DETERMINATION OF POLLUTION TREND OF HEAVY METALS IN IRRIGATION FARMS (WATER, SOIL AND PLANTS) IN KEFFI METROPOLIS USING ATOMIC ABSORPTION SPECTROPHOTOMETER (AAS)
(B- TECH INDUSTRIAL CHEMISTRY, ATBU)
BEING AN M.SC RESEARCH PROJECT
SUBMITTED TO THE DEPARTMENT OF CHEMISTRY
FACULTY OF NATURAL AND APPLIED SCIENCE NASARAWA STATE UNIVERSITY, KEFFI
DR. I.N UFARUNA
1.1Background of the study
Irrigation is one of the most common farming systems in the tropics (especially Northern Nigeria). This has help in provision of food to the teeming populace. Irrigation farming is the application of water from rivers, lakes, wells etc to farm crops mostly vegetables during the dry season (Martin&Cughtrey,1982).
In recent times, pollution which affect the irrigation system are caused by water contamination which include, human waste-load, industrial waste and domestic waste (refuse dump) which are introduce into water bodies(Jorgensen & John,1981).These pollutants are natural components of the earth crust and cannot be degraded or destroyed.
Human activities such as mining, pesticides used in agriculture and transportation release high amount of heavy metals into the surface and ground water, soil, plant and the biosphere. Heavy metals in the air, soil, water and plant are global problems that threaten the environment (Alloway, 1995) the main routes through which heavy metals are transferred to the environment are the atmosphere and flowing waters.
Under normal conditions, the end results of the migration are sediments, soil and underground water. Heavy metals may enter the food chain by edible plants such as vegetables. With the increased knowledge that vegetables play a special role in human nutrition, especially as sources of vitamins, minerals and dietary fibers, proteins and essential fatty acids, there is increased interest in its consumption. However, these heavy and essential trace metals are given special attention through the world due their toxic effect in the body when their concentrations exceed limits of safe exposure. Thus the determination of heavy metals in the vegetable samples in the selected study area is important (Margesin & Schinner, 2005).
Heavy metals are natural component of the soil. Most elements are only present in minimal, insignificant eco-toxicological concentrations in the undisturbed locations. A few heavy metals are important as trace elements in physiological processes in plant and animals. Heavy metals contamination of soil is wide spread due to chemical waste from industries, mining activities, combustion of wood, coal and mineral oil, and pesticide used in agriculture (Ozores & Stuanes, 1997). Heavy metals contaminate and accumulate in plants, vegetables, fruits and canned foods, through the soil and waste water used in the irrigation (Geert et al., 1989)
The accumulation of heavy metals in crop plants is of great concern due to the probability of food contamination through the soil root interface. Heavy metals have great significance due to their tendency to accumulation in vital human organs over a prolong period of time (Afzal et al., 2011). Inhalation of and indigestion of heavy metals may cause various diseases such as anaemia, neuropsychological effect, liver disease, gastro intestinal pathologies, teratogenic implications (Cocaruetet al., 2006). Moreover, it is known that the DNA – damaging effects of certain metals in humans can lead to induction of cancer and decrease fertility (Husain et al., 1995). In addition, heavy metals in soils may adversely affect soil ecology, agricultural production or products, and water quality (Wang et al., 2001. Heavy metal concentration in soil solution plays an important role in controlling metal bioavailability to plants. Studies have shown that use of waste water contaminated with heavy metals for irrigation over a long period of time increases the heavy contents of soil above the permissible limit. Furthermore, increasing the uptake of heavy metals by plants depends upon the soil type (Khan & Franklan, 2008). Some metals are essential for life, but if an individual’s intake exceeds a certain threshold, toxicity may develop. Metals and minerals in food and fodder are of great interest because of their potential effects on human and animal health. Some have no beneficial biological function and exposure may be harmful to health. For example, organic mercury compounds are neurotoxins, exposure to lead can be harmful to neurophysiological development; inorganic arsenic is a human carcinogen and cadmium can affect renal function. While some elements, such as cobalt, iron and copper are essential too health, they may be toxic at high level of exposure. Exposure to metals can be in a number of ways including at work in certain industries, from drinking water and eating contaminated foods (Maleki ; Zarasvand, 2008).
Heavy metal pollution is raising environmental problem, which requires immediate attention. The risk to health from certain elements in food can be assessed by comparing estimates of dietary exposures with the Provisional Tolerable Weekly Intake (PTWIs) and Provisional Maximum Daily Intakes (PMTDIs) recommended by the Joint Expert.
Committee on Food Addictive (JECFA) of Food and Agriculture Organization (FAO) and World Health Organization (WHO) programs on chemical safety (Nguyen et al., 2011).Extreme accumulation of heavy metals in Agriculture soils through waste water irrigation, may not only result in soil contamination, but also lead to elevated heavy metal uptake by crops, and thus affect food quality and safety. Heavy metal accumulation in soil and plants is of increasing concern because of the potential human health risk. This food chain contamination is one of the important pathways for entry of these toxic pollutants into the body of human. Heavy metal accumulation in plant depends on plant species, and the efficiency of the different plants in absorbing metals. This is evaluated by either plant uptake or soil to plat transfer factors of the metals. Vegetables cultivated in waste water irrigated soils take up heavy metals in large quantity to cause potential health risk to consumers. In to assess the health risk, it is necessary to identify the potential sources that introduce risk agent into the environment and estimate the amount of risk agents that come into contact the human environment (Khan et al., 2008).
Anthropogenic activities (mining, ultimate disposal of treated and untreated waste) effluents containing toxic metals as well as chelates from different industries and the indiscriminate use of heavy metal containing fertilizer and pesticides in agriculture resulted in deterioration of water quality rendering serious environmental problems posing threat on human beings. However, some metals for example Cu, Fe. Mn, Ni and Zn are essential as micro nutrients for life processes in plants and microorganisms, while many others like Cd, Cr and Pb have no known physiological activity (Gaikwad ; Gapta., 2008).
As a result, monitoring heavy metals is important for safety assessment of the environment and human health in particular. Regarding this background, it is therefore necessary to determine heavy metals in water, soil and plant.
1.2Statement of the problem
During the past few years, many death causes of human beings and animals have been reported by the Veterinary Research Institute in Vom, Plateau State (Nigeria),National Hospital in Abuja and Federal Medical Center in Keffi including the infectious and noninfectious diseases. In addition, some animal diseases which could be related to animal fodder or drinking water may be correlated to heavy metals. However, there are some animals’ fatalities for which the potential cause of death could not be agreed upon and affected animals showed no specific symptoms before death. It was therefore of interest to conduct a study to estimate the levels of heavy metals concentration in water, soil and plants of the different irrigation sites in Keffi metropolis,Keffi Local Government area of Nasarawa state.
1.3Aim and Objective of the Study
i.To determine the concentration of heavy metals in the selected samples from irrigation farms in Keffi metropolis in Nasarawa State.
ii.To assess the potential toxic and non-essential heavy metals in the selected samples.
iii.To provide data of heavy metals in the selected samples
iv.To find correlation between the concentration of heavy metals in soil, water and plants.
v.To monitor the pollution trend and the presence of heavy metals in water, soil and plants in the selected samples location.
1.4Significance of the Study
The study will provide the baseline data of the levels of cadmium, nickel, lead, Zinc, Chromium and copper in water, soil and plants of the selected areas in keffi metropolis in Nasarawa State and will help to make a basis for further studies monitoring of their concentration in soil, water and plants of those areas. Moreover, it will help in forecasting the potential threats caused by their excess or deficiency to human and animal population of the environmental agency, veterinary agency and agricultural societies in the different areas of Nasarawa State.
In view of that, it is very important for this type of research work in order to ascertain the levels of heavy metals in the vegetable grown in these areas and to also know if they pose danger to the consumer.
1.5Scope of Study
The scope of the study encompasses the analysis of heavy metals cadmium, nickel, lead, Zinc, Chromium and Copper. Environmental samples for analysis will include water, soil and vegetables. The analysis will cover four areas of Nasarawa State namely Manu, Antau, Ngwar Lambu and Army Barracks and the method that will be used is Atomic Absorption Spectroscopy(AAS).
2.0 HEAVY METALS AND THEIR SOURCES IN THE ENVIRONMENT
Heavy metals are transition metals with density greater than 5g/cm. they exist among other metals in the earth crust and find their way into the environment through different sources(Reilly,1980). The very toxic nature of trace metals warrant a knowledge of their sources and fate in the environment, that is the mechanism involved in their transport and transformation from one source to another. They are essentially to maintain the metabolism of the body. However, at higher concentration they can lead to poisoning (Sorensen & Nobe,1972). Heavy metals are “Bio accumulate” in biological organisms overtime, compared to the chemical concentration in the environment (Fennely,1975).
Their main source to plants is their growth media (e.g. air, soil, nutrient solution) from which they are taken up by the roots or the foliage, which depends on both soil and plant factor (e.g. source and chemical form of element in soil, PH, organic matter, plant species and plant age) hence the interaction between the element at the surface of the root within the plant can affect uptake as well as translocation and toxicity.
Heavy metals are classified as essential and non-essential. The essential are those considered to be useful in trace amount such as chromium, cobalt, zinc, manganese and iron. The non-essential are those which there is no evidence at the presence of their essentiality or toxicity (Darely,1996).
The toxic metals are those in which the elements have neither an essential or beneficial effect, but a positive catastrophic effect on normal metabolic function, even when present in only small amount such as: Cadmium, Lead, Mercury and Antimony. However, heavy metals are classified into three groups according to their biological roles.
2.1 CLASSIFICATION OF HEAVY METALS
Essential Non-Essential Toxic
Copper Tin Lead
Iron Rubidium Cadmium
Chromium Aluminium Manganese Titanium Nickel Zirconium Zinc Boron R. CONOR APPLIED SCIENCE PUBLISHERS LIMITED, 1980
Stationary sources of heavy metals are industrial processes and their products. For example battery industry is a major source of lead so also the art gallery where paint is used regularly (Bolt & Bruggenwert,1978). Incinerators and metallurgical processes are also responsible for environmental pollution by the heavy metal. Mobile source of heavy metals are responsible for the highest amount of heavy metal in the environment. The automobiles are wholly responsible for about 75% of lead in the environment (Alloway,1990).
Lead is added to motor gasoline as tetraethyl lead in order to prevent knock in the internal combustion engine. The resulting lead-oxide from combustion of fuel is converted to volatile lead halide and then sent out into the atmosphere as tiny droplets. These droplets of average size of 0.2 um may stay in the atmosphere for a period of 7-30 days. They may be dropped very far away from their point of discharge (Monier,1994).
The presence of Nickel depends on the rate at which it is released to the environment through mechanical wear of vehicles. It also enters the environment through fuel combustion and lubricating oil (Schroeder,1971).
The presence of iron and copper in the environment depends in the amount in the soil and refuse burning and fertilizer application. Industries such as metal finishing, pigment dye manufacturers, textiles, ceramics and tanneries are good source of chromium to the environment. Manganese concentration is due to its presence in the soil. Cadmium is released into the environment through the disposal of Nickel-cadmium batteries and municipal waste (Baker,1974).
2.2 WATER FOR IRRIGATION
In order to determine threshold values for the introduction of polluted water, a distinction must be made between direct and indirect introduction. The direct discharge of waste into waterways has caused series of pollution trends in irrigation. The amount of organic waste which rivers, wells, lakes, can effectively handle, is determined by the level of dissolved oxygen (DO) and the volume of water passing through it(Jones & Belling,1967). Analysis has shown that polluted waters are those with biochemical oxygen demand (BOD) greater than 12mg/1(7).
REQUIRED HEAVY METAL VALUE FOR IRRIGATION WATER
HEAVY METALS VALUES (mg/L
(FAO/WHO food standards program/UNESCO publication)
The essential heavy metals are those that are either natural present in biological system as metalloproteinase examples. Manganese or those that are required for certain biological functions like trivalent chromium which serves as constituent at glucose tolerance factor (Linsey,1972).
The non-essential heavy metals are those, whose function in the body is not yet established or confirmed. Toxic heavy metals are deleterious to the biological system and hence they are excreted by the body mechanism at a constant rate. The body can excrete these metals through urine and sweat. The amount of these metals excreted through urine and sweat are shown below (Baucherter,1973).
EXCRETION OF HEAVY METALS BY THE BODY
Heavy metal Urine (mg/day) Sweat(mol/day)
Cadmium 0.03 Lead 0.03 0.256
Copper 0.06 1.59
Iron 0.25 0.5
Chromium 0.008 0.059
Manganese 0.225 0.097
Nickel .011 0.083
Zinc 0.5 5.08
(FAO/WHO food standards program/UNESCO publication)
If the rate of excretion is below that of intake through ingestion or inhalation accumulation of heavy metals in the body leads to the breakdown of many biological reactions, thus if preventive measures are not taken, it may lead to various diseases and death(Linsay,1973). The estimated safe and adequate daily dietary intakes of heavy metals are shown below.
ESTIMATED SAFE AND ADEQUATE DAILY INTAKES OF HEAVY METALS (MG/DAY).Age Cu Cd Pb Ni
Infants 0-0.5 0.4-0.6 0.125 550 0.3-0.6
0.5-1 0.6-0.7 0.125 550 0.3-0.6
Children 1-3 0.7-10 0.125 550 0.3-0.6
Adolescent 4-6 1.0-1.5 0.125 550 0.3-0.6
7-10 1.02.0 0.125 550 0.3-0.6
12-17 1.5-2.5 0.125 550 0.3-0.6
Adults 18 –above 1.5-3.0 0.125 550 0.3-0.6
(Recommended dietary allowances, 10th edition food and nutrition board, National Research Council, National academy of science, 1989).HEAVY METAL
2.3 COPPER (Cup)
Copper is a chemical element with atomic number 29 and atomic weight 63.546g/mol (Brandy,1974). The predominant ionic form of copper in most soil is a divalent cation. It is reported that an adverse influence in plant growth result if copper concentration in the soil exceeds 0.Ippµ. Normal copper variations over the range of 2-100ppm. The mobility and displacement of copper in soil is low(Linsay,1973) . As a result of bonding with organic matter, clay minerals etc. the downward movement of copper in the soil is almost nil. Lindsay (1972) suggested the reaction of copper in soil by the general equation.
Cu2+ + soil= Cu-soil+2H+
The effect of high copper contents depends on uptake of certain other micronutrients by plant. High copper level may cause iron deficiency, which is demonstrated as typical chlorosis feature. It is reported that an adverse influence in plant growth result, if copper concentration in the soil exceeds 0.1 ppm.
Absorption of copper occurs mainly in the stomach, normally about 30% of ingested copper is absorbed in a low diet (Davies,1992) . This level of absorption has been shown to increase to between 50 and 65%. The percentage absorbed decreases when levels of copper ingested are increased.
Wilson’s disease results in excessive uptake and accumulation of copper by the body, with a build up especially in the liver and brain(Vanselow,1966).
2.4 CADMIUM (Cd)
A relatively rare chemical element, atomic number 48, closely related to zinc with which it is usually associated in nature. It is divalent in all its stable compound and its ions are colourless because of the predominant occurrence of cadmium as a divalent cation, electrostatic electrostatic adsorption on exposing adsorption sites probably acts as the main bonding mechanism. Cadmium content of soil in non-polluted areas is usually below 1ppm. Agamata and Shigematsu (1970) described for contaminated rice soil level up to 50ppm cadmium. For topsoil sample near a zinc smelter values as high as 1700ppm has been reported.
The physical effects of cadmium on plants are as follows:
The reduction of fruit setting and blocking of the stomata (Baker,1974) . This result in barrenness of the plant.There is evidence that many factors can affect the level of cadmium absorption. As a result of such efficient retention from the amount of cadmium absorbed by the body, the biological half-life of cadmium in human body is very long, perhaps as much as forty years.
The ingestion of cadmium in Food causes symptoms of nausea, vomiting, abdominal cramp and headache within minutes of ingestion Itai-Itai is a disease resulting from cadmium ingested in rice, which had been irrigated with cadmium-polluted water.
2.5 NICKEL (Ni)
Nickel is a chemical element with atomic number 28 and mass number 58.71 g/mol. It is usually di-positive in its compound, but can also exist in the oxidation states 0,+1, +2, and +4. It is adsorbed on the soil complex as a divalent cation, Ni+ and is easily taken up by plants when present in soil (Soane ; Saunder,1959) .Total Ni-content in soil may vary from 5-50 ppm with 100ppm as a rough mean value. Serpentine soils exhibit much higher values. Nickel is a highly value. Serpentine soils exhibit much higher values. Nickel is a highly toxic element to plants when it is in high concentration in soils.
REQUIRED PROPORTION OF HEAVY METALS IN IRRIGATED SOILS
Cu Cd Ni Pb Zn Cr
Irrigated Soils 2-100 1-3 5-50 10-100 300 100
FAO. UNESCO publication
2.6 LEAD (Pb)
The physical effects of lead on plants are as follows, reduction in growth and reproductive system causing injury to plants amongst others. The most prominent effect is the inhibition of photosynthesis in crops (Singer ; Hanson,1970).
It is a chemical element with atomic number 82 and atomic weight 207. 19 g/m and the normal valency is +2 and +4. In soil, lead exist as a divalent cation (+2), lead particle reach the soil surface as precipitates and thus, soil pollution problems have been induced. Not much is known about lead’s chemistry in soils. Singer and Hanson (1969) describe how the danger of excess lead is probably decreased after deposition on the soil, due to formation of relatively insoluble compound like PbSO4, because of the formation of these solid and of the absorption of lead its displacement in soil is mostly small.
Lead has been listed, by Schroeder and Nason (1971), among the abnormal trace elements of interest in human body and blood. The symptoms of acute lead poisoning following the ingestion of large quantities of the metal are well known.
Acute poisoning usually manifests itself in gastro-intestinal effects. Anorexia, dyspepsia, and constipation manifest maybe followed by an attack of colic with intense paroxysmal abdominal pain. The disease has been in Africa with children living in the vicinity of higher concentration of lead in food (Brandy,1974) .
Nickel is poorly absorbed from food. The metal is excreted mainly in faces, with a smaller amount in urine. Distribution in the body seems to be fairly uniform with no evidence for accumulation to any significant extent in particular organ (Vanselow,1966) .
Nickel is apparently non-toxic to man, though acid foods con pick up the metal from nickel-plated alloy looking utensil. However, cancer of the respiratory track as well as dermatitis occurs in workers in nickel refineries.
Nickel at higher concentration in soil usually increases the soil pH that leads to problems of crop nutrition and herbicides efficacy. The effect ranges from blocked stomata and leaf injury symptoms to an overall reduction in crop structure (Davies,1992). It also enhances plasmolysis in leaf cells, irregular distribution of chloroplast and inability to form starch on the cells.
This review on the pollution trend analysis at heavy metals in irrigated farms is sparse. However, (Olaitan and Lombin,1988) reported that a soil is said to be suitable for crop production when it absorbs and retain moisture, has moderate in-filtration rate, moderate organic matter and is free from toxic substances. Heavy metals can enter a water supply by industrial and consumer waste or even from acid rain by releasing heavy metals into streams, lakes, rivers and ground water (Lennted, 2005). Heavy metals are natural component of the earth’s crust. They are dangerous because they tend to bioaccumulate. Bioaccumulation which is the increased of chemical in a biological organism over time, compared to the chemical concentration in the environment. (Usman and Shall, 2003) reported that irrigation soil is slightly acidic probably due to lack of basic cations as a result uptake of the cations by growing plants or their being leaching out of the soil profile due to flooding.( Owonubi et al, 1992) reported that the level of organic matter content of irrigation soils range from less than 0.05% to greater than 2%. There is no significance correlation between organic matter and clay content at 5% level.
The exchangeable bases of certain element such as magnesium and calcium range from 0.482 to 0.71cmol(+) kg with a mean of 0.59 cmol(+)/kg indicating a low magnesium and calcium content in the soil. (Issaka et al ,1996) reported that irrigation soils of the tropics have low to moderate exchangeable basic cations. Gouge et al (1979) reported that plants, animals and man can be seriously affected by heavy metals contamination particularly in surface soil and become immediately accessible to plant roots.
Chromium usually appears commonly in the environment as a trivalent salt cr-III or cr3+ (ATSDR, 2008). Found in air, water, soil and some foods, it is an essential trace element, aiding in the metabolism of carbohydrates etc. (ATSDR, 2008). Chromium attaches tightly to soil particles, and the usual exposure pathways are due to exposure to dusts and, sediments (ATSDR, 2008) leaching from topsoil and rocks is the most important natural source of chromium entry into bodies of (ATSDR, 2008). Chromium causes respiratory problems, a lower ability to fight diseases, birth defects, infertility and tumour formation (Dennis et al., (2003). Chromium (III) is an essential nutrient for humans and shortages may cause heart conditions, disruptions of metabolism and diabetes (Cheryl and Susan, 2010). Excess chromium (III) causes negative health effects for instance skin rashes (Cheryl and Susan, 2000). Chromium may exist in a number of oxidation states, but the most stable and common forms are Cr (III) and Cr (VI) (Alloway, 1995a)
Zinc is an element of moderate abundance in the earth crust and the presence of zinc in the environment is associated with mining and smelting which pollutes the air, water and soil with fine particles (Tiimub et al., 2015). Zinc is an essential mineral that is naturally present in some foods (National Institute of Health, 2013). Plant – based foods are good sources of zinc (Institute of Medicine, 2001). Gastrointestinal distress is an common symptom following acute oral exposure to zinc compounds (USEPA 2009).
3.0 Study Areas
The study will be carried out in four different of Keffi Local Government Areas (Ngwar Lambo,Manu,Antau and Army Barrack) in Nasarawa state, Nigeria. According to Ministry of Local Government ; Chieftaincy Affairs Nasarawa state in 2015 Report, Ngwar Lambo has an area of 5,14km2 and estimated population of about 1×104 and it’s the second most populated area in the Local Government. Manu Bassa has an area of 143km2 and estimated population of 7,000 and shares borders with Kaduna State, Antau has an area of 132km2 with estimated population of 8,500. According to 2015 Report by Ministry of Agriculture & Natural resources Nasarawa State, the areas have an annual rainfall of between 131. 5cm to 146cm to 146cm. these areas were selected for their industrial areas, residential and mining sites, and randomly located farm lands. These four areas have diverse range of ethnic group indigenous to the state, according to Ministry of Land & Survey Nasarawa state 2015 Report; keffi has an estimated population of 430,650, and full of hospital and culturally rich people. It is composed of different ethnic group each with its own distinct local dialect. Angwar Lambo and Antau are predominantly hausa fulani people, while Manu and Army Barracks are predominantly the Afor People. They all have common history and share similar ideologies. Farming is the main occupation of these people and crops produced include: Maize, water melon, carrot, pepper, tomatoes, cabbage, green beans and vegetables. The soil of the areas is sandy-loamy soil which enhances the growth of vegetables and other perishable crops (Duruibe et al, 2007).
3.1 Sample Location
Four sampling site will be selected,from the local government area of study (Ngwar Lambo,Manu,Antau and Army Barracks). They are Farm in Ngwar Lambo,Manu,Antau in Keffi LGA. On each of the sites, samples will be by Grid method (Jarvis & Younger, 1997) to give a reasonable overview of the soil and vegetable characterization of the entire area (Jarvis & Younger, 1997).
3.2 Sample Collection
Three irrigated vegetables will be collected from irrigation site of farm in Keffi Local Government Area of Nasarawa State. The vegetables will be tomato, spinash and green beans. Samplings will be done randomly, in all the farmlands along the entire lengths of the stream used for the irrigation. The same type of vegetables will be mixed to give the representative fraction of each of the vegetable in the irrigated farmland. Also, soil samples will be collected at each place and time the vegetables will be uprooted and the soil mixed thoroughly to give a representative fraction. The soil samples were air dried ground and sieved though 200 mm mesh size. The water sample will be collected from the stream used to water the farm in a container rinsed with some few drops of nitric acid to avoid the activities of microorganisms from the water sample prior to analysis.
The same procedures will be used for the other areas in the Local Government Area (Keffi). In all the process, precautionary measures will be taken to avoid any form of contamination.
3.3 List of Chemical and Reagents and Apparatus
The instruments and reagents that will be used for this research work will be of analytical grade. The materials are in (Appendix 1)
3.4 Samples Preparation and Analysis
Sampling will be carried-out during the dry season because mining wells and stagnant water used for irrigation have been established to play significant role in heavy metals concentration in irrigation sites. Soils and vegetable samples will be collected using a clean shovel and a kitchen knife. Soil sample will be collected from the immediate vicinity of the vegetable root depth of 0.5cm. Four edible vegetables plants samples tomato, spinash, green pepper, green beans which are grown from within the vicinity of various irrigation sites in the Local Government Area will be randomly collected with kitchen knife. The separate randomly selected vegetables and soils will be combined to give a composite representation of the samples from these areas and will be labeled appropriately. The vegetables, soil and water samples will be collected from three different farms one from each area within the local government area in Nasarawa State and will be brought to the laboratory. The leaves will be plucked from the stem and will be properly washed with de-ionised water, the leaves will then be dried at room temperature until it was ready for grinding. The dried vegetables samples will then be grounded with crucible to fine powder sieved and stored in a sample bottle well labeled for identification.
Soil will be collected from the farms from points where the vegetables were uprooted to the depth of about 0-5cm. the collected dried soil samples will thoroughly be mixed in clean plastic bucket to obtain a representative sample, crushed and sieved through 2mm mesh size and stored in a labeled polythene bags awaiting analysis (Marshal et al, 2003). From the sieved sample, 2g will be weighed and poured into a beaker. 25cm3 of HNO, and 5cm3 of HCI will be added at a ratio of 4:1. The mixture in a beaker will be heated gently for about 45min. and filtered while warm to prevent re-precipitation of the metals. The filtrate will be poured into 100cm3 flask and made up to mark with distilled water and kept for analysis (Marshal et al, 2003).
3.6 Vegetable Sample Preparation
The plant leaves and fruits harvested will be plucked using knife. The samples will be washed with distilled water severally in order to remove dirt and dust particles (Khan et al. 2008). These will be sun dried for two weeks and ground using pestle and sieved to 500mm. the sieved samples will be kept inside a clean sample bottle prior to analysis. 20g of the powdered samples will be weighed into a beaker and 20cm3 of 2M concentrated HN3 and 5cm3 of 2M HCI will be added at a ratio of 4.1. the solution was heated for 45min. the leachate will be dissolved into 100cm3 of distilled water and placed into sample bottles for atomic
3.7 Stock Solution of Heavy Metals
Stock solution of metals that will be analyzed will be prepared from available salts of Lead, cadmium, nickel and copper.
3.8 Heavy Metal Analysis
Cadmium, Lead, Nickel and Copper will be determine in soil, water and vegetables samples using computer controlled atomic absorption spectrometer.
3.9 Experimental Procedure
The expected experiment to be carried out on this research work is divided into:
Drying of the samples
Grinding and sieving of the sample
Analysis of the digested sample using atomic absorption spectrometer
Some commonly consumed vegetable will be used as samples for the analysis of heavy metals. They include green beans, green pepper, peas and tomato.
3.9.1 Digestion of Vegetables, Water and Soil
Digestion is the process of combusting volatile materials in a given sample. The volatile materials are usually organic materials such as carbohydrate, fats and oil, protein and other materials. After digestion, it is the inorganic materials usually the trace metal elements that remain. The digestion procedure can be done by two broad methods. They are:
Wet ashing (MILACIC & KRALJ, 2003).
3.9.2 Dry Ashing
This method involves the complete combustion of all the organic matter only in the raw and processed sample to remain only the non-volatile inorganic mineral element. The combustion starts by burning the material on a non-luminous part of the Bunsen flame until it stops smoking and transferred into a muffle furnance which is set between 4500-5000 BC (Jarup, 2003)
3.9.3 Procedure for Dry Ashing of Sample
Crucible will be used for ashing
Weight of the crucible will be taken using a weighing balance and recorded.
2g of the different samples will be measured using a weigh balance and transferred into different crucible according to the sample
The samples will be arranged in the furnace
Ashing will be done at a temperature of 600oc for four hour
Ashed samples will be allowed to cool before bringing it out for extraction
The ashed samples will be extracted by the use of aqua Regia solution.
3.9.4 Preparation of Aqua Regia
Inside 2000ml volumetric flask, a little ultra-pure water will be added and 400ml of concentrated HCI
133ml of concentrated nitric acid will be added to the volumetric, flask in the first step and it will be made to mark by adding ultra-pure water and shaken well.
3.9.5 Extraction of Ash Samples
The ash samples from the different crucible will be transferred into a centrifuge tubes
Crucible will be rinsed with 5ml ultra-pure water
7.5ml each of aqua regia solution will be used to rinse the different crucible and transferred into the centrifuge tubes
7.5ml each of aqua regia will be to the different samples in the centrifuge tubes.
The centrifuge tube will be covered and the shaker will shake it for 5mins.
The clear solution of the different samples will be transferred into different sample bottles based on the sample name and location
The different clear solution of the samples will be labeled for identification and AAS analysis.
However, precautionary measure will be taken against low result which may be due to any of the following reasons:
Volatilization of Elements
Combination or adsorption of elements with ash constituent or vessel.
Incomplete extraction of the ash, such difficulties can usually be avoided.
3.9.6 Wet/Acid Digestion
All acid digestion makes use of oxidizing agents to break down the organic matter. This method has some advantage when compared with dry ashing as no volatilization loss occurs. The nutrient elements can be determined in one digest solution, but cannot be used for some very hard materials as incomplete digestion may result. Various chemicals such as nitric acid, perhloric and sulphric acid can be used in the determination of lead, zinc, manganese, cadmium and other heavy metals. The use of hydrochloric acid will be employed in this project because the digestion is very fast through it is dangerous because explosion may occur if care is not taken. The digested solution is made up to mark in a volumetric flask and stored in a sample bottle well labeled for further analysis (Milacic & Kralj. 2003).
3.9.7 Procedure for Wet/Acid Digestion
a)2.0g of the sample was weighed out into a Kjaedahl flask mixed with 20cm3 of concentrated sulphric acid, concentrated perchloric acid and concentrated nitric acid in the ratio 1:4: 40 by volume respectively and left to stand overnight.
b)The flask was heated at 70oC for about 40 min and then, the heat was increased to 120oC. The mixture turned black after a while. The digestion was complete when the solution became clear and white fumes appeared.
c)The digest was diluted with 20cm3 of distilled water and boiled for 15mins.
d)This was then allowed to cool, transferred into 100cm3 volumetric flasks and diluted to the mark with distilled water. The sample solution was then filtered through a filter paper into a screw capped polyethylene bottle well labeled (Milacic & Kralj, 2003)
3.9.8 Water Sample Preservation
The water sample that will be collected will beaded few drops of nitric acid (HNO3) at the point of collection to prevent loss of metals and bacterial and fungal growth. Temperature and pH of the water samples will be measured at the time of collection. The water samples will be kept prior to AAS analysis.
3.9.9 Digestion of Soil Sample using Standard References Materials
Depending on the different metal concentration levels, soil obtained from irrigation site in selected areas within Keffi LGA, will be used for the digestion. Prior to the analysis, the samples will be dried at 110oc for two hours. The calibration for Cd, Ni, Cu and Pb will be prepared by using Merck standard solutions with a purity of 99.8%.
The solutions will be prepared by using doubly de-ionized water, before digestion, the sample flask and digestion vessels will be soaked into 10% nitric acid for 24hours and then washed with de-ionized water. There are two basic methods employed for the digestions are:
i.Environment Protection Agency Method 3050B
A procedure recommended by Environmental Protection Agency will be used as the conventional acid extraction method. 2g of the soil sample will be placed in 20ml flask for digestion. The first step will be to heat the sample to 950c with 10ml of 50% of HNO3 without boiling. After cooling the sample, it will be refluxed with repeated additions of 65% of HNO3 until no brown fumes will be given off by the sample. Then the solution will be allowed to evaporate until the volume was reduced to 5ml. after cooling, 10ml of 30% H2O2 will be added slowly without allowing any loses. The mixture will be refluxed with 10ml 37% HCI at 950oc for 15minutes. The digestate obtained will be filtered through a 0.45 µm membrane paper, diluted to 100ml with de-ionized water and stored at 40oc for analysis.
Microwave Acid Digestion
The question Micro prep Q20 Microwave digestion system with four digestion vessels will be used for microwave assisted acid digestion. Samples will be placed in liners (TFM Teflon, softening point 250oc) which are mounted in ultern caps. The vessels support an operating pressure of 350psi and a maximum temperature of 260oc and they are resistant to HF. Rupture disks will be placed in the over pressure valve stems in the vessels to become pressure control device in the digester.
The system allows digestion of four samples at the same time. Three different programs labeled as P1, P2 and P3 will be tested with the SRMs.02g of sample will be used for each digestion. Combination of nitric acid (65% HNO3 used for easily oxidizable material), hydrofluoric acid (40% HF-used for extraction of inorganic matrixes), and hydrochloric acid (37% HCI) will be added to each of the digestion vessels. For microwave-assisted digestion process, the total extraction time will be set at 26min. the highest power applied for all the process will be 600 watts. Held for 1min. in P1 and P2, and 2min for P3.08ml of HCI will be filtered through 0.4µum membrane filter, diluted to 20ml for storage and further analysis.
3.9.10 Atomic Absorption Spectrophotometer
Atomic absorption spectrometry is an analytical technique used to determine a wide range of elements in materials such as alloys, pottery and glass. Although it is a destructive technique, the sample size needed is very small (typically about 10milligrams i.e one hundredth of gram) and its removal causes little damage. The sample is accurately weighed and dissolved using strong acids. The resulting solution is spayed into the flame of the instrument and atomized. Radiation whose wavelength is in resonance with the wavelength of the element to be determined is directed to the sample and when this is done, some of this light is absorbed by atoms of the sample. The amount of light absorbed is proportional to the concentration of the element in the solution. The concentration of each element of interest is determined individually to achieve a complete analysis of a sample. The technique is therefore very sensitive and it can measure trace elements is part per million level, as well as being able to measure elements present in minor or major amount.
3.9.11 Principle of operation of AAS
The basic principle of AAS involves the measurement of resonance radiation absorbed by free, unexcited, unionized ground state atoms. These ground state atoms are capable of absorbing radiation of their own specific resonance wavelength, which in general is the wavelength of the radiation that the atoms would emit if excited from the ground state, hence if light of the resonance wavelength is passed through a flame containing the specified atoms part of the light will be absorbed and extent of absorption will be proportional to the number of ground state atoms in the flame. This technique is therefore, quite different from emission spectrometry where measurement is made from excited ground state atoms. An Alpha 4 model atomic absorption spectrophotometer (Chemtec Analytical, UkK) equipped with photomultiplier tube detector and hollow cathode lamps was used for the determination of metal concentrations. Working standards were also prepared by further dilution of 1000 ppm stock solution of each of the metals (Agrawal, 2003). In this process, a flame system is generally employed to dissociate elements from their chemical bonds. The atoms absorb light at a characteristic wavelength when present in ground state. A mixture of air and acetylene produces flame which is sufficiently at high temperature to ensure the presence of free atoms of most elements. The use of nitrous oxide in place of air results in a higher temperature and this is necessary for the estimation of certain elements (Obuobie et al., 2006)
Instrument for AAS
The AAS is made up of five basic components as follows:
The light source
The atom cell
Light Source in AAS
The source of light most commonly used in AAS is the hollow cathode lamp (HCL). The major components of the hollow cathode lamp are:
Quartz glass window
The hollow cathode lamp (HCL) is made of a glass casing that has a quartz window. The anode is usually made of tungsten although some are made of deuterium. The cathode is usually made of the same material as the analytic. The remaining space within the glass cashing is filled with inert gas such as Neon or Argon. The cathode and anode terminals are connected to the source with high potential difference when the circuit is complete, the enclosed inert gas undergoes ionization. This will give rise to small current that will vary 5-30mA. The positive ions proceed to the cathode while the negative will move to the anode. In the cathode, the positive ions will collide and knock off atoms of the cathode material. This phenomenon is known as CATHODIC SPUTTERING. The ejected atoms will further collide with ionized inert gas and become collisionally excited. The excited atom on going back to the ground state omits immensity that is absorbed by the analytic in the atom cell. This therefore means that only light of a wavelength similar to that of the element to be determined is emmited by the HCI. This method with restriction ensures that there will be no spectral interference.
Atomizer and Nebulizer
The atom cell contains the analytic. For the AAS, flame from the burner provides the heat necessary for desolation, vapourization and atomization of the analyte. The atom cell incorporates the nebulizers/atomization chamber and so produces the ground state atoms that are needed to absorb resonance radiation. The solution of the sample is aspirated into the nebulizer/spray chamber which convert the liquid sample into a mist or aerosol, selects the mist droplet of correct size distribution, mixes the mist with the flame gases and introduces the mixtures to the burner. The sample is drawn into the nebulizer with the aid of the oxidant. Large droplets drop down the drain only about 10% of the total amount of the sample nebulized reaches the flame. The efficiency of nebulization and therefore the population of ground state atoms in the flame will depend on certain physical properties of the sample e.g viscosity, surface tension etc.
This is a special spectral selection device. It screens the radiation available and chooses a limited wavelength region that can be absorbed specifically by the material of interest. The monochromator placed between the flame and the detector allows the later to measure only the wavelength of light being absorbed.
In a crude sense, the detector is a moving coil galvanometer and deflects to indicate the amount of current that had been imparted to it by the sample. The more sophisticated and recent equipment have computerized and digitalized detectors (Yusuf & Oluwole, 2009).
TIME FRAME AND EXPECTED OUTCOMES
Considering the fact that there is increase in knowledge that vegetables play a special role in human nutrition, especially as sources of vitamins, minerals, dietary fibre, proteins and essential fatty acids. There is increase interest in its consumption. The analysis of the various components of metals in the vegetable is important to humans. By the end of this research, cognizance of the level of the heavy metals whether it within the approved limit or they are not. Also, the knowledge from this research will be applied in reducing the risk of consumption of vegetables contaminated with heavy metals.
Sample collection 30 days
Sample preparation 21 days
Sample analysis 21 days
Collection of result and interpretation 60 days
Total 132 working days
3390900180975 Taken Volume or Weight
00 Taken Volume or Weight
396240018097500Actual Conc of metal in sample Dilution factor (df) = Total Volume
Actual concentration = Conc. Of AAS Result X of metal in the dilution factor (df)
1638300247015 Sample Weight
00 Sample Weight
163830024701500Final Concentration = ConcMetal x DFactor x Vnominal
(European Community, Commission Regulation (EC6R) No 629/2008)
TABLE 1: HEAVY METALS CONCENTRATION (Mg /L) in irrigation water Sample collected from the study areas.
SITES N.S Cu Ni Cr Cd Pb Zn
MAN U 7 0.042 0.65 0.41 0.01 0.91 0.231
ANTA U 3 ND 0.50 0.91 ND 0.087 0.037
GWAR LAMBU 3 0.012 0.29 0.15 ND 0.065 0.008
ARMY 3 0.031 0.01 0.47 0.010 0.035 .0004
ST LIMITS 0.2 0.2 0.1 0.01 5 0.05
SITES N.S Cu N1 Cr Cd Pb Zn
MANU 3 530.15 56.61 420.2 2 201.0 500.0
ANTAU 3 180.50 42.83 276.0 1 81.3 554.0
GWAR LAMBU 3 75.32 36.21 123.7 ND 47.16 190.2
ARMY BARRACKS 3 87.10 39.17 217.9 ND 52.13 93.17
ST LIMITS 100 50 100 3 100 300
N.S – Number of Sampling
N.D – Not Detected
TABLE 2: HEAVY METALS CONCENTRATIONS (Mg / Kg) in selected soil samples collected from irrigation in study areas
TABLE 3: HEAVY METALS CONCENTRATIONS (Mg/ Kg) in some Vegetables samples collected from irrigation farms in the study area
N.S LOCATION PLANT SPECIES Cu N1 Cr Cd Pb Zn
MAN U 3 C1 SPINACH 8.17 56.17 9.07 0.006 14.00 25.06
3 C2 SPINACH 7.69 35.00 10.05 ND 11.12 56.28
3 C3 SPINACH 19.17 29.17 10.17 ND 14.50 45.69
ANTA U 3 C1 TOMATO 9.12 50.06 25.16 ND 16.60 59.88
3 C2 TOMATO 20.18 19.83 17.86 ND 12.17 38.84
NGWAR LAMBU 3 C1 ONOINS 6.12 95.00 5.19 ND 11.36 15.12
3 C2 ONOINS 16.17 48.19 10.08 ND 14.32 22.19
AMRY BARRACKS 3 C1 LETIVCE 20.19 52.08 10.03 ND 13.79 14.03
3 C2 LETIVCE 19.16 72.11 19.11 ND 11.00 42.19
ST LIMIT 73 44.61 14.36 0 13.78 100
MEAN TRACE OF Pb IN WATER, SOIL AND PLANTS ARE COMPARED LEAD (Pb)
WATER(Mg/L) SOIL (Mg/Kg) PLANT (Mg/Kg)
SAMPLE SITES MAN U 0.091 201.0 13.21
ANTA U 0.087 81.3 14.49
NGWAR LAMBU 0.065 47.18 12.84
ARMY BARRACK 0.035 52.13 13.00
ST LIMIT 5.000 100 13.78
LEAD CONCENTRATION IN WATER, SOIL AND PLANT
MEAN TRACE OF CU IN WATER, SOIL AND PLANETS ARE COMPARED COPPER (CU)
WATER(Mg/L) SOIL (Mg/Kg) PLANT (Mg/Kg)
SAMPLE SITES MAN U 0.042 530.15 11.68 ANTA U ND 180.5D 14.65 NGWAR LAMBU 0.012 75.32 11.15 ARMY BARRACK 0.031 87.10 19.68 ST LIMIT 0.2 100 73
COPPER CONCENTRATION IN WATER, SOIL AND PLANT
MEAN TRACE Ni IN WATER, SOIL AND PLANTS ARE COMPARED. NICKEL (Ni)
WATER(Mg/L) SOIL (Mg/Kg) PLANT (Mg/Kg)
SAMPLE SITES MAN U 0.65 56.61 40.11
ANTA U 0.50 42.83 34.95
NGWAR LAMBU 0.29 36.21 71.60
ARMY BARRACK 0.031 87.10 19.68
ST LIMIT 0.2 50 44.61
NICKEL CONCENTRATION IN WATER, SOIL AND PLANT
MEAN TRACE OF Zn IN WATER, SOIL AND PLANTS ARE COMPARED. ZINC (Zn)
WATER(Mg/L) SOIL (Mg/Kg) PLANT (Mg/Kg)
SAMPLE SITES MAN U 0.231 500.0 42.34
ANTA U 0.037 554.0 49.36
NGWAR LAMBU 0.008 190.0 18.66
ARMY BARRACK 0.004 93.17 28.11
ST LIMIT 0.05 300 100
ZINC CONCENTRATION IN WATER, SOIL AND PLANT
MEAN TRACE OF CHROMIUM (Cr) IN WATER, SOIL AND PLANTS ARE COMPARED CHROMIUM (Cr)
WATER(Mg/L) SOIL (Mg/Kg) PLANT (Mg/Kg)
SAMPLE SITES MAN U 0.41 420.0 9.76
ANTA U 0.19 276.0 21.51
NGWAR LAMBU 0.15 123.7 7.64
0.47 217.9 14.57
ST LIMIT 0.1 100 14.36
CHROMIUM CONCENTRATION IN WATER, SOIL AND PLANT
MEAN TRACE OF CADMIUM (Cd) IN WATER, SOIL AND PLANTS ARE COMPARED CADMIUM
WATER(Mg/L) SOIL (Mg/Kg) PLANT (Mg/Kg)
SAMPLE SITES MAN U 0.01 2 0.002
ANTA U ND 1 ND
NGWAR LAMBU ND ND ND
ARMY BARRACK 0.01 ND ND
ST LIMIT 0.01 3 0
CADMIUM CONCENTRATION IN WATER, SOIL AND PLANT
4.1 WATER SAMPLES
Results summarized in Table 1 indicate that concentration (Mg/L) of heavy metals in waste water used for irrigation were highest relatively for Ni, Cr and Zn. However, heavy metals concentrations in ground water meet the permissible limit of (FAO 1985) in Cu, Pb and Cd. Same defection was also obtained by Rattan et al and Singh et al who have found higher concentrations of heavy metals in sewage effluents when compared to the ground water overall concentrations of heavy metals in the different types of used water samples over the study area did not exceed the permissible limits like Cu and Pb with an average of 0.028 Mg/L and 0.0695 respectively and else does not exceed the allowable o.2mg / L (Cu) and 5.0 Mg/L (Pb) (FAO 1985). It’s know that chromium element is a toxic and has been considered one of a noxious elements carcinogens which cause lung carcinoma when is exposed to substantial concentrations. Then, it is often found in waste plants dyes, sewage waste discharge, and plastic and rubber waste and from cottage factories, electrical panel, batteries and other man – made waste (Refuse dump). The concentration (Abdul – Majid 1995)
FAD, User’s Manual For Irrigation With Pleated waste water (2003) it increase of this elements in the water sources happened as a result of across the sample collection sites. This result indicates that the use of this water for irrigation purposes could expose population to dangerous healthy risks and could damage the environment (Nikel 2006).
4.2 SOIL SAMPLES
Data presented in (Table 2) demonstrated that concentration of heavy metals in some selected soil sample where low while in other. However, chromium concentration was seen to be very high in all soil samples compared to 100mg/kg of WHO (FAO, – UNESCO; 1985) maximum allowable in soil. A study done by catterine (catterine 2009) in Nairobi has shown that chromium accumulation in the soils would be attributed to long term continuous application of waste water that indeed passes through sewage waste disturbed plants, lubricants letter and textile. The soil concentration of Cd, Zn and Ni were normal in most of the soil samples except for Cu which had relatively higher concentration in most of the soil, sample. Also, it was reported in Australia that irrigation with waste water may lead to accumulated heavy metals in soils, which can affect soil flora. This effect was attributed to toxic metals present in wastewater on soil microbes (Brookes, 1984) and may therefore result in crop condemnation over a period of time (Hanjaraa et al, 2012). It was inferred from the study that sludge of waste water and sewage waste discharge constitutes totes potentials source of heavy metals contamination. Hence may contribute an environmental and health challenges in the long – term. Therefore, enrichment of the soil with heavy metals confirms the sanitary risk related to waste water application in agricultural lands (Azita et al, 2008) then using of sludge as fertilizer source or as a mixed with soil at 50/50 is not suitable to produce quality vegetables nor, to protect the environment which is necessary for a sustainable life of animals and humans.
4.3 VEGETABLES SAMPLES
Heavy metal present in edible portions of studied vegetables are in tables 3. The vegetable concentrations of Ni, Cr, and Pb in every tested sample with respectively average 14.29, 34.62. 52.19, 13.37 and 13.26 (Mg/Kg) Ni, Cr and Pb had higher concentration of 52.19, 13.37 and 13.26 (Mg/Kg) above the FAO/WHO standard respectively (FAP/WHO). These economics were likely to be a health hazard to human consumers. They may further lead to toxicity not only fat plants and animals but also to consumers through the food chain (FAO/WHO, 2001). High concentration of Ni, was recorded in Spinach 56.17 (Mg/Kg) Tomato’s recorded high concentration in Cr of 25.16 (Mg/Kg).lead can be aborted through ingestion into the body. It is reported that young children absorb from 40% to 53% of lead ingested from food. It enters either a distribution to the soft tissues (blood liver, lung, spleen, kidney and bone marrow). Or a “slow turnover” pool with distribution mainly to the skeleton. This causes brithle bones and weakness in the wrists and fingers (Rabinowitz et al, 1976). According to Gupta et al (Gupta et al, 2010) among the heavy metals a foremen fronted Cr, is of greatest concern due to its high uptakes rates in plants, its accumulation in vegetles tissue and the possibility of implicating in a health hazard associated with the consumption of these heavy metal – contaminated vegetables over a long period. Several species of vegetable have the tendency to hyper accumulate certain of heavy metals it they are present in soil and water (Sheldon 2005). The concentration of Ni, Pb, and Cr that were obtained in every sample from the selected area are alarming therefore, it was concluded that Cr, Ni, and Pb, in Vegetables pose a real risk to consumers (Sheldon, 2005).
In all heavy metals such as cadmium and lead are common air pollutants being emitted mainly as result of various industrial activities. Although the atmosphere levels are low, they contribute to the deposition and build up in the soils. These important sources of these heavy metals in waste water which is a real health risk, if these waters are used for irrigation. It is obvious that water used in irrigation contains higher concentration of heavy metals due to some human activities like dumping of refuse, sewage waste e.t.c. into water bodies’ use for irrigation.
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