ABSTRACT
The study was undertaken to assessed the accumulation of heavy metals (Cd, Cu, Mn, Ni, Pd and Zn) in riverside soils of River Niger and River Benue around their confluence and their uptake by Amarantus hybridusand Corchorus olitorius L.grown on these soils. Samples were collected in dry and rainy seasons of 2013 and 2014, samples were prepared, digested and taken for AAS analysis. The result shows thatthe concentrations of metals in the soil ranged from3.95-8.4for Cd; 11.6 – 20.2for Cu; 150.3-211.5 for Mn; 177.0 -281.0 forNi; 20.3-34.2 for Pb and 40.5-77.8mg/kg for Zn. Levels of nickel and cadmium were higher than the European Union Standards (2002).The levels of Ni, Zn, Pb and Cd in the vegetableswere higher than the WHO permissible value in plants.The total metal contents in A. hybridus and C. olitorius Lgrown on the riverside soils follow the order: Ni > Mn > Zn > Pb > Cu > Cd. The order of the percentage of extracted metal by EDTA to the total metal content was Pb > Zn > Cu > Ni > Mn > Cd. Geoaccumulation index showed that Cd and Ni were the major pollutants of the soil samples. Of all the metals studied, Pb had the highest bioaccumulation factor, 0.5691 and 0.6301 in the plant for A. hybridus and Corchorus olitorius Lrespectively.
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TABLE OF CONTENTS
Title Page …………………………………………………………………………………………i Declaration…………………………………………………………………………..…………….ii Certification ………………………………………………………………………………………iii Acknowledgements ……………………………………………………………………………….iv Dedication …………………………………………………………………………………..…..v Abstract ………………………………………………………………………………………….vi Table of Contents ………………………………………………………………………………vii List of Tables …………………………………………………………………………….……..xi List of Figures ………………………………………………………………………………….xiii List of Appendices ……………………………………………………………………………..xv Abbreviations …………………………………………………………………………………xviii CHAPTER ONE
1.0 INTRODUCTION …………………………………………………………………………..1
1.1 Characteristics of Heavy Metal Contaminated Soils ………………………………………………….2
1.1.1 Wide distribution of heavy metals in soils…………………………………………………2
1.1.2 Strong latency of heavy metals in soil …………………………………………………..3
1.1.3 Irreversibility and difficulty in the remediation of soil …………………………….……4
1.1.4 Complexity of heavy metal contamination ……………………………………….……4
1.2 Pathways of Sewage and Solid Waste to Soil …………….………………………………..4
1.2.1 Pathway of agricultural supplies to soils …………….…….……………………………..5
1.3 Impact of Heavy Metal Contamination of Soils ……………………….………………….6
1.3.1 Impact on soil microorganisms and enzymatic activity ………………….………………..6 1.3.2 Impact of heavy metals on the plants ……………………………………….………..……7 1.3.3 Impact of heavy metals on humans ………………………………………….………..…..7 1.4 Soil Quality ………………………………………………………………………….………8 1.4.1 Cation exchange capacity of soil ……………………………………………….…………9
1.4.2pH of soil ……………………………………………………………..……………..……9
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1.4.3Soil texture and soil colour …………………………………………….………….……….9 1.5 Effects of Some Heavy Metals on the Environment..……………………………….10 1.5.1 Arsenic…………………….……………………………………………………….…..10 1.5.2 Cadmium ………………..…………………………………………………………..…..11 1.5.3 Copper …………….……………………………………………………………….…12 1.5.4 Lead …………….……………………………………………………………….…..12 1.5.5 Manganese ……….……………………………………………………………………..14 1.5.6 Zinc ………….………………………………………………………………..……..15 1.6 Justification for the Study ……………………..……………………………………..16 1.7 Aim and Objectives of the Study …………………………..………………….….…16 CHAPTER TWO 2.0 LITERATURE REVIEW…………………..…………………………………………18 2.1 Study Area ……………………………………..……………………………………….18 2.2 Polluted Soils and the Environmental Impact ….……………………………….…..19 2.3 Indices for Assessing Pollution of Soil ………………..………………………….…21 2.4 Analysis of Heavy Metal Contamination in Agricultural Soils………………………….23 2.5 The Implication of Soils and Plants Polluted by Heavy Metals …………..…….…28 2.6 Chelation of Heavy Metals…………………………………………………..……….34 CHAPTER THREE 3.0 MATERIALS AND METHODS …………………………..…………………………36 3.1 Preparation of Stock Solutions……………………………….……………………..36 3.1.1 Arsenic solution of concentration 1000mgL-1 …….….……………………………..36 3.1.2 Cadmium solution of concentration 1000 mgL-1 …….….……………………….……36 3.1.3 Copper solution of concentration 1000 mgL-1 ………..……………………….…….36 3.1.4 Lead solution of concentration 1000 mgL-1 ………………………………….……..36 3.1.5 Zinc solution of concentration 1000 mgL-1 …………………….…………………37 3.1.6 Manganese solution of concentration 1000 mgL-1 ………………….…………………37
3.2 Description of the Study Area ……………………………………………………..37
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3.3 The Sources of the Two Rivers………..…………………………………….…………40 3.4 Sample Collection……………………………………………………………………………………………40 3.5 Pot Culture Experiment for the Plants ………………………………………………42 3.6 Pre – Treatment of the Soil and Plant Samples ………………….…………………..42 3.7 Characterization of the Soil Collected from the Riverside ………………………………….44 3.7.1 Measurement of physico-chemical parameters of the soil samples …………………….44 3.8 Digestion of Soil Samples ……..………………………………………………………48 3.9 Calibration Curves for Determining the Concentrations of Heavy Metals …..…..49 3.10 Determination of EDTA-Extractable Heavy Metals in the Soil Samples …………49 3.11 Digestion ofthe Plant Samples………………………………………………..….50 3.12 AAS Determination of Metal Concentration …………………………………………50 3.12.1 Wavelength, current, burner height and slit width of measurement…….………….…..50 3.12.2Steps employed in spectrophotometre measurement ……………………………………52 3.13 Determination of the Pollution Indices of the Farmland Soils ……..….…………..53 3.13.1Geoaccumulation indices ………………………………………………………………..53 3.13.2Bioaccumulation factor …………………………………………………………………..53 3.14 Statistical Analysis…………………………………………………….………..….55
3.14.1 Students t-test ……………………………………………..……………….……………55
3.14.2 Pearson correlation ………………………………………………………….………..55 3.12.3 Analysis of variance ……………………………………………………….…………….55 CHAPTER FOUR
4.0 RESULTS……………………..…………………………………………………….…56
4.1 Physicochemical Parameters and Heavy Metal Contents of Riverside Soil of River Niger and Benue across the Seasons ………………………………………….56 4.2 Permissible Limits of Heavy Metals in Soils and Plant …………………………….56 4.3 Mean concentration of Heavy Metals in Riverside Soil of River Niger, Benue and Confluence withEU Limit ………………………………………………..……..62
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4.4 Geoaccumulation Index of theFarmland Soils …………………………………..…..67 4.5 Heavy Metals Concentration in Farmland Soils beside River Niger, Benue and Confluence at Different Depths …………………………………………….……74 4.6 Result of t-test Analysis for Metal Ion Concentrations at 15cm and 30 cm Depth of the Soil Samples ……………………………………………………………74 4.7 Mean Concentration of EDTA Available Fractions for Heavy Metals in the Riverside Soils of River Niger and Benue Collected in May 2014…….…………74 4.8 Levels of Some Heavy Metals inAmarantus hybridusand Corchorus olitorius L.Planted in the Pot Experiment…….……………………………………………..…84 4.9 Bioaccumulation Factor (BF) of the Heavy Metals in Amarantus hybridusand Corchorus olitorius L.…………………………………………….……………….……94 4.10 Correlation between the Total Metal Content, EDTA Fraction Content of Soil andMetal Ion Levels in A. hybridus and Corchorus olitorius L.…………………….94 CHAPTER FIVE
5.0 DISCUSSION…………………………………………………………….………….…99
5.1 Physicochemical Parameters of the Farmland Soils from the Bank of River Niger, Benue and Beyond Confluence Point ……………………………………………..99
5.2 Heavy Metal Content in Riverside Soil Samples ……….….………………….…….101
5.3 Geoaccumulation Index (Igeo) of the Soils of the Farmland from River Niger and Benue..………………………………………………………………..…….106 5.4Statistical Analysis on the Concentration of Metals at 15cm and 30 cm Depth of Soil Samples ………………………………………………………………………..107 5.5Concentraion of the Available Essential Heavy Metals Extracted by EDTA from the Soil ……..…………………………………………………………………………107 5.6 Level of Heavy Metal in Amarantus hybridus and Corchorus olitorius L .….…,,,…108 5.7 Bioaccumulation factor (BF)of the Heavy Metals in A. hybridus and Corchorus olitorius L. …..………..……………………………………………………111 5.8 Correlation of the Heavy Metals in the Soil of River Niger and Benue to the Planted Vegetables………..……………………………….……………………..112 CHAPTER SIX
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6.0 CONCLUSION AND RECOMMENDATION……………………………………114 6.1 Conclusion……………………………………………………………………………114 6.2 Recommendations………………………..……………………………………………115 REFERENCES …………………………………………………………………………..….117 APPENDICES…………………………………..……………………………………………
CHAPTER ONE
1.0 INTRODUCTION About ninety natural elements exist in the environment and are distributed through the environment in the geochemical and bio-chemical cycles (Kaim and Schwederski, 1994). Heavy metals are metallic chemical elements that have a relatively high density precisely greater than 5gcm-3. This classification includes transition metals and higher atomic weight metals of group IIIA to VA of the periodic table (Ademoroti, 1996a). Heavy metal contamination refers to the excessive deposition of toxic heavy metals in the soil caused by human activities. This includes some significant metals of biological toxicity, such as mercury, cadmium, lead, chromium, arsenic,zinc, copper, nickel, stannium, vanadium. In recent years, with the development of the global industrialisation, both the type and content of heavy metals in the soil caused by human activities have gradually increased, resulting in the deterioration of the environment (Chaoet al., 2014). Heavy metals are highly hazardous to the environment and organisms. As heavy metals get into the ecosystem they can be enriched through the food chain. Once the soil accumulates heavy metal and is contaminated, it is difficult to get it remediated. In the past, soil contamination was not considered as important as air and water pollution, because soil contamination was not often and was more difficult to be controlled and taken care of than air and water pollution. However, in recent years soil contamination in developed countries has become an environmental concern(Chaoet al., 2014).
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1.1 Characteristics of Heavy Metal Contaminated Soils 1.1.1 Wide distribution of heavy metals in soils Excessive heavy metals in soils originate from many sources, which include atmospheric deposition, sewage, irrigation, improper stacking of the industrial solid waste, mining activities, the use of pesticides, fertilizers and so on (Zhang et al., 2011). Arsenic (atomic number 33) is a silver-grey brittle crystalline solid with atomic weight of 74.9, specific gravity 5.73, melting point 817°C (at 28 atm), boiling point 613°C, and vapour pressure 1 mm Hg at 372°C. It is odourless and tasteless, Arsenic exists in the −3, 0, +3, and +5 valence oxidation states, and is in a variety of chemical forms in natural waters and sediments. The environmental forms include arsenious acids (H3AsO3, H3AsO3), arsenic acids (H3AsO4), arsenites, arsenates, methylarsenic acid, dimethylarsinic acid and arsine. The two most common forms in natural waters are arsenite (AsO33-) and inorganic arsenate (AsO43-), referred to as As3+ and As5+. From both the biological and the toxicological points of view, arsenic compounds can be classified into three major groups. These groups are inorganic arsenic compounds, organic arsenic compounds and arsine gas.
Lead, with atomic number 82, atomic weight 207.19 and a specific gravity of 11.34 is a bluish or silvery-grey metal with a melting point of 327.5°C and a boiling point of 1740°C at atmospheric pressure. It has four naturally occurring isotopes with atomic weights 208, 206, 207 and 204 (in decreasing order of abundance). Despite the fact that lead has four electrons in its valence shell, its typical oxidation state is +2 rather than +4, since only two of the four electrons ionize easily due to inert pair effect.Apart from nitrate, chlorate and chloride, most of the inorganic salts of Pb2+ have poor solubility in water. Lead exists in many forms in the natural sources throughout the world and is now one of the most widely and evenly distributed trace
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metals. Soil and plants can be contaminated by lead from car exhaust, dust and gases from various industrial sources. Mercury is a naturally occurring metal that is present in several forms. Metallic mercury is shiny, silver-white, odourless liquid. It combines with other elements, such as chlorine, sulphuror oxygen, to form inorganic mercury compounds or salts, which are usually white powder or crystals. The element also combines with carbon to form organic mercury compounds. Mercury, which has the lowest melting point (−39°C) of all the pure metals, is the only pure metal that is liquid at room temperature. As any other metal, mercury could occur in the soil in various forms. It dissolves as free ion or soluble complex and is nonspecifically adsorbed by binding mainly due to the electrostatic forces, chelated, and precipitated as sulphide, carbonate, hydroxide, and phosphate. There are three soluble forms of Hg in the soil environment. The most reduced is Hgo metal with the other two forms being ionic of mercurous ion(Hg22+) and mercuric ion (Hg2+), in oxidizing conditions especially at low pH. Hg+ ion is not stable under environmental conditions since it tranforms into Hg0 and Hg2+. A second potential route for the conversion of mercury in the soil is methylation to methyl or dimethyl mercury by anaerobic bacteria. 1.1.2 Strong latency of heavy metals in soil Heavy metal contamination of soil is difficult to notice, since the changes cannot be identified by colour or odour. The contamination does not explicitly damage the environment in a short period. Nevertheless, when it exceeds the environmental tolerance, or when environmental conditions have changed, heavy metals in the soil may be activated and cause serious ecological damage. So heavy metal contamination is usually termed chemicalTime Bombs (CTBs) (Wood, 1974).
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1.1.3 Irreversibility and difficulty in the remediation of soil If air and water are polluted, the pollution problem can be reversed certainly by dilution and self-purification after switching off from the sources of pollution. However, it is difficult to use dilution or self-purification techniques to eliminate heavy metal contamination and to get soils improved. Some soils contaminated by heavy metals are likely to take one or two hundred years to be remediated (Wood, 1974).Therefore, heavy metal contamination needs relatively high cost of remediation and the remediation cycle is relatively long. 1.1.4 Complexity of heavy metal contamination In the past, soil contamination was mainly caused by a single heavy metal. However, in recent years more cases are found to be caused by a variety of heavy metals (Zhou, 1995). The complex contamination is caused by the presence of a variety of heavy metals,this always amplify the contamination of heavy metals compared to whenthey are separately present(Zhang et al., 2011). 1.2Pathways of Sewage and Solid Waste to Soil Heavy metals in the atmosphere are mainly from gas and dust produced by energy, transport, metallurgy and production of construction materials. Except mercury, heavy metals basically go into the atmosphere in the form of aerosol and deposit to the soil through natural sedimentation and precipitation, etc. (Chao, et al., 2014).
Wastewater can be divided into several categories, sanitary sewage, chemical wastewater, mining wastewater and urban mining mixed sewage, etc. Heavy metals from sewage are brought to the soil by irrigative sewage and are subsequently fixed in the soil in different ways. Indiscriminate passing of sewage to soil surface do cause heavy metal to continually accumulate
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in the soil year by year. Irrigation using sewage is a feasible way to solve the problem of crop irrigation in arid area. However heavy metal contamination caused by sewage irrigation must be paid enough attention. Quality of irrigative sewage must be strictly controlled within the national quality standard for irrigation water (Chao, et al., 2014). There are a variety of solid wastes with complex composition. Of this mining and industrial solid waste contamination are the most serious. When these wastes are deposited on land or used as landfills, heavy metals leach into groundwater to the soil due to the facilitation of sunlight, raining and washing. The pollutant spread to the surrounding water and soils,which pose a serious environmental concern. With the development of industry and the acceleration of urban environmental construction, technology for sewage treatment continue to be strengthened. China now has more than 80 sewage treatment plants, with an estimated 400 million tonnes of sludge production. Solid wastes can expand contamination scope easily with the help of wind and water. 1.2.1Pathway of agricultural supplies to soils Fertilizers, pesticides and mulch are important agricultural inputs for agricultural production (Chaoet al., 2014). Nevertheless, the excessive application on a long term has resulted in the heavy metal contamination of soils. The vast majority of pesticides are organic compounds, and while a few are organic – inorganic compound or pure mineral; some pesticides contain Hg, As, Cu, Zn and other heavy metals (Arao et al., 2010).
Heavy metals are the most reported pollutants in fertilizers. However, heavy metal content is relatively low in nitrogen and potash fertilizers, while phosphoric fertilizers usually contain considerable toxic heavy metals. Heavy metals in compound fertilizers are mainly from master materials and manufacturing processes. The content of heavy metals in fertilizers is
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generally in the following ranking: phosphoric fertilizer> compound fertilizer>potash fertilizer> nitrogen fertilizer (Boyd, 2010). Cd is an important heavy metal contaminant in the soil. Cd is brought to soils with the application of phosphoric fertilizers. Many studies have shown that, with the application of a large amount of phosphate fertilizers and compound fertilizers, the content of Cd in soils increases constantly, and Cd taken by plants increases accordingly. In recent years, usage of mulch has been promoted and used in large areas, which results in white pollution of soils, because the heat stabilizers, which contain Cd and Pb, are always added in the production process of mulch. This increases heavy metal contamination of soils (Satarug et al., 2003). 1.3 Impact of Heavy Metal Contamination of Soils 1.3.1 Impact on soil microorganisms and enzymatic activity Microbial activity and enzymatic activity of soil can reflect the quality of the soil, Chao, et al.(2014) stated that microbial biomass of soil is an important indicator for determining the extent of soil contamination. Microbial activity is inhibited significantly in heavy metal contaminated soil. Kandeler et al. (1997) indicated that the microbial biomass in soil contaminated by Cu, Zn, Pb and other heavy metals are inhibited severely. The soil‟s microbial biomass near the mine was significantly lower than that far away from the mine. And the effects of different concentrations of heavy metals and different heavy metals on soil microbial biomass were different.
Chander et al. (1995) studied the effect of different concentrations of heavy metals on soil microbial biomass, and found out that it is only if the concentration of heavy metals in the soil is three times above the environmental standard, established by the European Union, that it could inhibit microbial biomass. Fliepbach et al. (1994) also discovered that low concentrations
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of heavy metals could stimulate microbial growth and increase microbial biomass; while high concentrations could decrease soil microbial biomass significantly. The enzymes in the soil play an important role in the process of organic matter decomposition and nutrient cycling. Studies have showed that the activities of enzymes in the soil are related to the heavy metal contamination. Chander et al. (1995) found that the activities of almost all enzymes in the soil are significantly reduced by 10 to 50 times with increase in the concentration of heavy metals. 1.3.2 Impact of heavy metals on the plants Low concentration of soil heavy metals, regardless of whether it is necessary or unnecessary to plants, will not affect the growth of plants in a certain range. But if the concentration is too high, the content of heavy metals bioaccumulated by the plant exceeds its tolerance threshold, and thus the plant physiological composition is altered and it may even lead to death of the plant. In Florida, it was found that if the copper content in soil was more than 50 mg/kg, it would affect citrus seedlings; if soil copper content reached 200 mg/kg, wheat would wither (Zhang et al., 1989). Research has indicated that the growth of cabbage and bean seedling under Cd concentration of 30 μmol/L was inhibited: the root length decreased, and the plant height and leaf area dropped (Qin et al., 1994). Cd may interfere with crop photosynthesis and protein synthesis, and may cause membrane damage etc (Chao et al., 2014). 1.3.3 Impact of heavy metals on humans
Cadmium may damage the metabolism of calcium, which will cause calcium deficiency and result in cartilage disease and bone fractures, etc. Agency for Toxic Substances Management Committee has listed Cd as the sixth most toxic substance that damages human health. Pb mainly enters human body through the digestive tract and respiratory tract, and then goes into the blood
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circulation in the form of soluble salts, protein complexes or ions, etc. It is reported that 95% of the insoluble lead phosphate accumulates in bones. Pb is strongly pro-organizational, it affects and damages many of the body organs and systems, such as kidney, liver, reproductive system, nervous system, urinary system, immune system and the basic physiological processes of cells and gene expression. Cu, Zn and Ni are essential trace metals in the human body, but if the body takes excessive Cu, Zn and Ni from the outside environment, they will damage human health. Ni and Cu are tumour promoting factors, whose carcinogenesis effect has attracted global concerns. Workers who are in close contact with the nickel powder are more likely to suffer from respiratory cancer, and the content of Ni in the environment is positively correlated with nasopharyngeal carcinoma (Chen, 2011). 1.4 Soil Quality Soil is a crucial component of rural and urban environments and in both places land management is the key to soil quality. Flooding, mining, manufacturing and the use of synthetic products such as pesticides, paints, batteries, industrial waste and domestic waste can result in heavy metal contamination of urban and agricultural soils (Chaoet al., 2014). The quality of soil depends both on its physical properties (colour, texture, moisture content, pH)and chemical properties (cation exchange capacity, phosphate-phosphorous, sulphate-sulphur, nitrate and nitrite-nitrogen). The physical properties and chemical properties of soil largely determine the suitability of a soil for its planned use. The management requirements to keepsoil quality is worthwhile and should be intensified by all, since the benefits is unquantifiable.
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1.4.1 Cation exchange capacity of soil Cation exchange capacity of soil is the capacity of the soil to hold cations. Soil particles are composed of silicate and aluminosilicate clay. Cation exchange capacity therefore increases as the clay content increases and also as the organic matter increases in the soil (Frank, 2006). Cation exchange capacity also depends on the density of the negative charges on the surfaces of soil colloids and the relative charges on the metal species in solution and on the soil surface. 1.4.2 pH of soil In agriculture, pH is probably the most important single property of the moisture associated with a soil, since that parameter reveals what crops will grow readily in the soil and what adjustments must be made to adapt it for growing any other crops. Acidic soils are often considered infertile and so they are for most conventional agricultural crops, although conifers and many species of shrub will not thrive in alkaline soil. As soil acidity increases so does the solubility of aluminium and manganese in the soil and many plants (including agricultural crops) will tolerate only slight quantities of these metals. Acid content of soil is however heightened by the decomposition of organic material (Andrew, 1990). pH is generally acknowledged to be the principal factor governing concentration of soluble and plant available metals (Brallier et al., 2001). As metal solubility tends to increase at lower pH and decrease at higher pH values (Garcia et al., 2009). 1.4.3 Soil texture and soil colour
The colour of soil can give clues to its health, origin and long-term changes. It can also indicate the colour of the parent material. Subsoil colour can be a valuable indicator of how well
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the subsoil drains, which can be influenced by topography. Dark colour in the soil usually indicate that the soil has a high organic matter content. The more humus the black the soil, it could mean that the parent from which soil developed was also rock (Frank, 2006). Soil texture is a property of soil that refers to relative proportions of sand, silt and clay particles in a sample of soil. Clay size particles are smallest being less than 0.003 mm in size. Silt is medium size between 0.002 – 0.05 mm while sand particles being greater than 0.05 mm (Vaskorg et al., 2010). Soil colour when examined, indicates the condition of the soil. The colour of the surface soil varies from almost white through shades of brown and grey, to black. Light colour indicates low organic matter content while dark colour indicates high organic matter content (Jais et al., 2011). 1.5 Effects of Some Heavy Metals on the Environment 1.5.1 Arsenic The toxicity of arsenic and its compounds varies widely, ranging from the exceedingly poisonous arsine and its organic derivatives to the elemental arsenic itself, which is relatively inert (Prett et al., 1995). Arsenical compounds in general are skin irritants, which easily cause dermatitis. Protection against inhalation of arsenic containing dusts is recommended, but most poisoning appears to come from ingestion (Yadav et al., 2000). Arsenic is believed to exert its toxicity by combining with certain enzymes, thereby interfering with cellular metabolism. Individual susceptibility to arsenic poisoning varies widely; some persons have been known to develop a tolerance to doses that would kill others. Poisoning may result from a single large dose (acute poisoning) or from repeated small doses (chronic poisoning). Symptoms of acute poisoning from swallowing arsenic include nausea, vomiting, burning of the mouth and throat and severe abdominal pains (Heilman et al., 2003).
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With the exposure of human to arsenic compounds, circulatory collapse may occur and be followed by death within a few hours. In persons exposed to arsine, the outstanding effects are destruction of red blood cells and damage to the kidneys. With chronic exposure, the more common effects include gradual loss of strength; diarrhea or constipation; pigmentation and scaling of the skin, which may undergo malignant changes; nervous manifestations marked by paralysis and confusion; degeneration of fatty tissue, aneamia and the development of characteristic streaks across the fingernails (Revitt et al., 2009). 1.5.2 Cadmium Cadmium occurs in a few minerals and in small quantities in other ores, especially zinc ores, from which it is produced as a by – product. Some lead ores also contain small quantities of cadmium and if it is present in sufficient quantity it is recovered by a cycle of operations similar to that used by zinc smelters. The concentrations of cadmium in agricultural soils depend upon the amounts present in the parent rocks from which the soil is formed, the amounts added in the form of fertilizers and soil amendments, the amounts deposited onto soils from the atmosphere and the amounts removed by harvested crops and by leaching. On the average, sedimentary rocks contain greater concentrations of Cd than either igneous or metamorphic rocks and therefore, recent soils derived from sedimentary rock should contain greater concentrations of Cd than those derived from igneous or metamorphic rocks. Among the commercial fertilizers, phosphorus fertilizers contain somewhat elevated levels of Cd. Results show that the long – term use of phosphorus fertilizers will slightly increase the concentration of Cd in surface soils (Wedelpohl, 1998).
In acute cadmium poisoning by ingestion, irritation of the gastrointestinal tract is the major toxicity, causing nausea, vomiting, diarrhea and abdominal cramps. With chronic exposure
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by inhalation, however, kidneys and lungs are the target organs. Cadmium compounds do damage many organs. They cause skin lesions, decrease heart contractility, damage blood vessel and injuries of the nervous system, kidney and liver. Cadmium compounds also produce skin and lung tumours in humans (Jenne et al., 2011). 1.5.3 Copper The major portion of copper produced in the world is used by electrical industries; most of the remainder is combined with other metals to form alloy. Important series of alloys in which copper is the chief constituent are brass (copper and zinc) and bronze (copper and tin) (Morse, 1994). Copper resists the action of the atmosphere and seawater on exposure for long periods to air, however, this results in the formation of a thin green protective coating (patina) that is a mixture of hydroxocarbonate, hydroxosulphate and small amounts of other compounds. Copper is a moderately noble metal, being unaffected by non-oxidizing or non-complexing dilute acids in the absence of air; it will however, dissolve readily in HNO3 and in H2SO4 in the presence of oxygen (Frits et al., 2000). Copper is among heavy metals that are essential to life but could be toxic at elevated levels. It is toxic at low concentration in water and is known to cause brain damage in mammals. Elevated levels of this metal has however, been found to be toxic (Hukabee et al., 2011). Toxicity of Copper in plants as a result of high level in sewage treated agricultural soil has been reported. Contribution of copper to environmental burden could be by atmospheric deposition from metal industries, dumpsites and power plants that burn fuels (Baryla et al., 2011). 1.5.4 Lead
Lead is present in several minerals but all are of minor significance except the sulphide, PbS (galena), which is the major source of lead production throughout the world. Lead is also
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found in anglesite (PbSO4) and cerussite (PbCO3). The elimination of lead from insecticides and paint pigments and the use of respirators and other protective devices in areas of exposure have reduced lead poisoning materially. The recognition that the use of tetraethyl lead [Pb(C2H5)4] as an antiknock additive in gasoline was polluting the air and water led to the compound’s elimination as a gasoline constituent in the 1980s (Taylor, 1995). Lead and its compounds are toxic and are retained by the body, accumulating over a long period of time, a phenomenon known as cumulative poisoning until a lethal quantity is reached. The toxicity of lead compounds increases as their solubility increases. In children and adults the accumulation of lead may result in progressive renal disease. Symptoms of lead poisoning include abdominal pain and diarrhea followed by constipation, nausea, vomiting, dizziness, headache and general weakness. Elimination of contact with a lead source is normally sufficient to effect a cure (Leonard et al., 1998). In humans the main sources of lead are usually lead – based paint and drinking water carried through lead pipes; lead-based paints are especially harmful to children who chew on painted toys and furnishings and eat paint peelings from walls. Industries in which workers encounter lead-containing solids, dusts or fumes include the petroleum industry, mining, smelting, printing, cutlery, storage-battery manufacture, plumbing, gas fitting, paint and pigment manufactureand manufacture of ceramics, glass and ammunition. Other possible sources of lead poisoning include the agricultural use of insecticides containing lead compounds; the spraying of fruits and vegetables that may affect the workers and eventually, the consumers. In the mid-20th century, constant exposure to exhaust fumes of motor vehicles powered by fuel containing tetraethyl lead became a significant cause of lead poisoning, especially in children (Kersten et al., 2003).
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Symptoms of lead poisoning vary, they may develop gradually or appear suddenly after chronic exposure. The poisoning affects the entire body especially the nervous system, the gastrointestinal tract and the blood forming tissues. The victim usually becomes pallid, moody irritable and may complain of a metallic taste. Digestion is deranged, the appetite fails and there may be severe abdominal pain, with spasms of the abdominal muscles and constipation. A black line (lead line) may appear at the base of the gums. There is often anaemia, in later stages, headache, dizziness, confusion and visual disturbances may be noted. Peripheral nerve involvement results in a paralysis (lead palsy) that generally first affects the fingers, hands and wrists (wrist drop). The most serious effects are seen in children under the age of six, in whose brain and nervous system development is still occurring. In these children, even a small amount of lead can result in permanent damage and loss of function of the affected area of the brain. Complications may occur, such as learning disabilities, slowed growth, blindness, deafness, and, in extreme cases, convulsions and coma ending in death. Brain injury may also occur in adults after massive exposure (Sahu et al., 2008). 1.5.5 Manganese Manganese combined with other elements is widely distributed in the earth’s crust. Manganese is second only to iron among the transition elements in its abundance in the earth’s crust; it is roughly similar to iron in its physical and chemical properties but is harder and more brittle. It occurs in a number of substantial deposits, of which the most important ores (which are mainly oxides) consist primarily of manganese (IV) oxide (MnO2) in the form of pyrolusite, romanechite and wad (Uba etal., 2008).
Manganese is essential to plant growth and is involved in the reduction of nitrates in green plants and algae. It is an essential trace element in higher animals, where it participates in
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the action of many enzymes. Deficiency of manganese do cause testicular atrophy. An excess of this element in plants and animals is toxic. Manganese always associates with iron deposits, known to block calcium channels. It is also an essential element to plants and animals as it aids in activating enzymes in man (Awwal, 2008). In some circumstances it can pose health risk to man when it is associated with steel, iron, battery manufacture and coal burning processes. The availability of this metal is highest in acidic soils but drops in calcareous soil (Lloyd et al., 2011). 1.5.6 Zinc The major uses of zinc metal are in galvanizing iron and steel against corrosion and in making brass and alloys for die-casting. Zinc itself forms an impervious coating of its oxide on the surface when exposed to the atmosphere, and hence the metal is more resistant to ordinary atmosphere than iron and corrodes at a much lower rate. Zinc is an essential trace element in the human body, where it is found in high concentration in the red blood cells serving as an essential part of the enzyme carbonic anhydrase, which promotes many reactions related to carbon (IV) oxide metabolism. The zinc present in the pancreas may aid in the storage of insulin. Zinc is a component of some enzymes that digest protein in the gastrointestinal tract. Zinc deficiency in nut-bearing and fruit trees causes such diseases as pecan rosette, little leaf and mottle leaf (Noltze et al., 2003).
The toxicity of zinc is low, in drinking water zinc can be detected by taste only when it reaches a concentration of 15 mg/kg; water containing 40 mg/kg zinc has a definite metallic taste. Vomiting is induced when the zinc content exceeds 800 mg/kg. Cases of fatal poisoning have resulted through the ingestion of zinc chloride or sulphide, but these are rare. Both zinc and zinc salts are well tolerated by the human skin. Excessive inhalation of zinc compounds can
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cause such toxic manifestations as fever, excessive salivation and a cough that may cause vomiting; but the effects are not permanent (Klineet al., 2010). 1.6 Justification for the Study Irrigation on river side soils of River Niger and Benue help to provide vegetable crops for the people of Lokoja and the environs during the dry season and early part of the rainy season. Kogi State faced the problem of flooding in 2012, consequently, large items were washed into the water body, thus the level of heavy metals in both soils and plants grown on the river side soils are expected to be elevated beyond the threshold levels. It is worthy of note that these two rivers come from far distance, therefore, domestic industrial, mining, metallurgical and agricultural activities contribute to the heavy metal loading of the water and neighboured riverside soils being irrigated with water from the rivers. These activities lead to heavy metal loading of the soil, therefore the determination of the heavy metal levels of the riverside soils post flooding becomes imperative. Determination of the heavy metal uptake is further justified, since these metals are taken up by plants and from here enter into the food chain where they may cause health hazards. The pollution indices of the riverside soil will help to determine the level of pollution loading after the flooding of 2012 when data is compared to that in literature before the flood. 1.7 Aims and Objectives of the Study
This study is aimed at determining the levels of some heavy metals in riverside soils of River Niger, River Benue and beyond the confluence point, and to assess the heavy metal uptake by spinach(Amarantus hybridus) called “aleyafu” in Hausa, “Inine” or “Opotoko” in Igbo and “Efo” in Yoruba and jute (Corchorus olitorius L.) called “Laalo” or “Malafia” in Hausa, “Arira”
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or “Ahihara” in Igbo and “Oyoyo” or “Ewedu” in Yoruba,planted on the soils, for possible contamination. The objectives set to achieve the aims include:
I. To determine the physico-chemical parameters of the river bank soils (pH, CEC, Organic matter, colour, textural class and so on);
II. To carry out characterization of the soil;
III. To determine the total metal content of the soil;
IV. To determine the EDTA-extractable heavy metals in samples of thefarmland soil near the rivers and control soil collected from farmland soil far away from the river, which is not in any way associated with the river;
V. To determine the concentration of heavy metals in the Amarantus hybridus and Corchorus olitorius L. grown on the soil samples obtained from the farmland near the river bank and the control soil;
VI. To assess the metal mobility and their availability to Amarantus hybridus and Corchorus olitorius L.;
VII. To establish and assess the level of heavy metal pollution of the riverside soil with seasonal variation and
VIII. To use some pollution indices to assess the level of the contamination or otherwise on the riverside soil used for agricultural activity.
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