The soil is not only the medium for the growth of plants and the disposal of waste substances in the environment but also a vector of many waste matter that contaminates underground water, surface water, atmospheric air and food.
The pollution of the soil does not only threaten human health through its effects on the quality of food and potable water but also through its effects on the quality of atmospheric air in the environment. In the past, little attention has been given to soil pollution when compared to food contamination (Wong, 1996). In the recent past however, the impact of soil pollution on the function of the soil and the biosphere has been emphasized by Environmental Protection Agencies, the Government, and the general public (Tiller, 1992) and thus stimulating the interest in researches at evaluating quantitatively, the levels of heavy metals at dumpsites. Specifically, significant improvements have been made with respect to mining related heavy metal pollutants of the soil in different parts of the world (Pulford et al., 2003).
A survey of heavy metals have shown that they accumulate in some specific areas of human activities compared to areas that have remained under virgin conditions (Kabata-Pendias et al., 2001). Apart from mining activities, accumulation of heavy metals in the terrestrial environment have increased significantly due to human activities such as emission from thermal power stations, waste disposal and vehicular traffic/ road infra-structures (Hursthouse et al., 2004). Other sources of contamination which mainly affects agricultural soils include inputs such as fertilizers, pesticides, herbicides, sewage sludge, organic manure and compost (Singh, 2001). Some of the anomalous accumulation may be geologically related (Thornton et al., 1980.)
The soil is a primary recipient of solid wastes (Nyle et al., 1999). Millions of tonnes of these wastes from a variety of sources such as industrial, domestic and agricultural sources, find their way into the soil. These wastes substances end up interacting with the system of the soil and as a result altering the physical and chemical characteristics of the soil (Piccolo et al., 1997). The organic matter of the soil influences the level of aggregation of the soil and the aggregate stability of the soil. It can reduce bulk density and increase total porosity and hydraulic conductivity in heavy clay soils. Municipal waste increases the nitrogen, pH, cation exchange capacity, percentage base saturation and organic matter (Anikwe et al., 2001). Organic waste can provide nutrients for increased crop yield and such positive effects have increased the application of these wastes. Dumpsites are known to be rich in soil nutrients for plant growth and development because decayed waste and compost enhance the fertility of the soil (Ogunyemi et al., 2003). Dumpsites especially in most third world countries are composed of higher proportion (50-90%) of organic matter (Asomani-Boateng et al., 1999); but a considerable proportion of plastic, paper, metal rubbish and batteries which are known sources of heavy metals that are hazardous to man and his environment are also present (Pasquini, et al., 2004). Heavy metals have adverse effect on soils, crops and human health (Smith et al., 1996). Many heavy metals act as biological poisons even at parts per billion (ppb) levels. These metals are extremely persistent and have toxicological effects on living organisms at certain levels of concentration. The exposure of man to such toxic heavy metals may result in blood and bone disorders, kidney damage, decreased mental capacity and neurological damage (NIEHS, 2004). The assessment of dumpsite soils for hazardous heavy metals is imperative for healthy crop production and healthy living. The purpose of this research is to quantitatively determine the amount of cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) in dumpsites around three (3) hostels near the University for Development Studies (UDS), Navrongo campus.
1.1 PROBLEM STATEMENT
Heavy metals are currently of much environmental concern. By contaminating food chain, these elements pose a risk to environmental and human health. Because of their release and presence in the ecosystems, these pollutants are accumulated by living organisms in their bodies and subsequently biomagnified as they pass from one trophic level to the next. Since man is at the top of food chain, he is vulnerable to heavy metal pollution. Heavy metals, such as cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) are important environmental pollutants, particularly in areas with high anthropogenic pressure (US EPA., 1997). Higher levels of heavy metals disrupt the normal physiology and biochemistry of living systems.
Unorganized dumping of solid waste which is a popular form of pollution in the environment has become predominant in hostels, especially the private ones, around the University for Development Studies, Navrongo campus. Sources such as electronic goods, tins from canned foods and drinks when dumped with various solid wastes may increase the level of heavy metals in dumpsites. Similarly, solid waste dumping without the separation of hazardous waste can raise toxic environmental effects. Slow leaching of these heavy metals under acidic environment during the degradation process leads to leachates with high metal concentrations. The environmental problem with heavy metals is that they are unaffected during degradation of organic waste and have toxic effects on living organisms when they exceed certain concentrations.
Heavy metals are non- biodegradable and non-thermo-degradable and thus their accumulation readily reaches to toxic levels. It is known that systematic problems can develop as a result of increased accumulation of dietary heavy metals such as lead and cadmium in the human body.
The non-biodegradable nature of heavy metals makes them to persist in the soil and hence their accumulation in the soil. This poses harmful threats to the quality of soil, contaminates crops (in terms of heavy metal uptake by plants), surface and underground water pollution, and influence plant growth (Peter Ryser et al, 2006).
1.2 JUSTIFICATION
The negative impact of heavy metals cannot be overlooked and hence the need to always update and research more into it for better understanding to minimize them and to manage their negative impact on the environment when they exceed their permissible limits.
1.3 OBJECTIVES
The aim of this project is to determine the levels of some heavy metals in dumpsites near Gaza Hostel (Gaza), Vatican City Hostel (Vatican) and St. John Boscos College of Education (Boscos) all around the University for Development Studies (UDS), Navrongo campus.
The specific objectives are;
‘ To determine the levels of cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) at a depth of 20 cm to 30 cm from the three (3) dumpsites.
‘ To compare the amount of each heavy metal concentration among the three (3) dumpsites.
‘ To infer the influence of pH on the distribution of cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) in the soil at each dumpsite.
‘ To compare the levels of cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) to the permissible range in soil.
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 INTRODUCTION
Heavy metals are natural components of the Earth’s crust and cannot be degraded nor destroyed. They enter the human body through food, water, and air and are widely distributed in all environmental components. Focusing on vegetables and fruits, contamination can result from soil, irrigation water loaded by heavy metals, application of fertilizers and pesticides containing heavy metals, deposition of heavy metal particulates from air on plantations, industrial emissions, transportation, the
harvest process, storage, and/ or at the
point of sales (Maleki and Zarasvand, 2008). Heavy metal pollution of surface and underground water sources also results in considerable soil pollution, and pollution increases when mined ores are dumped on the ground surface for manual dressing (Garbarino et al., 1995).
When agricultural soils are polluted, these metals are taken up by plants and consequently accumulate in their tissues. Animals that graze on such contaminated plants and drink from polluted waters, as well as marine lives that breed in heavy metal-polluted waters, also accumulate such metals in their tissues and milk, if lactating (Garbarino et al., 1995; Osakwe, 2010). Humans are in turn exposed to heavy metals by consuming contaminated plants and animals, and this has been known to result in various biochemical disorders. In summary, all living organisms within a given ecosystem are variously contaminated along the cycles of the food chain.
Plants absorb a number of elements from soil, some of which have no known biological function and some are known to be toxic at low concentrations. As plants constitute the foundation of the food chain, some concerns have been raised about the possibility of toxic concentrations of certain elements being transported from plants to higher strata of the food chain. Bioaccumulation takes place when substances are taken in the food chain from food and water. These substances accumulate because they cannot be broken down and used up by the organism or they are taken in faster than they are used up by organisms. Bioaccumulation is not hazardous when the substance accumulated is not harmful, but when compounds and heavy metals that are harmful to human health accumulate like chromium, zinc, cadmium and lead then bioaccumulation becomes dangerous. (Brookes et al., 1984)
2.2 PATHWAYS OF HEAVY METALS THROUGH THE FOOD CHAIN
Special attention has been given to the uptake and biotransformation mechanisms occurring in plants, their role in bioaccumulation, and impact on consumers, especially human beings. Peralta-Videa et al. (2009) reviewed plant uptake of cadmium, and lead and their possible transfer to the food chain. These elements were selected because they are well established as being toxic for living systems and their effects in humans have been widely documented. Zhuang et al. (2009) investigated the accumulation and transfer of lead, zinc, and cadmium along a soil’plant’insect’chicken food chain at contaminated sites in China. The study site near a lead/zinc mine was severely contaminated by heavy metals. Cadmium and lead concentrations steadily declined with increasing trophic level, but concentration of zinc slightly increased from plant to insect larva. The concentrations of heavy metals were the highest in chicken muscle, with lower values in liver and blood. The bioaccumulation of lead was observed in chicken livers. The eliminations of lead, zinc, and cadmium through insect and chicken faeces avoid metal bioaccumulation in insect and chicken body. These results suggest that the accumulation of heavy metals in specific animal organs or tissues could not be neglected, although transfer of metals to chicken from plant and insect was limited.
2.3 TRANSFER OF HEAVY METALS FROM THE SOIL TO PLANTS
A majority of heavy metals are the natural components of the Earth’s crust, from which they are taken by plants and transferred to the food chain. These metal concentrations vary from soil to soil. The concentration of metals in vegetables mainly depends on the texture of the soil or media on which they grow, but this also depends on the type and nature of plant (Kabata-Pendias, 1984). As vegetables are the source of human consumption, so the soil-to-plant transfer quotient is the main source of human exposure. Cultivation of crops for human or livestock consumption on contaminated soil can potentially lead to the uptake and accumulation of heavy metals in the edible plant parts with a resulting risk to human and animal health (Gupta and Gupta, 1998; Monika and Katarzyna, 2004; McBride, 2007). Islam et al. (2007) reviewed the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assessed soil heavy metal thresholds for potential dietary toxicity. They reported that soil threshold for heavy metal toxicity is an important factor affecting soil environmental capacity of heavy metal and determines heavy metal cumulative loading limits.
For the soil/plant system, heavy metal toxicity threshold is the highest permissible content in the soil (total or bio-available concentration) that does not pose any phytotoxic effects or heavy metals in the edible parts of the crops which exceed food hygiene standards. Factors affecting the thresholds of dietary toxicity of heavy metal in the soil/crop system include: soil type, which includes soil pH, organic matter content, clay mineral, and other soil chemical and biochemical properties; and crop species regulated by genetic basis for heavy metal transport and accumulation in plants. In addition, the interactions of soil/plant/root/microbes play important roles in regulating heavy metal movement from soil to the edible parts of crops.
Agronomic practices such as fertilizer and water management as well as crop rotation systems can affect bio-availability and crop accumulation of heavy metals, thus influencing the thresholds for assessing dietary toxicity of heavy metals in the food chain. Wastewater irrigation, solid waste disposal, sludge applications, vehicular exhaust, and industrial activities are the major sources of soil contamination with heavy metals
In order to assess the health risks, it is necessary to identify the potential of a source to introduce risk agents into the environment, to estimate the amount of risk agents that come into contact with the human’environment boundaries, and to quantify the health consequence of the exposure (Khan et al., 2008). Plants take up essential and non-essential elements from soils in response to concentration gradients induced by selective uptake of ions by roots, or by diffusion of elements in the soil. The level of accumulation of elements differs between and within species (Huang and Cunningham, 1996). Baker (1981) suggested that plants could be classified into three categories: Excluders: Those that grow in metal-contaminated soil and maintain the shoot concentration at low level up to a critical soil value above which relatively unrestricted root-to-shoot transport results; Accumulators: Those that concentrate metals in the aerial part; and Indicators: Where uptake and transport of metals to the shoot are regulated so that internal concentration reflects external levels, at least until toxicity occurs.
A convenient way for quantifying the relative differences of bioavailability of metals to plants is the transfer quotient (Cui et al., 2004). The transfer quotient for cadmium was higher than for lead. The higher transfer quotient of heavy metal indicates the stronger accumulation of the respective metal by that vegetable (Khan et al., 2008). A transfer quotient of 0.1 indicates that the plant is excluding the element from its tissues (Thornton and Farago, 1997). The greater the transfer coefficient value above 0.50, the greater the chances of vegetables for metal contamination by anthropogenic activities, indicating that environmental monitoring of the area is required (Sponza and Karaoglu, 2002).
Leafy vegetables accumulate much higher contents of heavy metals as compared to other vegetables. This is because leafy vegetables have a higher translocation and transpiration rate as compared to other vegetables, in which transfer of metals from root to stem and then to fruit is longer which results in lower accumulation than leafy vegetables (Itanna, 2002). The trend of transfer of these metals was of the order cadmium > lead (Khan et al., 2008).
In Lebanon, Al-Chaarani et al. (2009) monitored the levels of lead, cadmium, chromium, and arsenic in a total of 181 vegetable samples of which 66 are leaf
y vegetables, 84
are over ground vegetables, and 31 are underground grown vegetables. Overall, the levels ranged from non-detectable to 3.0904 ”g/g for lead, 0.0137’3.6170 ”g/g for cadmium, non-detectable to 19.55 ”g/g for chromium, and non-detectable to 0.0636 ”g/g for arsenic, where ”g/g refers to the weight of the metal per gram of dry sample weight. In all samples, the leafy vegetables contained considerably higher levels for all metals as compared to over-ground or underground vegetables.
2.4 HEAVY METAL DEPOSITION FROM THE AIR
Cadmium and lead are common air pollutants, being emitted mainly as a result of various industrial activities. Although the atmospheric levels are low, they contribute to the deposition and build-up in soils. Long-range trans-boundary air pollution is only one source of exposure to these metals but, because of their persistence and potential for global atmospheric transfer, atmospheric emissions affect even the most remote regions. Sharma et al. (2009) presented data on heavy metals (Cu, Zn, Cd, and Pb) concentrations in some key Indian vegetables such as palak (Beta vulagaris L.; Family Chenopodiaceae), lady’s finger (Abelmoschus esculentus L.; Family Malvaceae) and cauliflower (Brassica oleracea; Family: Brassicaceae) grown locally in sub-urban and rural areas and sold in urban open markets. Generally, contamination levels with heavy metals were higher in market sites vegetables than those from production sites, indicating deposition of heavy metals on the vegetables during transport and marketing in the more polluted urban environment. It was hypothesized that atmospheric depositions in urban areas may increase the levels of heavy metals during transport and marketing, leading to significant contamination of vegetables at the market sites rather that at the production sites.
Heavy metal contamination in the street dust due to metal smelting in the industrial district of Huludao city, China was investigated by Zheng et al. (2010). The maximum Hg, Pb, Cd, Zn, and Cu contents in the street dust were found to be 5.212, 3903, 726.2, 79,869, and 1532 mg kg-1, 141, 181, 6724, 1257, and 77.4 times as high as the background values in soil. The biggest contribution to street dust is atmospheric deposition due to metal smelting, but traffic density makes a small contribution to heavy metal contamination. According to the calculation of hazard index (HI), the ingestion of dust particles by children and adults in Huludao city appear to be the route of exposure to street dust that results in a higher risk for heavy metals, followed by dermal contact. The inhalation of re-suspended particles through the mouth and nose is almost negligible. The inhalation of Hg vapour as the fourth exposure pathway to street dust accounts for the main exposure. The hazard index for lead (HI > 1) indicates that children are exposed to a potential health risk; for cadmium HI ~ 1, implying a probably health risk.
2.5 REVIEW OF HEAVY METALS UNDER STUDY
2.5.1 CADMIUM (Cd)
Cadmium is a lustrous, silver-white, ductile, very malleable metal. Its surface has a bluish tinge and the metal is soft enough to be cut with a knife, but it tarnishes in air. It is soluble in acids but not in alkalis. It is similar in many respects to zinc (Zn) but it forms more complex compounds. Together with Mercury (Hg) and Lead (Pb), Cd is one of the big three heavy metal poisons and is not known for any essential biological function. In its compounds, Cd occurs as the divalent Cd (II) ion. Cadmium is directly below Zn in the periodic table and has a chemical similarity to that of Zn, an essential micronutrient for plants and animals. This may account in part for Cd’s toxicity; because Zn being an essential trace element, its substitution by Cd may cause the malfunctioning of metabolic processes (Campbell, 2006).
The most significant use of Cd is in Ni/Cd batteries, as rechargeable or secondary power sources exhibiting high output, long life, low maintenance, and high tolerance to physical and electrical stress. Cadmium coatings provide good corrosion resistance coating to vessels and other vehicles, particularly in high-stress environments such as marine and aerospace. Other uses of cadmium are as pigments, stabilizers for polyvinyl chloride (PVC), in alloys and electronic compounds. Cadmium is also present as an impurity in several products, including phosphate fertilizers, detergents and refined petroleum products. In addition, acid rain and the resulting acidification of soils and surface waters have increased the geochemical mobility of Cd, and as a result its surface-water concentrations tend to increase as lake water pH decreases (Campbell, 2006).
Cadmium is produced as an inevitable byproduct of Zn and occasionally lead refining. The application of agricultural inputs such as fertilizers, pesticides, and bio-solids (sewage sludge), the disposal of industrial wastes or the deposition of atmospheric contaminants increases the total concentration of cadmium (Cd) in soils, and the bioavailability of this cadmium (Cd) determines whether plant cadmium (Cd) uptake occurs to a significant degree (Weggler et al., 2004).
Naturally, a very large amount of cadmium is released into the environment, about 25,000 tonnes a year. About half of this cadmium is released into rivers through weathering of rocks and some cadmium is released into air through forest fires and volcanoes. The rest of the Cadmium is released through human activities, such as manufacturing.
No cadmium ore is mined for the metal, because more than enough is produced as a byproduct of the smelting of zinc from its ore, sphalerite (ZnS), in which Cadmium Sulphite is a significant impurity, and making up as much as 3%. Consequently, the main mining areas are those associated with zinc.
2.5.1.1 HEALTH AND ENVIRONMENTAL EFFECTS OF CADMIUM (Cd)
Cadmium is very bio-persistent but has few toxicological properties and, once absorbed by an organism, remains resident for many years. Food intake and tobacco smoking are the main routes by which cadmium enters the body (Manahan; 2003).
Cadmium in the body is known to affect several enzymes. It is believed that the renal damage that results in proteinuria is the result of Cd adversely affecting enzymes responsible for reabsorption of proteins in kidney tubules. Cadmium also reduces the activity of delta aminolevulinic acid synthetase, arylsulfatase, alcohol dehydrogenase, and lipoamide dehydrogenase, whereas it enhances the activity of deltaaminolevulinic acid dehydratase, pyruvate dehydrogenase, and pyruvate decarboxylase (Manahan; 2003). The most spectacular and publicized occurrence of cadmium poisoning resulted from dietary intake of cadmium by people in the Jintsu River Valley, near Fuchu, Japan. The victims were afflicted by itai itai disease, which means ouch, ouch in Japanese. The symptoms are the result of painful osteomalacia (bone disease) combined with kidney malfunction. Cadmium poisoning in the Jintsu River Valley was attributed to irrigated rice contaminated from an upstream mine producing lead (Pb), zinc (Zn), and cadmium (Cd). The major threat to human health is chronic accumulation in the kidneys leading to kidney dysfunction.
Cadmium waste streams from the industries mainly end up in soils. The causes of these waste streams are for instance zinc production, phosphate ore implication and bio-industrial manure. Cadmium waste streams may also enter the air through household waste combustion and burning of fossil fuels. Because of regulations, only little cadmium now enters the water through disposal of wastewater from households or industries.
Another important source of cadmium emission is the production of artificial phosphate fertilizers. Part of the cadmium ends up in the soil after the fertilizer is applied on farmland and the rest of the cadmium ends up in surface waters when waste from fertilizer productions is dumped by production companies.
Cadmium can be transported o
ver great distances when
it is absorbed by sludge. This cadmium-rich sludge can pollute surface waters as well as soils.
Cadmium strongly adsorbs to organic matter in soils. When cadmium is present in soils it can be extremely dangerous, as the uptake through food will increase. Soils that are acidified enhance the cadmium uptake by plants. This is a potential danger to the animals that are dependent upon the plants for survival. Cadmium can accumulate in their bodies, especially when they eat multiple plants. Cows may have large amounts of cadmium in their kidneys due to this.
Earthworms and other essential soil organisms are extremely susceptive to cadmium poisoning. They can die at very low concentrations and this has consequences for the soil structure. When cadmium concentrations in soils are high, they can influence soil processes of microorganisms and a threat to the whole soil ecosystem.
In aquatic ecosystems cadmium can bio-accumulate in mussels, oysters, shrimps, lobsters and fish. The susceptibility to cadmium can vary greatly between aquatic organisms. Salt-water organisms are known to be more resistant to cadmium poisoning than freshwater organisms.
Animals eating or drinking cadmium sometimes get high blood-pressures, liver disease and nerve or brain damage.
2.5.2 LEAD (Pb)
Lead is a metal belonging to group IV and period 6 of the periodic table with atomic number 82, atomic mass 207.2, density 11.4 g cm-3, melting point 327.4 ”C, and boiling point 1725 ”C. It is very soft, highly malleable, ductile, and a relatively poor conductor of electricity.
It is a naturally occurring, bluish gray metal usually found as a mineral combined with other elements, such as sulphur (i.e., PbS, PbSO4), or oxygen (PbCO3), and ranges from 10 to 30 mg kg-1 in the earth’s crust (USDHHS, Toxicological profile for lead; 1999). Typical mean lead (Pb) concentration for surface soils worldwide averages 32mg kg-1 and ranges from 10 to 67 mg kg-1 (Kabata-Pendias et al., 2001). It is very resistant to corrosion but tarnishes upon exposure to air. Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements.
Lead ranks fifth behind iron (Fe), copper (Cu), aluminium (Al), and zinc (Zn) in industrial production of metals. About half of the Lead (Pb) used in the United States (U.S.) goes for the manufacture of lead (Pb) storage batteries. Other uses include solders, bearings, cable covers, ammunition, plumbing, pigments, and caulking. Metals commonly alloyed with lead (Pb) are antimony (in storage batteries), calcium (Ca) and tin (Sn) (in maintenance-free storage batteries), silver (Ag) (for solder and anodes), strontium (Sr) and Sn (as anodes in electro winning processes), tellurium (Te) (pipe and sheet in chemical installations and nuclear shielding), Sn (solders), and antimony (Sb), and Tin (Sn) (sleeve bearings, printing, and high-detail castings) (Manahan; 2003)
Lead occurs naturally in the environment. However, most lead concentrations that are found in the environment are a result of human activities. Due to the application of lead in gasoline, an unnatural lead-cycle has consisted. The most serious source of exposure to soil lead is through direct ingestion (eating) of contaminated soil or dust. In general, plants do not absorb or accumulate lead. However, in soils testing high in lead, it is possible for some lead to be taken up. Studies have shown that lead does not readily accumulate in the fruiting parts of vegetable and fruit crops (e.g., corn, beans, squash, tomatoes, strawberries, and apples). Higher concentrations are more likely to be found in leafy vegetables (e.g., lettuce) and on the surface of root crops (e.g., carrots). Since plants do not take up large quantities of soil lead, the lead levels in soil considered safe for plants will be much higher than soil lead levels where eating of soil is a concern (pica). Generally, it has been considered safe to use garden produce grown in soils with total lead levels less than 300 ppm. The risk of lead poisoning through the food chain increases as the soil lead level rises above this concentration. Even at soil levels above 300 ppm, most of the risk is from lead contaminated soil or dust deposits on the plants rather than from uptake of lead by the plant (Rosen, 2002).
In car engines lead is burned, so that lead salts (chlorines, bromines, and oxides) will originate. These lead salts enter the environment through the exhausts of cars. The larger particles will drop to the ground immediately and pollute soils or surface waters, the smaller particles will travel long distances through air and remain in the atmosphere. Part of this lead will fall back on earth when it is raining. This lead-cycle caused by human production is much more extended than the natural lead-cycle. It has caused lead pollution to be a worldwide issue.
2.5.2.1 HEALTH AND ENVIRONMENTAL EFFECTS OF LEAD (Pb)
Inhalation and ingestion are the two routes of exposure, and the effects from both routes are the same. Lead (Pb) accumulates in the body organs (i.e., brain), which may lead to poisoning (plumbism) or even death. The gastrointestinal tract, kidneys, and central nervous system are also affected by the presence of lead. Children exposed to lead are at risk for impaired development, lower IQ, shortened attention span, hyperactivity, and mental deterioration, with children under the age of six being at a more substantial risk. Adults usually experience decreased reaction time, loss of memory, nausea, insomnia, anorexia, and weakness of the joints when exposed to lead (NSC, Lead Poisoning, National Safety Council; 2009). Lead is not an essential element. It is well known to be toxic and its effects have been more extensively reviewed than the effects of other trace metals. Lead can cause serious injury to the brain, nervous system, red blood cells, and kidneys (Baldwin and Marshall, 1999).
Exposure to lead can result in a wide range of biological effects depending on the level and duration of exposure. Various effects occur over a broad range of doses, with the developing young and infants being more sensitive than adults. Lead poisoning, which is so severe as to cause evident illness, is now very rare. Lead performs no known essential function in the human body, it can merely do harm after uptake from food, air, or water. Lead is a particularly dangerous chemical, as it can accumulate in individual organisms, as well as in entire food chains.
Leaded gasoline causes lead concentrations in the environment to rise. Other human activities, such as fuel combustion, industrial processes and solid waste combustion, also contribute.
Lead can end up in water and soils through corrosion of leaded pipelines in a water transporting system and through corrosion of leaded paints. It cannot be broken down; it can only converted to other forms.
Lead accumulates in the bodies of aquatic organisms and soil organisms. These organisms experience health effects from lead poisoning. Health effects on shellfish can take place even when only very small concentrations of lead are present. Body functions of phytoplankton can be disturbed when lead interferes. Phytoplankton is an important source of oxygen production in seas and many larger sea-animals eat it. That is why we now begin to wonder whether lead pollution can influence global balances.
Soil functions are disturbed by lead intervention, especially near highways and farmlands, where extreme concentrations may be present. Soil organisms can suffer from lead poisoning, too.
2.5.3 NICKEL (Ni)
Nickel is silvery-white hard, malleable, and ductile metal. It is of the iron group and it takes on a high polish. It is a fairly good conductor of heat and electricity. In its familiar compounds nickel is bivalent, although it assumes other valences. It also forms a number of complex compounds. Most nickel compounds are blue or green. Nickel dissolves slowly in dilute acids but, like iron, becomes passive w
hen treated with nitric
acid. Finely divided nickel adsorbs hydrogen.
It is an element that occurs in the environment only at very low levels and is essential in small doses, but it can be dangerous when the maximum tolerable amounts are exceeded. This can cause various kinds of cancer on different sites within the bodies of animals, mainly of those that live near refineries. The most common application of Ni is an ingredient of steel and other metal products. The major sources of nickel contamination in the soil are metal plating industries, combustion of fossil fuels, and nickel mining and electroplating. (Khodadoust et al; 2004).
Humans use nickel for many different applications. The most common application of nickel is the use as an ingredient of steal and other metal products. It can be found in common metal products such as jewelry. The major use of nickel is in the preparation of alloys. Nickel alloys are characterized by strength, ductility, and resistance to corrosion and heat. About 65 % of the nickel consumed in the Western World is used to make stainless steel, whose composition can vary but is typically iron with around 18% chromium and 8% nickel. 12 % of all the nickel consumed goes into super alloys. The remaining 23% of consumption is divided between alloy steels, rechargeable batteries, catalysts and other chemicals, coinage, foundry products, and plating.
Nickel is easy to work and can be drawn into wire. It resist corrosion even at high temperatures and for this reason it is used in gas turbines and rocket engines. Monel is an alloy of nickel and copper (e.g. 70% nickel, 30% copper with traces of iron, manganese and silicon), which is not only hard but can resist corrosion by sea water, so that it is ideal for propeller shaft in boats and desalination plants.
Nickel is a compound that occurs in the environment only at very low levels. Most nickel on Earth is inaccessible because it is locked away in the planet’s iron-nickel molten core, which is 10 % nickel. The total amount of nickel dissolved in the sea has been calculated to be around 8 billion tons. Organic matter has a strong ability to absorb the metal which is why coal and oil contain considerable amounts. The nickel content in soil can be as low as 0.2 ppm or as high as 450 ppm in some clay and loamy soils. The average is around 20 ppm. Nickel occurs in some beans where it is an essential component of some enzymes. Another relatively rich source of nickel is tea which has 7.6 mg/kg of dried leaves.
Nickel occurs combined with sulphur in millerite, with arsenic in the mineral niccolite, and with arsenic and sulphur in nickel glance. Most ores from which nickel is extracted are iron-nickel sulphides, such as pentlandite.
2.5.3.1 HEALTH AND ENVIRONMENTAL EFFECTS OF NICKEL (Ni)
Foodstuffs naturally contain small amounts of nickel. Chocolate and fats are known to contain severely high quantities. Nickel uptake will boost when people eat large quantities of vegetables from polluted soils. Plants are known to accumulate nickel and as a result the nickel uptake from vegetables will be eminent. Smokers have a higher nickel uptake through their lungs. Finally, nickel can be found in detergents.
Humans may be exposed to nickel by breathing air, drinking water, eating food or smoking cigarettes. Skin contact with nickel-contaminated soil or water may also result in nickel exposure. In small quantities nickel is essential, but when the uptake is too high it can be a danger to human health.
An uptake of too large quantities of nickel has the following consequences:
– Higher chances of development of lung cancer, nose cancer, larynx cancer and prostate cancer
– Sickness and dizziness after exposure to nickel gas
– Lung embolism
– Respiratory failure
– Birth defects
– Asthma and chronic bronchitis
– Allergic reactions such as skin rashes, mainly from jewelry
– Heart disorders
Nickel fumes are respiratory irritants and may cause pneumonitis. Exposure to nickel and its compounds may result in the development of a dermatitis known as ‘nickel itch’ in sensitized individuals. The first symptom is usually itching, which occurs up to 7 days before skin eruption occurs. The primary skin eruption is erythematous, or follicular, which may be followed by skin ulceration. Nickel sensitivity, once acquired, appears to persist indefinitely.
Carcinogenicity- Nickel and certain nickel compounds have been listed by the National Toxicology Program (NTP) as being reasonably anticipated to be carcinogens. The International Agency for Research on Cancer (IARC) has listed nickel compounds within group 1 (there is sufficient evidence for carcinogenicity in humans) and nickel within group 2B (agents which are possibly carcinogenic to humans). OSHA does not regulate nickel as a carcinogen. Nickel is on the ACGIH Notice of Intended Changes as a Category A1, confirmed human carcinogen.
Nickel is released into the air by power plants and trash incinerators. It will than settle to the ground or fall down after reactions with raindrops. It usually takes a long time for nickel to be removed from air. Nickel can also end up in surface water when it is a part of wastewater streams.
The larger part of all nickel compounds that are released to the environment will adsorb to sediment or soil particles and become immobile as a result. In acidic ground however, nickel is bound to become more mobile and it will often rinse out to the groundwater.
There is not much information available on the effects of nickel upon organisms other than humans. It is known that high nickel concentrations on sandy soils can clearly damage plants and high nickel concentrations in surface waters can diminish the growth rates of algae. Microorganisms can also suffer from growth decline due to the presence of nickel, but they usually develop resistance to nickel after a while.
For animals, nickel is an essential foodstuff in small amounts. But nickel is not only favorable as an essential element; it can also be dangerous when the maximum tolerable amounts are exceeded. This can cause various kinds of cancer on different sites within the bodies of animals, mainly of those that live near refineries.
Nickel is not known to accumulate in plants or animals. As a result nickel will not bio magnify up the food chain.
2.5.4 ZINC (Zn)
Zinc is a transition metal with the following characteristics: period 4, group IIB, atomic number 30, atomic mass 65.4, density 7.14 g cm-3, melting point 419.5 ”C, and boiling point 906 ”C. Zinc occurs naturally in soil (about 70 mg kg-1 in crustal rocks) (Davies and Jones, 1988), but Zn concentrations are rising unnaturally, due to anthropogenic additions. Most zinc is added during industrial activities, such as mining, coal, and waste combustion and steel processing. Many foodstuffs contain certain concentrations of zinc. Drinking water also contains certain amounts of zinc, which may be higher when it is stored in metal tanks. Industrial sources or toxic waste sites may cause the concentrations of zinc in drinking water to reach levels that can cause health problems. Zinc is a trace element that is essential for human health. Zinc shortages can cause birth defects. The world’s Zn production is still on the rise which means that more and more zinc ends up in the environment. Water is polluted with zinc, due to the presence of large quantities present in the wastewater of industrial plants. A consequence is that zinc polluted sludge is continually being deposited by rivers on their banks. Zinc may also increase the acidity of waters.
Some fish can accumulate zinc in their bodies, when they live in Zn-contaminated waterways. When zinc enters the bodies of these fish, it is able to bio-magnify up the food chain. Water-soluble zinc that is located in soils can contaminate groundwater. Plants often have a Zn uptake that their systems cannot handle, due to the accumulation of zinc in soils.
Finally, zinc can interrupt the
activity in soils, as it negat
ively influences the activity of microorganisms and earthworms, thus retarding the breakdown of organic matter (Greany, 2005).
It is used principally for galvanizing iron, more than 50% of metallic zinc goes into galvanizing steel, but is also important in the preparation of certain alloys. It is used for the negative plates in some electric batteries and for roofing and gutters in building construction. Zinc is the primary metal used in making American pennies, is used in die casting in the automobile industry. Zinc oxide is used as a white pigment in water colors or paints, and as an activator in the rubber industry. As a pigment, zinc is used in plastics, cosmetics, photocopier paper, wallpaper, printing inks etc., while in rubber production its role is to act as a catalyst during manufacture and as a heat disperser in the final product. Zinc metal is included in most single tablet, it is believed to possess anti-oxidant properties, which protect against premature aging of the skin and muscles of the body.
Zinc is a very common substance that occurs naturally. Many foodstuffs contain certain concentrations of zinc. Drinking water also contains certain amounts of zinc, which may be higher when it is stored in metal tanks. Industrial sources or toxic waste sites may cause the zinc amounts in drinking water to reach levels that can cause health problems.
Zinc occurs naturally in air, water and soil, but zinc concentrations are rising unnaturally, due to addition of zinc through human activities. Most zinc is added during industrial activities, such as mining, coal and waste combustion and steel processing. Some soils are heavily contaminated with zinc, and these are to be found in areas where zinc has to be mined or refined, or were sewage sludge from industrial areas has been used as fertilizer.
Zinc is the 23rd most abundant element in the Earth’s crust. The dominant ore is zinc blende, also known as sphalerite. Other important zinc ores are wurzite, smithsonite and hemimorphite.
2.5.4.1 HEALTH AND ENVIRONMENTAL EFFECTS OF ZINC (Zn)
Zinc is a heavy metal that is essential for human health. When people absorb too little zinc they can experience a loss of appetite, decreased sense of taste and smell, slow wound healing and skin sores. Zinc-shortages can even cause birth defects.
Although humans can handle proportionally large concentrations of zinc, too much zinc can still cause eminent health problems, such as stomach cramps, skin irritations, vomiting, nausea and anemia. Very high levels of zinc can damage the pancreas and disturb protein metabolism, and cause arteriosclerosis. Extensive exposure to zinc chloride can cause respiratory disorders.
In the work place environment, zinc contagion can lead to a flu-like condition known as metal fever. This condition will pass after two days and is caused by over sensitivity.
Zinc can be a danger to unborn and newborn children. When their mothers have absorbed large concentrations of zinc, the children may be exposed to it through blood or milk of their mothers.
The world’s zinc production is still rising. This basically means that more and more zinc ends up in the environment. Water is polluted with zinc, due to the presence of large quantities of zinc in the wastewater of industrial plants. This wastewater is not purified satisfactorily. One of the consequences is that rivers are depositing zinc-polluted sludge on their banks. Zinc may also increase the acidity of waters.
Some fish can accumulate zinc in their bodies, when they live in zinc-contaminated waterways. When zinc enters the bodies of these fish it is able to bio-magnify up the food chain.
Large quantities of zinc can be found in soils. When the soils of farmland are polluted with zinc, animals will absorb concentrations that are damaging to their health. Water-soluble zinc that is located in soils can contaminate groundwater.
Zinc cannot only be a threat to cattle, but also to plant species. Plants often have a zinc uptake that their systems cannot handle, due to the accumulation of zinc in soils.
On zinc-rich soils, only a limited number of plants have a chance of survival. That is why there is not much plant diversity near zinc-disposing factories. Due to the effects upon plants, zinc is a serious threat to the productions of farmlands. In spite of this, zinc-containing manures are still applied.
Finally, zinc can interrupt the activity in soils, as it negatively influences the activity of microorganisms and earthworms. The breakdown of organic matter may seriously slow down because of this.
CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 SCOPE OF RESEARCH
Research Area
The samples for this study were taken from three (3) dumpsites near Vatican City Hostel (Vatican), Gaza Hostel (Gaza), and St. John Boscos College of Education (Boscos) all around the University for Development Studies (UDS), Navrongo campus.
3.2 MATERIALS
The materials used to conduct this study included chemicals and reagents, glassware, equipment and soil samples from the three (3) dumpsites.
3.2.1 Chemicals and reagents
Conc. Hydrochloric acid (HCl) which is 37 % (w’v) with a density of 1.18 and produced by VWR international, BH15 LTD, in England, Conc. Nitric acid (HNO3) which is 67 % (w’v) with a density of 1.42 which was supplied by BDH laboratory in England, and distilled water.
3.2.2 Equipment and glassware
Sartorius electronic balance-TE 601, HM digital pH meter-80, BUCHI acid digester K-425, iCE 3000 series AA Spectrometer, 2 mm sieve, 250 ml conical flasks, 10 ml pipettes, pestle and mortar, 100 ml volumetric flask, test tubes, funnels, and spatula.
3.2.3 Soil Samples
Samples of soil were taken from a dumpsite each located around Vatican, Gaza, and Boscos. Five (5) samples and one (1) control sample were taken from each dumpsite.
3.3 METHODS
The study was conducted in three phases; sampling and sample pre-treatment, sample digestion, and analyses.
3.3.1 Sampling and Sample Pre-Treatment
Each dumpsite was divided into five (5) zones and one sample taken from each zone. The control sample was taken 10 m away from each dumpsite. The samples were all taken at a depth between 20 cm to 30 cm.
The five (5) soil samples collected from each dumpsite were mixed to form a composite sample. The composite sample from each dumpsite was then divided into three (3) parts and stored in clean labeled plastic containers for use later on in the laboratory. The samples were later air-dried to constant weight, pulverized, and sieved using a mesh sieve (Brigden et al., 2008).
3.3.2 Determination of pH of the Soil Samples
Soil pH was determined electrometrically in soil-to-water ratio of 1:1 suspensions in the laboratory. 10 g of air-dried soil was mixed with 10 ml of distilled water and after 30 minutes, the pH was measured using an HM digital pH meter-80.
3.3.3 Sample Digestion
To determine the levels of heavy metals in each sample, 0.5 g of each soil sample was weighed using Sartorius electronic balance-TE 601 into a test tube. A mixture of Conc. HCl and Conc. HNO3 acids (3:1, HCl to HNO3) was added to the sample in each test tube. The test tubes were then put into the BUCHI acid digester K-425 until digestion was complete, indicative by disappearance of yellow fumes produced in the process. The mixture was cooled, filtered into a 100 ml volumetric flask and diluted to the 100 ml mark with distilled water, and was used for the AAS analyses.
As a control, 6 ml of HCl was added to 2 ml of HNO3 in a test tube and digested in the digester until there was reduction in the volume. The solution was then allowed to cool, before it was filtered into a 100 ml volumetric flask and diluted to the 100 ml mark with distilled water, and used for the AAS analyses.
3
.3.4 Sample Analysis
The digestates of the soil sam
ples were analyzed for cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) using the iCE 3000 series AA Spectrometer.
3.4 Statistical Analysis
The analysis of variance (ANOVA) was used to examine the variability of cadmium, lead, nickel and zinc concentrations in the soil samples from dumpsites around Boscos, Gaza and Vatican. In the analysis of variance, where significant results were obtained, the Fisher’s Least Significant Difference (LSD) was used to test the source of the variation.
Spearman rank correlation analysis was conducted to infer the influence pH on the distribution of heavy metal concentration in the dumpsite soil.
Analysis of variance, the Fisher’s Least Significant Difference (LSD) test and the Spearman rank correlation analysis were all performed using the IBM SPSS statistics 20 PC package program.
Column charts were used to compare the mean concentration of each heavy metal and its control. From the column charts, standard error bars were used to determine whether or not there is a significant difference between the mean concentration of the heavy metal and its control. Where the standard error bars overlapped each other, it denoted that there is no significant difference between the mean concentration and the control, but where the standard error bars do not overlap, it suggested a significant difference between the mean concentration and its control. This was performed using the Microsoft office word 2013.
CHAPTER FOUR
RESULTS AND DISCUSSIONS
4.1 Results
4.1.1 Samples pH
The tables below show the pH obtained from the dumpsites at Boscos, Gaza and Vatican (Table 4.1a) and the mean pH with their respective controls (Table 4.1a).
TABLE 4.1a pH values of soil samples
DUMPSITE LOCATION REPLICATES SAMPLE
1 2 3 MEAN
BOSCOS 9.5 9.4 9.4 9.4 A
9.5 9.5 9.5 9.5 B
9.5 9.5 9.5 9.5 C
8.0 8.0 8.0 8.0 CONTROL
GAZA 8.2 8.2 8.2 8.2 A
8.2 8.2 8.2 8.2 B
8.1 8.1 8.1 8.1 C
8.4 8.4 8.4 8.4 CONTROL
VATICAN 8.5 8.4 8.4 8.4 A
8.4 8.4 8.4 8.4 B
8.4 8.4 8.4 8.4 C
7.5 7.5 7.5 7.5 CONTROL
TABLE 4.1b Mean pH (M) values of the soil samples
DUMPSITE LOCATION MEAN pH ” SD
SAMPLE CONTROL
BOSCOS 9.5 ” 0.058
8.0
GAZA 8.2 ” 0.0578
8.4
VATICAN 8.4 ” 0.00 7.5
It can be seen from the pH values obtained above that soil samples of dumpsites at Boscos, Gaza and Vatican are generally alkaline in nature with the dumpsite at Boscos having the highest pH value and that of Gaza having the least pH value. The respective pH values of the control samples also showed alkalinity where Gaza has the highest pH value with Vatican having the least pH value. The pH value of the control at Vatican is near neutrality. Figure 4.1 below shows the difference in mean pH of the samples and their controls.
FIGURE 4.1 A graph showing the pH values of soil samples from the three dumpsites
4.1.2 Concentration of heavy metals in soil samples at dumpsites
The concentration of cadmium, lead, nickel and zinc obtained from the soil samples from the dumpsites at Boscos, Gaza and Vatican and their controls respectively are shown in the table 4.2a.
TABLE 4.2a Concentration of heavy metals
DUMPSITE LOCATION CONCENTRATION (mg kg-1) SAMPLE
CADMIUM LEAD NICKEL ZINC
BOSCOS 1.32 443.40 43.10 48.88 A
4.70 3.86 38.48 36.24 B
6.18 11.00 44.52 42.22 C
6.32 6.60 43.18 28.06 CONTROL
GAZA 2.90 17.96 78.54 50.12 A
4.66 8.06 80.48 65.38 B
4.92 7.98 88.30 67.14 C
0.88 6.58 81.98 8.88 CONTROL
VATICAN 6.66 6.56 46.08 95.84 A
9.44 9.14 46.04 71.56 B
5.24 7.52 54.74 102.02 C
7.54 4.62 52.28 16.84 CONTROL
From the results obtained, the mean concentration of each heavy metal was calculated using any two consistent values of the three measured concentrations.
TABLE 4.2b Mean concentration of heavy metals
DUMPSITE LOCATION MEAN CONCENTRATION (mg kg-1)
(M ” SD)
CADMIUM LEAD NICKEL ZINC
BOSCOS SAMPLE 5.44 ” 1.047
7.43 ” 5.049
43.81 ” 1.004
39.23 ” 4.228
CONTROL 6.32 6.60 43.18 28.06
GAZA SAMPLE 4.79 ” 0.184
8.02 ” 0.057
79.51 ” 1.372
66.26 ” 1.245
CONTROL 0.88 6.58 81.98 8.88
VATICAN SAMPLE 5.95 ” 1.004
7.04 ” 0.679
46.06 ” 0.028
98.93 ” 4.370
CONTROL 7.54 4.62 52.28 16.84
The following figures (4.2a, 4.2b, 4.2c, and 4.2d) show the differences in mean concentration of each heavy metal and the control.
FIGURE 4.2a Differences in concentrations of cadmium and controls
FIGURE 4.2b Differences in concentration of lead and controls
FIGURE 4.2c Differences in concentration of nickel and controls
FIGURE 4.2d Differences in concentration of zinc and controls
4.1.2.1 Correlation analyses
The mean concentration of each of the heavy metals was correlated with the mean pH at the dumpsites. This was done to infer the influence of pH on the concentration of heavy metals in the dumpsites. Tables 4.3a – 4.3d below show the correlation between the mean concentration of each heavy metal and the mean pH of the soil at the dumpsite.
TABLE 4.3a Correlation between mean cadmium concentration and mean pH
Mean Cadmium concentration Mean pH
Spearman’s rho Mean Cadmium concentration Correlation Coefficient 1.000 .500
Sig. (2-tailed) . .667
N 3 3
Mean pH Correlation Coefficient .500 1.000
Sig. (2-tailed) .667 .
N 3 3
TABLE 4.3b Correlation between mean lead concentration and mean pH
Mean Lead concentration Mean pH
Spearman’s rho Mean Lead concentration Correlation Coefficient 1.000 -.500
Sig. (2-tailed) . .667
N 3 3
Mean pH Correlation Coefficient -.500 1.000
Sig. (2-tailed) .667 .
N 3 3
TABLE 4.3c Correlation between mean nickel concentration and mean pH
Mean Nickel concentration Mean pH
Spearman’s rho Mean Nickel concentration Correlation Coefficient 1.000 -1.000**
Sig. (2-tailed) . .
N 3 3
Mean pH Correlation Coefficient -1.000** 1.000
Sig. (2-tailed) . .
N 3 3
**. Correlation is significant at the 0.01 level (2-tailed).
TABLE 4.3d Correlation between mean zinc concentration and mean pH
Mean Zinc concentration Mean pH
Spearman’s rho Mean Zinc concentration Correlation Coefficient 1.000 -.500
Sig. (2-tailed) . .667
N 3 3
Mean Ph Correlation Coefficient -.500 1.000
Sig. (2-tailed) .667 .
N 3 3
4.1.2.2 Analysis of variance
The following tables (Table 4.4a1 ‘ 4.4c3) show the Analysis of Variance (ANOVA) of the mean concentration of the heavy metals in each dumpsite.
TABLE 4.4a1 Descriptives for the concentrations of heavy metals at Boscos dumpsite
N Mean Std. Deviation Std. Error 95% Confidence Interval for Mean Minimum Maximum
Lower Bound Upper Bound
Cadmium 3 4.0667 2.49113 1.43826 -2.1216 10.2550 1.32 6.18
Lead 3 152.7533 251.73271 145.33795 -472.5854 778.0921 3.86 443.40
Nickel 3 42.0333 3.15812 1.82334 34.1881 49.8785 38.48 44.52
Zinc 3 42.4467 6.32305 3.65061 26.7393 58.1540 36.24 48.88
Total 12 60.3250 122.07959 35.24134 -17.2407 137.8907 1.32 443.40
TABLE 4.4a2 ANOVA for the concentrations of heavy metals at Boscos dumpsite
Sum of Squares Df Mean Square F Sig.
Between Groups 37086.650 3 12362.217 .780
.538
Within Groups 126851.038 8 15856.380
Total 163937.688 11
There was no LSD test for the heavy metals at Boscos dumpsite because there was no significant difference found in the means (sig. value was 0.538 from table 4.4a2 above).
From table 4.4a2 above, the means for cadmium, lead, nickel and zinc are 4.0667, 152.7533, 42.0333 and 42.4467 mg kg -1 respectively. The standard deviations for cadmium, lead, nickel and zinc are 2.49113, 251.73271, 3.15812, and 6.32305 mg kg -1 respectively. The standard deviation is the measure of how concentrated the data are around the mean; the more concentrated, the smaller the standard deviation. The standard deviations for nickel and zinc are very small compared to their means. This implies that the concentrations of nickel and zinc are more clustered around their means.
However, the standard deviations of cadmium and lead are very large compared to their means. This is as a result of outliers (extremely low or extremely high concentrations in the data set) found in the concentrations of cadmium and lead at Boscos dumpsite. The outliers for cadmium and lead were 1.32 mg kg -1 (extremely low concentration of cadmium) and 443.40 mg kg -1 (extremely high concentration of lead) respectively (Table 4.2a). Outliers in a data set affect both the mean and the standard deviation.
TABLE 4.4b1 Descriptives for the concentrations of heavy metals at Gaza dumpsite
N Mean Std. Deviation Std. Error 95% Confidence Interval for Mean Minimum Maximum
Lower Bound Upper Bound
Cadmium 3 4.1600 1.09891 .63446 1.4302 6.8898 2.90 4.92
Lead 3 11.3333 5.73900 3.31341 -2.9231 25.5898 7.98 17.96
Nickel 3 82.4400 5.16678 2.98304 69.6050 95.2750 78.54 88.30
Zinc 3 60.8800 9.35989 5.40394 37.6287 84.1313 50.12 67.14
Total 12 39.7033 34.80605 10.04764 17.5886 61.8180 2.90 88.30
TABLE 4.4b2 ANOVA for the concentrations of heavy metals at Gaza dumpsite
Sum of Squares Df Mean Square F Sig.
Between Groups 13029.178 3 4343.059 117.027 .000
Within Groups 296.894 8 37.112
Total 13326.072 11
From the ANOVA table 4.4b2, there is a significant difference in the mean concentration of at least one of the heavy metals. But the ANOVA does not show which of the mean concentrations contributed to the significant difference hence the need to use the LSD to identify which mean concentration(s) is/ are responsible for the difference.
Table 4.4b3 below shows the LSD test for the mean concentration of the heavy the metals at Gaza dumpsite.
TABLE 4.4b3 LSD test for the mean concentration of the heavy metals at Gaza dumpsite
Multiple Comparisons
(I) Heavy Metals (J) Heavy Metals Mean Difference (I-J) Std. Error Sig. 95% Confidence Interval
Lower Bound Upper Bound
Cadmium Lead -7.17333 4.97405 .187 -18.6435 4.2968
Nickel -78.28000* 4.97405 .000 -89.7502 -66.8098
Zinc -56.72000* 4.97405 .000 -68.1902 -45.2498
Lead Cadmium 7.17333 4.97405 .187 -4.2968 18.6435
Nickel -71.10667* 4.97405 .000 -82.5768 -59.6365
Zinc -49.54667* 4.97405 .000 -61.0168 -38.0765
Nickel Cadmium 78.28000* 4.97405 .000 66.8098 89.7502
Lead 71.10667* 4.97405 .000 59.6365 82.5768
Zinc 21.56000* 4.97405 .002 10.0898 33.0302
Zinc Cadmium 56.72000* 4.97405 .000 45.2498 68.1902
Lead 49.54667* 4.97405 .000 38.0765 61.0168
Nickel -21.56000* 4.97405 .002 -33.0302 -10.0898
*. The mean difference is significant at the 0.05 level.
From the LSD Table 4.4b3 above, for cadmium and lead comparison, the difference was 0.187. Since this value is greater than the 0.05 required for statistical significance, cadmium and lead concentrations are not significantly different. Applying this same procedure to the cadmium and nickel comparison, the result indicated a statistically significant difference (sig. = 0.000 which is less than 0.05). After each of the heavy metal had been compared to the other three, the final results showed that cadmium and lead were not significantly different but nickel and zinc were significantly different from cadmium and lead, and also, nickel and zinc were significantly different from each other. Hence, nickel and zinc were the sources of the significant differences in the concentration of heavy metals at Gaza dumpsite.
TABLE 4.4c1 Descriptives for the concentrations of heavy metals at Vatican dumpsite
N Mean Std. Deviation Std. Error 95% Confidence Interval for Mean Minimum Maximum
Lower Bound Upper Bound
Cadmium 3 7.1133 2.13638 1.23344 1.8063 12.4204 5.24 9.44
Lead 3 7.7400 1.30399 .75286 4.5007 10.9793 6.56 9.14
Nickel 3 48.9533 5.01144 2.89336 36.5042 61.4024 46.04 54.74
Zinc 3 89.8067 16.10136 9.29612 49.8087 129.8047 71.56 102.02
Total 12 38.4033 36.43175 10.51694 15.2557 61.5510 5.24 102.02
TABLE 4.4c2 ANOVA for the concentrations of heavy metals at Vatican dumpsite
Sum of Squares Df Mean Square F Sig.
Between Groups 14018.728 3 4672.909 64.314 .000
Within Groups 581.266 8 72.658
Total 14599.993 11
From the ANOVA table 4.4c2, there is a significant difference in the mean of at least a pair of mean concentrations of the heavy metals. But the ANOVA does not show which of the mean concentrations that contributed to the significant difference hence the need to use the LSD to identify which mean concentration(s) is/ are responsible for the difference.
Table below 4.4c3 shows the LSD test for the mean concentration of the heavy the metals at Vatican dumpsite.
TABLE 4.4c3 LSD test for the mean concentration of the heavy metals at Vatican dumpsite
Multiple Comparisons
(I) Heavy Metals (J) Heavy Metals Mean Difference (I-J) Std. Error Sig. 95% Confidence Interval
Lower Bound Upper Bound
Cadmium Lead -.62667 6.95980 .930 -16.6760 15.4227
Nickel -41.84000* 6.95980 .000 -57.8893 -25.7907
Zinc -82.69333* 6.95980 .000 -98.7427 -66.6440
Lead Cadmium .62667 6.95980 .930 -15.4227 16.6760
Nickel -41.21333* 6.95980 .000 -57.2627 -25.1640
Zinc -82.06667* 6.95980 .000 -98.1160 -66.0173
Nickel Cadmium 41.84000* 6.95980 .000 25.7907 57.8893
Lead 41.21333* 6.95980 .000 25.1640 57.2627
Zinc -40.85333* 6.95980 .000 -56.9027 -24.8040
Zinc Cadmium 82.69333* 6.95980 .000 66.6440 98.7427
Lead 82.06667* 6.95980 .000 66.0173 98.1160
Nickel 40.85333* 6.95980 .000 24.8040 56.9027
*. The mean difference is significant at the 0.05 level.
From the table 4.4c3 above, for cadmium and lead comparison, the significance level was 0.930. Since this value is greater than the .05 level required for statistical significance, cadmium and lead concentrations are not significantly different. Applying this same procedure to the cadmium and nickel comparison, the result indicated a statistically significant difference (sig. = 0.000 which is less than 0.05). After each of the heavy metal had been compared to the other three heavy metals, the final results showed that cadmium and lead were not significantly different but nickel and zinc were significantly different from cadmium and lead, and also, nickel and zinc were significantly different from each other. Hence, the sources of the significant differences in the concentration of heavy metals at Vatican dumpsite were nickel and zinc.
4.2 Discussion
From the results obtained (table 4.2a), all the concentrations of nickel and zinc were within the lower threshold concentration of nickel and zinc in the soil, while all the concentrations of lead was far below the lo
wer threshold except for one concentration which was above the higher threshold concentration of lead required for soils. Al
l but two of the concentrations of cadmium were above the higher threshold concentration of cadmium required in soils (table 4.5a)
TABLE 4.5a Threshold values of heavy metals
Heavy metal Concentration of metal in soil (mg kg-1)
Cadmium 1-3
Lead 100-400
Nickel 1-100
Zinc 20-300
Source: Tahar and Keltoum, 2011
TABLE 4.5b Comparison of heavy metal concentration range in soil analyzed in this study with the levels in similar studies elsewhere (mg kg-1)
Metal This study US Soil a China Soil b Poland Soil c India soil d Ethiopia soil e
Cd 1.32-9.44 NA 0.02-0.33 0.1-1.7 NA 0.12-1.61
Pb 3.86-443.40 4.62-554 9.95-56.0 7.1-50.1 ND-623.95 20.3-325.4
Ni 38.48-88.30 2.44-69.4 7.73-70.9 2.0-27.0 343-1409 47.3-200.6
Zn 36.24-102.02 12.6-183 28.5-181 10.5-1547 ND 140.9-302.8
a=Shacklette and Boerngen, (1984), b = Bradford et al. (1996), c = Dudka (1992), d = Abida et al. (2009), e = Melaku et al. (2005), ND = not detected, NA = not available.
4.2.1 Cadmium
From figure 4.2a, it can be deduced that for the dumpsites at Boscos and Vatican, there is no significant difference between the mean concentration of cadmium and the control since the standard error bars overlapped each other. This implies that cadmium concentration has spread from the dumpsite within a ten-metre radius away from the dumpsites at Boscos and Vatican. But there is a significant difference between the mean concentration of cadmium and its control at Gaza dumpsite since the standard error bars do not overlap each other. This suggests that the mean concentration of cadmium at Gaza is more localised at the dumpsite and found in trace amounts with increase in distance away from the dumpsite. Hence, the distribution of cadmium is high at Boscos and Vatican dumpsites and very low at Gaza dumpsite.
From table 4.2a, the concentration of cadmium ranged from 1.32 mg kg-1 to 6.18 mg kg-1 at Boscos, 2.90 mg kg-1 to 4.92 mg kg-1 at Gaza, and 5.24 mg kg-1 to 9.44 mg kg-1 at Vatican. The highest concentrations of cadmium at Boscos, Gaza and Vatican dumpsites were 6.18 mg kg-1, 4.92 mg kg-1, and 9.44 mg kg-1 respectively. All the dumpsites investigated had their cadmium levels higher than the recommended 1 ‘ 3 mg kg-1 limit specified by EU standard. The concentration range of cadmium obtained from this research was similar to the concentration obtained from a similar study conducted in Kaduna (Okunola et al, 2007).
From Table 4.5b, the concentration range of cadmium at the three dumpsites are extremely higher the concentration ranges for all the five countries.
The findings for cadmium in the soil samples in this research showed higher levels and there is a risk of contamination of cadmium in the three dumpsites.
The application of agricultural inputs such as fertilizers, pesticides, bio-solids (sewage sludge), and the disposal of industrial waste and the deposition of atmospheric contaminants increases the total concentration of Cd (Asio, 2009; Wuana and Okieimen, 2011). It can also result from burning of fossil fuels, sewage sludge, plastics waste, byproduct of Zn and lead refining, insecticides and motor oil (Asio, 2009; Bhagure and Mirgane, 2010;).
The absence of any major industry in the sampling sites suggests that the sources of cadmium could be from plastic waste, cadmium-nickel batteries, glasses, ceramics and miscellaneous sources such in rubber, paper and inks.
4.2.2 Lead
From figure 4.2b, there is no significant difference between the mean concentration of lead and the control at Boscos dumpsite which implies that the concentration of lead has spread almost uniformly around the dumpsite within a ten-metre radius but there exist significant difference between the mean concentration of lead and the control at Gaza and Vatican dumpsites. This implies that the concentration of lead at Gaza and Vatican dumpsites are more localised on the dumpsite and reduces in concentration as one moves away from the dumpsites. Hence, lead had a low distribution for Gaza and Vatican dumpsites and a high distribution for Boscos dumpsite.
From table 4.2a, the concentration of lead ranged from 3.86 mg kg-1 to 443.4 mg kg-1 at Boscos, 7.98 mg kg-1 to 17.96 mg kg-1 at Gaza, and 6.56 mg kg-1 to 9.14 mg kg-1 at Vatican. The highest concentrations of lead at Boscos, Gaza and Vatican dumpsites were 443.4 mg kg-1, 17.96 mg kg-1, and 9.14 mg kg-1 respectively. The concentration range of lead obtained from this research was similar to the concentration obtained from a similar study conducted in west Algeria, except for the highest concentration of lead at Boscos which was above (Kebir and Keltoum, 2011).
Comparing these values with the threshold values of lead in table 4.5a, the concentration of lead for the three dumpsites fall far below the threshold values range of 100 to 400 mg kg-1 except for the highest concentration at Boscos dumpsite (443.4 mg kg-1) which falls slightly above the threshold value range. This concentration at Boscos may be due to low distribution of lead from the source of contamination at the dumpsite and hence did not spread to other parts of the dumpsite evenly.
From table 4.5b, the concentration range of lead for this study falls within the concentration range of lead for the United States, and India but it is extremely higher than concentration obtained in China and Poland, and slightly above that obtained in Ethiopia.
According to Wuana and Okieimen (2011), lead is a naturally occurring and found as a mineral combined with other elements such as sulphur (PbS, PbSO4) and oxygen (PbCO3). Also waste incineration contributes to a greater amount of lead available in urban areas. The suspected sources of lead in these dumpsites are tins, cans, batteries, electronic waste and plastics. Atmospheric deposition from car exhaust fumes are also possible sources of lead to the dumpsites.
4.2.3 Nickel
From figure 4.2c, it can be deduced that there are no significant differences between the mean concentration of nickel and the controls for all the three dumpsites namely Boscos, Gaza and Vatican. This suggests that for nickel, it is spread almost evenly from the dumpsite and within a ten-metre radius around the three dumpsites. Therefore, the distribution of nickel is high for all the three dumpsites.
From table 4.2a, the concentration of nickel ranged from 38.48 mg kg-1 to 44.52 mg kg-1 at Boscos, 78.54 mg kg-1 to 88.3 mg kg-1 at Gaza, and 46.04 mg kg-1 to 54.74 mg kg-1 at Vatican. The highest concentrations of nickel at Boscos, Gaza and Vatican dumpsites were 44.52 mg kg-1, 88.3 mg kg-1, and 54.74 mg kg-1 respectively. The concentration range of nickel obtained from this research was similar to the concentration obtained from a similar study conducted in Lagos, Nigeria (Olafisoye et al, 2013). The concentration range of nickel fall within the threshold value range for nickel in the soil in table 4.5a.
From table 4.5b, the concentration range of nickel for this study generally falls within the concentration range of nickel for the United States, China and Ethiopia but is above concentration obtained in Poland, and below that obtained in India.
The global input of nickel to the human environment from e-waste sources is mostly from nickel batteries and magnets, as an alloying metal in steel, and in the production of pigments and magnetic tapes (Adelakun and Abegunde, 2011). Nickel contaminations in the soil are metal plating industries, combustion of fossil fuels, nickel mining and electroplating (Bhagure and Mirgane, 2010).
4.2.4 Zinc
It can be deduced from figure 4.2d that, there is no significant difference between the mean concentration of zinc and the control at the Boscos dumpsite, which implies that zinc has been distributed from the dumpsite within a radius of ten metres. But for the Gaza and Boscos dumpsites, there is a significant difference between the mean concentration of zinc an
d the control which implies the concentratio
n of zinc is more localised at the dumpsite and decreases in concentration as one moves away from the dumpsites. Hence, the distribution of zinc at Boscos dumpsite was high but very low for the Gaza and Vatican dumpsites.
From table 4.2a, the concentration of zinc ranged from 36.24 mg kg-1 to 48.88 mg kg-1 at Boscos, 50.12 mg kg-1 to 67.14 mg kg-1 at Gaza, and 71.56 mg kg-1 to 102.02 mg kg-1 at Vatican. The highest concentrations of zinc at Boscos, Gaza and Vatican dumpsites were 48.88 mg kg-1, 67.14 mg kg-1, and 102.02 mg kg-1 respectively. These values when compared with the threshold value range of zinc in the soil as shown in table 4.5a which is 20 mg kg-1 ‘ 300 mg kg-1, they fall within the range. The concentration range of zinc obtained from this research was similar to the concentration obtained from a similar study conducted in Yauri, Nigeria (Yahaya et al, 2009).
From table 4.5b, the concentration range of zinc for this study falls within the concentration range of zinc for the United States, China and Poland but below concentration range obtained in Ethiopia.
Most additions of zinc are from industrial activities such as mining, coal, waste combustion and steel processing (Wuana and Okieimen, 2011) and also from the use of liquid manure, composted materials, fertilizers and pesticides in agriculture (Bhagure and Mirgane, 2010). Possible sources of zinc to the dumpsites are, plastics, electric batteries, cooking utensils, photocopier papers and printing inks.
4.2.5 Correlation analysis.
The correlation analysis was used to compare the mean concentration of the heavy metals and the mean pH of the soil samples in this research. This was used to infer the influence of pH on the distribution of the heavy metals in the three dumpsites understudy. The behaviour of
heavy metals in the soil depends on the soil pH, properties of metals, redox conditions, soil chemistry, organic matter content, clay content, cation exchange capacity and soluble ligands in the surrounding fluid (Oyedele et al, 2008).
From table 4.3a, there is an existence of a strong positive correlation between the mean concentration of cadmium and the mean pH of the soil sample at the three dumpsites. The correlation coefficient was 0.500 but it can also be deduced that relationship between the concentration of cadmium and the pH is not significant since the sig. value is 0.667 (Table 4.3a). Hence the distribution of cadmium in the soil is not solely affected by the pH of the soil but other factors such the organic matter content, clay content and redox conditions.
According to table 4.3b, there is a strong negative correlation between the mean concentration of lead and the mean pH of the soil at the three dumpsites because the correlation coefficient was -0.500. However, testing the significance of the correlation indicated that the relationship between concentration of lead and the pH of the soil is not significant since the sig. value was 0.667 (Table 4.3b). This indicates that the distribution of lead in the soil is not limited to the influence of pH of the soil but other factors such as clay content, soil chemistry and organic matter content.
From table 4.3c, there is a very strong negative correlation between the mean concentration of nickel and the mean pH of the soil at the three dumpsites. The correlation coefficient was -1.00 and also testing of the relationship showed that there exist a significant influence on the concentration of nickel by pH of the soil. This implies that the distribution of nickel in the three dumpsites is inversely proportional to the pH of the soil, that is, highly alkaline soil tend to decrease the concentration of nickel in the soil.
Table 4.3d shows that, there is a strong negative correlation between the mean concentration of zinc and the mean pH of the soil at the three dumpsites because the correlation coefficient was -0.500. But the correlation between them is not significant as the sig. value was 0.667. This is indicative that the distribution of zinc is not solely dependent on the pH of the soil.
5.0 Conclusion and Recommendations
5.1 Conclusion
From the study, the pH of the soil samples at Boscos, Gaza, and Vatican dumpsites were 9.5, 8.2 and 8.4 respectively showing that the dumpsite soils were of alkaline nature.
In order of high to low mean concentration of the heavy metals, the following were found:
Concentration of cadmium was Vatican > Boscos > Gaza and the highest concentration of the control samples for cadmium was 7.54 mg kg-1 at Vatican; concentration of lead was Gaza > Boscos > Vatican and the highest concentration of the control samples for lead was 6.60 mg kg-1 at Boscos; concentration of nickel was Gaza > Vatican > Boscos and the highest concentration of the control samples for nickel was 81.98 mg kg-1 at Gaza and concentration of zinc was Vatican > Gaza > Boscos and the highest concentration of the control samples for zinc was 28.06 mg kg-1 at Boscos. The Gaza dumpsite was probably the most contaminated having highest concentrations of lead and nickel but the least contaminated in terms of cadmium whilst the Vatican dumpsite was also probably the most contaminated with cadmium and zinc but the least contaminated lead, and the Boscos dumpsite probably the least contaminated with nickel and zinc in terms of this study.
Cadmium was the lowest in concentration among the four heavy metals but notably, it was the only metal that exceeded its permissible range. Cadmium had a high distribution at Boscos and Vatican dumpsites but a low distribution at the Gaza dumpsite. Lead showed a high distribution at Boscos dumpsite and a low distribution at the Gaza and Vatican dumpsites. The distribution of nickel was high at all the three dumpsites. Zinc distribution was very low at the Gaza and Vatican dumpsites but high at Boscos dumpsite. Lead, nickel and zinc did not exceed their permissible ranges as recommended.
Among other factors, the distribution of cadmium, lead and zinc in the soil at the three dumpsites was probably not influenced by the pH of the soil. However, the distribution of nickel in the soil of the dumpsites was likely influenced by the pH of the soil negatively, that is, increasing pH of the soil decreases the concentration of nickel in the soil.
5.2 Recommendations
It is recommended that;
‘ Further research work be carried out in these areas for other heavy metals.
‘ Other factors such as clay content and organic matter content which may also influence the
distribution of heavy metals in the soil be analysed.
‘ Farming around these dumpsites should be avoided since it can lead to heavy metal poisoning in humans especially cadmium poisoning.
‘ The concentration of heavy metals be determined in both the dry season and wet seasons and compared.
‘ The crude burning of solid especially electronic wastes should be avoided.