COMPARATIVE TOXICITY OF CRUDE OIL AND KEROSENE ON THE GROWTH OF NITRIFYING BACTERIA ISOLATED FROM SOIL

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ABSTRACT

Crude oil and kerosene have useful applications in the society and are, therefore, used as sources of income and energy. However, the spills arising from crude oil and kerosene in our environment are becoming a visible problem in our ecosystem. Crude oil and kerosene pollute our farmlands and other arable lands and may negatively affect the growth and activities of nitrifying bacteria responsible for nitrification process, leading to loss of soil fertility. Considering the important roles played by nitrifying bacteria in soil fertility in our ecosystem, the assessment of the response of the nitrifying bacteria to pollution stress exerted by crude oil and kerosene on them was investigated. Two genera of nitrifying bacteria were isolated from the soil and were identified asNitrosomonas sp and Nitrobacter sp based on their morphological, biochemical and physiological characteristics. Nitrosomonas sp was isolated using Winogradsky medium for nitrification phase I while Nitrobacter sp was isolated using Winogradsky medium for nitrification phase II. A range of crude oil and kerosene concentrations (in triplicates) were prepared and introduced into sterile Winogradsky salt broth to arrive at final concentrations of 0.5%, 1%, 2%, 5% and 10% (v/v) respectively. The flasks were thereafter inoculated with standardized pure cultures of Nitrosomonas sp and Nitrobacter sp using a uniform inoculum size of 1ml of 1.5 x106 cells for Nitrosomonas sp and 1.2 x106 cells for Nitrobacter sp and incubated for 120 hours. The result of the toxicity test carried out on these isolates showed that the sensitivity of each test organism was a function of both the contact time and concentrations of crude oil and kerosene. The effect of different concentrations of crude oil and kerosene on the oxidation of nitrite to nitrate showed that oxidation of nitrite to nitrate was hindered at higher concentrations of the two pollutants, but, at lower concentrations, crude oil and kerosene did not hinder oxidation of nitrite to nitrate. Information generated from various tests can be of use in the management of pollution for the purpose of prediction of environmental effects of crude oil and kerosene, comparison of toxicants or organisms or test conditions and regulation of crude oil and kerosene spills. For instance this study will help us to provide information for regulatory purposes that a soil contaminated with certain percentage of crude oil or kerosene should not be used for agricultural purposes or practices.

CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.1 Introduction

Crude oil and kerosene have useful applications in our society and are, therefore, used as

source of income and energy. However, the spill arising from crude oil and kerosene dumped into our environment is becoming a visible problem in our ecosystems ( Njoku et al., 2009). The environment is increasingly exposed to changes resulting from both crude oil and refined petroleum products contamination. These changes could be drastic and as such affect the ecosystem substantially (Ikhajiagbe and Anoliefo, 2010). Crude oil and its refined products can be released into the environment from a number of sources, which can pollute both land and water (Jane, 2010). Refined petroleum products result when crude oil is split into fractions such as petrol, kerosene, diesel oil, engine oil and many other petroleum products by a process called fractional distillation. Crude oil, which has accumulated underground, can reach the surface if not contained by impermeable rock.

Apart from this release of crude oil, the main sources of crude oil and refined petroleum products such as petrol, kerosene, diesel and motor engine oil, released on land comes from the disposal of waste motor oil, the leaking of storage tanks, and other spillages and accidents during the transportation of crude oil and other petroleum-based products (Raina et al., 2009). The spill arising from crude oil and refined petroleum products dumped into our environment is becoming a visible problem in our ecosystem. Crude oil and kerosene can pollute our farmlands and other arable lands and may, negatively, affect the growth and activities of nitrifying bacteria responsible for nitrification process, leading to loss of soil fertility (John et al., 2011). These contaminants/pollutants may contain components that may be toxic to soil microorganisms including the nitrifying bacteria and as a result may display some levels of toxicity on the growth of the nitrifying bacteria indigenous to the soil thereby affecting their activities in the soil.

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