Format: MS-WORD Chapters: 1-5
Pages: 157 Attributes: MSc PROJECT
1.0 INTRODUCTION AND LITERATURE REVIEW
The ever increasing pollution of the environment is one of the greatest challenges facing scientists and the general public in this century. The rapid industrialization, agricultural development, and the need to generate cheap forms of energy have led to a continuous release of heavy metals and man-made organic chemicals into the natural ecosystem (Schime, 2001). Heavy metals are metallic elements that have relatively high density, with atomic number of 21 and above, and are toxic at low concentrations. Examples are mercury, copper, cadmium, cobalt, zinc, arsenic, chromium, lead etc. They are natural components of the earth crust and cannot be degraded or destroyed. The elevated levels of heavy metals in the soil can decrease the soil microbial biomass, activities and diversity and change the structure of microbial community (Baath, 1989). Bioremediation of soil pollutants is affected by a number of chemical and environmental factors such as moisture content, pH, temperature, the microbial community, nutrients and toxic substances.
Petrochemical plants generate solid wastes and sludge, some of which may be considered hazardous because of the presence of toxic organic substances and heavy metals (Kabir, 2008). Increasing accumulation of these heavy metals has been observed in cultivated soil, lakes and even air. These accumulations from sewage and industrial wastes which contaminate the soil, water and air may additionally cause eutrophication problems for living organisms including man not only in the impacted locations but also in the non-polluted areas and the entire ecosystem.
Heavy metal stress can exert a negative effect on physiological functions within plants by increasing oxidative stress which will alter membrane permeability and impair mineral nutrition (Reddy et al., 2005). These effects lead to impairment of photosynthesis by changing chloroplast ultrastructure and disassembly of the thylakoid and hence, the inhibition of photosynthetic pigments biosynthesis (Azzarello et al., 2012; Vassilev et al., 2011).
Sources of heavy metals and metalloid contaminants in the soil include mine tailings, leaded gasoline and paint, fertilizers, animal manure, sewage sludge, pesticide, waste water irrigation, coal combustion residue, petrochemical and atmospheric deposition (Khan et al., 2008; Zhan et al., 2010). These metals get accumulated in soil causing harm and damage to plant growth and food production. Heavy metals that are most commonly found at contaminated sites are Lead (Pb), Chromium (Cr), Arsenic (As), Zinc (Zn), Cadmium (Cd), Copper (Cu), Mercury (Hg), and Nickel (Ni) (GWRTAC, 1997).
Soil is the major biological sink for most pollutants released into the environment by the aforementioned activities. Unlike organic contaminants which are oxidized to carbon (IV) oxide by microbial action, metals do not undergo microbial or chemical degradation (Kirpichtchikova et al., 2006) rather, they bio accumulate and their total concentration in soil persists for a long time after their introduction (Adriano, 2001). Although some heavy metals are essential micronutrients for animals, plants and microorganisms, they also demonstrate toxic effect on living organisms via metabolic interference and mutagenesis at certain levels of concentrations. When soil microorganisms are adversely affected by heavy metals, their crucial roles in bioremediation of pollutants, nutrients cycling as well as decomposition of dead organic matter will also be impeded. Several processes such as physical, thermal and chemical treatment have been developed so as to remediate heavy metals contaminated sites. However, these technologies are costly and damage the soil structure and fertility (Simonnot and Cruz, 2008). Hence, phytoremediation provides a cost effective, long lasting and aesthetic solution for a more friendly environmental cleanup (Ma et al., 2001). This is why the study was tailored to evaluate the effects of some heavy metals on soil bacteria, shoot growth, and nodulation of cowpea (Vigna unguiculata) and groundnut (Arachis hypogea) grown in sandy loam soil, along with their bioaccumulation and translocation potentials.
1.2 Statement of Problem
The continuous build-up of heavy metals and metalloids in the environment with their potentials for bioaccumulation and magnification poses a lot of risk to microorganisms and legumes which help in nutrients cycling and ecosystem restoration. The quest to determine the effects of some of these heavy metals on soil bacteria and legume nodulation led to this research work.
To determine the effects of some heavy metals (Co, Cr, and Pb) on soil bacteria, shoot growth and nodulation of cowpea (Vigna unguiculata) and groundnut (Arachis hypogea) grown in sandy loam soil.
|BANKING AND FINANCE||11|
|CONSTRUCTION AND BIULDING||1|
|ELECTRICAL AND ELECTRONICS||1|
|ENGLISH LITERARY STUDIES||29|
|GEOGRAPHY AND PLANNING||1|
|HOM SCIENCE AND MANAGEMENT||3|
|LIBRARY AND INFORMATION SCIENCE||4|
|OFFICE TECHNOLOGY AND MANAGEMENT||21|
|SCIENCE LABORATORY TECHNOLOGY||19|
|SOIL AND ENVIRONMENTAL SCIENCE||1|
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