ABSTRACT

Ten representative soil samples were collected along major gutters within Nkpor metropolis. The soil samples were digested using mixtures of HF and aqua regia in ratio1:1. The heavy metals contents of the digested soil samples were determined via Flame Atomic Absorption Spectrophotometer FAAS. Sample A had the highest concentration of heavy metal and the trend was Ni > Cr > Hg > Zn > As ~ Cd, it was followed by sample B with Ni > Cr > Zn > Zn > Cd >g > As, sample C had Ni>Cr >Zn>Hg>Cd>As, sample E had Ni > Zn > Cd > Cr > Hg > As. While sample D had Cr > Ni > Zn > Cd > Hg > As. Also the results of the sequential extraction of each soil sample indicated that Ni had the highest percentage bioavailability (49.61%), Hg (47. 72%), Cr (42. 19%), Zn (39.66%), Cd (35.10%), As (0.00%). The high concentration of Hg, Cr and Cd in most areas of the metropolis indicated gross contamination, which could have resulted from human activities, hence the need to adequately monitor the release of these toxic metals to the environment.

CHAPTER ONE

INTRODUCTION

1.0     GENERAL INTRODUCTION

Minerals, metals and metalloids, toxic or essential, are present in soils or sediments in various forms with varying bioavailability, toxicities and mobilities. Heavy metals are natural components of the earth’s crust and the ecosystem with variations in concentration. They cannot be degraded or destroyed and they enter our bodies via food, drinking water and air [1].

Unlike organic contaminants, most metals do not undergo microbial or chemical degradation and the total concentration of these metals in soils persist for a long time after their introduction [2].

These metals are a cause of environmental pollution (heavy-metal pollution) from a number of sources. For example lead in petrol, industrial effluents and leaching of metal ions from the soil into lakes and rivers by acid rain [3].

Living organisms require varying amounts of “heavy metals”. Iron, cobalt, copper, manganese, molybdenum and zinc are required by humans. Excessive levels can be damaging to the organisms. Other heavy metals such as mercury, plutonium and lead are toxic metals that have no beneficial effect on organisms and can cause serious illnesses (3).

Therefore, with greater public awareness of the implications of contaminated soils on humans and animal health, there has been increasing interest among scientific communities in the development of technologies to determine the total concentrations of these elements of interest in the soil as well as their chemical forms.

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The use of sequential extraction techniques to fractionate metals in soils and evaluate their potential effects has become very useful and well recognized (4)

1.1     SCOPE OF STUDY

This research covers the analysis of six heavy metals in each of the five selected drainage pathways or gutters in Nkpor. The heavy metals are mercury (Hg) Nickel; (Ni), Zinc (Zn), Arsenic (As), Cadmium (Cd), Mercury (Hg)

Soil samples were collected from each of the drainage systems as follows:

Five soil samples each along Nkpor/Enugu Old Road, Nkpor/Obosi Road (site for Geolis Cables Industry), Limca Road Nkpor, New Market Road Nkpor and Nkpor/Enugu Express Road.

The samples will be collected at a distance of 10 meters each to avoid bias. A total of 25 soil samples will be analysed to determine the total concentration of each metal in each sample.

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1.2      AIMS AND OBJECTIVES OF STUDY

Heavy metal content of soil sample in some selected drainage systems in Nkpor will be investigated. As earlier on stated, heavy metals are dangerous because they tend to bioaccumulate i.e increase in their concentration over time. Also heavy metals can enter water supply by industrial and consumer waste or even from acidic rain and release heavy metal into streams, lakes, rivers and ground water.

Hence, the study will help in assessing the potential environmental impacts of these metals by determination of their concentrations in soils as well as the chemical form of these metals in the soil.

OBJECTIVES OF THIS STUDY

The objectives of this study are:

(a)              To determine the total concentration of some selected heavy metals in gutter.

(b)              To use sequential extraction technique to fractionate metals in soil samples.

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1.3     LITERATURE REVIEW

A heavy metal is a member of an ill defined subset of elements that exhibit metallic properties, which would mainly include the transition metals, some metallic lanthanides and actinides. Many different definitions have been proposed – some based on density, some on atomic number or atomic weight and some on chemical properties or toxicity [5]

Pollution is the release of substances which alter the environment and make it unfavourable to man, animals and plants [6]. Water, air and soil stand the risk of being polluted.

1.3:1                 SOIL POLLUTION

Soil pollution is the introduction of undesirable materials such as solids, liquids or even gases into the soil, which interfere with its sustenance of plant or animal life [7]. Soil particles may hold chemicals and nutrients making them available for plant roots and keeping them from moving into lakes or streams or entering the ground water [8]. Metals from soils come from various sources. They may have been present in the geologic rock, or they may occur as atmospheric additions of copper, mercury, lead and zinc [9]. Metals also may have been deposited by past industrial activities, such as; battery productions, brass and steel manufacturing industries, mining and many different processes involving Nickel, Cadmium, Copper and Lead. Lead is especially evident in the soil near roadways because of automobile emissions. [10]. Again as lead paints and some soldered pipes used in houses wear and deteriorate they add lead to nearby soils [11]. Other on-going sources of metals and organic waste materials in the soil are landfills [12] and dump sites that are poorly maintained or unregulated

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[13].    Land fill materials eventually decompose and form a highly variable type of unseen soil. Heavy metals remain in topsoil layer which is a result of chemical reaction between heavy metals and organic matter [14].

1.3.2                  SOIL POLLUTION AND PLANT GROWTH

Metal contamination on a site maybe evidenced by plant growth [15], animal behaviour [16] or paint flasks containing lead from older building [17]. Many plants simply cannot grow well where the level of certain metals is high. Other plants grow well in contaminated soil but fail to set seed or do not grow as well as expected [15]. Absence of plant growth in a locality is a warning sign that a site may be severely contaminated. Metals may be present at a site but with no risk for gardening or recreation, depending on the soil properties, drainage and vegetation at the site.

1.3:3                 SOIL ORGANISMS AND BIOCHEMISTRY

Soil is made up of mineral particles and organic matter [12] as well as the decomposed remains of living things [18]. Bacterial fungi and other micro organisms are largely responsible for breaking down dead plants and animals in the soil. Small organisms (microbes) have negatively charged sites where soil nutrients and metals can bond to form soil aggregates and compounds [19]. Earthworms and larger animals eat and digest organic materials and minerals; transform them into soil aggregates and deposit them as waste.

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