ANALYSIS OF HEAVY METALS CONCENTRATIONS IN COMMERCIALLY AVAILABLE FISH FROM THE YOLA-JIMETA REGION, NORTHEASTERN NIGERIA AND PUBLIC-HEALTH IMPLICATIONS

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ANALYSIS OF HEAVY METALS CONCENTRATIONS IN COMMERCIALLY AVAILABLE FISH FROM THE YOLA-JIMETA REGION, NORTHEASTERN NIGERIA AND PUBLIC-HEALTH IMPLICATIONS

ABSTRACT

Commercially available (farmed and wild) fish in the Yola-Jimeta region, Northeastern Nigeria were investigated to find out if they present a public health threat. The fish species used for the study was catfish from the farm and the wild (Benue River) fish. The concentrations of six heavy metals were analyzed. These metals include: cadmium (Cd), iron (Fe), zinc (Zn), manganese (Mn), lead (Pb), and nickel (Ni). The metal concentrations were obtained using atomic absorption spectrophotometer (AAS). The results from AAS were expressed as part per million (ppm) and converted to µg/g dry weight in the result section. The result shows that the gills of farmed fish with exception of manganese accumulate more metals than in the flesh. However, the flesh of wild fish has significantly higher metals concentration than in the gills. Nevertheless, concentrations of heavy metals were higher in the gills of farmed fish but the results were not statistically significant except for lead and zinc. In addition to this, the concentrations of lead, nickel, and cadmium in both the tissues of farmed and wild fish except for zinc in the gills of farmed fish were above the recommended levels provided by WHO.

TABLE OF CONTENTS

CHAPTER 1. 1

INTRODUCTION.. 1

Freshwater fish. 6

Bioaccumulation in fish. 6

Health impact of heavy metals from fish consumption. 8

Water pollution in developing countries. 8

River Benue, a source of fish in northeast Nigeria. 9

AIMS & OBJECTIVES. 12

CHAPTER 2. 13

MATERIALS AND METHODS. 13

Study site. 13

Sampling. 14

Sample preparation. 14

Heavy metals analysis. 15

Statistical analysis. 15

CHAPTER 3

RESULTS. 16

CHAPTER 4. 22

DISCUSSION.. 22

CHAPTER 5. 27

CONCLUSION.. 27

REFERENCES. 29

LIST OF TABLES

Table 1. Results of independent-sample t-tests to compare metal concentrations between farmed fish and wild-caught fish. 17

Table 2: World Health Organization (WHO) permissible limits of heavy metals in fish tissues compared to the mean concentrations of heavy metals in gills and flesh recorded in this study. All values are in (µg/g). 21

LIST OF FIGURES         

Figure 1: Sources of heavy-metal contamination affecting aquatic organisms. 3

Figure 2: Pathways through which toxicants are transferred from one trophic level to another 4

Figure 3: Map of River Benue, which passes through the city of Yola (Adamawa State) 13

Figure 4: Mean concentration of heavy metals in the gills and flesh of farmed fish. 18

Figure 5: Mean concentration of heavy metals in the gills and flesh of wild-caught fish. 19

Figure 6: Comparison of heavy metals in the gills and flesh  of farmed and wild-caught fish. 20

CHAPTER 1

INTRODUCTION

Water is regarded as contaminated or polluted if there are substances in it to such an extent that it cannot be utilized for a particular reason. Polluted water is not safe for cooking, drinking, and other human uses. Water pollution occurs as a result of anthropogenic activities such as littering, mining, deforestation, and use of pesticides. It also occurs as a result of industrial activities such as oil spillage, sewage leakage, and industrial waste dumping. Other parameters that can contribute to water pollution include salinity pollution (the content of dissolved solids in water) and pathogenic pollution (coliform bacteria) from fecal contamination (UNEP, 2016).

More than 50% of river stretches in Latin America, Asia, and Africa are adversely affected by organic and pathogen pollution, whereas 33% of them are affected by salinity pollution. This deterioration is more pronounced in subdivision of these river stretches. In 1990, water pollution has risen to a serious level and by 2010, it worsened (UNEP, 2016).

In developed countries like China, increasing water pollution has been associated with the increase in industrial and economic activities. An example is Yangtze River in China. Waste from industries, mining process, and sewage discharged into the river weighs about 25 billion tons yearly. About 80% of this waste is not properly treated and 60% of the river’s length is affected by pollution (Yi, Yang, & Zhang, 2011). This pollution eventually spreads out to the other parts of the river, which have high densities of population and industry. The sewage discharge around the river also releases heavy metals into the river, which eventually accumulate in the water sediments, leading to ecological damage.

Heavy metals are those metals with relatively high density. About forty metals are classified as heavy metals based on their chemical properties (Zahra, Kalim, Mahmood, & Naeem, 2017). These metals are mostly found in rock formations, but are also frequently found in soil, aquatic habitats, and in the atmosphere in form of vapors. Some of these metals are not easily degradable and can therefore accumulate in the environment. Heavy metals are also classified as essential such as iron, zinc, manganese, copper, and non-essential metals such as mercury, lead, nickel, and cadmium. Essential metals are needed as micronutrients in the body. For example, zinc and copper act in two ways: as activators for enzyme-catalyzed reactions or as prosthetic group in metalloproteins. In addition, they are needed in redox reactions, electron transfer, and are essential in metabolism of nucleic acids (Zahra et al., 2017).  Essential metals only become toxic in high quantities while non-essential ones are toxic even in low quantities.

Heavy metals are released into aquatic habitats as a result of anthropogenic sources, such as mining of metals, metropolitan and sewage wastes, industrial emissions, and agricultural runoff (Fig. 1). They can also be released into an aquatic ecosystem due to natural causes such as biological weathering of rocks and atmospheric deposition (Iqbal, Tabinda, Yasar, & Mahfooz, 2017).

Figure 1: Sources of heavy-metal contamination affecting aquatic organisms (Credit: Modulators of water quality).  

The high concentration of heavy metals in the aquatic organisms can result in serious ecological changes. One of the most serious consequences of their persistence is the biomagnification of metals in the food chain (Fig. 2). Long-time accumulation of these metals affects the plant, surface water fishes, and benthic fish species. Benthic fish species are those species of fish that live at the bottom of the water body (Yi et al., 2011). In addition, metals transfer through aquatic food web affects human health. However, some organisms act as vectors and are responsible for transferring toxicants from one organism to another to the top level of the food web.