Level of Heavy Metals and Their Bioavailability in Soil in Kakuri Industrial Area of Kaduna, Nigeria
Chapter One
Aim and Objectives
This research aims to determine the distribution of heavy metals and their bioavailability from soils in the vicinities of the Kakuri industrial area of Kaduna state and to compare the soil heavy metal concentrations with regulatory standard values permitted by the Nigerian environmental guidelines as well as international standards.
The objectives set to achieve this aim include to:-
- Establish the spatial distribution and variability in concentrations of heavy metals for soils in Kakuri industrial area of Kaduna with reference to the activities in each of the sample sites.
- Investigate the dispersion of the heavy metal concentrations at two different soil depths of 0 – 10cm and 10 – 20cm.
- Investigate the influence of physicochemical parameters on the bioavailability of metals in soils around Kakuri industrial area.
- Assess the level and extent of contamination by comparing the results obtained with Nigerian environmental soil guidelines as well as international soil standards and also using soil contamination indices in order to identify any need for regular monitoring and/or remediation.
- Establish any correlation between the heavy metals in soils and the physicochemical parameters.
CHAPTER TWO
LITERATURE REVIEW
Heavy Metals in Soil and Toxicity
Heavy metals are defined as those metals whose density is above 5g/cm3(Pattabhiet al., 2008). High concentration of heavy metals in the environment can be detrimental to a variety of living systems. Excessive ingestion of these metals by humans can causes poisoning, cancer, nervous system damage and ultimately death (Corapcioglu and Huang, 1987; Issabayeva et al., 2007).
The toxicity of heavy metals is due to their ability to bind to oxygen, nitrogen, and sulphur groups in proteins, resulting in alterations of enzymatic activity. Most organ/systems are affected by heavy metal toxicity; the most common include the hematopoietic, renal, and cardiovascular organs/systems. To a lesser extent, lead toxicity involves the musculoskeletal and reproductive systems. The organ/systems affected and the severity of the toxicity vary with the particular heavy metal involved, the chronicity and extent of the exposure, and the age of the individual (Schwartz and Hu, 2007). Main sources of heavy metal contamination include urban industrial aerosols, solid wastes from animals, mining activities, industrial and agricultural chemicals. Increasing concern by environmentalists and governments on the effects of heavy metals and an attempt to protect public health has resulted in upsurge researches in development of advanced technologies to remove heavy metals from waters and wastewaters (Karbassi and Nadjafpour, 1996; Bong et al., 2004; Shetty and Rajkumar, 2009).
The most common heavy metals found at contaminated sites, in order of abundance are Pb, Cr, As, Zn, Cd, Cu, and Hg (USEPA 1986). These metals are capable of decreasing crop production due to the risk of bioaccumulation and biomagnifications in the food chain. There is also the risk of superficial and groundwater contamination. The fate and transport of a heavy metal in soil depends significantly on the chemical form and speciation of the metal. Once heavy metals are adsorbed in the soil by initial fast reactions (minutes, hours), slow adsorption reactions occurs (days, years) resulting in the redistribution into different chemical forms with varying bioavailability, mobility, and toxicity (Shiowatanaet al.,2001; Buekers, 2007). This distribution is believed to be controlled by reactions of heavy metals in soils such as mineral precipitation, dissolution, ion exchange, adsorption, desorption; aqueous complexation, biological immobilization, mobilization and plant uptake (Levy et al., 1992).
Sources of Heavy Metals in Contaminated Soils
Heavy metals occur naturally in the soil environment from the pedogenetic processes of weathering of parent materials at levels that are regarded as trace(<1000 mg/kg) and rarely toxic [(Kabata-Pendias and Pendias (2001), Pierzynskiet al., (2000)]. Anthropogenic activities and acceleration of nature’s slowly occurring geochemical cycle of metals by man resulted /caused most soils environments to have accumulated one or more of the heavy metals above defined background values high enough to cause risks to human health, plants, animals, ecosystems, or other media (D’ Amore et al., 2005). The heavy metals essentially become contaminants in the soil environments for the following reasons:
- Their rates of generation via manmade cycles are more rapid relative to natural ones,
- They become transferred from mines to random environmental locations where higher potentials of direct exposure occur.
- The concentrations of the metals in discarded products are relatively high compared to those in the receiving environment, and
- The chemical form (species) in which a metal is found in the receiving environmental system may render it more bioavailable (D’ Amore et al., 2005)
Heavy metals in contaminated soil from anthropogenic sources tend to be more mobile, than the heavy metal contamination from natural sources. (Kuoet al., 1983;Kaasalainen and Yli Halla., 2003). Metal-bearing solids at contaminated sites can originate from a wide variety of anthropogenic sources in the form of metal mine tailings, disposal of high metal wastes in improperly protected landfills, lead based paints, land application of fertilizer, animal manures, biosolids (sewage sludge), composts, pesticides, coal combustion residues, petrochemicals and atmospheric deposition (Khan et al., 2008. Zhang et al., 2010. Bastaet al., 2005).
CHAPTER THREE
MATERIALS AND METHODS
Sample Collection
Soil samples were collected from twelve (12) selected locations at two different depths well mapped around Kakuri industrial area in Kaduna state Nigeria. Table 3.1 shows the sample locations as well as the industrial activities common in each of the locations while Figure 3.1 shows the sample collection points on the map of Kakuri industrial area.
The surface of the soil was cleared with a hand trowel and samples at 0-10cm depth were collected with the aid of a stainless spoon. After every collection, the hand trowel and spoon were washed with soap and rinsed with distilled water to avoid sample contamination (Awofolu, 2005). Five soil samples from each sampling location were randomly collected. The collected sub-samples were then pooled together to form a composite from each location. Hand trowel was used to dig approximately 10cm to 20cm depth and measured with a measuring tape before the sample was collected using a stainless steel spoon to represent the 10 to 20cm depth sample.Control samples were collected from two locations to validate the heavy metal concentration in soil.
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CHAPTER FOUR
RESULTS
Table 4.1: Physicochemical Parameters of Samples and Control Soil in Kakuri Industrial Area
CHAPTER FIVE
DISCUSSIONS
Physicochemical Properties
The results of the physicochemical analysis of soils from Kakuri industrial area are shown in Tables 4.1.The percentages of particle size distribution in the sample soil werein the range 7 to 15, 21 to 30and 57 to 72% for clay, silt and sand respectively. Generally the soils were found to be sandy loam in majority of the areas and sandy in locations like IBB and SGA.
The pH result indicates the soil samples were slightly alkaline with values in the range 7.30 to 8.00 which is consistent with the value of 7.00 to 8.00 reported by Achi et al. (2011) in their studies of some mechanic workshops in Kaduna metropolis. Soil pHserves as a useful index of availability of nutrients, thepotency of toxic substances present in the soil as well as thephysical properties of the soil. Several studies haveshown that availability of heavy metals is pH dependent and their mobility in soil decreases with increased soil pH and vice versa (Iwegbueet al., 2006; Gonzalez-Fernandez et al., 2008). The high soil pH values suggest that heavy metals availability for plant uptake is low in the sample soils.
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