorbed on sediment particles or accumulated in aquatic organisms. Sediment acts as both carrier and potential sources of contaminants in an aquatic environment (Iwegbue et al., 2007). Contaminated sediments can cause lethal and sub-lethal effect in benthic and other sediment associated organisms (Arimoro, 2018). Thus, it tends to reduce ecological importance or eliminate the life of organisms either through direct effects or by affecting the food chain.

Heavy metals pollution may increase the susceptibility of aquatic animals to various diseases by interfering with the normal functioning of their immune, reproductive and developmental processes according to Environmental Protection Agency, EPA (2002). However, Kontagora Reservoir was constructed with major objective of providing good drinking  water  to  it  township  and  its  environment;  nevertheless,  the  reservoir  has become an excellent source of fish apart from being use for domestic purposes and also for dry season farming (irrigation) which is a common practice around this Reservoir. Hence, there is urgent need to evaluate the level of heavy metal  concentrations in surface water, sediment and dominant fishes from Tungan Kawo Reservoir, Kontagora.

1.2       Statement of Research Problem

Tungan Kawo Reservoir has witnessed constant discharge of domestic waste coupled with agricultural wastes  which have led  to contamination of the Reservoir thereby remains as an environmental threat (Abdullahi et al., 2015).

Farming activities along the shore area has haphazardly increased the nutrients of the water thereby causing algae bloom making it unfavourable and unfit to the aquatic organisms (fish) and humans (Paul et al., 2014). Consumption of fish derived from contaminated bodies of water is the result of 90 percent of human health risks as attributed by Demirak et al. (2013). These heavy metals are considered as the most important pollutants present throughout the ecosystem and are detected in critical amounts which may increase the susceptibility of aquatic organisms (fish) to various diseases by weaken the immune system and induce pathological changes (Adebayo, 2017). Currently, little or no information is available on the health status of aquatic organism (fish) found in Tungan Kawo Reservoir this might be the first of its kind. Therefore, there is urgent need to look into all the problems in order to conserve its biota due to pollution problems and to provide a management plans in improving the reservoir productivity.

1.3       Justification for the Study

Tungan kawo is an important source of drinking water for humans and animals. Dry season farming is a common practise among the people of the community. The reservoir is rich in varieties of fish species for human consumption and commercial uses which generate income for fishermen in the area (Ibrahim et al., 2009).

Human activities around the riparian communities near the reservoir have contributed to alternation of water quality and reducing the productivity of the reservoir. Assessment of the physico-chemical parameters and heavy metals of the reservoir will provide a baseline data and reference point for assessing seasonal changes and environmental impact assessment for the water body caused by anthropogenic activities of man overtime.

Monitoring water safety of Tungan Kawo Reservoir will provide information about its richness, sustainability and improvement of the aquatic ecosystem in general. The communities around this reservoir will be more aware on the risk involved in farming with excess agrochemicals and the health implication feeding on crops grown with contaminated water. Although, some studies have reported different levels of heavy metals in soil and the health risk issues involved with the consuming vegetables harvested (Ibrahim et al., 2009). Thus, these current studies will specifically target on ecological risk of heavy metals associated with surface water, sediment and dominant fish species from Tungan Kawo Reservoir, Kontagora, Nigeria.

1.4       Aim of the study

The aim of this study is to evaluate the ecological risk of heavy metals in surface water, sediments and dominant fish species from Tungan Kawo Reservoir, Kontagora, Niger state, Nigeria.

1.5       Objectives of the study

The objectives of the study are:

(i)        to determine some physico-chemical parameters of surface water in Tungan Kawo Reservoir.

(ii)        to determine some heavy metals in the surface water, sediment and dominant fishes species in Tungan Kawo Reservoir. (iii)       to assess the ecological risk index of heavy metals concentration in sediment samples in Tungan Kawo Reservoir.

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