The degree to which a substance or mixture of substances can harm humans or animals is called toxicity. Acute toxicity involves harmful effects in an organism through a single or short-term exposure. Chronic toxicity is the ability of a substance or mixture of substances to cause harmful effects over an extended period, usually upon repeated or continuous exposure sometimes lasting for the entire life of the exposed organism. Sub-chronic toxicity is the ability of the substance to cause effects for more than one year but less than the lifetime of the exposed organism.
Over the last three decades there has been increasing global concern over the public health impacts attributed to environmental pollution, in particular the global burden of disease. The World Health Organization reported that about a quarter of the diseases of human being occur today due to prolonged exposure of environmental pollution. Most of these environment-related diseases are however not easily detected and may be acquired during childhood and manifested later in adulthood. Improper management of solid waste is one of the main causes of environmental pollution and degradation in many cities, especially in developing countries. Many of these cities lack solid waste regulations and proper disposal facilities, including for harmful waste. Such waste may be infectious, toxic or radioactive. Municipal waste dumping sites are designated places set aside for waste disposal. Depending on a city’s level of waste management, such waste may be dumped in an uncontrolled manner, segregated for recycling purposes, or simply burnt. Poor waste management poses a great challenge to the well-being of city residents, particularly those living adjacent to the dumpsites due to the potential of the waste to pollute water, food sources, land, air and vegetation. The poor disposal and handling of waste thus leads to environmental degradation, destruction of the ecosystems and poses great risks to public health.
Environmental pollution: Bangladesh perspective
Bangladesh is a developing country. So the poverty reduction in Bangladesh is largely based on growth in agriculture, aquaculture and industrialization. In Bangladesh, industrial units are mostly located along the banks of the rivers and water bodies. There are obvious reasons for this, such as to make provision of transportation for incoming raw materials and outgoing finished products. Unfortunately as a consequence, industrial units discharge effluents directly into the rivers and water bodies without any consideration of the environmental degradation. The most problematic industries for the environment in Bangladesh are textiles, tanneries, pulp and paper mills, fertilizer, industrial chemical production and refineries. A complex mixture of hazardous chemicals is discharged into the air, soil and water bodies without treatment. The main reasons are the department of environment of Bangladesh has never implemented the environmental protection regulations properly due to the lack of environmental management, lack of man power, non-availability of the standards and so on. So, the industries are almost free to discharge indiscriminately its untreated wastes at will and to any extent and convenience it deem necessary. These wastes contain huge amount of organic and inorganic pollutants. The organic pollutants are both biodegradable and non-biodegradable in nature. The biodegradable organic components degrade soil and water quality during decomposition. Inorganic pollutants are mostly metallic salts, and basic and acidic compounds. These inorganic components undergo different chemical and biochemical interactions in the soil and water system, and also deteriorate the quality of soil and water. The polluted water further pollutes flora and fauna of the environment. The non-biodegradable organic and inorganic components persist in the soil and water system for a long time and pass into the food chain.
Use of wastewater (industrial effluent and sewage water) in agriculture and its application for other purposes is global practice. At least 20 million hectares of land in 50 countries are irrigated with raw and or partially treated wastewater. Wastewater is a complex resource, with both strong positive and negative aspects. Its nutrient contents can be used for crop production. However, the widespread use of wastewater with more toxic waste is likely to cause an increase in the incidence of wastewater borne diseases as well as more rapid degradation of the environment. The effluents of industries that are discharged into agricultural sectors have become a growing environmental problem now. Besides this the agriculture sector also to increase the pollution of air, water and soil due to the indiscriminate use of fertilizers, pesticides, insecticides and herbicides.
Contamination of arsenic in ground water of Bangladesh provides a crucial picture of environmental degradation. It causes pollution of drinking water and hence many life threatening arsenic diseases. Toxic chemical compounds, salts and radioactive materials are responsible for soil pollution which affects plant and animal life. Thus the presence of various toxic pollutants in ground water and soil as well as improper pollution management cause a lot of devastating problems for our life and environment of Bangladesh.
Heavy metal and food pollution
Heavy metals are metallic chemical elements e.g. Pb, Cd, Cr, Ni, As, Hg, Fe, Mn, Cu, Co, Zn etc. They have relatively high density and are toxic or poisonous over a threshold concentration. Heavy metal species can have serious impact if released into the environment by bioaccumulation. But small amount of some heavy metals such as Zn, Mg, Fe, Ni, Cr, Mn etc. are essential for the survival of all lives. Their deficiency or excess in human body causes many biological disorders. Some heavy metals such as Hg, Pb, Cd, As etc. are totally toxic for human body. Deliberately some heavy metals are partially toxic. For an example Cr+6 is toxic but Cr+3 is essential for man. Similarly Ni is toxic but Ni+2 is essential. The toxic heavy metals are originated from waste water and solid wastes of industries, soil additives, fossil fuels, waste batteries, laboratories wastes etc. Other alternative sources of these heavy metals are the goods of electronics, mechanics, and the artifacts’ of every day life made by different heavy metals or by their alloys. Consequently these heavy metals tend to reach water body, soil and air (environment) from these sources. It is reported that once the toxic metals reach the soil, the metals are difficult to remove and their remediation is very costly or even impossible. Thus the environment is polluted by these toxic metals. These toxic pollutants may enter into plants along from the contaminated soil and water through natural geochemical process. Through this process the plant food chain is contaminated. In addition, these toxic pollutants may also be entered into the domestic animal’s body, when they take polluted plant as their foods. In this way foodstuffs (plant and animal) are contaminated by different types of toxic metals.
Consumption of foods and health problems
We consume different types of foods. They supply necessary carbohydrates, fats, vitamins, minerals etc. into the human body for maintaining the life process. People, especially those who take the contaminated foods are exposed to heavy metals. Moreover, the toxic metals are taken into the body through inhalation, ingestion and skin absorption. If toxic metals enter and accumulate in body tissues faster than the body’s detoxification system, these toxins will increase gradually. Higher accumulation of toxic heavy metals in human body may lead to health disorder
Many researchers from different parts of the world have been working on toxic effects of these metals on organisms. Their finding is that organisms can tolerate a metal up to a certain concentration and beyond the concentration create different malfunctions in the organism. For an example, toxic metals above threshold limit in the body can impair the functions of blood and cardiovascular organ, eliminative pathways (colon, liver, kidneys, skin), endocrine (hormonal), energy production pathways, enzymatic process, immune system, nervous system (central and peripheral), reproductive and urinary systems. Toxic metals may alter, remove or impair the production of specific molecules needed in the body. They may alter the structure of various entities such as the mitochondria or a cell nucleus. Toxic metals may create disturbances in the cell-to-cell communication occurring between inflammatory mediators, nerve cells or hormones. Toxic metals tend to be accumulated at the target sites such as membrane or structural proteins, enzymes or DNA molecules. Once at the target site, they can displace an important mineral from its binding site and “pretend” to be this mineral. This is called “molecular mimicry”; however, they cannot perform the mineral’s function and so inhibit any activity at the binding site, affecting cellular function
The metals required in the living cells for maintaining metabolic functions are known as essential metals or minerals. Essential metals are the building blocks of body. For an example, they are required for body structure, fluid-balance, protein structures and produce hormones. They may act as cofactors or catalysts of all enzymes in the body. These play vital roles at the molecular level in the living systems. Without the proper metals in the appropriate amounts, the organic molecules can not assist the body in carrying out its primary functions. Unlike most organic molecules, metals are absolutely essential. Because metals are the catalysts or may be a centre atom of an organic bio-molecules, which create a healthy environment in which the body is using vitamins, proteins, carbohydrates and fats that can grow, function and heal itself. This is why a complete spectrum of metals is necessary for good health. Regarding the importance of the metals in body metabolism, both the deficiency and excess of the essential metals produce undesirable effect. For an example, the deficient supply of the metals in the human body will result in the shortage of enzymes and provoke to accumulate the non essential elements which leads to metabolic dysfunction causing diseases, whereas, the excess of the metals in the body impaired the metabolic functions of the respective organs in the body. Therefore, appropriate amount of the essential metals are required for body to maintain the sound health
Some metals such as Na, K, Mg and Ca are needed by the human body in relatively large amount i.e. more than 100 g every day; these are called macro minerals or macronutrients. But the metals such as V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo and Sn are required in micro/trace amount i.e. less than 100 g each per day for body, known as micronutrients . Despite being required in smaller amounts, these are not less important than other metals. Acute imbalance of these metals can be potentially fatal for the body. Diet can effect levels of macronutrients or micronutrients in the body, but effects are generally chronic e.g. a high intake of Na can lead to hypertension. Plants take up these metals from the ground, animal assimilate the metals into the body when consume the plants as foods. Therefore, naturally these essential metals are found in a broad range of plant and animal foods, as well as drinking water. But all metals are not same according to their sources and functions. Varied diets will ensure an adequate supply of most essential metals for healthy people. The best way to overcome this problem is to include very wide range of foods in our life. So the proper knowledge about their sources and functions help us to take the appropriate foods.
The macro and micro minerals that our body needs for normal physiology and functions properly are described below:
Iron is an essential element for almost all organisms with the exception of certain members of the lactic acid bacteria. All living cells require iron for growth, replication, respiration and DNA synthesis. Iron is also required for some proteins within the mitochondrion, including heam and iron-sulfur protein that involves in electron transport and energy production. It is a component of various enzymes and is concentrated in bone marrow, liver and spleen. Therefore, iron is the key element of many bio-molecules such as hemoglobin, myoglobin, ferredoxin, ferritin, transferrin etc. in human body. It plays a significant role in bio-chemical activities by taking position in human body. Iron can promote resistance to diseases and prevent fatigue.
An adult person needs 10-15 mg of iron in a day for maintaining the physiological functions of iron in human body [19, 20]. This recommended daily allowance (RDA) must enter into the body through different type of foods. Iron deficiency creates many abnormalities in the body. For an example, the concentration of haemoglobin in human body can be depleted. As a result, they can’t carry enough oxygen from lungs to the tissues, so energy metabolisms are hampered in the cell. The result is fatigue, weakness, headaches, apathy, pallor and poor resistance to cooled temperatures . Generally iron deficiency is very scarce for man but woman, especially pregnant woman may suffer iron deficiency. Iron deficiency of human body can easily be overcome by taking iron-rich foods. The best natural iron-rich foods are meat, leafy vegetables, fruits, green beans, tomato juice, dried fruits, mussels, yeast, molasses, beans, nuts, seeds and cereals. On the other hand, large amount of iron above the RDA limit when ingested, the body’s ability to control its absorption is failed because a human being can only excrete about 1-2 mg iron per day. As a result, iron poisoning is occurred due to the iron overload. Sometimes iron overload is due to defective genes that somehow impair the body’s ability to regulate iron absorption. This may cause malfunction of organs resulting in serious illness
Amongst the essential metals, zinc is the second in term of quantity found in the human body. Zinc is essential for the development and normal function of the nervous system. Zinc is required for optimal vitamin A metabolism. More than 200 enzymes in human body require zinc as cofactor. Zinc induces the synthesis of metallothionein, which is a cofactor in regulating the metabolism of zinc including absorption and storage. Zinc is a functional component of several proteins that contribute to gene expression and regulation of genetic activity. Moreover, zinc is antioxidant and boosts immunity, it helps the body to maintain healthy cell functions. It helps the body to build new immunization of cells to help recover viral infections. It is important for the production of collagen that helps the healing process of internal and external wounds. It also combines with vitamin A to maintain healthy eyes. The recommended daily allowance of Zn for an adult is 12 – 15 mg day-1. Therefore, an adult must take the amount through diets in a day. Generally the Zn overload is not found but the Zn deficiency is often found in human body. Nutritional deficiencies of Zn may arise from inadequate intakes and /or poor availability of dietary Zn. Zinc deficiency is associated with poor growth, poor appetite, mental lethargy, loss of body hair, night blindness, sickle cell anemia, depressed immune function and increased susceptibility to infection, adverse outcomes of pregnancy, neurobehavioral abnormalities etc.
Zinc is ubiquitous in the environment, so that it is present in most of the foodstuffs, water and air, sea foods, meats, whole grains, dairy products, nuts, and legumes contain higher amount of zinc, while vegetables contain lower quantity, although zinc applied to soil is taken up by growing vegetables. There is a strategy for controlling Zn deficiency and it is fortification of an appropriate food vehicle with an absorbable Zn salt. Five Zn compounds are currently listed as generally recognized as safe (GRAS) by the US Food and Drug Administration: Zinc sulfate, zinc chloride, zinc gluconate, zinc oxide and zinc stearate
Human body uses Vitamin B12 for numerous purposes e.g. this vitamin is necessary for the normal formation of all cells especially blood cell and it is also necessary for the proper digestion of the food that we eat. Additionally Vitamin B12 prevents nerve damage by contributing to the formation of the protective sheath that insulates nerves cells. Without cobalt, Vitamin B12 could not exist. The total body burden for cobalt has been estimated as 1-1.5 mg, where the maximum deposition takes place in the liver, heart and hair than other organs. Therefore, certain amount of cobalt must enter into our body through foods. Small amounts of cobalt are naturally found in most rocks, soil, water, plants, and animals. But the vitamin B12 is greatly found in animal sources such as red meat, fish, eggs, cheese, milk and sea vegetables.
The deficiency of cobalt and vitamin B12 is one of the causes of anemia. Symptoms of anemia include loss of energy, loss of appetite, and moodiness. B12 deficiency can also cause nerve cells to form incorrectly, resulting in irreversible nerve damage. This situation is characterized by symptoms such as delusions, eye disorders, dizziness, confusion and memory loss. Other problems are anorexia, starved look, and pale mucus membranes. When too much cobalt is taken into the body, harmful health effects can occur. Some symptoms are asthma, pneumonia, wheezing, and skin rashes
Magnesium is known as anti-stress mineral. This is a nutritionally essential metal that can be responsible for adverse health effects due to deficiency or excess. Magnesium is a cofactor of many enzymes involved in energy metabolism, protein synthesis, RNA and DNA synthesis and maintenance of nervous tissues and cell membranes. More than 300 enzymes are known to be activated by magnesium. The body burden of Mg is 300 – 500 mg day-1. Majority of magnesium is accumulated in the bone and muscle including the myocardium, but some magnesium is present in every cell of the body. It is necessary for vitamin C and Calcium metabolism. It keeps teeth healthy, brings relief from indigestion and can aid in fighting depression. It controls cellular metabolism and maintains electrical potentials of nerve and muscle membranes for transmission of impulses across junctions. Magnesium is called the natural tranquilizer due to its relaxing action on nerve and muscles. On the other hand, the deficiency of magnesium in humans causes neuromuscular irritability and even convulsions
Magnesium is widely distributed in plant and animal foods, especially nuts, legumes, green vegetables (present at the inorganic ion of chlorophyll), cereals, banana, sea foods and meats are high dietary sources of magnesium. Hard drinking water may also be an important source of dietary Magnesium
Magnesium overload can occur when magnesium containing drugs, usually antacids are ingested chronically by a person. The toxic effects of magnesium in human may progress from nausea and vomiting to hypertension, electrocardiograph abnormalities and secondary central nervous system effects
Copper is a component of all living cells. It is an essential component of several enzymes. In animal, the important copper containing compounds are cytochrome oxidase, lysyl oxidase, phenolase, laccase etc. in mitochondria of both plants and animal. Plastocyanin is a copper containing compound found in chloroplast. Copper is essential for hemoglobin and collagen synthesis, normal bone and brain formation, and the maintenance of myelin within the nervous system.
The copper enzymes catalyze many bio-reactions in human body. Impairment of the function of these enzymes is responsible for the various diseases associated with copper deficiency . Generally foods are enriched by copper. For this reason, copper deficiency is uncommon in humans. But copper absorption in human body may hinder for many reasons. However, 1.5 mg to 3.0 mg copper per day has been recommended daily allowance as a safe and adequate range of dietary copper intake for adult . Copper deficiency can manifest in parallel with vitamin B12 deficiency and zinc toxicity. Copper deficiency is also accompanied by bone abnormalities. Due to copper deficiency in human body, the less frequent manifestations are hypopigmentation of the hair and hypotonia. Copper deficiency may produce gastrointestinal symptoms including nausea, vomiting and diarrhoea. Ingestion of large amounts of copper salts, most frequently copper sulfate, may produce hepatic necrosis and death . A small amount of 60 µg copper is excreted by the kidney via the urine per day and lesser amounts appear in hair and sweat. This interplay among the various systems maintains homeostasis and balance throughout the organism. The excessive accumulation of copper in liver, brain, kidneys and cornea is responsible for Wilson’s disease in human. Moreover, copper is responsible for hyperactivity in autistic children. An excess of Cu can cause oily skin, loss of skin tone (due to blocking ability of vitamin C) and cause dark pigmentation in the skin of face and hair loss. The best source for copper is found in beef, liver, kidney, shellfish, whole grain cereals, nuts seeds, fruit and beans etc.
A metal is said to be toxic if it injures the growth of a cell or manifests the symptom of severe infections related to the nature of poison. In fact, no metals are toxic unless and until to be accumulated in human body to a certain concentration. Once the metals liberated into the environment through the air, drinking water, food or countless human made chemicals and products, these are taken into the body via inhalation, ingestion and skin absorption. If the metals enter and accumulate in body tissues faster than the body’s detoxification pathways can dispose of them, a gradual build up of these toxins will occur. High concentration exposure is not necessary to produce a state of toxicity in the body tissues and over time, can reach toxic concentration levels. The symptoms of toxic effects of the metals vary widely at the physiological level but the basic toxicity mechanism at the molecular level is limited. For an example, the toxic metal can block the essential groups of bio-molecules, displacing the essential metal ions from bio-molecules, modifying the active confirmation of bio-molecules and disrupting the integrating of bio-membrane. As a result they can impair the normal functions of the bio-molecules in the body
Among the metals present in the environment, Pb, Cd, Hg, Cr, Ni and As are commonly associated with pollution and toxicity problems. These toxic metals are sources of concern to people living near specific toxic metal sources (industrial plants and waste dumps). Their effects are causing severe damage to crops or the ecosystems; through related products, they may pose serious risks to human as well. Although toxic metals differ widely in their chemical properties, they are used widely in electronics, mechanics and the artifacts of everyday life as well as high tech applications. Consequently they tend to reach the environment from a vast array of anthropogenic sources as well as natural geochemical process
The toxic metals that investigated in the study are described below:
Sources of lead
The sources of lead are lead gasoline, auto exhaust, cigarette smoke and ash, organ meats, canned fruits, tobacco, toothpaste, refineries, rainwater, snow, wine, water (municipal & well) etc. Lead is widely used in the production of storage batteries, car batteries, ups, ceramic glazes, bronze products and pipes, utensils, hair dyes, insecticides, iron and steel production, water pipes, lipstick, mascara, lead-based paints, pesticides, PVC containers, solder, toys, and more., These are the alternative sources of lead for contamination of air, water, soil, and as well as plant and animals.
Exposure to lead
Lead (Pb) can be exposed to living being by consumption of food, drinking water and inhalation of airborne lead particles. Most of the lead compounds are insoluble in vivo environments, so only a small amount of lead is absorbed by the gastrointestinal tract. However, it is slowly extracted and accumulates in liver, kidneys and bones of the body . But tetra-alkyl lead compounds are soluble in lipid, hence easily absorbed them by the respiratory and gastrointestinal tracts or through the skin. The major fractions of these alkyl lead compounds are accumulated in the brain [48, 50 and 51]. Once lead enters into the blood, most of it (approximately 97%) is rapidly taken by erythrocytes and is distributed into soft tissues like liver and kidneys while some of its parts go to the brain, spleen and heart and only 3% of lead remains in the blood plasma. Eventually 90% of the body lead is deposited in bones. Any alteration of acid-base metabolism of the body, which mobilizes calcium, may also mobilize lead from the bones into soft tissues
Toxic effect of lead
The toxicity of lead is in general due to its binding affinity to thiol (-SH) and phosphate (-PO4) groups of majority of systems like numerous enzymes, proteins and cell membranes. In these groups, it shows inhibiting or interfering effects on the function of those enzymes. Lead is not harmful to certain extent for human body. It is reported that 0.3 mg of lead is allowed to enter into the body in a day from all sorts of foods because this ingested amount may be excreted from the body through different mechanisms. There is no chance to accumulate of any lead in the body. When more than 0.3 mg of lead is ingested into the body in a day then it might have chance to accumulate lead in different target organ of the body. Thus, with constant exposure, lead accumulates gradually in the selected organ of the body. As a result, these organs and systems are adversely affected by the lead. Mostly the four major target organs and systems are the central nervous system, the peripheral nerves, the kidney and the hematopoietic system The effects in all four cases have been observed in men and have been studied extensively.
There are numerous reports of a severe, often fatal condition of central nervous system of human due to chronic or sub chronic exposure to high doses of inorganic lead. The major features are dullness, restlessness, irritability, headache, muscular tremor, ataxia and loss of memory. These signs and symptoms may divert to convulsions, coma and death. A high incidence of residual damage is seen, including epilepsy, hydrocephalus and idiocy. A major concern today is subtle behavioral effects, particularly in children, at levels of exposure below those causing encephalopathy. Epidemiologic studies suggest that moderately elevated lead exposure in infants and young children may cause deficits as reflected in psychometric performance tests and in certain neurological tests.
The older literature cites the frequent occurrence of lead palsy among workers in the lead trades. The major manifestation of lead palsy is weakness of the extensor muscles. Sensory disturbances also occur, e.g., hyperaesthesia and analgesia. The anatomic lesion is characterized by segmental demyelination and by axonal degeneration. Functionally, nerve conduction velocity is slowed, even in the absence of palsy, an effect seen in both children and adults.
Two distinct types of renal effect have been observed in man. In the first type, the effects are manifestations of damage to the proximal tubules. Tubular re-absorption of glucose, amino acids and phosphate is depressed. These effects are readily reversible with chelation therapy. The other type of renal effect occurs with prolonged high lead exposure. It is a progressive disease characterized by interstitial fibrosis, sclerosis of vessels and glomerular atrophy. Death may ensue due to renal failure
It has long been known that anemia is one of the early manifestations of lead poisoning. It results from reduction of the lifespan of circulating erythrocytes as well as from inhibition of synthesis of hemoglobin. The shortened lifespan of erythrocytes is inconstant, occurring only in some cases of lead induced anemia. Erythrocytes exposed to lead in vitro show increased osmotic resistance but also show increased mechanical fragility. In addition, it has been shown in vitro that, even in moderate lead exposure, erythrocyte Na-K-ATPase is somewhat inhibited, suggesting a loss of cell membrane integrity. This may account for the shortened lifespan of erythrocytes that sometimes occurs.
Sources of Cadmium
Cereals and grains (refined), cigarette smoke, coffee and tea, candy, milk, ocean fish, processed foods, vending machine soft drinks, water (municipal, softened & well) etc. are the main sources of cadmium for human. Dental alloys, batteries, ceramics, electroplating, fertilizers, fungicides, rubber, plastics, paint pigments, pesticides, pipes (galvanized), polyvinyl plastics, rust-proofing, silver polish, tools, welding material, rechargeable nickel – cadmium batteries, oil paints, municipal and medical waste, sewage sludge etc. are the indirect sources of cadmium. Cadmium is taken up by plants and animals and enters the foodstuffs.
Exposure to Cadmium
Urban peoples or the peoples living in industrial environments are exposed to cadmium levels well over a thousand times higher than rural inhabitants. Though small concentrations of cadmium are found in rocks and soil all over the world, therefore almost every one is exposed to low levels of cadmium in their air, water and food. Cadmium can enter the water or soil from hazardous waste sites. It can also be absorbed in the bodies of fish and other animals. Through these routes, people can be exposed to cadmium through contaminated water or foods. Exposures to cigarette smoke can double one’s daily exposure to cadmium. When Cd exposure to human is high then it accumulates especially in the kidney and the liver.
Toxic effect of Cadmium
Cadmium is totally toxic like lead. The maximum tolerable intake of cadmium is 0.06 mg per day from all sorts of foods. If more than 0.06 mg of Cd enters into body in a day then it will be toxic for human because the excess amount of the cadmium is accumulated in the body. Cadmium and solutions of its compounds are toxic, being more easily absorbed through inhaled dusts and fumes. Chronic dust or fume exposure can irreversibly damage the lungs, producing shortness of breath and emphysema. The risk of absorption via dermal contact is negligible. The International Agency for Research on Cancer (IARC) lists cadmium metal and several of its compounds as carcinogens .
The kidney is the critical target organ for the general population as well as for occupationally exposed populations. Cadmium is known to accumulate in the human kidney for a relatively long time, from 20 to 30 years and at high doses, is also known to produce health effects on the respiratory system and has been associated with bone disease. Bone disease i.e. Itai– Itai disease is known to damage the joints, causes bones to soften and the body to shrink while the affected person approaches to a painful death. Most of the available epidemiological information on cadmium has been obtained from occupationally exposed workers. Recent studies have suggested that overall nutritional status is a more important determinant of cadmium uptake into the body than the actual amount of cadmium ingested. For example, women subsisting upon a vegetarian diet and with reduced iron stores have increased uptake of ingested cadmium. Iron deficiency is a more important determinant of cadmium uptake for these women, than the actual amount of cadmium ingested.
Depending upon the level and duration of cadmium exposure, a wide variety of effects has been observed in occupationally exposed groups. For acute exposure by ingestion, the principal effects are gastrointestinal disturbances such as nausea, vomiting, abdominal cramps and diarrhea. For chronic cadmium exposure, effects occur mainly on the kidneys, lungs and bones. A relationship has been established between cadmium air exposure and proteinuria (an increase in the presence of low molecular weight proteins in the urine and an indication of kidney dysfunction) [69, 70]. Metabolically Cd also inhibits the essential metabolic function of Zn, Cu and Fe. Furthermore it inhibits sulfhydryl enzymes systems necessary for cellular metabolism. Cadmium is known to accumulate in the renal cortex and there is evidence that the level of cadmium in the renal cortex associated with increased urinary excretion is about 200 to 250 µg g-1 (wet weight). Depending upon the exposure level and other sources of cadmium, this level might be reached after 20 years occupational exposure. However, recent work has demonstrated that these effects are reversible at low exposure levels once the cadmium exposure has been removed or reduced.
Sources of Chromium
Chromium is a naturally occurring element found in rocks, animals, soil etc. Among several different forms, the most common are trivalent chromium Cr (III) and hexavalent chromium Cr (VI). Chromium is steel-grey, lustrous and hard that is used on a large scale in the metallurgical and chemical industries. Therefore, chrome-plated metal goods, different paints, colored cloths and leather goods, temporarily coated toys and tools, pigments [Cr (VI) and Cr (III)], wood preservatives [Cr (VI) only], leather tanning chemicals [Cr (III) only], fungicide, the laboratory chemicals and oxidizing agents etc. are the secondary sources of cadmium for contamination of environment [69, 72-74]. The dietary sources of chromium are beef, brown rice, calves liver, cereals, dairy products, pulses, eggs, fishes, fresh fruits, meats, grains, corn oils, black peppers, mushrooms, nuts, and brewers’ yeast.
Exposure to Chromium
Food consumption that accounts more than 96% of daily chromium exposure for most people through inhalation, drinking water, skin contact (occurs during the use of consumer products like wood preservatives, cement, cleaning products, textiles and tanned leathers). People who work in industries that use chromium can be exposed to higher levels of the metal. Municipal waste water contains mainly Cr (VI), which is toxic to marine animals, algae and microorganisms. Stainless steel vessels in contact with acidic foods may contribute additional chromium. Beverage including milk may also increase the daily increase of chromium.
Effect of Chromium
Nutritionally, Cr (III) is an essential component of a balanced diet for preventing adverse effects in the metabolism of glucose and lipids (e.g., impaired glucose tolerance, elevated fasting insulin, elevated cholesterol and triglycerides, and hypoglycemic symptoms). Trivalent chromium, Cr (III) was identified as the active component of a molecule called the glucose tolerance factor (GTF). GTF acts as a cofactor to bind insulin to receptor sites on membranes and therefore improves the efficacy of insulin. It is a cofactor of insulin, promoting insulin activity and enhancing amino acid uptake into muscular cells for protein synthesis. Chromium also functions in the transport of proteins from one part in the body to another. The chromium deficient animals often show genetic disorders. Although Cr (III) in small amounts is an important nutrient needed by the body, swallowing large amounts of Cr (III) may also cause health problems, e.g., lung cancer [80, 81]. Hexavalent chromium, Cr (VI) is associated with cancer formation in human body. But the mechanism of cancer formation caused by Cr (VI) is not known exactly; however, it has been claimed that Cr (VI) binds to double stranded deoxyribonucleic acid (DNA), therefore altering gene replication, repair and duplication. The recommended daily allowance of Cr is 0.06 mg per day for an adult. This small amount of chromium comes from different types of daily diet of a man. Therefore, chromium deficiency is very scarce for human. In spite of that if the deficiency of chromium is found in human body this can produce the hapatic necrosis and diabetes.
When excessive intake (more than RDA) of Cr [Cr (VI) and Cr (III)] is occurred in human body then some Cr may be accumulated to some target organ of human. The target organs of human body for accumulation are lung, kidney, skin and liver. As a result, severe and often deadly pathological changes are associated with excessive intake of Cr, especially Cr (VI). Inhalation and retention of materials containing Cr (VI) can cause perforation of the nasal septum, asthma, bronchitis, pneumonitis, inflammation of the larynx and liver and increased incidence of bronchogenic carcinoma. Skin contact of Cr (VI) compounds can induce skin allergies, dermatitis, dermal necrosis and dermal corrosion. Acute intoxication with Cr (VI) leads to acute renal tubular necrosis characterized by significant interstitial change and subsequent renal failure.
Sources of Nickel
The main sources of Ni are hydrogenated fats and oils, margarine, oat meals, legumes, nuts, cocoa, whole wheat bread, refined grains and cereals, and some leafy vegetables such as kale and lettuce. Metallic nickel, Ni (0) itself as well as its compound such as Ni (CO)4 are found to be toxic for health. The main sources of metallic nickel are electronic goods, coins, batteries, butter, fertilizers, food processing, fuel oil combustion, hydrogenated fats & oils, imitation whipped cream, industrial waste, kelp, margarine, stainless steel cookware, tea, tobacco smoke, unrefined grains and cereals etc.
Exposure to Nickel
Approximately 90% of total intake of nickel comes from food. Occupational factors have also a great influence on exposure to nickel. For example, welders may inhale dust or fumes when working with metals that contain nickel. Nickel alloys are also used in medical devices such as clips and screws used to repair fractural bones, joint prostheses and structures. The most common exposure to nickel results from contact with consumer products (like jewelry) which can trigger skin allergies.
Effect of Nickel
The health effects are highly dependent on the manner and degree of exposure and on the oxidation state in which the nickel atoms are present. Nickel in oxidation state of +2 is essential in small quantities e.g. an appropriate amount of nickel in human body play an important role in regulating prolactin and stabilization of RNA and DNA structures. The maximum tolerable intake of Ni is 0.3 mg per day for an adult. Nickel deficiency is also harmful for human health. Many abnormalities in plasma choleatero, liver, glycogen, and mitocondrial morphology have been reported due to nickel deficiency.
When the uptake is too high than the maximum tolerable limit of human body it can be a danger to human health. An uptake of too large quantities of nickel in human body provokes to accumulate some nickel in different liking organs of the body like skin, lung, throat, kidney etc. As a result, the following diseases are the consequences of nickel accumulation in the body, lung cancer, nose cancer, larynx cancer and prostate cancer, sickness and dizziness, lung embolism, respiratory failure, birth defect, asthma and chronic bronchitis, allergic reactions such as skin rashes (mainly from jewellery), heart disorders etc.
Dermatitis (nickel itch) and eczema is the most frequent effect of exposure of nickel. This occurs from direct contact with metals containing nickel such as coins and costume jewelry. Nickel in zero oxidation state seems to be more toxic than its other state. Nickel carbonyl is the most toxic nickel (0) compound. The immediate symptoms of acute exposure to nickel carbonyl are respiratory tract irritation, dizziness, frontal headache, nausea, vomiting, irritability and upper airway irritation etc. And delayed symptoms are chest pain, cough, dyspnoea, tachycardia, weakness and fever with leukocytosis. Moreover, pulmonary haemorrhage, cerebral oedema, toxic myocarditis, pulmonary oedema and pneumonitis may occur in severe cases. The respiratory tract is the primary site of toxicity following inhalation of nickel and its compounds. Rhinitis, sinusitis, asthma, chronic bronchitis, emphysema and nasal septal perforations have frequently been reported in individuals occupationally exposed to nickel or nickel compounds. Hyposmia or anosmia was also noted in many of the workers with sinusitis. Pulmonary changes with fibrosis were also observed in workers exposed to nickel dust or fumes.
Sources of Arsenic
Arsenic is a natural constituent of the bedrock, topsoil and ground water. The important source of arsenic is ground water. Laboratory chemicals, wood preservatives, agricultural products (pesticides, herbicides and fungicides), textile chemicals, tanning agents of leather, anticorrosive agents, glass ceramics products etc. are nickel containing substances, so these are the secondary sources of arsenic.
Exposure to Arsenic
Significant exposure of arsenic to human occurs through both anthropogenic and natural sources. Arsenic is a natural contaminant of some deep water wells. Occupational exposure of arsenic is common in the arsenic based industry and is increasing in the microelectronics industry. Low level arsenic exposure continues to take place in the general population through the commercial use of inorganic arsenic compounds in common products such as wood preservatives, pesticides, herbicides, fungicides and paints. Arsenic enters into the human body mainly with drinking water and smoking, and accumulates in liver, muscle, hair, nail and skin.
Effect of Arsenic
Arsenic is one the 20 most abundant elements in the earth crust and the 12 most elements in the biosphere, it is almost found in relatively low concentration everywhere in nature. As a result arsenic is common to all living organisms. The International Agency for Research on Cancer (IARC) has listed arsenic as a human carcinogen since 1980. Arsenic is a unique carcinogens, it is the only known human carcinogen for which there is adequate evidence of carcinogenic risk by both inhalation and ingestion. A significant relationship between As exposure and skin cancer has been observed. Moreover, epidemiological evidence indicates that As is associated with cancers of skin and internal organs, as well as with vascular disease. Mortality from lung cancer was significantly increased with increasing As ingestion.
Arsenic has +3 and +5 oxidation states. Elemental arsenic is not toxic but trivalent form of arsenic is more toxic than pentavalent form of arsenic and the natural oxidation favors the conversion of trivalent arsenic to pentavalent form. In fact, arsenic at pentavalent form is essential and functional in humans in very small amounts. A small amount of 0.7 mg of arsenic may be allowed for human body in a day . Organic arsenic as arsenates (+5 forms of arsenic) and elemental arsenic both found naturally in the earth and in foods. So, the deficiency of arsenic is not found in human body generally. Moreover, these are handled fairly easily by the body and eliminated by the kidneys. On the other hand, the use of inorganic arsenites or trivalent forms of arsenic such as arsenic trioxide used industrially and found as a food contaminate, seem to create problems. The use of deep tube well water in irrigation or in agriculture is increased tremendously. This water also contains higher amount of trivalent arsenic than other sources. So, it might have chance to transfer some amount of arsenic from the water to the crops. Thus, our foodstuffs may be contaminated by the arsenic. Arsenic’s toxic effects largely depend on its chemical and physical form and how one is exposed. It has been shown in some instances that the arsenate is reabsorbed by the proximal renal tubule and excreted as the arsenite. Arsenites bind to tissue proteins and are concentrated in the leukocytes. They accumulate in the body primarily in the liver, muscles, hair, nails and skin, perhaps because of combination with sulfhydryl groups.
Chronic arsenic intoxication is characterized by malaise and fatigue. Gastrointestinal disturbances, hyperpigmentation and peripheral neuropathy may ultimately occur. Pale bands on the fingernails and toes may develop. Red cell disruption, decreased red cell production and leukopenia are frequently observed. These signs disappear rapidly when exposure is halted, except for neuropathy, which may regress at a slower rate. Increased arsenic content of hair nails and urine is frequently present for long periods after exposure has been discontinued. Arsenic neuropathy is a recognized complication of As toxicity. The neuropathy is usually sensor (affects sensation) and the course of development is chronic. Sensory and sensorimotor (sensation and muscles are affected) neuropathy have also been observed. The sub-acute arsenic toxicity involves the respiratory, gastro-intestinal, cardiovascular nervous and haematopoietic systems. It may cause loss of appetite, fainting, nausea and some vomiting, dry throat, shooting pain, diarrhoea, tingling of the hands and feet, jaundice etc.
Aim of the present work
Every human being requires food for their living as well as for the production of necessary energy like other animals. A nutritious food should contain proteins, carbohydrates, minerals, vitamins, fat and water. Among them minerals is the most important component for human beings. The metals like Na, K, Ca, Mg, Fe, Zn, Mn, Co etc. are known as minerals. Human body requires definite amount of these minerals for functioning some bio-molecules such as hemoglobin, myoglobin, cytochrome, ferredoxin, transferine, ferritin etc. and they may act as cofactor of many other macro molecules in the body. Naturally different food contains different proportion of the important component. So, the level of these metals in bodies can be maintained by taking different food in our daily life. But the consequence of environmental pollution might be responsible for the easy entrance of toxic metals like Pb, Cd, Cr, Ni, Hg, As etc. into the food chain that we take everyday. As a result, when we take food, these toxic metals are also ingested into the body. These metals have no specific useful function in the body. Moreover, they act as toxic if their presence is beyond the tolerance level in the body and they disrupt normal cellular processes, leading to toxicity in a number of organs. Thus a number of diseases are produced in the human body. It is therefore necessary to control the levels of these toxic metals in foodstuffs in order to protect human health. So we should be alert about them. Here we should also keep in mind that the essential metals are also harmful for human body if they deficient or excess in the body. For this reason, many researches on the determination of essential and toxic metals in foods are going on in developed countries. They can select their foods depending on the essential and toxic metal content in the foods. But the developing country like Bangladesh does not give enough emphasis on this type of research. As a result, we have very little information about the safety of our foods regarding essential and toxic metal levels. But we need a complete food list that should be available in Bangladesh, which gives a clear idea about the content of the essential and toxic metals of the foodstuffs. It was in this context that the present research work was initiated. Therefore, the main objective of the research work was to study the level of exposure of human beings to metallic pollutants such as cadmium, lead, chromium, nickel and arsenic. The possible way to assess the exposure of these contaminants was to determine their concentrations in foods such as meat, organ meat, meat product, egg, pulses, spices, sauces, fruits, juices, jellies, cereal, chips, hot drinks, edible oil, ghee and tobacco. In view of the importance of the role of essential metals in human health, this study was also initiated to determine essential metals of iron, copper, magnesium, zinc and cobalt in the same foodstuffs. So the main points of this research are emphasized as described below:
- Determination of the concentrations of essential metals such as iron, copper, magnesium, cobalt and zinc in the most commonly consumed foodstuffs.
- Determination of the concentrations of toxic metals such as lead, cadmium, chromium, arsenic and nickel in the same foodstuffs.
- Formulation a food chart for comparative study about the essential and toxic metals, which helps the people to select the quality foods or avoid the contaminated foods according to the concentration of the essential and toxic metals in the foodstuffs.
- Determination of the daily intake of the toxic metals from the various food sources.
- To create the public awareness about the toxicity of the foodstuffs and thereby assisting the concern government authority for making new national policy to reduce the contamination of the environment.
Review of the past work
Atomic absorption spectroscopic method (AAS) is a specialized analytical technique for analysis of a large number of elements, especially at trace levels. It is a widely used technique for analysis of a wide variety of sample matrices including biota, soils and water. AAS is very reputed technique that is inexpensive and delivers accurate results even in a complex matrix. Bernhard et al. showed simultaneous background correction automatically eliminates lamp flicker noise and continuous background absorption. As a result, the instrument can determine trace metals as well as non-metals accurately within the wave length between 190 nm–900 nm.
Many researches are going on to find out the contamination level of trace metals in foodstuffs by AAS. Some of these works are cited below.
Firdevs et al. determined the concentration of toxic metals in some foodstuffs. They found the concentrations as follows: Bread (As:0.005, Cd: 0.028, Pb: 0.02 mg kg-1), Meat (As: 0.003, Cd: 0.0008, Pb: 0.006 mg kg-1), Meat product (As: 0.003, Cd: 0.0097, Pb: 0.003 mg kg-1), Poultry (As: 0.004, Cd: 0.0025, Pb: 0.005 mg kg-1 ) and Egg ( As: 0.0009, Cd: 0.0004, Pb: .003 mgkg-1).
Okoye and Ugwu evaluated the concentration of Cd, Pb, Cu and Zn in the goat meat of Nigeria. The mean concentrations of Cd, Pb, Cu and Zn in the samples were 0.83 mg kg-1 (ranging from 0.07-3.08 mg kg-1), 0.53 mg kg-1 (ranging from not detected, nd-0.63 mg kg-1), 134.02 mg kg-1 (ranging from 26.36-398.16 mg kg-1) and 131.55 mg kg-1 (ranging from nd-417.00), respectively.
Rahimi and Rokni determined the amount of Cd in the muscle, liver and kidney of cattle of Iran. The mean concentrations of Cd in muscle, liver and kidney were 3.3, 49.7 and 137.1 μg kg-1, respectively.
Magdaléna Skalická et al. collected some samples of breast muscle, leg muscle, liver and heart of poultry from a polluted area of Eastern Slovakia. They found the mean concentrations of Cd in breast muscle, leg muscle, liver and heart to be 0.019, 0.021, 0.061, 0.099 mg kg-1, respectively. They reported that Cd levels in poultry meat were below the maximum permissible limits of 0.1 mg kg-1 in muscle and 0.5 mg kg-1 in internal organs of poultry, according to Codex Alimentarum of the SlovakRepublic.
Adei and Forson-Adaboh determined the concentration of Fe, Mn, Pb, Cu, Cd and Zn in liver of cow, sheep, goat, pig, grass-cutter, giant rat, red deer, chicken and antelope. The highest concentration of Fe was found in the grass-cutter and pig liver (500.5 and 645.4 mg kg-1, respectively) and the highest concentration of Mn was found in grass-cutter and rat liver (16.5 and 30.2 mg kg-1, respectively). 1.3-13.8 mg kg-1 of Pb was found in these samples. The concentration of Pb was above the European Commission’s permissible limit of 0.5 mg kg-1 in all the samples. They also reported that the permissible limits of Cu, Zn and Cd in internal organ of cattle are 20, 50 and 0.5 mg kg-1, respectively.
The concentrations of Cu, Cd, Pb and Zn were determined in muscles and internal organs (liver, kidneys, heart, and lungs) of cattle, sheep, goat and poultry sample of West Bank of Palestine by Swaileh et al. . The concentration ranges of the metals in the samples were as follows: Cd: 0.34–0.57 mg kg-1, Pb: 0.2–4.7 mg kg-1, Cr: 0.44–3.62 mg kg-1 and Cu: 1.03–217.9 mg kg-1.
Canli and Kalay analyzed some river fishes of Turkey. The concentrations of Cd, Pb, Cu, Cr and Ni in gill, liver and muscle of these samples were as follows: Cd : 1.26-6.10, 0.96-4.72 and 0.51- 1.67; Pb: 9.41-44.75, 5.22-37.15 and 2.94-13.73; Cu: 5.43-58.63, 5.91-201.1 and 3.27-7.35; Cr: 1.72-6.10, 0.23-5.35 and 0.36-1.71 and Ni: 6.83-28.03, 3.42-27.05 and 1.62-13.35 mg kg-1, respectively. They reported that the metals present in river system were taken up by the fishes through food, water and sediment.
Chukwujindu Maxwell and Azubuike Iwegbue determined the levels of Cd, Cr, Cu, Pb, Fe, and Ni in the livers and kidneys of cattle of southern Nigeria. The mean and the ranges of concentrations (mg kg-1) for each metal in livers and kidneys were as follows: Cd: 0.08 (0.01-0.23) and 0.14 (0.01-0.46); Cr: 3.62 (0.98-6.33) and 3.63 (1.08-5.87); Cu:1.99 (0.11-8.99) and 3.27 (0.22-7.49); Pb: 0.8 (n.d-0.23) and 0.04 (n.d-0.95); Fe 37.75 (2.64 85.60) and 32.26 (0.10-78.65); Ni: 0.12 (0.01-0.55) and 0.20 (0.02-0.46), respectively. They found significant differences in concentration of the heavy metals in livers and kidneys collected from the different locations and the samples of liver and kidney of the same location also showed significant difference in concentration of the metals.
The concentration of the metals of As, Pb, Hg, Zn, Ca, Na and K were determined in organ meat of beef, mutton and poultry by Mariam et al. . The concentrations of As (40.80-52.44 ppm), Pb (2.02-4.25 ppm) and Hg (31.47-78.96 ppm) were found higher than the permissible limit, whereas Zn (66.26-28.52ppm), Ca (1.72-2.27 ppm), Na (5.38- 3.20 ppm) and K (1.44-2.43 ppm) levels were found normal.
Carmen Cabrera et al. evaluated the amount of essential elements of Cu, Cr, Fe and Zn and toxic elements of Al, Ni, Pb and Cd in legumes and nuts of Spain. The ranges of concentration of Cu, Cr, Fe, Zn, Al, Ni, Pb and Cd in legumes were as follows: 1.5-5.0 mg kg-1, 0.05-0.60 mg kg-1, 18.8-82.4 mg kg-1, 32.6-70.2 mg kg-1, 2.7-45.8mgkg-1, 0.02-0.35 mg kg-1, 0.32-0.70 mg kg-1 and nd-0.018 mg kg-1, respectively. In nuts the levels of the metals were 4.0-25.6 mg kg-1, 0.25-1.05 mg kg-1, 7.3-75.6 mg kg-1, 25.6-69.0 mg kg-1, 1.2-20.1 mg kg-1, 0.10-0.64 mg kg-1, 0.14-0.39 mg kg-1, and nd-0.018 mg kg-1, respectively.
Umit Divrikli et al. determined the concentrations of some trace metals in spices of Turkey. The contents of the trace metals in the samples were found to be 3.8-35.4 mg kg−1 for copper, 0.2-2.7 mg kg−1 for cadmium, 0.1-2.8 mg kg−1 for lead, 1.4-11.3l mg kg−1 for nickel, 0.1-9.7l mg kg−1 for chromium, 30.0-945.3l mg kg−1 for iron, 7.9-152.5l mg kg−1 for manganese and 5.2-83.7l mg kg−1for zinc.
Mubeen et al. determined the concentrations of Fe, Cu, Cr, Pb, Cd and Co in spices of Pakistan. The concentrations of Fe, Cu, Cr, Co, Cd and Pb in the samples were 144.5-1260, 9-44, 115-368, 1.5-15, 0.5-1.0 and 54-70 mg kg-1, respectively. They also calculated the daily intake of these metals from these foods.
Faruk et al. analyzed some spices of Turkey. The highest amount of Cd was found in clove (13 mg kg-1) and in black pepper (206 mg kg-1). Clove also contained the highest amount of Mn (355 mg kg-1). The concentration of Fe in nutmeg and black pepper was 28 mg kg-1 and 374 mg kg-1, respectively, while the level of Cu in the samples was ranged 3.0-11 mg kg-1. The lowest amount of Mn was recorded in turmeric (10 mg kg-1). The highest amount of Zn was found in cardamom (25 mg kg-1) with ranged 4-25 mg kg-1.
Williams et al. determined the concentration of Fe, Cu, Cr, Co, Pb and Cd in some selected fruit juices and carbonated beverages of Lagos, Nigeria. They found that the metal contents in fruit juices were higher than the metal contents in carbonated beverages. They found the concentration of Pb in the fruit juices to be 0.08-0.57 mg l-1 but the metal was not detected in the carbonated drinks. The concentrations of Cd, Cu, Cr, Fe and Co were not detected in the selected juices and beverages.
Khairiah et al. determined the level of some metals in soil and plant parts (fruits, leaves and roots) of two cultivars of guava. They found the concentration of Ni in the samples to be 2.71-4.52 mg kg-1. The concentrations of Pb, Cd and Mn were very low in the soil of this plantation. Pb and Cu content in roots, leaves and fruits of Guava plants were not detected. But very small amount of Cu (0.01 mg kg-1) was found in seeds of the Guava.
Ahmed K. Salama and Mohamed A. Radwan determined the concentrations of Cu Zn, Cd and Pb in legumes, cereals, cereal products and fried potatoes of Egypt. The amounts of the metals in legumes were as follows: 0.010-0.178 mg kg-1 of Cd, 0.013-0.281 mg kg-1 of Pb, 2.839-8.012 mg kg-1 of Cu and 6.111-15.861 mg kg-1 of Zn. In the case of cereals: 0.091-0.142 mg kg-1 of Cd, 0.116-0.398 mg kg-1 of Pb, 0.241-1.962 mg kg-1 of Cu and 4.893-15.450 mg kg-1 of Zn. The highest concentrations of Cd, Pb, Cu and Zn were found in cereal products of popcorn (0.194 mg kg-1), pasta (0.299 mg kg-1), salted biscuits (1.386 mg kg-1) and pizza crust (13.70 mg kg-1), respectively. Fried potatoes contained 0.054-0.10 mg kg-1 of Cd, 0.065-0.159 mg kg-1 of Pb, 1.626-1.992 mg kg-1 of Cu and 3.837-6.844 mg kg-1 of Zn.
Bhutto et al. investigated the accumulation of toxic (Pb, Ni & Cr) and essential (Zn & Cu) metals in wheat of Sindh Mirpurkhas, Nawabshah and Khairpur of Pakistan. The mean concentration of Zn in the wheat species of Sarsabz, Inqlab, Anmol, V-7001, Rabel, Yakora, Mehran, Sindh- 83, V- 7005, Moomal, TD- 1, TJ- 83, Wattan and V- 5000 was 18.72, 21.29, 21.75, 30.28, 37.53, 21.17, 18.81, 20.89, 24.44, 27.70, 21.93, 24.98, 22.11 and 17.25 mg kg-1, respectively. The mean concentration of copper in the samples was 1.64, 2.29, 2.85, 2.06, 3.87, 3.38, 3.80, 4.32, 2.86, 2.57, 1.74, 2.67, 2.17 and 2.0 mg kg-1 respectively. While the concentration of Pb, Ni and Cr were not detected in the samples. The concentration of Cu and Zn in the samples of Mirpurkhas, Nawabshah and Khairpur of Pakistan were as follows 20.95 and 2.19, 24.98 and 3.38, 21.64 and 2.20 mg kg-1, respectively.
Potato and corn chips have an important place in our daily diet. Especially, children consume big amounts corn and potato chips. Narin et al. determined the heavy metal content in potato and corn chips of Turkey. The metal content in corn and potato chips have been reported as follows 0.28-1.26 mg kg-1 of Copper, 2.4-3.55 mg kg-1 of Iron, 2.52-3.50 mg kg-1 of Zinc and 0.884-8.40 mg kg-1 of Manganese.
Heavy metals composition in foods is of an immense interest because of its essential or toxic nature. Gopalani et al.  determined the concentrations of heavy metals in food items of potato chips and biscuits of Nagpur City, India. They found that the accumulation of metals in potato chips followed the order Fe>Al>Zn>Ni> Cu>Mn>Co>Cr>Pb and Cd, while for Biscuits it was as the order Al>Fe>Zn>Ni>Mn>Co>Cr>Pb>Cu and Cd.
Nkansah and Amoako determined the concentration of Pb, Zn, Ni, Cu, Fe, and Hg in spices of Ghana. They found the concentrations of Pb, Zn, Ni, Cu, Fe and Hg in the samples to be 0.1153-0.0973, 0.074-0.059, 0.0735-0.0593, 0.0210-0.009, 0.4942- 0.1100 and 1.300 x 10-6-2.493 x 10-5 g kg-1, respectively. Lead levels in ginger, pepper and cinnamon were above the standard value of 0.01 g kg-1.
Glam Reza determined the concentration of zinc in the bread of Tehran, Iran. The mean concentration of Zn in breads of lavash, barbari, taftoon, and sangak were 12.17 ± 1.91, 10.75 ± 2.64, 10.41 ± 3.54 and 14.25 ± 3.56 mg kg-1, respectively (± = Standard deviation). They calculated the daily intake of Zn from this food and the value was 3.499 mg per person per day. This study revealed that the flat breads were good sources of Zn for the Iranian and they suggested that the foods can supply some of Zn requirements of human body for preventing of Zn deficiency.
Harun et al. determined the concentration of Fe, Cu, Zn and Cd in cigarettes of Turkey. The mean concentrations of Fe, Cu, Cd and Zn in five different brands of cigarette were as follows: 312-650, 18.4-30.8, 0.91-2.24 and 16.2-61.85 mg kg-1, respectively.
Nnrom et al. investigated the Cd contents in cigarettes of Nigeria. The concentration of Cd in the cigarettes was 0.7-2.3 g kg-1 (mean value 0.46 mg kg-1). The investigation revealed that the concentration of Cd in imported cigarettes (0.46-1.52 mg kg-1) was higher than the Nigerian local cigarettes (0.35-1.10 mg kg-1). The average Cd content in cigarettes available in Nigeria was 1.28 μg per cigarette. They also showed that if a person smokes 20 cigarettes per day is estimated to increase his daily Cd retention approximately 0.53 – 1.65 μg day -1.
Yasmeen et al. carried out a study for determination of Mn, Co, Cu, Cd, Pb and Zn in local and imported cigarettes, Pakistan. Their results showed that the highest concentration of Mn (84.78 mg kg-1), Cd (0.525 mg kg-1) and Zn (14.34 mg kg-1) was in imported cigarette. But the highest concentration of Co (3.344 mg kg-1), Pb (14.16 mg kg-1) and Cu (7.889 mg kg-1) was found in local brands.
Llobet et al. determined the concentration of As, Cd, Hg and Pb in different food samples. They also estimated the daily intake of these toxic metals from the foods for children, adolescents, adults, and seniors of Catalona, Spain. The highest dietary intake of As, Cd, Hg, and Pb were 223.6 μg day-1, 15.7 μg day-1, 21.2 μg day-1, and 28.4 μg day-1 respectively.
Boardajandi et al. determined the concentration of Cu, Cd, Zn, Pb Hg and As in fruits, milk, dairy products, chicken eggs, meat and meat products and vegetable oils of Huelva of Spain. The concentration ranges of the metals in fruits, milk, dairy products, eggs, meat and meat products, and vegetable oils were as follows: 138-132 mg kg-1, 0.559-11.9 mg kg-1, 0.243-159 ng g-1, 1.82-484 ng g-1, 0.745-22008 ng g-1 and 1.00-296 ng g-1 respectively.
Carmen Rubio et al. determined the concentration of Pb in dairy products, eggs, meat, cereals, fruits and non alcoholic drinks. The mean concentration of Pb in the samples were 1.56 μg kg-1, 10.0 μg kg-1, 37.30 μg kg-1, 1.66 μg kg-1, 52.0 μg kg-1, and 6.0 μg kg-1 respectively.
Shamsuddin et al. determined the concentration of Cr, Zn, Mg, Cd and Pb in rice of Bangladesh. They found the concentrations of Cr, Zn, Mg, Cd and Pb in the samples to be 0.017-0.74, 11-43, 160-370, 0.024-0.075 and 0.016-0.77 mg kg-1 respectively.
Ahmed et al. investigated about the amount of Mn, Mg, Fe, Ca, Na and K in processed foods of noodles of Bangladesh. The concentrations of Mn, Mg, Fe, Ca, Na and K in the samples were as follows 0.001-0.002, 0.020-0.035g, 0.001-0.002, 0.004-0.015, 0.054-1.208 and 0.133-0.211 g/100g respectively.
Rahman et al. carried out a study for estimation of Fe, Co, Cu, K, I, Zn, P in fruits of Bangladesh. Their investigation showed that mango contains the highest amount of Fe (16.6 mg L-1) and Co (0.08 mg L-1), banana contains the highest amount of Cu (6.2 mg L-1) and jack fruit, banana and papaya contain highest amount of K (1809-2690 mg L-1) and Zn (13-34 mg L-1).
Ahsan et al. investigated the heavy metals of As, Cd, Pb, Se, Co, Hg, and Mn in flood plain agricultural land of Faridpur and Damrai of Bangladesh. They found that the average concentration of these metals were more than the world standards.
Divrikli et al. studied on the accumulation of trace metals in spices and herbal of Turkey. The contents of Cu, Cd, Pb, Ni, Cr, Fe, Mn and Zn in the samples were 3.8-35.4, 0.2- 2.7, 0.1-2.8, 1.4-11.3, 0.1-9.7, 30.0-945.3, 7.9-152.5 and 5.2-83.7 mg kg-1 respectively.
Chowdhury et al. determined the concentration of Mg, Fe, Zn, Cu, Mn, Pb, Cd, As and Cr in rice and fishes of Bangladesh. The concentrations of the metals were the following ranges 595-272, 14.3-3.0, 13.7-5.7, 2.2-0.3, 3.2-0.004, 2.9-0.18, 1.10-0.02, 4-0.02 and 3.02-0.20 mg kg-1 respectively. They revealed that the studied samples contain higher amount of toxic metals than the tolerance limit for human body.
Layout of the dissertation
Chapter one contains general introduction, back ground of the study, short description of the essential and toxic metals in health perspective, aim, objectives and, some reviews of the relevant works; these include the trend of the use of AAS on the related subject in our country and abroad. Chapter two contains the theoretical aspects of the used techniques, research plan, methodology (sample preparation), analytical techniques, and the quality control on the measurements. The content of essential and toxic metals in meat, meat products and eggs; pulses, spices and sauces; fruits, juices and jellies; cereals, chips and hot drinks; oil and ghee and, local and imported cigarette and, their results and discussions are elaborated in chapter three to chapter eight. Chapter nine contains the dietary intakes of the toxic metals and finally chapter ten contains the conclusion of the research work.