1.0 INTRODUCTION AND LITERATURE REVIEW
Heavy metals include both non-toxic and toxic elements. Iron (Fe), Cobalt (Co) Copper (Cu) Manganese (Mn) Molybdenum (Mo) and Zinc (Zc) Magnesium(Mg) are the trace elements and are required in a very minute amount, whereas other metals are non-essential, toxic to animals and even fatal when accumulated these metals includes; Mercury (Hg), Arsenic (As), Lead (Pb) Plutonium (Pu), Vanadium (v), Tungsten (w) and Cadmium (Cd), (Deevikaet al., 2012).
Heavy metals with established toxic action to humans include cadmium (Morrow, 2010 and Hayes, 2007) lead (Eric, 2013 and Patrick, 2006 and mercury (Bojorklund, 1995).Each of these has been studied in isolation for toxicity (Morrow, 2010; Patrick,2006 and Clarkson, and Magoss. 2006). But in the ecosystem, be it air, (atmosphere, land and water) where they occur they do not exist in isolation. They occur in close association with other metal and non-metallic elemental pollutants. Among the metallic pollutant could be calcium, copper, zinc, magnesium, manganese, iron and others. Metals are known to interact with one another. Interaction can bring about two element together include proximately and could cause out right displacement with one another. When ingested in food and water they can antagonize each other. When it comes to intestinal hand and pulmonary absorption it is there conceivable that the presence of other element can affect the toxic potential of each of the heavy metal that has been study in isolation.
Egborge (1994) reported that Warri River had and unacceptability high cadmium level, 0.3mg/l of H2O, was 60-fold above the maximal allowable level of 0.005mg/l. This report prompted our early studies on the hepato-, nephro- and goladal toxicity of cadmium in rat expose to this high close via water and diet. The diet was formulated with fish expose to 0.3mgCd/water in the ambient water, as protein source and the toxic effects investigated and reported. (Asagba and Obi, 2000; Asagba and Obi, 2001; Obi and Ilori, 2002; Asagba and Obi, 2004a; Asagba and Obi, 2004b; Asagba and Obi, 2005). The studies focus on cadmium without taken into consideration the fact that other metal were also present the river water and as such were co-consumed by the communities using the river water for cooking drinking and other domestic purposes. Hence it is desirable to know if the presence of other metal would enhance or diminish the toxic potential of cadmium or indeed that of any other metal such as lead that was mention above. Therefore the aim of this present studies was to re-examine the toxic potential of cadmium in the presence of other metals such as magnesium. The objective set out to achieve were:
- Re-examination of the kidney toxicity of cadmium using established toxicity index for kidney such as Creatinine, Blood urea nitrogen and Alkaline phosphatase.
- Re-examine the status of the parameters in the absence of cadmium but in the presence of magnesium.
- Re-examine this parameterin the presence of cadmium and magnesium.
1.2 LITERATURE REVIEW
Cadmium (Cd) in its purest form is a soft silver-white metal that is found naturally in the earth’s crust. It melts at 3210c and boils at 7670c. The divalent element has an atomic number of 48, a relative atomic mass of 112.41 and belongs to group 12, period 5 and block – d of the periodic table. It is insoluble in water, although its chloride and sulphate salt are freely soluble. The most common forms of cadmium found in the environment exist in combination with other elements. For example, cadmium oxide (CdO),(a mixture of cadmium and oxygen),cadmium chloride (CdCl) (combination of cadmium and chlorine), and cadmium sulphide(CdS) (a mixture of cadmium and sulphur) are commonly found in the environment.
Cadmium is typically a metal of the 20th century, even though large amount of this by- product of zinc production have been emitted by non ferrous smelters during the19th century. Currently, cadmium is mainly used in rechargeable batteries and for the production of special alloys although emission in the environment have markedly declined in most industrialized countries, cadmium remains a source of concern for industrial workers and for populations living in polluted areas,especially in less developed countries (Sethi and Khandelwal,2006). In the industries, cadmium is hazardous both by inhalation and ingestion and can cause acute and chronic intoxications. Cadmium dispersed in the environment can persist in soils and sediments for decades. When taken up by plants, cadmium concentrates along the food chain and ultimately accumulates in the body of people eating contaminated foods. Cadmium is also present in tobacco smoke, further contributing to human exposure. By far, the most salient toxicological property of cadmium is its exceptionally long-life in the human body. Once absorbed, cadmium irreversibly accumulates in the human body, particularly in the kidneys and other vital organs such as the lungs or the liver. In addition to its extraordinary cumulative properties, cadmium is also a high toxic metal that can disrupt a number of biological systems, usually at those that are much lower than those toxic metals (Norsbergget al., 2007; Bernard, 2004).
18.104.22.168 USE OF CADMIUM
Cadmium metals havea specific property that makes it suitable for a wide variety of industrial applications. These include excellent corrosion resistance, low melting temperature, high ductility, high thermal and electrical conductivity (National resources Canada, 2007). It is used and traded globally as a metal and as a component in 6 classes of products, where it impacts distinct performance averages. According to the US geological survey, the principal use of cadmium where: nickel-cadmium (Ni-Cd) batteries, 83%, pigments 8%; coating and platting 7%; stabilizer for plastics, 1.2%; and others (including non ferrous alloys, semi conductors and photovoltaic devices). 0.8% (USGS, 2008).Cadmium is also present as an impurity in the non ferrous metals (Zinc, Lead and copper), iron and steel, fossil fuels (coal, oil, gas, peat and wood), cement and phosphate fertilizers. In these products the presence of cadmium generally does not affect performance; rather, it is regarded as an environmental concern (international cadmium association, 2011). Cadmium is also produced from recycled materials (such as Ni-Cd batteries and manufacturing scrap) and some residues (e.g. cadmium containing dusts from electrical and furnaces) or intermediate products. Recycling accounts for approximately 10- 15% 0f the production of cadmium in developed countries (National Resources Canada, 2007).
The primary use of cadmium in the form of cadmium hydroxide is the electrode Ni-Cd batteries because of their performance characteristics (e.g. higher cycle lives, excellent low- and high – temperature performance), Ni-Cd batteries are used extensively in the rail-roads and air craft industries(for starting an emergency power), and in consumer products (e.g. cordless power tools telephones, portable computer, camcorders, portable household appliances and toys) (ATSDR, 2008; USG, 2008). Cadmium sulphide compounds (e.g. cadmium sulphide, cadmium sulphoselenide and cadmium lithopone) are used as pigments in a wide variety of applications, including engineering plastics, glass,glazes, ceramics, rubber, enamels, artists colours and fireworks. Ranging in colour from yellow to deep-red maroon, cadmium pigments have good covering power, and are highly resistant to a wide range of atmospheric and environmental conditions (e.g. the presence of hydrogen sulphide orsulphur dioxide. Light, high temperature and pressure) (Herron, 2001; ATSDR,2008; International Cadmium Association, 2011).
Cadmium and cadmium alloys are used as engineeredor electroplated coatings on iron, steel, aluminum, and other non-ferrous metals. They are particularly suitable for industrial applications requiring, a high degree of safety or durability (e.g. aerospace industry, industrial fastenerselectrical parts automotive systems military equipment, and marine /offshore installations) because they demonstrate good corrosion resistance in alkaline or salt solutions, have a low coefficient of friction and good conductive properties, and are readily solderable (UNEP, 2008; International Cadmium Association, 2011).Cadmium salts of organic acid (generally Cadmium Laurate or Cadmium Stearate, used in combination with barium sulphate) were widely used in the past as heat and light stabilizers for flexible polyvinyl chloride and other plastics (Herron, 2001; UNEP, 2008). Small quantities of cadmium are used in various alloys to improve their thermal and electrical conductivity, to increase the mechanical properties of the base alloy (e.g. strength, durability, extrudability, hardness, wear resistance, tensile and fatigue strength), or to lower the melting point. The metals most commonly alloyed with cadmium include copper, zinc, and lead, tin, silver and other precious metals. Other minor use of cadmium includes telluride and cadmium sulphidein solar cells. And other semi-conducting cadmium compounds in a Varity of electronic applications (Morrow, 2011; UNEP, 2008; International Association, 2011).
22.214.171.124 ROLE OF CADMIUM IN OXIDATIVE STRESS INDUCTION
The first evidence of increased lipid peroxidation (LPO) in mice hepatocytes co-cultured with Cd was given by Muller in 1987. The author described Cd-induced production of reactive oxygen species (ROS) through interaction with critical subcellular sites such as mitochondria, peroxisomes and microsomes that resulted in the generation of free radicals and LPO in subcellular membranous structures. Production of ROS has been reported later in a variety of cell culture systems, as well as in intact animals via all routes of exposure (Hartet al., 1999; Amaraet al., 2008). They also found early signs of oxidative stress in the liver of mice exposed to a single oral Cd dose (20 mg kg-1 b. w. in the form of CdCl2) through increased LPO level, expressed as malondialdehyde (MDA) after 6 h, 12 h, and 24 h (Djukić-Ćosićet al., 2008). Since Cd has no redox activity, it may enhance ROS production by suppressing free-radical scavengers suchas glutathione (GSH) and by inhibiting detoxifying enzymes such as superoxide dismutase, catalase, and GSH peroxidase, and/or through other indirect mechanisms (Valko et al., 2005). The ways in which Cd can induce the formation of reactive species are summarised in Figure 1. Available data confirm that the formation of free radicals such as superoxide ion, hydrogen peroxide, and hydroxyl radicals involves depletion of GSH and changes in the activity of antioxidant enzymes (Liuet al.,2009). Our recent findings (Djukić-Ćosićet al., 2007) showed that an acute oral Cd dose (20 mg Cd kg-1 b. w.) significantly decreased the glutathione (GSH) content in mice liver 4 h, 6 h, and 12 h after Cd administration and increased GSH in the kidney after 12 h, 24 h, and 48 h, but did not cause significant GSH changes in the testis. A twoweeks oral Cd exposure (at dose of 10 mg kg-1 b. w. of Cd given as aqueous solution of CdCl2) lowered renallevels and increased liver and testicular levels of GSH.These results, together with related findings of otherauthors, show that the effect of Cd on GSH tissue levelsvaries with animal species, dose, route, and durationof exposure. In general, acute exposure to metalsdecreases GSH levels due to the formation of metal-GSH complexes and/or consumption by the GSHperoxidaseunder oxidative stress induced by metals.
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