CHAPTER ONE
1.0 INTRODUCTION
Several studies have indicated that vegetable, particularly leafy crops, grown in heavy metals contaminated soils have higher concentrations of heavy metals than those grown in uncontaminated soil (goldsmith et a; 1988; Dupler and Lee 1999). A major pathway of soil contamination is through atmospheric deposition of heavy metals from point sources as: metaliferous mining, smelting and industrial activities. Other non-point source of contamination affecting predominantly agriculture soil includes inputs such as, fertilizer, pesticide, sewage sludge organic manures and composts (cobb, 2000). Additionally, foliar uptake of atmospheric heavy metals emissions has also been identified as an important pathway of heavy metal contamination in vegetable crops (Bassuk 1986; Salim et al; 1992).
Vegetable growing areas are often situated in, or near source of atmospheric deposits, and thus have an elevated risk of potential contamination. There are regions in “Eka Street waste dumpsite” in Uyo municipal were there indiscriminate dumping of both industrial and domestic waste materials which result in polluting the immediate environment and thereby causing the higher concentration of heavy metal around the vicinity.
There have been a number of studies which have investigated atmospheric deposition of heavy metals in soil and/or vegetables/growing in the vicinity of industrial area (Gupta, 1994, Vasquez, et al; 1993).
These studies indicate high concentration of heavy metals in vegetable grown in the vicinity of industries and identify leafy vegetable at greatest risk of accumulating elevated concentration.
There is however, limited published information contamination of vegetable grown in the vicinity Australian industrial area. In Australia, the national environmental protection (Assessment of site combination) measures (NEPM, 1999). Identified environmental investigation levels (EIL) also which define threshold values of certain heavy metals in soil. Maximum levels (ML) also exist for Cd and Pb in vegetable crops (fresh weight basis). And are applied by the Australian and New Zealand food Authority.
1.1 POLLUTION
Pollution is an undesirable change in the physical, chemical or biological characteristic of our air, land and water that may or will harmfully affect human life or that of other desirable species (Udosen, 2001).
Our industrial processing, living conditions, cultural assets or that may or will waste or deteriorate our raw material resources. Pollution is a disorder within an environment and is a by- product of energy conversion and the use of resources. It is a contamination, defilement, a mischief, a perturbation and a reduction in the value of an object or things. Pollutants released into the soil, water and air can find their way into the human body as a result of breathing, eating or drinking. Thus pollution, however defined, depends on the component of the earth that contaminated. (Udosen,1995). The various type of environmental pollution includes air pollution, water pollution and land (soil or terrestrial) pollution.
Water Pollution
The common source of water supply includes rain, spring, stream, Lake river, sea, oceans, and wells.
Natural water bodies are dynamic system full of different type of substances ranging from organic to inorganic. According to Stump and Morgan (1981) in natural waters, organisms and their a biotic environment are interrelated and interact with each other. In pollution studies, emphasis is never placed on the quantity of water (since water as a substance is abundant) but on the quantity of the water and its distribution. (Since water as a substance is abundant) but on the quality of the water and its distribution.
Water pollution therefore could be looked at as the disruption of stability of surface water by gases, sewage, industrial wastes and other refuse. It could be defined as the degradation of water by gases, sewage, industrial wastes and other refuse. It could be defined as the degradation of water environment by man’s activities. Infact, any change in nature waters, which may impair their use caused by the introduction of organic or inorganic substances or a change in temperature of the water is termed water polution
Land (Soil or Terrestrial) Pollution
Many communities are already facing land pollution problem resulting from improper disposal habit of soild wastes like scraps, furniture, used batteries, old mattresses, empty cans, paper, glasses, damaged radios, old refrigerators, abandoned old vehicle and trucks, buckets, vegetable matter and a host of other unused materials too numerous to mention.
These wastes when improperly disposed of may affect the physical, mental and social health of the inhabitant. Terrestrial pollution therefore involves the contamination of earth by any of a Radioactive materials, (Radio-nuclides and other compounds) municipal solid waste disposal practices also contribute to terrestrial pollution as do automobile junkyards at uncontrolled dumping grounds.
Terrestrial pollution could be regarded as the presence in the land (soil) of contaminants such as toxic heavy metals, radioactive materials, radio nuclides, toxic anions and other toxic compounds in quantities characteristics and duration such as to be injurious to plants which would in turn be harmful to humans and animal that feed plants and terrestrial lives (Udosen, 1987).
Air Pollution
The additions of any substance to air can alter to some extent the physical and chemical properties of clean air. Such a substance is regarded as air pollution. However, pollutants are usually classified as only those substances that are added in amounts sufficient to exceed tolerance levels. Such substances may occur as solid particles, liquid droplets, gasses or mixture of these forms. Most air pollution problems involve a large number of different kinds of pollutions in various forms rather than a single substance.
Therefore air pollution could be defined as the presence of pollutants in various forms rather than a single substance.
Therefore air pollution could be defined as the presence of foreign matter (gaseous or particulate or a combination of both) in the air which is detrimental to the health and/or welfare of man.
Sources of Environmental Pollution
Waste disposal sites, whether active or closed, can result in serious pollution of ground water due to leachate. Therefore the main sources of pollution are land fill leachate, chemical and metal processing industries, power stations, petrol service stations and oil exploitation. In mixed composite waste, including kitchen and garden refuse, there is also a diverse range of other materials, some of which are potentially hazardous. These hazardous substances include decorating products like paints, vanishes, garden products like pesticides, herbicides and vehicle products which include engine oil, brake fluid, antifreeze and carbatteries. These items may contain heavy metal like mercury, nickel, cadmium; when such household waste sites is acted on by rainwater, the organic and inorganic toxic leachate results, collecting of base from the landfill. Disposal of waste material (either solid or product or wastes) such waste materials are likely to be poisonous.
1.2 HEAVY METAL
The term heavy metal refers to any metallic chemical element that has a relatively high density or specific gravity that is at least five times the specific gravity of water. Example of heavy metal include mercury (Hg), lead (Pb), Thallium (Ti), Cadmium (Cd), Arsenic (As), and Chromium (Cr). Heavy metals are natural components of the earth ‘s crust, they cannot be degraded or destroyed. The specific gravity of water is at 40C. Simply stated, specific gravity is a measure of density of a given amount of solid substance when it is compared to an equal amount of water-some well-known toxic metallic elements with that of water are arsenic, 5.7; Cadmium 8.65, Lead, 11.34; Iron,7.0; and Mercury, 13.546 (Lide,1992).
1.3 ESSENTIAL TRACE METALS
In small quantities, certain heavy metals are nutritionally essential for a healthy life. Some of these are referred to as the trace element (e.g Iron, Copper, Manganese, and Zinc). These elements are commonly found naturally in food stuff, fruits and vegetables.
The diagnostic medical application of heavy metals include direct infection of gallium during radiological procedures dosing with chromium in parental nutrition mixtures and the use of lead as a radiation shield around x-ray equipment (Roberts, 1999).
Heavy metals are also common in industrial applications such as in the manufacture of pesticides, batteries, alloys, electroplated metal parts, textile dyes, steel etc. many of these products are in our homes and actually add to quality of life when used properly.
1.4 HEAVY METAL TOXICITY
Heavy metal becomes toxic when they are not metabolized by the body and accumulate in soft tissues. This metal may enter the human body through food, water, air or absorption through skin when they come in contact with human in agricultural, pharmaceutical, industrial, or residential settings (Robert, 1999).
Toxicity level in children can be developed from the normal hand-to-mouth feeding activity or contaminated soil by actual eating of objects that are not food (dirt or paint chips) (Dupler, 2001). Less common routes of exposure are during a radiological procedure, from in appropriate dosing or monitoring during intravenous (Parental nutrition, from a broken thermometer (Smith, et al; 1997). Arsenic is the most common cause of acute heavy metal poisoning in adults because its released into the environment by the smelting process of Copper, Zinc and Lead, as well as by the manufacturing of chemicals and glasses.
Arsenic gas is common by-product produced by the manufacturing of pesticides that contain arsenic. Arsenic may be also found in water supplies worldwide, leading to exposure to shellfish, cod and had dock other sources are paints, rat poison, fungicides, and wood preservatives. Target organs are the blood, kidneys and central nervous digestive and skin system (Roberts, 1999).
1.5 HEAVY METAL UPTAKE BY PLANTS
The study of polluted soils has shown heavy metal contamination as well as the uptake of these toxic elements by plants. The sources of these heavy metal in plant is their growth media i.e (air, soil, nutrients) from which heavy metal are taken up by roots or foliage. There is considerable availability in actual uptake by plants of these elements from soil depending on such properties as pH and organic matter contents, cationic exchange capacity, binding to different soil components and the plant species involved (Nyles, 1999).
Heavy metals have been reported in crops grown in abandoned polluted area (Okoronkwo et al; 2005) and also in soil irrigated with sewage water (Chiroma et al; 2003). The uncontrolled input of heavy metals in soil is undesirable because once accumulate in the soil, the metals are generally very difficult to remove (Smith et al; 1996). Subsequent problems may be toxic to the plant growing on the contaminated soil and uptake by the plant resulting in high metal levels in plant tissues. Since one of the main sources of these heavy metal contamination included discharged of metals polluted waste water to land, attempts have been made by various researches to find more effective means of eliminating, controlling or managing these heavy metal discharges from industrial effluent, sewage water etc.
The accumulation of heavy metals by plants, roots, stem and leaves grown in polluted soil have been reported that lead does not readily accumulate in the fruiting part of vegetable and fruit crops (eg. lettuce) and on the surface of root crops (Rosen 2002).
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