ABSTRACT
This study investigated the level of heavy metal contamination in soils at 0 to 10cm and 10 to 20 cm depths from twelve (12) sample locations in Kakuri industrial area of Kaduna, Nigeria. The phisco-chemical parameters such as organic matter content (OM), soil pH, calcium carbonate and particle size distribution of the soil samples were determined. The total concentrations of Cu, Zn, Pb, Cr, Ni, Hg and V were also determined using XRF spectrophotometer with the results showing a mean concentrations (in mgkg-1) of 100.5 ± 19.82, 60.02 ±3 .60, 26.25 ± 6.44, 42.42 ± 5.21, 32.00 ± 1.68, 28.80 ± 9.35 and 73.08 ± 3.52 respectively.Significant spatial variation in concentrations was observed for all metals across the locations as metal concentrations (mgkg-1) ranged: Zn, 20-420; Cu, 26-110; Ni, 9-72; Cr, 22-157; Pb, 27-34; Hg, 10-60 and V, 47-120. The degree of pollution varies with the level and proximity to industrial activities. The data was subjected to descriptive analysis to determine the Geo-accumulation index (Igeo) and contamination factor (Cf) with results indicating that the soils can be considered uncontaminated with Igeo ≤ 1 for virtually all the locations with the exception of KGW with 1˂ Igeo ≤ 2 indicating it is considerably contaminated according to the Igeo classification guideline. The contamination factor Cf also confirms the soil is uncontaminated having Cf values 1.31, 1.40 and 1.70 for Zn, Cu and Pb respectively which falls under the classification 1 ≤ Cf ˂ 3 meaning the soil is considerably contaminated. Correlation analysis shows Zn, Hg and Cu have common source(s) in the environment and also strongly correlated to pH and organic matter.Bioavailable concentrations of the studied soil were equally low due to basic soil pH and to high content of free calcium carbonate. The relative bioavailability followed the order of Zn>Cu>Hg>Pb>Ni>Cr>V.
TABLE OF CONTENTS
Cover page……………………………………………………………………………………..i Fly leaf…………………………………………………………………………………………ii Title page……………………………………………………………………………………..iii Declaration…………………………………………………………………………………….iv Certification……………………………………………………………………………………v Dedication……………………………………………………………………………………..vi Acknowledgment……………………………………………………………………………..vii Abstract……………………………………………………………………………………….viii Table of Content………………………………………………………………………………ix List of Tables……………………………………………………………………………..….xv List of Figures………………………………………………………………………………..xvi List of Appendices…………………………………………………………………………..xvii Abbreviations………………………………………………………………………………xviii CHAPTER ONE 1.0 INTRODUCTION……………………………………………………………………….1
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1.1 Background Study………………………………………………………………………1 1.2 Justification for the Research…………………………………………………………..2 1.3 Aims and Objectives……………………………………………………………………4 CHAPTER TWO 2.0 LITERATURE REVIEW………………………………………………………………6 2.1 Heavy Metals in Soil and Toxicity..………………………………………………….5 2.2 Sources of Heavy Metals in Contaminated Soil……………………………………..7 2.2.1 Metal Mining, Milling Processes and Industrial Waste…….….………………………8 2.2.2 Air Borne Sources……………………………………………………….……………..9 2.2.3 Fertilizers……………………….……………………………….…………………….10 2.2.4 Pesticides……………………………………………………………………………..10 2.2.5 Biosolids and Manures……….……………………………………….………………12 2.2.6 Wastewater……………………………………………………………………………13 2.3 Methods of Soil Analysis for Heavy Metals………………………………….……15 2.4 Soil Chemistry and Potential Risks of some Heavy Metals…………..…………..19
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2.4.1 Lead………… ……………………….……..………………….……….……………..19 2.4.2 Zinc…………………………………………………………………………….……20 2.4.3 Chromium………………………………………………………………….………..21 2.4.4 Copper……………………………………………………………….…….…………22 2.4.5 Mercury…………………………………………………………….………………..23 2.4.6 Nickel……………………………………………………………….………………..24 2.4.7 Vanadium……………………………………………..……………………………….24 2.5 Bioavailability of Metals in Soil…………………………………………..………….25 2.6 Influence of Plants on Mobility and Bioavailability of Heavy Metals in Soil……28 2.7 Impacts of Heavy Metals on Soil Functions………………………………………..29 2.8 Evaluation of Metal Ion Concentration in Soil………..………..………….……..30 CHAPTER THREE 3.0 MATERIALS AND METHOD……………………………………………………35 3.1 Sample Collection……………………………………………………………………35 3.2 Sample Treatment…………………………………………………………..………38 3.3 Measurement of Physicochemical Parameters………………….…………………38
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3.3.1 pH Measurements……………………………………………………….…..……….38 3.3.2 Particle Size Distribution……………………………………………………………….38 3.3.3 Calculation of percent sand, silt and clay……………………………………………40 3.3.4 Calcium Carbonate Determination……………………………………………………..41 3.3.5 Organic Matter Measurement…………………………………………………………43 3.4 Preparation of Reagents………………………………………………………..…….44 3.4.1 Preparation of Methyl Orange Indicator………………………………………..………44 3.4.2 Preparation of Calcimeter Bernard Filling Solution………………………………..…..42 3.4.3 Preparation of Solution of 4M HCl………………………………………………..……45 3.4.4 Preparation of 0.16moldm-3 Potassium Dichromate (K2Cr2O7)…………………………45 3.4.5 Preparation of 1.0moldm-3 Ferrous Sulphate (FeSO4.7H2O)……………………………45 3.4.6 Preparation of Ortho-phenanthroline Solution……………………………………..……45 3.5 Heavy Metal Content Measurement.…………………………………………………46 3.5.1 Total Heavy Metal Content…………………………….………………………….……46 3.5.2 Theory of X- Ray Spectrophotometer…………………………………………….……46 3.5.3 Bioavailable Metal Content……………………………………………………..………47
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CHAPTER FOUR 4.0 RESULTS ……………………..…………………………………………………….49 CHAPTER FIVE 5.0 DISCUSSION……………………………………………………………………….59 5.1 Physicochemical Properties…………………………………………………………59 5.2 Total Heavy Metal Concentration…………………………………………………60 5.2.1 Zinc…………………………………………………………………………………61 5.2.2 Copper………………………………………………………………………..……….62 5.2.3 Nickel………………………………………………………………………….…….62 5.2.4 Lead…………………………………………………………………………..……..63 5.2.5 Vanadium…………………………………………………………………..……….64 5.2.6 Mercury…………………………………………………………………….………..64 5.2.7 Chromium…………………………………………………………………..……….65 5.3. Correlation Analysis of Heavy Metals, pH and Organic Matter……….…………65 5.4 Heavy Metals Contamination in Soil………………………………………………..66
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5.4.1 Contamination Factor (Cf)……………………………………………..……,,………..67 5.4.2 Geo-accumulation Index (Igeo) ……………………………………………….……..68 5.5 Heavy Metals Concentration in Sample and Control Soil………………………….69 5.6 Heavy Metal Concentration at 0 to 10cm and 10 to 20cm Depths…………….….70 5.7 Bioavailability of Heavy Metals in Soil…………………………..…………………71 CHAPTER SIX 6.0 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS………………..73 6.1 Summary and Conclusions…………………………………………………………73 6.2 Recommendations for Further studies……………………………………………..74 REFERENCES………………………………………………………………………75 APPENDICES………………………………………………………………….……89
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CHAPTER ONE
1.0 INTRODUCTION 1.1 Background Study Heavy metals are among the most common environmental pollutants and their occurrence in soils indicates the presence of natural or anthropogenic sources. The main natural sources of metals in soils are weathering of parent material and soil erosion (Yoon et al., 2007). The anthropogenic sources are associated mainly with industrial activities such as metal finishing, paint pigment and battery manufacturing, leather tanning, mining activities, foundries and smelters, diffuse sources e.g., piping, constituents of products, combustion by-products, traffic emissions and other human activities like urban composts and municipal waste water sludges depositions and use of pesticides and phosphate fertilizers (Omar and Al-Khashman, 2004., Boularbah et al., 2006). Heavy metals constitute an ill-defined group of inorganic chemical hazards, and those 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). Soils are the major sinks for heavy metals released into the environment by aforementioned anthropogenic activities and unlike organic contaminants which are oxidized to carbon (IV) oxide by microbial action, most metals do not undergo microbial or chemical degradation (Kirpichtchikova et al., 2006) and the total concentration of heavy metals in soil persist for a long time after their introduction (Adriano, 2003). Changes in their chemical forms (speciation) and bioavailability are, however, possible.
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The presence of toxic metals in soil can severely inhibit the biodegradation of organic contaminants (Maslin and Maier, 2000). Heavy metal contamination of soil may pose risks and hazards to humans and the ecosystem through: direct ingestion or contact with contaminated soil, the food chain (soil-plant-human or soil-plant-animal-human), drinking of contaminated ground water, reduction in food quality (safety and marketability) via phytotoxicity, reduction in land usability for agricultural production causing food insecurity, and land tenure problems (McLaughlin1et al., 2000 and Linget al., 2007). Adequate protection and restoration of soil ecosystems contaminated by heavy metals require their characterization and remediation. The high toxicity of these metals has drawn increasing interest in the development of techniques for their removal from waste water before they are disposed into the environment. Some of the techniques which have been used in the removal of metals from effluents include ion exchange, chemical precipitation, electro-dialysis, electrolytic extraction, reverse osmosis, and cementation. These methods are expensive and have the inability to remove metals at low concentration (Faur-brasquetet al., 2002; Bishnoiet al., 2004). Consequently, due to the high cost of treatment, many industries do not treat their waste properly but rather dispose them untreated. This practice goes a long way to cause damage to our environment (Okuo and Ozioka, 2001). 1.2 Justification for the Research
Heavy metals are usually present in wastewaters which are released into the soil environments from various industries as there is no clear demarcation between residential and industrial area in Nigeria. The adverse effects caused by these heavy metals are of great concern. Heavy metals are non-biodegradable and tend to accumulate in living organisms
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thereby causing various diseases and disorders (Bailey et al., 1999). It is worthy of note that the major industrial activities in Kakuri industrial area has declined following the closure of some textiles industries. However there has been increase in population and vehicular traffic, as well as the creation of a variety of ancillary activities such as vehicle repairs, vulcanizer, welders, auto-electricians, battery chargers etc. Their activities could have resulted to heavy metals contamination of waterways and are subsequently deposited into nearby soils (Adefolalu, 1980; Mabogunje, 1980). Several research works have been reported on heavy metals in soil and waterways in Kaduna and its environs in recent times. These include Chemical Fractionation of Heavy Metals in Soils around the Vicinity of Automobile Mechanic Workshops in Kaduna Metropolis (Achi et al., 2011), Levels of Toxic Metals in Soil from Irrigated Farmland in Kaduna Metropolis (Umoru, 2013), Assessment of Cd and Zn in Roadside Surface Soils and Vegetation along Some Roads of Kaduna Metropolis, Nigeria (Okunola et al., 2008);Assessment of Heavy Metals Bioaccumulation by Eleusine indicafrom refuse dumpsites in Kaduna Metropolis, Nigeria (Mohammedet al,. 2012) and other similar works but none has been specific on soil of highly populated Kakuri industrial area.
Contemporary legislation in respect to environmental protection and public health, at both national and international levels, are based on data that characterize chemical properties of environmental phenomena (Zhao and Kaluarachchi, 2002). Soil characterization would provide an insight into heavy metal speciation and bioavailability. In addition, attempt at remediation of heavy metal contaminated soils would entail knowledge of the source
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ofcontamination, basic chemistry, environmental and associated health effects (risks) of these heavy metals. There is therefore need for a continuous monitoring of level of heavy metal in the area in order to keep a check on the environment and to provide data for future research works. 1.3 Aim and Objectives The aim of this research is to determine the distribution of heavy metals and their bioavailability from soils in the vicinities of Kakuri industrial area of Kaduna state and to compare the soil heavy metal concentrations with regulatory standard values permitted by the Nigerian environmental guideline as well as international standards. The objectives set to achieve this aim include to:-
1. 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.
2. investigate the dispersion of the heavy metal concentrations at two different soil depths of 0 – 10cm and 10 – 20cm.
3. investigate the influence of physicochemical parameters on the bioavailability of metals in soils around Kakuri industrial area.
4. 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.
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5. establishany correlation between the heavy metals in soils and the physicochemical parameters.
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