fertilizer usage and lead and cadmium contamination in
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Chemistry Thesis and Dissertations
2019-12-04
Fertilizer Usage and Lead and Cadmium
Contamination in Agricultural Soils and
Fertilizer Used In Sire Woreda, Arsi
Zone, Ethiopia
WORDOFA, SHURA
http://hdl.handle.net/123456789/10027
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i
BAHIR DAR UNIVERSITY
OFFICE OF GRADUATE STUDIES
COLLEGE OF SCIENCE
DEPARTMENT OF CHEMISTRY
Fertilizer Usage and Lead and Cadmium Contamination in
Agricultural Soils and Fertilizer Used In Sire Woreda, Arsi
Zone, Ethiopia
BY:-WORDOFA SHURA
September, 2019
BAHIR DAR
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BAHIR DAR UNIVERSITY
OFFICE OF GRADUATE STUDIES
COLLEGE OF SCIENCE
DEPARTMENT OF CHEMISTRY
Fertilizer usage and Lead and Cadmium Contamination in Agricultural
Soils and fertilizer Used, In Sire Woreda, Arsi Zone, Ethiopia
A Thesis Submitted to College of Sciences, Department of Chemistry in
Partial Fulfillment of the Requirements for the Degree of Master of Science
in Chemistry (inorganic Chemistry)
BY
WORDOFA SHURA TUFA
ADVISOR: Dr. GIRMA KIBATU(PhD, ASSOCIATE PROFESSOR)
September, 2019
BAHIR DAR, ETHIOPIA
iii
SCHOOL OF GRADUATE STUDIES
BAHIR DAR UNIVERSITY
Approval Sheet for Postgraduate Program Coordinator Office
I hereby certify that I have read and evaluated the thesis titled “Fertilizer usage and
Lead and Cadmium Contamination in Agricultural Soils and fertilizer used , in Sire
Woreda, Arsi Zone, Ethiopia" prepared under my guidance by WORDOFA SHURA TUFA. I
recommend that it be submitted as fulfilling the M.Sc. thesis requirement.
1. Girma Kibatu Berihie (PhD)
Advisor Signature Date
As a member of the Board of Examiners of the M.Sc. thesis Open Defense Examination,
we certify that we have read and evaluated the Dissertation prepared by Wordofa Shura
Tufa and examined the candidate. We recommend that the thesis be accepted as fulfilling
the thesis requirements for the degree of Master of Science in Inorganic Chemistry.
1. _______________________ ______________ ____________
Chairperson Signature Date
2. ________________________ _______________ _____________
Internal Examiner Signature Date
3. ________________________ ______________ ______________
External Examiner Signature Date
iv
STATEMENT OF THE AUTHOR
I declare and affirm that this thesis is my own work. I have followed all ethical and
technical principles of scholarship in the preparation, data collection, data analysis and
compilation of this Thesis. Any scholarly matter that is included in the Thesis has been
given recognition through citation.
This Thesis is submitted in partial fulfillment of the requirements for an M.Sc. degree at
Bahir Dar University. The Thesis is deposited in the Bahir Dar University Library and is
made available to borrowers under the rules of the Library. I solemnly declare that this
Thesis has not been submitted to any other institutions anywhere for the award of any
academic degree, diploma or certificate.
Name: Wordofa Shura Tufa Signature: ________________
Place: Bahir Dar University, Bahir Dar
Date of Submission: __________________
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DEDICATION
I dedicate this thesis manuscript to my Wife DEMITU LAMI, My Son SIFAN and
KENANI; plus My best Friend Birhanu Hunde for their continuous support and
encouragement during my study.
ii
BIOGRAPHICAL SKETCH
The author was born from his father Ato Shura Tufa and his Mother Lomi Chukala
in June 1975 E.C at Jawi Uduga Kebele in Sire Woreda Arsi Zone Oromia Region,
Ethiopia . He attended his elementary and junior school studies at Ufura Agemsa
Elementary School ; he then attended his secondary education at Sire Secondary
and Comprehensive High School. After completion of his secondary school education he
joined Jima teachers College (TTC) in October1995 E.C and graduated with diploma in
chemistry teacher. After that, he worked as Chemistry teacher in Arsi zone, Aseko
Woreda, Aseko high school and then, he joined Arba Minch University Summer
Program in July 1998 E.C and attended his undergraduate studies and received B.Ed.
degree in chemistry in September 2002 E.C. After completion of his undergraduate
study he changed to Sire Woreda until he joined the School of Graduate Studies at
Bahir Dar University in July 2008 EC to follow his M. Sc study in Chemistry.
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ACKNOWLEDGEMENTS
First of all I would like to thank my advisor Dr. Girma Kibatu Berihie for his useful
comments, suggestions during title selection, proposal preparation, for providing me
with immense supports as well as for guiding and supervising my work during the entire
period of the research and for shaping the final write-up of the thesis. My especial thanks
go to the Bahir Dar University, School of Graduate Studies, and Chemistry Department
for the financial and Equipment support. I would also like to express my special
appreciation to all my staff of Sire Preparatory School teachers and to all friends for
financial and material support for my study. Especially Bekelu shura, Eshetu Lammi, Ifa
Lammi ,Kasu Mihretu, Fikru Dejen ,Sintayehu Tadesse, Genene Tibebu ,Henok Dida,
Belete Urgie,Belete Taye and all my friends. Similarly I would like to extend my gratitude to
Sire Preparatory School Director Dejene Tesama who gave me PC for this work. I have
especial appreciation to my wife Demitu Lami and Sifan Hordofa for taking the whole
responsibility and in taking care of my children, for her unreserved encouragement
during this study.
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ACRONYMS AND ABBREVIATIONS
CRMs Certified Reference Materials
DAP DiammoniumPhosphate
ETHIOSIS Ethiopian soil information system
FAO united Nations food and agriculture organization
GPS Geographical Positioning System
ha hectare
ICP-OES Inductively Coupled Plasma Optical Emission Spectrometer
IFDC International Fertilizer Development Center
MoA Ministry of Agriculture
MoE Ministry of Education
NPSB Urea Diammonium Phosphate Ammonium Sulphate and Borax
MOARD Ministry of Agriculture and Rural development
G.C Gregorian calendar
E.C Ethiopian calendar
AISE Agriculture Input Supply Enterprise
WHO World Health Organization
iii
TABLE OF CONTENT
ACKNOWLEDGEMENTS ................................................................................................. i
ACRONYMS AND ABBREVIATIONS ........................................................................... ii
LIST OF TABLE ............................................................................................................... vi
LIST OF FIGURE............................................................................................................. vii
ABSTRACT ....................................................................................................................... viii
1. INTRODUCTION .......................................................................................................... 1
1.1. Crop Fertilization and Heavy Metal accumulation in Agricultural Soil .................. 1
1.2. Statement of the Problem ......................................................................................... 3
1.3. Significance of the Study ......................................................................................... 4
1.4. Research Questions .................................................................................................. 4
1.5. Objectives of the Study ............................................................................................ 5
1.5.1General Objective ................................................................................................ 5
1.5.2. Specific Objectives ............................................................................................ 5
2. LITRATURE REVIEW .................................................................................................. 6
2.3 .Heavy Metals Accumulations in Agricultural Soil of Ethiopia ............................... 9
2.4. Metal: Toxicity of Selected Heavy Metals in the Food Chain ............................... 10
2.4.1. Heavy Metals. .................................................................................................. 10
2.4.2. Heavy Metals in Fertilizers.............................................................................. 11
2.4.3. Effects on Soil ................................................................................................. 12
2.4.4. Effects on Plants .............................................................................................. 13
2.4.5. Effects on Human Health ................................................................................ 14
2.4.6. Selected Toxic Heavy Metals under Study...................................................... 14
2.4.6. Lead (Pb) and Lead (Pb) as Contamination ..................................................... 14
2.4.7. Cadmium (Cd) and Cadmium as Contamination ............................................ 15
2.4.8. Effect of Heavy Metals (Pb and Cd) on Living Organism .............................. 16
2.5. Regulatory limits trace elements content of fertilizers........................................... 17
2.6. Methodology in Fertilizers and Soils Analysis ...................................................... 18
2.6.1. Sample Decomposition Techniques ................................................................ 19
2.6.1.1. Dry ashing techniques ............................................................................... 20
2.6.1.2. Wet-ashing techniques .............................................................................. 21
iv
2.6.1.3. Microwave-assisted digestion ................................................................... 22
2.6.2. Measuring Methods: ICP-OES (Inductively coupled plasma - optical emission
spectrometry) ............................................................................................................. 23
2.7. Remediation of Cd and Pb polluted soils/ Bioremediation .................................... 23
2.7.1 Phytoremediation .............................................................................................. 24
2.7.2 Microbial remediation ...................................................................................... 24
2.7.3 Animal remediation .......................................................................................... 24
2.8 The effect of Fertilizer Used and Cultural Soil Fertility Management Practices in
the Area ......................................................................................................................... 24
3. MATERIALS AND METHODS ................................................................................ 25
3.1. Description of the Study Area ................................................................................ 25
3.1.1Population .......................................................................................................... 25
3.1.2Crop Production System of the Area ................................................................. 26
3.2. Sampling and Chemical Analysis .......................................................................... 26
3.2.1.Soil Sampling and Digestion ............................................................................ 26
3.2.3. Fertilizer Sampling and Digestion....................................................................... 28
3.2.4. Fertilizer Digestion .......................................................................................... 28
3.2.5. Equipment and Reagents ................................................................................. 29
3.3. Quality Control and Statical Analysis .................................................................... 30
4. RESULTS AND DISCUSSION .................................................................................. 32
4.1 The Extent of Fertilizer Use in the Study Area ....................................................... 32
4.2. Optimization for digestion procedure of Fertilizer and Soil samples .................. 34
4.3 .Method validation and quality control ................................................................ 34
4.3.1. Limit of detection ............................................................................................ 34
4.3.2. Limit of quantification ..................................................................................... 34
4.3.3. Precision and accuracy .................................................................................... 35
4.3.4. Regression analysis and detection limits ......................................................... 35
4.3.5. Accuracy and precision ................................................................................... 35
4.4. Heavy Metal Concentrations in Fertilizer and Soil ................................................ 36
4.4.1. Comparisons with Literature Value ................................................................. 39
4.5. Statical Data Analysis ............................................................................................ 41
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5. CONCLUTION AND RECOMENDATION ............................................................... 43
5.1. CONCLUTION ...................................................................................................... 43
5.2. RECOMENDATION ............................................................................................. 44
6. References ..................................................................................................................... 45
vi
LIST OF TABLE
Table 1: The Use and Health Effects of Some Heavy Metal on Human Being ............................. 17
Table 2: Regulatory limits for trace element content of fertilizers in different countries .............. 18
Table 3:Total Agriculture used in Arsi sire woreda ..................................................................... 26
Table 4: pH Determined in Soil sample ......................................................................................... 27
Table 5: Fertilizer digestion and time it taken ............................................................................... 29
Table 6: Recovery test for fertilizer (NPSB) ................................................................................. 30
Table 7: Pb recovery test for Soil C1 (Cirao) ................................................................................ 31
Table 8: Types of fertilizers and fertilizer consumptions trend of the study area (Arsi Sire
Woreda) from (in quintals) ............................................................................................................ 32
Table 9: Macronutrient composition of Fertilizers used in Sire Woreda, Arsi Zone 2006-2011 E.c
....................................................................................................................................................... 33
Table 10: Linear regression equations, coefficient of determination, instrumental detection limit
(IDL), limit of detection (LOD), and limit of quantification (LOQ) ............................................. 35
Table 11: The content of Cd and Pb (mg/Kg) indifferent soil site of Sire Woreda, Arsi Zone. .... 37
Table 12: The content of trace elements ( Cd and Pb) levels of Fertilizers used In sire Woreda
Arsi Zone , ( mg/Kg) from Doublet measurements ...................................................................... 38
Table 13: Heavy metal Pb an Cd in soil determination by some country ...................................... 40
Table 14: Concentrations of trace elements in fertilizers analyzed in this study and in some other
countries (mg/kg) ........................................................................................................................... 41
vii
LIST OF FIGURE
Figure 1: Location of study area (Blue color is soil site selected) .................................... 25
Figure 3: Digestion process .............................................................................................. 29
Figure 4. Calibration Graph .............................................................................................. 31
Figure 5: Fertilizer consumption in the Area .................................................................... 33
viii
ABSTRACT
The presence of heavy metal Cadmium and Lead in relatively low concentrations in
fertilizers as impurities can be toxic to soil, plants and food produced and to the
environment; and consequently to the animal-human health and productivity. The aim of
this study was to evaluate Fertilizer usage, Lead and Cadmium Contamination in
Agricultural Soils and fertilizer, in Sire Woreda, Arsi Zone, Ethiopia. Samples of
fertilizers used in the area including Urea, Diammonium Phosphate (DAP) and a
blended fertilizer Urea, Diammonium Phosphate ,Ammonium Sulphate with Borax
(NPSB) and soil from four(4) site total of twelve (12) were collected, wet digested in
acids(3HNO3 : HCl) and total concentrations of cadmium and lead in fertilizers and soil
were determined using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-
OES).The total contents of cadmium in DAP, Urea, and NPSB were found to be (23.25 ±
5.21),(Not detected), and (30.02 ± 4.69) in mg/kg respectively. The total contents of
Lead in DAP, Urea, and NPSB were found to be (30.17 ± 0.16), (13.8 ± 6.53), and (86.37
±49.87) in mg/kg respectively. .The total contents of lead in Soil were found to be Michika
(40. 7 ± 0.16 ) ,Bale( 22.48 ± 0.34) ,Shameda (S)( 18.73 ± 0.09 ) , Cirao (C) (9.83± 0.11)in
mg/kg respectively. The concentration of cadmium in Soils are not detected .Long term
applications of such impure fertilizers in Soil may lead to accumulation of cadmium and
Lead in the Soil and food system. The high concentration of toxic heavy metals in fertilizers
may lower the soil productivity, quantitative and qualitative value of food produced by and may
cause poisoning effects to animal-human health and productivity. Thus, the quality of
fertilizers used in ones country has to be regulated periodically for both essential and
non-essential trace metal levels for sustainable use in food production.
Keywords: Cadmium and Lead; Fertilizers; Soil and ICP-OES
1
1. INTRODUCTION
1.1. Crop Fertilization and Heavy Metal accumulation in Agricultural Soil
Soil is unconsolidated minerals and organic material found on the immediate earth
surface that serves as a natural medium for plants growth and other developmental
activities [1].Soil is composed of mineral constituents, organic matter (humus), living
organisms, air, and water, and it regulates the natural cycles of these components [2].The
soil is a very essential component for all the living organisms. Especially for plants, it’s
considered as the basic living factor. Soil serves as a nutrient media for the growth of
plants. The soil is essential for agriculture production and it also maintained all life form.
The quality of water and air is of immediate concern for most people because we all
consume these natural resources on a daily basis. The soil is the biogeochemical engine
of Earth’s life support system. It provides us with food, fodder, fiber, and fuel .Soils
deliver ecosystem services that cannot be easily traded in markets. These life-supporting
functions include, for example, recycling of carbon and essential nutrients of all
living materials, filtering, and storage of water, regulation of the atmosphere and
biological control of pests [3].Heavy metals occupy a special position in soil chemistry
because they play very important physiological roles in nature. Generally, topsoil layer
contain largest amount of pollutants. The contaminant concentration in soil mainly
depends on the adsorption properties of soil matter. The solubility of heavy metal ions in
soil was mainly influence by many factors such as pH, conductivity, moisture content. As
a result of increasing anthropogenic activities, heavy metals pollution of soil, water, and
atmosphere represents a growing environmental problem affecting food quality and
human health. Heavy metals may enter the food chain as a result of their uptake by edible
plants [4]
The world population continues to increase at an alarming rate. As a result, new farmland
in previously non-arable locations will be called for to help support this growing
population, and more fertilizers will have to be utilized to increase food production [5].
There are concerns about whether continuous use of such fertilizers over a long period of
time will cause an accumulation of metals to high levels, thereby increasing risk to
2
environmental and human health [6]. Fertilizers and soil amendments can contain
significant amounts of potentially hazardous trace elements of geologic or man-made
origin. The risk of soil and environmental pollution through the application of these
materials to agricultural lands has therefore raised some concern [7]. Inorganic fertilizers
contain elevated quantities of metals like Cd, Pb, as, and other trace elements of
environmental relevance.
Metals can be toxic to humans and plants; therefore a long-term application of
inorganic fertilizers, organic waste, and pesticides to soils requires a detailed risk
assessment of heavy metal accumulation in agricultural lands [8] .Cadmium and lead
concentrations in soils in many countries are increasing due to inadvertent additions in
fertilizer, biosolids, and soil amendments, as well as additions from the atmosphere [9].
The management of phosphate (P) fertilizer application, both in the short and long term,
can influence the potential accumulation of Cd and Pb in foods. The Cd and Pb added to
agricultural systems in P fertilizers accumulates over time if application rates are in
excess of Cd and Pb removal as an effect of long-term P fertilizer application
[10,11]predicated that P fertilizers, in particular, are an important source of metals,
particularly for Zn, Cu, Pb, and Cd, entering agricultural soils. High application rates of
nitrogen fertilizer to agricultural soils resulted in increased accumulation of some heavy
metals such as Cd and Pb in agricultural products [12].
The total concentration of Pb and Cd in a soil comprises the contribution from the
geological parent material together with inputs from extraneous sources, which for the
most part are Phosphorus Fertilizer in origin. The amounts of Pb and Cd accumulating in
a soil from environmental pollution will depend on the scale of emissions from the
respective sources, the transport of the metal from the source to the site and the retention
of the metal once it has reached the soil. The fate of Pb, Cd and all other heavy metal
pollutants in the soil depends mainly on the relative balance between sorption, leaching,
and plant uptake. These processes are strongly affected by soil properties such as pH,
redox status and the contents of organic matter, clay, hydrous oxides, and free carbonates.
Hence, there will be marked variations in the fate of the metal between distinctly
3
different types of soils, such as those under forest and intensively cultivated arable
land.[13].
During the past few years, total fertilizer use in Ethiopia has increased significantly. The
quality of fertilizers being sold to the farmers is often exploited by the unscrupulous
elements. Recently reports regarding fertilizer adulteration are very common. Depending
on the source, harmful heavy metals like cadmium (Cd), arsenic (As), chromium
(Cr), lead (Pb), and mercury (Hg) may be introduced into the soil along with the
fertilizer, which are then absorbed by growing crop plants causing significant health
related [14].Fertilizer is the most critical and costly input for sustaining agricultural
production and ensuring food security. Supplying crops with essential (macro and
trace) elements is the major aim of any type of fertilizer. However, fertilizers may also
contain less beneficial elements, particularly heavy metals [15] .Adulteration in fertilizers
is one of the emerging problems for intensive agriculture in World and Ethiopia.
1.2. Statement of the Problem
Fertilizers are applied to increase soils productivity by increasing soil fertility and plant
production. Enlarged food production volume begins by increasing crop yields through
the use of higher amounts of fertilizers. Although fertilizers are predominantly beneficial
in terms of plant production, they may also be potentially harmful as substances
contaminating soil and both groundwater and surface waters. Fertilizers usually get
insufficiently purified in the manufacturing process and therefore often contain various
levels of impurities, including Pb and Cd depending on the quality of raw materials used
for their production. As a result of accumulation of heavy metals in soil and plants toxic
effects of these elements can become very harmful [16]. .Farmers in the study area
usually apply large amounts of fertilizers to achieve maximum yields. Based on
experience from the area, interview with farmers and the information available at
agricultural centres, the application of fertilizers in this area is not properly managed
based on quality control and specific requirements and follow general prescriptions,
which can result in high concentration of heavy metal in the soil. From the above
concentration of Pb and Cd and toxic of metals found in soil and plants is greatly varies
.Heavy metals with a range of concentration from low to high. Related to this, a research
4
has not been done to determine the level of heavy metal and toxic metals in fertilizers
used in sire woreda and soil found in “sire Woreda”. So, this study attempt to determine
the level Pb and Cd in soil and fertilizers sire woreda.
1.3. Significance of the Study
Adding fertilizers to soil and plants is a common agricultural practice aimed at improving
soil fertility and plant production. However, they become toxic at high concentration
[17]. Heavy Metals cannot be degraded including bio treatment and are very toxic even at
low concentration (1.0-10.0 mg/L) [18] .Heavy metal toxicity can result in damaged or
reduced mental and central nervous function, lower energy levels, and damage to blood
composition, lungs, kidneys, liver, and other vital organs[19]
Nowadays, Toxic heavy metals have adverse effects on plants, animals and humans.
Excess heavy metals in the soil originate from many sources, which include the use of
fertilizers and pesticides, atmospheric deposition, sewage irrigation, improper stacking of
the industrial solid waste, mining activities [20]
Therefore, the main purpose of this study was to determine the levels of Pb and Cd in
inorganic fertilizers (DAP,UREA and NPSB) and Agricultural soil that were commonly
used for Agriculture in Sire Woreda and to provide reliable data, which can be
compared with existing guidelines and limits set by some countries and international
organization. Hence, the results of this study could very important from health and
environmental point of view in terms of using fertilizers for crop production that affect
soils
1.4. Research Questions
This study was attempt to answer the following basic research questions
1. Does the fertilizer (DAP, UREA and NPSB) use in the area accumulated Pb and
Cd as impurity?
2. Does the Agriculture soil contained Pb and Cd?
3. Does the Pb and Cd accumulate in fertilizers and Agriculture soil is bellow or
above Regulatory limits?
5
1.5. Objectives of the Study
1.5.1General Objective
The main objective of the this study was to analyze selected heavy metals Pb &Cd in
fertilizers and in Soil Sire Woreda, Arsi Zone, Ethiopia.
1.5.2. Specific Objectives
To determine the concentrations of some selected heavy metals Pb, Cd in Samples
of soil using ICP OES
To determine the concentrations of selected heavy metals Pb, Cd in sample of
fertilizers (DAP, UREA ,NPSB) using ICP OES
To compare the levels accumulation of heavy metals Pb and Cd in the soil ,
fertilizers and with that of the data in the literature
6
2. LITRATURE REVIEW
2.1. Fertilizers over View
It knows that it is necessary to apply a fertilizer to the soil to keep cultivated plants
healthy. As they grow, plants extract nutrients they need from the soil. Unless these
nutrients are replenished, plants will eventually cease to grow. In nature, nutrients
are returned to the soil when plants die and decay. However, this does not occur
with cultivated plants. Humans cultivate plants mainly for food, either for themselves or
for livestock. When cultivated plants are harvested, the nutrients that the plants
extracted from the soil are taken away. To keep the soil productive, it is
necessary to replace these nutrients artificially. The kinds and amounts of nutrients
that plants need have been determined and can be supplied by applying to the soil
substances that contain these nutrients[21]
The sources of nitrogen used in fertilizers are many, including ammonia (NH3),
Diammonium phosphate ((NH4)2HPO4), ammonium nitrate(NH4NO3), ammonium
sulfate ((NH4)2SO4), calcium cyan amide (CaCN2), calcium nitrate (Ca(NO3)2), sodium
nitrate (NaNO3), and urea (N2H4CO). Phosphorus is generally supplied as a
phosphate, such as Diammonium phosphate ((NH4)2HPO4) or calcium dihydrogen
phosphate (Ca(H2PO4)2). Potassium comes from potassium sulfate (K2SO4) or
potassium chloride (KCl), which is also called muriate of potash. The phosphorus content
of a fertilizer is specified as the amount ofP2O5because this is the anhydrous form of
phosphoric acid. In this sense it is the most concentrated form of phosphate,
which is the form of phosphorus required by plants. The potassium content is
designated in terms ofK2O, which is also called potash. Potash is a component of the
residue left when plant materials are incinerated. The spreading of ashes on fields is an
ancient method of replenishing potassium. Modern chemical fertilizers usually contain
KCl instead, but the potassium content is still specified as the equivalent amount of
potash. Potassium chloride is 52% by weight K. Potash is 83% potassium. Thus, KCl
provides only about 2/3 as much potassium as the same weight ofK2O. Thus, if a
fertilizer is 25% KCl by weight, its potassium rating, based on potash, would be only16%
[21, 22].Generally Fertilizer Product covers Nitrogen, Potassium, Phosphate fertilizers.
7
2.2. Crop Production and Fertilizer used In Ethiopia
Chemical fertilizer was first introduced to Ethiopia under the Freedom from Hunger
Program of the FAO in the late 1960s (Agricultural Transformation Agency, 2012 -
unpublished). Despite successful field demonstrations and several deliberate policy
attempts to increase fertilizer use in the late 1970s and early 1980s, fertilizer application
levels remained very low (Agricultural Transformation Agency, 2012 -
unpublished). Chemical fertilizer is primarily used in cereal production in Ethiopia.
According to Ministry of Agriculture and Rural Development (MoARD) statistics,
cereals account for 90 percent of the country's total chemical fertilizer application; and
during 2005/2006–2010/2011 G.C, only two regions, Oromia and Amhara, accounted for
70 percent of total use, with Oromia alone accounting for about 40 percent. The shares of
the other two major cereal-growing regions are the Southern Nations, Nationalities, and
Peoples’ Region (SNNPR) and Tigray were 10 and 3 percent, respectively [21].
Fertilizer markets in Ethiopia have been controlled by the government through its input
marketing agency, called Agricultural Input Supplies Corporation, later renamed as
Agricultural Input Supplies Enterprise in 1992. This agency had its own marketing
network throughout the country, which included marketing centers and service
cooperatives for distributing fertilizers to the farmers. As in many other African
countries, Agricultural Input Supplies Corporation’s controlled marketing was inefficient,
involved large direct subsidies, and incurred large administrative costs [21].
In the new marketing system introduced in 1992, the transitional government articulated
its desire to end government monopoly as part of its overall market liberalization policies.
The private-sector entry, however, was slow in the early years: Only one private
company (Ethiopian Amalgamated Limited) actively participated in fertilizer marketing
up until 1996. Subsequently, three other companies entered into the markets and
attempted to develop their own marketing network. Around this time, a new breed of
companies, owned by the regional governments, started to flourish. The first such
company to enter was Ambassel Trading, a private limited company owned by the
Amhara regional government. In the initial years, until 1995, Ambassel worked mainly as
8
an agent to AISE, but it began importing in 1996 and started serving as the sole
distributor and wholesaler of AISE in the Amhara region [21,22].
In Ethiopia, since 2007, fertilizer imports have been controlled by Agricultural Inputs
Supply Enterprise (AISE) and cooperatives. Regional governments in Ethiopia have also
intervened in fertilizer supply, initiating a 100 percent credit guarantee scheme on
farmers’ fertilizer purchase since 1994 [23]. As of 2007, two regional holding
companies (Ambassel and Wondo), the fertilizer parastatal (AISE), and cooperative
unions accounted for 100 percent of fertilizer imports and local distributions. The
total fertilizer consumption in Ethiopia has increased from 250,000 tons in 1995 to
400,000 tons in 2008 [23]. However, the intensity of the fertilizer use has increased only
marginally over the past decade from 31 kilograms per ha in 1995 to 36 kilograms per ha
in 2008 [24].
Soil is the primary source of plant nutrients. It is composed of minerals, organic matter,
air and water [25]. For proper growth of the Plant, the nutrients in the soil must be in
plant available forms. Nutrients in the soil can be in one of the following forms: nutrients
in the soil solution; nutrients adsorbed onto the exchange complex; nutrients bound in
water-insoluble forms but easily mobilizable nutrient sources. Only the first fraction is
plant available. The availability of other forms of nutrients in the soil depends on soil
physical, chemical and biological properties [26].Soil physical properties such as soil
texture and soil structure are of special importance for soil fertility and thus for plant
growth by providing the movement of air, water and nutrients so that plants use them
easily. Soil texture is related to nutrient and moisture holding capacity of the soil,
aeration and drainage. Salty soils are more suitable than sandy and clay soils for crop
production. On the other hand, soil structure which, is a measure of soil particle
aggregation is related to good porosity. Moisture retention capacity and drainage.
Granular structure having rounded porosity is considered as good for crop growth [27].
The availability of plant nutrients is also dependent on soil chemical properties like soil
reaction which is a measure of soil acidity or alkalinity that is expressed in pH. The pH
for optimum crop production is 6.5 - 7.5. At very acidic soil or low PH, the availability of
9
P is rendered because of precipitations as insoluble Fe or Al phosphate and at higher PH,
P precipitates as calcium phosphate. Soil reaction has also effect on the biological
properties. At intermediate PH, soil microbes are able to break down soil organic matter
into plant available forms of nutrients such as N, P and S [26]. Cations Exchanging
Capacity of the soil is another chemical property of the soil and it is the ability of a soil
to retain actions such as potassium (K+ ), ammonium (NH4+ ), hydrogen (H+), calcium
(Ca+2) and magnesium (Mg+2 ) in a form that is available to plants [28].
Trace elements accumulate in living organisms any time they are taken up faster than
they are broken down (metabolized) or excreted. The soil to plant transfer factor is one of
the most important parameters used to estimate the possible accumulation of toxic
elements. Several studies have indicated that crops grown on soils contaminated with
heavy metals( Pb& Cd) have higher concentrations of heavy metals than those grown on
uncontaminated soil and these elements accumulated in the soil directly enter food
chains, thus endangering herbivores, indirectly carnivores and the top consumer humans
[29,30]. Accumulation of heavy metals can also cause a considerable detrimental effect
on soil ecosystems, environment and human health due to their mobility and solubility
which determine their speciation [31].
Trace elements (heavy) metals exist in one of four forms in the soil: mineral, organic,
absorbed (bound to soil), or dissolved. Absorbed metals represent generally very tightly
bound to soil surfaces. Although mineral, organic, and absorbed metals are not
immediately absorbed by plants, they can slowly release metals into solution [32].
Migration of metals in the soil is influenced by physical and chemical characteristics of
each specific metal and by several environmental factors such as soil type, total organic
content, redox potential, and pH. Although heavy metals are generally considered to be
relatively immobile in most soils, their mobility in certain contaminated soils may exceed
ordinary rates and pose a significant threat to water quality [33].
2.3 .Heavy Metals Accumulations in Agricultural Soil of Ethiopia
Food is the most common source of heavy metal for humans around the world,
due to crops grown on heavy metal contaminated soils .Metals are bind with negative-
10
charged particles of soil, once metals can detach, enter in the soil solution and become
bio-available to plants . Once uptake by plants, this metal may accumulate in plant
tissues and prejudice food security. In populations which consuming regionally foods the
contamination risks are higher. For example, subsistence farmers who live in soil
contamination. In this case, the heavy metal in their diet is not diluted with food from
other non-contaminated areas, while food source produced in contaminated and non-
contaminated areas and heavy metal content predominate in low levels in
developed cities .Agricultural practices add heavy metal in soil and recent studies
indicate health risks in consumer cereals and vegetables cultivates in contaminated
soils .Plants may uptake essential and nonessential elements from soils in response to
electrochemical potential gradient of the plasma membrane in the root cells or by
diffusion of elements in the soil. The level of heavy metals accumulation differs
between species and there are different defenses strategies to plant avoid heavy metal
contamination [34]
Synthetic fertilizer use for agricultural development in support of food security and for
maintaining soil productivity in Ethiopia. The consumption of synthetic fertilizers in
Ethiopia is increasing from less than 200Mt in the year 2002 to more than 700Mt in the
year 2013 [13]
In the study area, fertilizer consumption also shows increasing trend [35]. Fertilizer use in
Ethiopia has focused mainly on the use and application of nitrogen and phosphorous
fertilizers in the form of UREA and Di-ammonium phosphate (DAP) regardless of
differences in crop need, soil types and agro-ecology [36]. In Ethiopia, imported
fertilizers are regulated by Ethiopian standards Authority and the standards for fertilizers
includes storage, packaging and macronutrient content analysis and some impurity
specification
2.4. Metal: Toxicity of Selected Heavy Metals in the Food Chain
2.4.1. Heavy Metals.
Metals are elements, present in chemical compounds as positive ions, or in the form of a
cations (+ ions) in solution. Heavy metals are among the most serious environmental
11
pollutants due to their high toxicity, abundance and ease of accumulation by various plant
and animal organisms. Increasing of heavy metals in soil can be attributed to the
contribution of effluent from waste water treatment plants, industries, mining, power
stations and agriculture [37]. Heavy metals are extremely persistent in the environment.
They are non-biodegradable and non-thermo degradable and therefore readily accumulate
to toxic levels [38].
Nowadays, Toxic heavy metals have adverse effects on plants, animals and humans.
Excess heavy metals in the soil originate from many sources, which include the use of
fertilizers and pesticides, atmospheric deposition, sewage irrigation, improper stacking of
the industrial solid waste, mining activities [20].
2.4.2. Heavy Metals in Fertilizers
Adulteration of fertilizers involves the practice of adding extraneous material to a
standard fertilizer to lower its quality. According to routine tests carried out by Soil
Resource Development Institute (SRDI), nearly 40% of all fertilizers used by farmers are
adulterated (FRG, 2012). The soil has been over exploited to produce more food from the
limited areas of land for the growing population. It is estimated that 54–58% of the Cd
and Pb found in the environment comes from the application of mineral phosphate
fertilizers [39]
Fertilizers are applied to increase soils productivity by increasing soil fertility and plant
production. Enlarged food production volume begins by increasing crop yields through
the use of higher amounts of fertilizers. Although fertilizers are predominantly beneficial
in terms of plant production, they may also be potentially harmful as substances
contaminating soil and both groundwater and surface waters. Fertilizers usually get
insufficiently purified in the manufacturing process and therefore often contain various
levels of impurities, including heavy metals, depending on the quality of raw materials
used for their production [36, 40].
Fertilizers in the broadest sense are products that improve the levels of available plant
nutrients and/or the chemical and physical properties of soil, thereby directly or indirectly
enhancing plant growth, yield, and quality [31] .Fertilizers play significant role in
12
increasing yield of crops and the quality of crops by supplying essential nutrients. This
will be achieved when fertilizers are used efficiently. The production of high yield and of
high quality crops is the basis for human and animal nutrition. Efficient use of fertilizers
involves application fertilizers at the right product, at the right amount, at the right time,
and at the right place based on soil test and plant needs [41].
As a result of this, many researches [24, 42] recommended the need for intensification of
synthetic fertilizer use for agricultural development in support of food security and for
maintaining soil productivity in Ethiopia. The consumption of synthetic fertilizers in
Ethiopia is increasing from less than 200Mt in the year 2002 to more than 700Mt in the
year 2013 [13]
In the study area, fertilizer consumption also shows increasing trend [35]. Fertilizer use in
Ethiopia has focused mainly on the use and application of nitrogen and phosphorous
fertilizers in the form of UREA and Di-ammonium phosphate (DAP) , NPS, NPSZn, and
NPSB regardless of differences in crop need, soil types and agro-ecology [36]. In
Ethiopia, imported fertilizers are regulated by Ethiopian standards Authority and the
standards for fertilizers includes storage, packaging and macronutrient content analysis
and some impurity specification. However, no relatively comprehensive research on trace
elements (Cd and Pb) concentration in inorganic fertilizers and Agricultural soil has been
done in the Sire Woreda, Arsi zone, in particular.
2.4.3. Effects on Soil
Heavy metal contamination in soils is a major environmental concern that affects
large areas worldwide. Agricultural practices have been the main source of heavy metals
in soil such as lead and cadmium, Soil contamination by heavy metals is of most
important apprehension throughout the industrialized world . Heavy metal pollution
not only result in adverse effects on various parameters relating to plant quality and
yield but also cause changes in the size, composition and activity of the microbial
community[20]. Therefore, heavy metals are considered as one of the major sources of
soil pollution. Heavy metal pollution of the soil is caused by various metals especially
Cu, Ni, Cd, Zn, Cr, and Pb [11]. The adverse effects of heavy metals on soil biological
13
and biochemical properties are well documented. The soil properties i.e. organic matter,
clay contents and pH have major influences on the extent of the effects of metals
on biological and biochemical properties [14].Heavy metals indirectly affect soil
enzymatic activities by shifting the microbial community which synthesizes enzymes
[15]. Heavy metals exhibit toxic effects towards soil biota by affecting key
microbial processes and decrease the number and activity of soil microorganisms
2.4.4. Effects on Plants
Some of these heavy metals i.e. As Cd, Hg, Pb or Se are not essential for plants
growth, since they do not perform any known physiological function in plants.
Others i.e. Co, Cu, Fe, Mn, Mo, Ni and Zn are essential elements required for normal
growth and metabolism of plants, but these elements can easily lead to poisoning
when their concentration greater than optimal values.[41]
Uptake of heavy metals by plants and subsequent accumulation along the food
chain is a potential threat to animal and human health [24]. The absorption by plant
roots is one of the main routes of entrance of heavy metals in the food chain [9].
Absorption and accumulation of heavy metals in plant tissue depend upon many factors
which include temperature, moisture, organic matter, pH and nutrient availability. Heavy
metal accumulation in plants depends upon plant species and the efficiency of
different plants in absorbing metals is evaluated by either plant uptake or soil to plant
transfer factors of the metals [10]. Elevated Pb and Cd in soils may decrease soil
productivity, and a very low Pb concentration may inhibit some vital plant processes,
such as photosynthesis, mitosis and water absorption with toxic symptoms of dark
green leaves, wilting of older leaves, stunted foliage and brown short roots
[8].Heavy metals are potentially toxic and phyto toxicity for plants resulting in
chlorosis, weak plant growth, yield depression, and may even be accompanied by
reduced nutrient uptake, disorders in plant metabolism and reduced ability to fixate
molecular nitrogen in leguminous plants [13]. Seed germination was gradually
delayed in the presence of increasing concentration of lead (Pb)
14
2.4.5. Effects on Human Health
The plant uptake of heavy metals from soils at high concentrations may result in a
great health risk taking into consideration food-chain implications. Utilization of food
crops contaminated with heavy metals is a major food chain route for human exposure.
The food plants whose examination system is based on exhaustive and continuous
cultivation have great capacity of extracting elements from soils. The cultivation of
such plants in contaminated soil represents a potential risk since the vegetal tissues can
accumulate heavy metals [9]. Heavy metals become toxic when they are not metabolized
by the body and accumulate in the soft tissues [43]. Chronic level ingestion of toxic
metals has undesirable impacts on humans and the associated harmful impacts
become perceptible only after several years of exposure[10].
2.4.6. Selected Toxic Heavy Metals under Study
Heavy Metals are defined as those elements which include Cadmium (Cd), Lead (Pb),
Zinc (Zn), Mercury (Hg), Arsenic (As), Silver (Ag), Chromium (Cr), Iron (Fe) and
Platinum groups [17]
Heavy Metals cannot be degraded. Most of these metal ion (Cd, Cu, Zn, Hg, As, Ag, Cr
and Fe) can be including bio treatment and are very toxic even at low concentration (1.0-
10.0 mg/L) [18]. Heavy metal toxicity can result in damaged or reduced mental and
central nervous function, lower energy levels, and damage to blood composition, lungs,
kidneys, liver, and other vital organs [19]
2.4.6. Lead (Pb) and Lead (Pb) as Contamination
Lead is a naturally occurring heavy metal. It is seldom found in its elemental form;
however, it is part of several ores including its own (galena, PbS). Pb has many industrial
and commercial uses. It is used in the production of ammunition, as solder, in ceramic
glass, and the production of batteries .Other sources of Pb in the environment include
automobile exhaust, industrial wastewater, wastewater sludge, and pesticides [44]
Because of its high toxicity, the use of lead in some products has been discontinued. Lead
is no longer used in house paint because of the concern about the toxic effects of the
15
accidental ingestion of paint chips or the inhalation of aerosolized lead from decaying
paint. Pb behavior in soil is similar to Cd behavior in soil. However, Pb was less mobile
in soil than Cd. Very little of either Pb or Cd was leached through the soil profile. In fact,
more Pb and Cd were removed from the soil by plants than was leached through the
profile [43] several factors may influence the content and distribution of heavy metals in
soil. Some of these factors are parent material, organic matter, particle size distribution,
drainage, pH,[45]. Strong ionic bonds are formed between the cation and the clay
particle. Acidic conditions will cause desorption of these cations into solution making
them available for uptake by plants. Decreased growth and yield have been observed in
plants grown in Pb contaminated soils.[44] showed a significant decrease in plant
biomass yield with increasing Pb treatments that varied with soil type. The highest
adverse effects were on those plants grown in soils with high clay content. [43]Also
showed decreased plant growth and yield in soils with Pb contamination.
Exposure to its high levels can severely damage the brain, kidneys and ultimately cause
death and long-term exposure result in decreased performance in some tests that measure
the functions of the nervous system; weakness in fingers, wrists, or ankles; small
increases in blood pressure; and anemia. Others are abdominal pain, anemia, arthritis,
attention deficit, back problems, blindness, cancer, constipation, convulsions, depression,
diabetes, migraine headaches, thyroid imbalances and tooth decay (NAS/NRC, 1999).
2.4.7. Cadmium (Cd) and Cadmium as Contamination
Cadmium (Cd) is also a hexagonal crystal, silver white malleable and a d-block metal.
This is a transition metal belonging to period 5 and group 12. It has atomic number 48,
atomic mass 112.2, density 8.65 g/cm3, melting point 594 K and boiling point of 1038
K[46]. Cadmium occurs as Cd+2 .It is not Known for any biological function. It is used in
Ni/Cd batteries which are rechargeable batteries used for high outputs. It is also used as
pigments and stabilizers in polyvinyl plastics and as coating to resist corrosion in vessels
and vehicle. Agricultural fertilizers, pesticides, sewage sludge and deposition of
industrial wastes increases total concentration of Cd in the soil [47].
16
Cadmium is a toxic metal and can cause serious health problems. Recently attention has
been focused on its availability in soil, water, milk, dietary products, medicinal plants,
herbal drugs, etc. The most common sources for cadmium in soil and plants are
phosphate fertilizers, non-ferrous smelters, lead and zinc mines, sewage sludge
application and combustion of fossil fuels [24]. Critical levels for cadmium in soil are
between 3-5 mg/kg. This level, in most cases, it cannot cause toxic or excessive
accumulation concentration in plants; the lowest level of the element concentration in
plants that can cause crop yield reduction is between 5-30 mg/kg. Surprisingly, a small
amount of cadmium was detected in the stem, leaves, and seeds of the plant sample
collected from polluted areas. This may be due to the polluted air from the surrounding
area. The major route of cadmium exposure for the general population is via food. An
increase in soil Cadmium content generally results in an increase of plant uptake of
Cadmium although some soil and plant factors may influence Cadmium accumulation by
plants. Crops grown in Cadmium contaminated areas have been found to contain elevated
Cadmium content compared with normal levels. Therefore, human Cadmium exposure
via food in contaminated areas can be many times above normal intakes and lead to
Cadmium toxicity. Cadmium is used in plating, alloying, pigments, plastics and batteries.
Cadmium is known to be toxic for living organism even if it is present in low levels.
Cadmium is obtained from the ore minerals Shalerite (ZnS, CdS) and Greenockite (CdS)
[47]
Cadmium is very toxic, its long-term exposure to lower levels leads to a build-up in the
kidneys and possible kidney disease, lung damage, and fragile bones. Hypertension,
arthritis, diabetes, anaemia, cancer, cardiovascular disease, cirrhosis, reduced fertility;
hypoglycaemia, headaches, osteoporosis, kidney disease, and strokes are its some odd
long term results (NAS/NRC, 1999).
2.4.8. Effect of Heavy Metals (Pb and Cd) on Living Organism
Living organisms require varying amounts of heavy metals. Iron, cobalt, copper,
manganese, molybdenum, and zinc are required by humans. All metals are toxic at higher
concentrations. Excessive levels can be damaging to the organism. Other heavy metals
17
such as mercury, plutonium, lead and cadmium are toxic metals that have no known
vital or beneficial effect on organisms, and their accumulation over time in the bodies of
animals can cause serious illness.[48]
Heavy metals disrupt metabolic functions in two ways:
i. They accumulate and thereby disrupt function in vital organs and glands such as
the heart, brain, kidneys, bone, liver, etc.
ii. They displace the vital nutritional minerals from their original place, thereby,
hindering their biological function. It is, however, impossible to live in an
environment free of heavy metals. There are many ways by which these toxins
can be introduced into the body such as consumption of foods, beverages, skin
exposure, and the inhaled air[49]
Table 1: The Use and Health Effects of Some Heavy Metal on Human Being
Heavy metal Uses Health effects Reference
Cadmium Electroplating ,mineral
processing ,and battery
manufacturing
Cancer ,lung
insufficiency
disturbance in liver
&kidney damage
[33]
Lead Metal plating, texture,
battery manufacturing and
petroleum industry
Spontaneous
abortion ,damage
nervous system,
kidney &brain
damage
[29]
2.5. Regulatory limits trace elements content of fertilizers
It is known that fertilizers, in addition to nutrients guaranteed by manufacturer, can
contain trace elements and other impurities arising from the raw materials from which
fertilizer is obtained and from manufacturing process [13]. However, trace elements label
is not usually included unless the element is added deliberately as micronutrient source.
In most countries, the effectiveness and safe use of substances to be registered as
18
fertilizers is ensured by law. Therefore, many countries have established regulations with
respect to maximum input rates of trace elements into agricultural soils and maximum
concentration limits in fertilizers [29].Table-2 shows maximum concentration of trace
elements as impurities in inorganic fertilizers in some countries.
Table 2: Regulatory limits for trace element content of fertilizers in different countries
Country Element Value Units
Australia Cd 300 mgkg-1 of p
Czech Republic Cd 50 mgkg-1of fertilizer
China Cd 8 mgkg-1of P
Finland Cd 50 mgkg-1of P
Germany Cd 20 mgkg-1of P
Netherlands Cd 35 mgkg-1of P
Norway Cd 100 mgkg-1of P
Sweden Cd 100 mgkg-1 of fertilizer
Canada As 75 mgkg-1 of fertilizer
Cd 20 mgkg-1of fertilizer
Co 150 mgkg-1of fertilizer
Mo 20 mgkg-1of fertilizer
Ni 180 mgkg-1of fertilizer
Pb 500 mgkg-1 of fertilizer
Zn 1850 mgkg-1 of fertilizer
USA
California
Cd 200 mgkg-1 of fertilizer
Pb 1000 mgkg-1 of fertilizer
Texas Cd 39 mgkg-11 of fertilizer
Assuming P fertilizers with 50% of P2 O5 .Source:[29]
2.6. Methodology in Fertilizers and Soils Analysis
Elemental analysis of the majority of organic and inorganic matrices requires the
partial or total dissolution of the sample prior to instrumental analysis. Only a few direct
methods allow the introduction of the samples without any preparation. In this case lack
of reliable calibration is the major problem. On the other hand, sample preparation allows
the separation and /or pre-concentration of analytes and makes possible the use of
several determination methods. Sample preparation of Soil and Fertilizer involves
digestion, extraction and preparation of Analyte before analysis. So this step is time
limiting, requiring 61% of the total time required to perform the complete analysis and
is responsible for 30% of the total analysis error, Nowadays the goals to be reached
19
are the best results, in the shortest time, with minimal contamination, low reagent
consumption and generation of minimal residue or waste. In order to achieve the real
objectives of the analysis, some aspects of sample preparation should be taken in to
account; Focusing on the chosen procedure, thus, simplification is simple
manipulation, use of high purity water and reagents in suitable amounts, correct
cleaning of recipients and blank preparation in parallel to sample are desirable.
Also the validation of methodology is important. Usually with certified reference
materials (Bock, 1979). [50]
Sample digestion processes prior to quantification of heavy metals includes closed
or open digestion systems and the use of different combinations of acids, such as HNO3,
HCl, HClO4, HF and others, as well as oxidants such as H2O2. Due to their chemical
composition, degree of polymerization and the presence of molecules resistant to
digestion, the recovery of heavy metals in organic residues is subject to variation.
Therefore, digestion methods must be chosen considering the residue and the recovery
rate of the heavy metals investigated .Wet digestion in open systems, according to
Azcue & Mudrock (1994), is time consuming and subject to contamination and loss
of some chemical elements by volatilization. In the case [50]
2.6.1. Sample Decomposition Techniques
Sample decomposition is useful for converting all the species in which a given element is
present in such a way that it becomes present in one defined form eliminating interfering
substances from the matrix and obtaining the element in a homogeneous and easily
accessible matrix. The choice of decomposition techniques should take into account the
objective of the final determination and factors such as the matrix composition, the
elemental contents, the possible interferences, the risk of loses and contaminations, the
practicality and possible safety hazards in the laboratory [50]. Different decomposition
methods could be classified into
20
1. Dry ashing,
2. Wet digestion and
3. Microwave digestion
2.6.1.1. Dry ashing techniques
Dry ashing or oxidation eliminates or minimize the effect of organic materials in mineral
element determination in food materials. It involves ignition of organic compounds in air
at atmospheric pressure and at relatively elevated temperatures (450-5500C) in a muffle
furnace.
For tissues high in carbohydrate and oils the ashing aids may be required to achieve
completed composition of organic matter. Water and other volatile materials are
vaporized and organic substances are burned in the presence of air. The resulting ash
residue is dissolved in an appropriate acid. The degree of volatilization loss is a limiting
factor and depends on;
(i) The applied temperature,
(ii) The forms in which the analyte is present in the sample and
(iii) The chemical environment in the ashing stage.
Dry ashing presents several useful features;
1. treatment of large amounts of sample and dissolution of the resulting ash in a
small acid volume resulted in element pre concentration
2. Complete destruction of the organic matter, which is a prerequisite for some
detection techniques, simplification of the sample matrix and the final solution
condition (clearness, colorless and odorless)
3. Application to a variety of complex samples. Nevertheless
Dry ashing presents some limitations.
(1) high temperature provokes volatilization losses of some elements; to avoid losses of
volatile As, Cd, Hg, Pb and Se, and improve procedure efficiency, ashing aids (high
purity Mg(NO3)2 and MgO) are used.(2) addition of ashing aids significantly increases
the content of inorganic salts, which may be a problem in subsequent determinations of
trace elements and contribute to contamination that Necessitates careful blank control
21
(3) it does not ensure dissolution of silicate compounds and consequently of all elements
associated with them (it can be encountered during plant analysis), after a procedure
without elimination of Si (by evaporation with HF), poor recoveries for some elements
can be observed, particularly traces(4) open dry ashing exposes samples to airborne
contamination [51]
2.6.1.2. Wet-ashing techniques
Wet digestion methods involve the use of both heat and mineral acid/s. Acids that have
been used in this procedure include H2SO4, HCl, HNO3 and HClO4, either in combination
or alone. Hydrogen peroxide [55] is also used to enhance the reaction speed and to ensure
complete digestion. Most laboratories have eliminated the use of HClO4due to risk of
explosion. Wet digestion can be carried out in open vessels, in tubes, on a hotplate or in
an aluminum heating block or in closed vessels at elevated pressure (digestion bombs)
with thermal or microwave heating. Microwave-assisted digestion is an attractive
method, especially for small samples. The applicability of this technique is strictly
depends on the type of sample, food: carbohydrates are easily mineralized with nitric acid
at 1800C, while fats ,proteins and amino acids cause incomplete digestion due to the
relatively low oxidation potential of nitric acid at 200oC; these materials require the
addition of sulfuric and/or per chloric acid with all the problems related to their use at
high temperature and pressure.
The type of acid/s used can have important consequences in the measurement step. It is
commonly known that in all atomic spectrometric techniques nitric acid is the most
desirable reagent. In spite of occasionally observed signal suppression in its presence
(e.g.in ICP-OES), no severe analytical problems are encountered in practice with nitric
acid at concentrations up to 10%, sometimes higher, in all atomic spectrometric
techniques as long as its concentration is similar in calibration and sample solutions.
Hydrogen peroxide added in most mineralization procedures is also rarely responsible for
analytical problems [52]
The presence of hydrochloric acid is not troublesome in ICP-OES analysis; however, its
exclusive use is prohibited in GFAAS analysis because of the possible formation of
22
volatile and difficult-to-dissociate analyte chlorides that could cause vapor phase and/or
spectral interference [50]. Main features associated with wet digestion methods are: (1)
much lower temperatures as
Compared to dry ashing procedures, however minimizing volatilization losses or
retentions
Caused by reactions between analytes and vessel materials, they may lead to incomplete
Solubilisation of sample constituents and (2) co-precipitation of analytes with precipitates
Formed by main matrix elements within reactive mixtures.
2.6.1.3. Microwave-assisted digestion
Microwave heating has several advantages, among the key advantages of MW-assisted
digestion are the much shorter reaction time (minutes) needed, direct heating of samples
and reagents, reduced need for aggressive reagents, minimal contamination and lack of
loss volatile elements.
There are two different systems available for MW- Microwave (MV)-assisted digestion
with nitric acid and mixture of nitric and hydrochloric acids without or with assisted
digestion; pressurized closed-vessel systems and open focused-MW systems that work
under atmospheric pressure. Microwave-assisted digestion in closed vessels under
pressure has gained popularity as a simple and fast dissolution technique that minimizes
acid consumption, the risk of sample contamination, and loss of volatile elements. One of
its limitations is the time required for cooling before the vessels can be opened, which
may take hours, depending on the type of equipment used. The main advantages of
focused MW radiation are safety, versatility, control of microwave energy released to the
sample, and the possibility for programmed addition of solutions during the digestion.
However, loss of volatile elements cannot be excluded in open-vessel digestion and
results for low-level elements might be affected by the high amount of reagents used and
hence the increased risk of sample contamination. This risk can be minimized by using
vapor-phase acid digestion, which has proven to be very effective in minimizing the
residual carbon content [51, 52]. The addition of hydrogen peroxide is a widely used
23
technique for the dissolution of food samples. Generally In this study we use Wet
digestion methods was used using acids HCl and HNO3
2.6.2. Measuring Methods: ICP-OES (Inductively coupled plasma - optical emission
spectrometry)
ICP/OES is one of the most powerful and popular analytical tools for the determination
of trace elements in a different types sample. Liquid and gas samples may be injected
directly into the instrument, while solid samples require extraction or acid digestion so
that the analytes will be resent in a solution. The sample solution is converted to an
aerosol and directed into the central channel of the plasma. At its core the inductively
coupled plasma (ICP) sustains a temperature of approximately 10, 000 K, so the aerosol
is quickly vaporized. Analyte elements are liberated as free atoms in the gaseous state.
Further coalitional excitation within the plasma imparts additional energy to the atoms,
promoting them to excited states. Sufficient energy is often available to convert the atoms
to ions and subsequently promote the ions to excited states. Both the atomic and ionic
excited state species may then relax to the ground state via the emission of a photon.
These photons have characteristic energies that are determined by the quantized energy
level structure for the atoms or ions. Thus the wavelength of the photons can be used to
identify the elements from which they originated. The total number of photons is directly
proportional to the concentration of the originating element in the sample
ICP-OES is a technique in which the composition of elements in (mostly water-
dissolved) samples can be determined using plasma and a spectrometer. The technique
has been commercially available since 1974 and thanks to its reliability, multi-element
options and high throughput, it has become a widely applied in both routine research as in
more specific analysis purposes. Is powerful for the determination of metal in variety of
different sample matrices.In ICP-OES the sample is usually transported into the
instrument as a steam of liquid sample [58].
2.7. Remediation of Cd and Pb polluted soils/ Bioremediation
Biological removal of heavy metals in soil involves the use of biological
techniques for the elimination of pollutants from soil. It is a selective technique
24
that utilizes the operational flexibility of microorganisms and plants. In
phytoremediation, plants play a great role in the biological process as they break
down, reduce, degrade and remove these contaminants using various parts, such as the
root, leaves, stomata, cell wall and the shoot [33]
2.7.1 Phytoremediation
Grow specific plants in the soil contaminated by heavy metals. These plants have the
certain hyper-accumulation ability for the contaminants in the soil. When the plants are
ripe or reach certain enrichment level of heavy metals, remove heavy metals in the
contaminated soil layer thoroughly by harvesting, burning and curing plants. Using plants
and their coexisting microbial system to remove heavy metals is a new technology. The
key of the method is to find the suitable plants with strong ability for heavy metal
accumulation and tolerance [53].
2.7.2 Microbial remediation
Microbial remediation refers to using some microorganisms to perform the absorption,
precipitation, oxidation and reduction of heavy metals in the soil. They found that fungi
could secrete amino acids, organic acids and other metabolites to dissolve heavy metals
and the mineral containing heavy metals [54].
2.7.3 Animal remediation
Some animals living in the soil (maggots, earthworms, etc.) can take heavy metals in the
soil. [18] Proved that when the concentration of heavy metal was low in the soil, the
activities and secretion of earthworms could promote the absorption.
2.8 The effect of Fertilizer Used and Cultural Soil Fertility Management
Practices in the Area
Cultural Soil Fertility in Woreda is aimed to maximize efficiency of nutrients in soil and
improve crop production through the use of grain legumes ( green manuring ), crop
rotation , fallowing of land, compost and manure are main soil fertility management
practices that have been carried out in the area and are still being carried out [35].
25
3. MATERIALS AND METHODS
3.1. Description of the Study Area
This study will conducted around Arsi Zone in Sire Woreda, Ethiopia. Oromia Regional
State, which is located about 144 Km distance from Addis Ababa City at south western
Ethiopia. The town has a latitude and longitude 08017N 39027E / 8.20N39.4500E with
altitude from 1665 - 1798 above sea level and55Km to East of Asella
Town.(www.https://en.m.wikipedia/sire)
Figure 1: Location of study area (Blue color is soil site selected)
3.1.1Population
According to the report of [35] the population of the district was estimated to be
120,447 of which 51,019 are male and 69,428are female. Out of the total population
99,971 are rural dwellers. The remaining 20,476 lived in the woreda capital. The total
number of rural households is 22,700. Estimated family size per household (rural) is
about 4.4 person. The woreda 450.6km2.
26
3.1.2Crop Production System of the Area
In smallholders farming practices, Crop production systems involves mostly the
traditional ‘Maresha’, plowing with a pair of oxen but this two year (2010 and 2011) the
farmers' started using farming Tractor. The agro-ecologies in the district is best suited for
diverse agricultural production but this year the woreda started same crop together (kuta
getem) farming.
Two cropping seasons are practiced in the study area where the Belg (short rainy season)
extends from March to April and Meher (main rainy season) extends from June to
September. The district is known for its best quality wheat, Teff, maize, barley, onion and
linseed production. The following show total Agriculture activities in Arsi sire
woreda[35]
Table 3:Total Agriculture used in Arsi sire woreda
Land used Hectares
2009/10 2010 /11 2011/12
Temporary crop Area 8,555 7,090 7,525
Permanent crop Area 30,850 31,550 31,550
Grazing land 12005 11,100 11,500
For Anther uses(school, office,
Religious place...)
600 605 605
Source [35]
3.2. Sampling and Chemical Analysis
3.2.1.Soil Sampling and Digestion
A total of 12 soil samples were collected in January 2019 from the four (4) different
agricultural areas (Bale, Michika, Shamed and Cirao) kebele that are used for
Agriculture. The soil samples were collected from topsoil at the depths of 0–20 cm. From
each of the four agricultural sites, three (3) sub-sites were taken for the purpose of
random sampling which based on the climate condition in each four agricultural areas
and pooled together to obtain a composite sample. Finally, 12 soil samples from each
stated areas were transferred in to polyethylene bags and transported to the laboratory.
The samples were air dried for one week, ground with porcelain mortar and pestle, passed
27
through 0.5 mm stainless steel sieve, and then kept in clean polythene bags for further
analysis.. Paste extract were subjected to the analysis of soil pH according to Eckerts and
Sims [55]
Samples of 0.5gram of each soil powder samples were digested in 200 ml volumetric
flask on hot plate stirrer by adding HNO3andHCl (3:1 ratio) in a fume hood at 175 oC for
5 hours. The contents were cooled and re-dissolved and filtered with Whatman No.42
filter paper into 50 ml volumetric flask and the residue were washed with distilled water
into the flask and diluted to the volume with distilled water as the procedure outlined in
[26,56]. The sample solutions were labeled and kept until the determination of the
concentration of the elements. The concentrations of metals Cd and Pb were analyzed by
inductively coupled plasma optical emission spectrometer (ICP-OES, PerkinElmer
optima8000).
3.2.2. Determination of soil PH
The soil pH was determined following the method of Eckerts and Sims [50]. The soil
samples were dried and 5 g of the dried soil was mixed with 5mL of de ionized water and
stirred. The mixture was allowed to stand for 30 min. to allow it settle. The slurry was
decanted into a beaker and the pH was measured using Aduwa PH electrode (PH-8000)
(The above procedure works for all soil sample Composite) .
Table 4: pH Determined in Soil sample
Soil Site Conc. of Pb pH of Soil
Michika M1 40. 9 ± 0.35 7.25
M2 40.5 ± 0.30 7.12
M3 40.7 ± 0.25 7.25
Bale B1 22.9 ± 0.2 7.20
B2 22.5 ±0.18 6.99
B3 22.05 ± 0.16 7.20
Shameda S1 18.8 ± 0.50 6.95
S2 18.6 ±0.23 6.90
S3 18.8 ± 0.30 6.93
Cirao C1 9.97 ± 0.86 6.90
C2 9.78 ± 0.80 6.89
C3 9. 70 ± 0.82 6.91
28
3.2.3. Fertilizer Sampling and Digestion
About 1000 grams of samples of commonly used fertilizers (UREA, DAP and NPSB) in
the area (Sire) were collected from multi- purpose cooperative (under the agriculture
office of Arsi sire Woreda and Cooperative office). NPSB is manufactured by OPC of
Morocco and supplied by YARA SWITZERLAND LTD. (country of origin Morocco
)and Urea and DAP are manufactured and supplied by Agra commodities and Finance
FZE(manufactured by Sabic ,country of origin Saudi Arabia 2019). All Fertilizer samples
were imported and distributed under Agricultural Inputs Supply Enterprise of Ethiopia.
The samples of each fertilizer were taken from six (6) different bags to make the sample
homogenous. The fertilizer samples were labeled and kept in air-tight plastic bags until
elemental analysis.
3.2.4. Fertilizer Digestion
Samples of 0.5 gram of each fertilizer powder samples were digested in 200 ml
volumetric flask on hot plate stirrer by adding HNO3 and HCl (3:1 ratio)in a fume hood
at 175 oC for five hour. The contents were cooled and re-dissolved and filtered with
Whatman No.42 filter paper into 50 ml volumetric flask and the residue were washed
with distilled water into the flask and diluted to the volume with distilled water as the
procedure outlined in [26,56]. The sample solutions were labeled and kept until the
determination of the concentration of the elements. The concentrations of metals Cd and
Pb were analyzed by inductively coupled plasma optical emission spectrometer (ICP-
OES, PerkinElmer optima8000).
29
Table 5: Fertilizer digestion and time it taken
Sample Step Reagent Duration of
time
Color
Fertilizer
(DAP,NPSB,Urea)
I 3ml HNO3 ,1ml HCl
and
2:00-2:30'
Deep yellow
color
Fertilizer
(DAP,NPSB,Urea)
II 9ml HNO3 ,
3ml HCl and
2: 30-4:30'
yellow color
Fertilizer
(DAP,NPSB,Urea)
III 12ml HNO3 ,
4ml HCl and
4:30-6:30'
pale yellow color
Fertilizer
(DAP,NPSB,Urea)
IV 24ml
8ml
6:30-7:00'
Clear solution
During digestion After dilution
Figure 2: Digestion process
3.2.5. Equipment and Reagents
The instruments used for this study was inductively coupled plasma optical emission
spectrometer (ICP-OES, Perkin Elmer optima8000) trace element (Cd and Pb)
determination in soil and fertilizer samples
The common laboratory apparatus which was used during the study include; different
sized beakers, flasks, funnels, volumetric flasks, fume hood, digestion flask, Digital
analytical balance (Mettler Toledo, Model AG204,Switzerland), glass pipettes, spatula,
measuring cylinders, gloves, polyethylene bags, conical flasks ,Whatman No.42 filter
30
paper,0.5 mm stainless steel sieve , oven, Aduwa PH electrode (PH-8000), hot plate
stirrer ,mortar and pestle
All the chemicals used were analytical reagent grade. De ionized water and distilled
water was used for all preparation and dilution purposes throughout the study. Nitric acid
(HNO3) and hydrochloric acid (HCl) was used for digestion. Sample of Soil and fertilizer
3.3. Quality Control and Statical Analysis
All reagents used were of Analytical grade (BLULUX Laboratories reagent P.LTd,
India). To overcome the lack of certified reference materials (CRMs), standard stock
solutions with concentration of 1000 mg/l were prepared based on accepted procedures
from analytical grade chemicals and distilled water. All glass wares and plastic containers
were socked in 2MHNO3 for 24 hours and washed with detergent and rinsed with
distilled water to ensure that any contamination does not occur. For preparation of
standards and dilution, distilled water was used. Triplicate measurements were taken for
precision.
The spike recovery study was carried out in two of the sample (NPSB, Soil C1) to ensure
the validity of the analytical method. The blanks were also prepared using the same
reagent and solvent for the sample and for the standards accordingly
Table 6: Recovery test for fertilizer (NPSB)
Element Spiking
(mg/kg)
Un Spiking
(mg/kg)
Spiking - un Spiking
(mg/kg)
Amount
added(ppm)
%recovery
Pb 1.510 0.046 1.464 1.5 97.6
Cd 1.623 0.237 1.386 1.5 92.4
As used for the original samples, Triplicate spiked and Un spiked samples were prepared
and the readings were recorded. Recovery was calculated using the equation given
below.
% R = (𝑠𝑝𝑖𝑘𝑒𝑑−𝑢𝑛𝑠𝑝𝑖𝑘𝑒𝑑
𝑎𝑚𝑜𝑢𝑛𝑡𝑎𝑑𝑑𝑒𝑑) 100 , % R=percent recovery
31
Table 7: Pb recovery test for Soil C1 (Cirao)
Element Spiking(m
g/kg)
Un Spiking
(mg/kg)
Spiking - un Spiking
(mg/kg)
Amount
added(ppm)
%recovery
Pb 0.978 0.012 0.966 1ppm 96.6
Figure 3. Calibration Graph
Calibration Curve for Cd Calibration curve for Pb
0 2 4 6
0.00
0.05
0.10
Inte
nsity (
M)
Concentration (mg/L)
Pb
r2 = 0.99963
y=732.74329 + 19856.277x
0 2 4 6
0.0
0.7
1.4
Inte
nsity (
M)
concentration (mg/L)
r2=0.9997
y = 5032.47814 + 294363.00857X Cd
32
4. RESULTS AND DISCUSSION
4.1 The Extent of Fertilizer Use in the Study Area
The main economic activities of Arsi Sire Woreda population ( 87.50%) is farming
.Main Crops like Teff ,wheat, Barley ,Maize ,linseed and Onion grow in the area. It is a
highland and Temperate zone area where soil fertility specially the (weyna Degas). The
Low land (Kola) slightly deteriorated due to soil erosion in some area. To restore the
soil fertility and to increase yield of crop production, the use of fertilizers along with soil
management practices is unquestionable.
Generally, the data obtained from agricultural and cooperative office of Arsi Sire Woreda
indicates an increasing trend in fertilizer consumptions for the past five years as can be
seen in Table-8
Table 8: Types of fertilizers and fertilizer consumptions trend of the study area (Arsi Sire
Woreda) from (in quintals)
No Types of
fertilizer
2006/2007 2007/2008 2008/2009 2009/2010 2010/2011 2011/2012
Plan
1 DAP 15,481.5 663.5 30.5 ____ ___ ____
2 UREA 2169 2331.5 523.5 443 1441 4,363
3 NPSB ___ ___ ____ 15,554.5 18,953 21,880
4 NPS ___ 14,836.5 18,077.5 4,446 3211 ____
5 NPSZn ___ ___ 1,234 1,535 ___ ___
Total fertilizers 17,650.5 17,831.5 19,865.5 21,978.5 23,605 26,243
Source [35]
As can be seen in Table-8 and figure- 4 bellow Urea and DAP have been used for the past
ten or more years regardless of Soil for crop production. However, recently, a new blend
of fertilizer, NPSB is in use since 2009 year based on soil analysis of the area by
ETHIOISIS. This fertilizer is made by mixing Urea, DAP, Ammonium Sulphate and
Borax.
33
Figure 4: Fertilizer consumption in the Area
Table 9: Macronutrient composition of Fertilizers used in Sire Woreda, Arsi Zone 2006-
2011 E.c
No Fertilize N(%) P2O5(%) %K2O S(%) B(%) Zn
1 UREA 46 _ _ __ __
2 NPSB 18.5 37.7 _ 6.95 0.1
3 DAP 18 46 _
__
__
4 NPS 19 38 _ 7 __
5 NPSZn 18.9 37.7 _ 6.95 0.1
Data from labels on fertilizer as provided by manufacture
0.00
5,000.00
10,000.00
15,000.00
20,000.00
25,000.00
2006 2007 2008 2009 2010 2011
Am
ou
nt
in K
uin
tal
years
DAP
UREA
NPS
NPSB
NPSZn
34
4.2. Optimization for digestion procedure of Fertilizer and Soil samples
The basic requirements for sample preparation for analysis are to get an optimum
condition for digestion. The optimum condition is the one which required minimum
reagent volume consumption, minimum digestion time reflection and clear digestion
solution, ease of simplicity and absence of undigested samples . In this study, to
prepare a clear colorless sample solution that is suitable for the analysis using ICP-
OES different digestions were carried out using HNO3 and HCl acid mixtures by
varying parameters such as volume of the acid mixtures, digestion time and digestion
temperature. Different conditions tested for optimization of digestion procedure for 0.5g
samples (3HNO3: HCl)
4.3 .Method validation and quality control
In order to validate the analytical method, the following method validation parameters
such as instrumental detection limit, limit of detection, limit of quantification, precision
and accuracy studies were carried out
4.3.1. Limit of detection
Limit of detection (LOD) is the minimum concentration of analytes that can be detected
but not necessarily quantified with an acceptable uncertainty. LOD for each metal was
determined from analysis of triplicates of method blanks which were digested in the same
digestion procedure as the actual samples LOD was calculated as [23]
LOD = 3 × SD where SD is the standard deviation of the method blank.
4.3.2. Limit of quantification
The limit of quantification (LOQ) is the lowest concentration of an Analyte in a sample
which can be quantitatively determined with acceptable uncertainty. LOQ was obtained
from triplicate analysis of for method blanks which were digested in the same digestion
procedure as the actual samples. The LOQ was calculated as LOQ = 10 × SD where SD
is the standard deviation of the method blank [23].
35
4.3.3. Precision and accuracy
Precision and accuracy of the results were assessed by determining recovery and
repeatability of the analysis of matrix spike matrix spike duplicate .For doing so each
sample was spiked in replicates of three at near mid-range calibration concentration. The
spiked sample were digested and analyzed following the same analytical procedure as the
soil and fertilizer samples. Precision was expressed as relative standard deviation (RSD)
of replicate results. The relative standard deviations of the sample were obtained
4.3.4. Regression analysis and detection limits
As can be seen from Table bellow and figure 4 calibration curves for the metals showed
good linearity with coefficients of determination (r2) ranged between 0.9996 and 0.9997
which were greatly acceptable for the linearity of the regression line. This showed that
there could be a good correlation between concentration and intensity indicating good
calibration of the instrument. The instrumental detection limits (IDL) ranged
0.0027mg/kg to 0.0420 mg/kg which were below the limits of detection (LOD) and LOQ
indicating good sensitivity of the measuring instrument for analysis. The (LOD) and
LOQ of Cd value is 0.032 and 0.107mg/kg respectively. The limits of detection (LOD)
and Limit of quantification (LOQ) of Pb value is 0.0562 and0.209mg/kg respectively
.The result shows both the LOD and LOQ values were greater than the IDL hence the
results of the analysis could be reliable.
Table 10: Linear regression equations, coefficient of determination, instrumental detection
limit (IDL), limit of detection (LOD), and limit of quantification (LOQ)
Metal
IDL
LOD
LOQ
r2correlation
coefficient
Linear regression equations
Cd 0.0027 0.032 0.107 0.9997 y = 294363.00857x +5032.4781
Pb 0.0420 0.0562 0.209 0.9996 y = 19856.277x 732.74329
4.3.5. Accuracy and precision
As it can be seen from Table 6 and7 the mean percent recoveries for the studied metals in
the matrix spike sample ranged between 92.5 and 97.6. All the recovery values were
within the acceptable range of 80–120% for metal analysis [56]. The precision of the
36
method was expressed as relative standard deviation (RSD) of the three replicate
readings. The RSD values obtained for soil matrix spike samples ranged from 0.401% to
1.54%which was under the required control limits ≤15% [53] These results indicate that
the proposed method is precise and accurate
4.4. Heavy Metal Concentrations in Fertilizer and Soil
The macronutrient composition of DAP, Urea and NPSB fertilizers as provided from
fertilizer manufacturer and the concentrations trace elements ( Cd and Pb) obtained from
triplicate measurements in this study are represented in Tables -10. The fertilizers studied
contain trace elements as impurities. The newly introduced NPSB fertilizers that used in
the area now contained more of the Pb and Cd level than Urea and DAP. While the soil
taken from four site(Cirao (C), Michika (M) , Shameda (S) , Bale ( B2)contain Pb. The
table below show this.
37
Table 11: The content of Cd and Pb (mg/Kg) indifferent soil site of Sire Woreda, Arsi Zone.
ND: Not Detected
Site Area Composite Sample Pb Cd
Cirao(C) C1 9.97 ± 0.86 ND
C2 9.78 ± 0.80 ND
C3 9. 70 ± 0.82 ND
Mean 9.816667
SD 0.113235
%RSD 1.1535
Michika (M) M1 40. 9 ± 0.35 ND
M2 40.5 ± 0.30 ND
M3 40.7 ± 0.25 ND
Mean 40.7
SD 0.163299
%RSD 0.401227
Shameda (S) S1 18.8 ± 0.50 ND
S2 18.6 ±0.23 ND
S3 18.8 ± 0.30 ND
Mean 18.73333
SD 0.094281
%RSD 0.503279
Bale (B) B1 22.9 ± 0.2 ND
B2 22.5 ±0.18 ND
B3 22.05 ± 0.16 ND
Mean 22.48333
SD 0.347211
%RSD 1.544304
Max. Safe /Limit
in Soil /
100 3 [19, 50]
38
Table 12: The content of trace elements ( Cd and Pb) levels of Fertilizers used In sire
Woreda Arsi Zone , ( mg/Kg) from Doublet measurements
Fertilizer Source Abbr. Molecular Form Pb Cd
UREA UREA CO(NH2)2 13.8 ± 6.53 ND
Ammonium phosphate
sulfate with Borax
NPSB NH4H2PO4(NH4)2SO4 86.37 ±49.87
30.02 ± 4.69
Diammonium phosphate DAP (NH4)2HPO4
30.17 ± 0.16 23.25 ± 5.21
ND: Not Detected
39
The mean concentration of Pb (86.37 ±49.87mg/kg) in NPSB is much greater than in Pb
(30.17 ± 0.16mg/kg) in DAP and Pb(13.8 ± 6.53) in Urea. While the mean concentration of
Cd (30.02 ± 4.69mg/kg) in NPSB fertilizer is much higher than the concentration of Cd
(23.25 ± 5.21) in DAP and Cd (ND) in urea. It is reported by [6] that the concentration of
Cd in phosphate fertilizers is higher than Nitrogen supplying fertilizers like urea. This
could be due to the raw materials from which the fertilizer is produced and phosphate rocks
contain Cd and other heavy metals.
Cadmium accumulation and contamination in soils has been of special interest because of
its toxicity [11]. For this reason most studies of trace element concentration in fertilizers
include this element. The data on this paper indicated that concentration of Cd analyzed in
NPSB Fertilizer is much lower than the regulatory limits of the metal in fertilizers for most
Countries But the concentration of Cd is higher than the regulatory limits set by China (8
mg/kg), Canada and Germany (20 mg/kg) as can be seen in Table-2
The mean concentration of Pb in soil of Michika(M) (40. 7 ± 0.16 ) much higher than in
Bale (B)(22.9 ± 0.46) ,than Shameda (S)(18.73 ± 0.09 ) ,than Cirao (C)(9.83 ±
0.11).The relatively high levels of lead might have resulted from accumulation of lead
through fertilizer application, and from some pesticides, Herbicides such as lead arsenates
applied during cultivation. The values of Pb obtained in this study were lower than Ewers,
1991 recommended maximum limit that is 100 mg/kg. In general, the results of the heavy
metals analyzed in the study areas showed that their concentration level is below the
standard guide lines for maximum limit proposed for agricultural soil
4.4.1. Comparisons with Literature Value
Generally the mean concentration of Pb in soil of Michika(M) (40. 9 ± 0.35 ) much
higher than East Gojjam in Bichene(23.2mg/kg ) ,Debre work ( 13.9mg/kg) , Debre
Markos(15.6mg/kg ) and Dejen ( 13.6 mg/kg)[4] .On the other hand the mean
concentration of Pb in Arsi Sire soil is lower than different country Netherlands
(140mg/kg), China (350mg/kg ) ,Canada( 140mg/kg ) , India( 500mg/kg ) as shown in
Table-12 bellow.
40
Table 13: Heavy metal Pb an Cd in soil determination by some country
Country Element
Pb (mg/kg)
Element
Cd (mg/kg)
Source
Netherlands 140 1.6
[29,55,57]
Romania 50 3
China 350 0.6
Canada 140 10
India 500 0.5
Debre Markos 15.6 2.50
[4]
Debre Work 13.8 2.30
Bichena 23.2 2.40
Dejen 13.9 2.30
Sire Woreda 22.94 ND This Study
ND: Not Detected
As we see from the above the mean concentration heavy metal Pb of Sire Woreda is 22.94
which is higher than East Gojjam in Bichene ,Debre work , Debre Markos and Dejen
,lower than Nether lands, Romania ,China ,Canada, India.
41
Table 14: Concentrations of trace elements in fertilizers analyzed in this study and in some
other countries (mg/kg)
Trace elements Pb Cd Reference
Study area
(Sire
Woreda)
Urea 13.8 ND
NPSB 86.37
30.02
DAP 30.17 23.25
In Lasta
Woreda,
Ethiopia
Urea NA 4.3 [58]
NPSB NA 66.1
In Kenya Urea NA 0.03 [8]
In Chile Phosphate
Fertilizer
3.6 [11]
NA Not analyzed, ND Not detected
For comparison, the concentrations of trace elements in fertilizers in some countries and
the concentration of trace elements obtained in this study are given in Table-14.In general,
the concentrations of trace elements in urea fertilizer in this study are not analyzed.
Moreover, the concentrations of trace elements In phosphate containing fertilizer (NPSB)
in this study (Sire Woreda)is higher than the concentrations of the Chile And lower than In
Lasta Woreda, Ethiopia. This could be due to the geological origin of the raw materials for
fertilizer production or the regulatory measures taken by the countries in controlling quality
of fertilizers used [11]. In general, fertilizers used in Sire Woreda, contain trace elements
(Pb and Cd) as impurities .Some of these elements are not essential for plants and animals
4.5. Statical Data Analysis
Sample analyses in this study were carried out in doublet (fertilizer) and Singlet (Soil).
The results were reported as mean ± standard deviation. The calibration curves and the
graphs for the analyzed elements were plotted using software (MICROSOFT EXCEL
2007). Six Standard solution with the concentrations of 5.05, 4.05, 3.05, 2.05, 1.05and 0.05
ppm for Pb and Cd were used for the calibration. And a blank was also prepared using the
same reagents used for the samples and the standards. The concentrations of heavy metal
(Pb and Cd) were analyzed by inductively coupled plasma optical emission spectrometer
(ICP-OES, Perkin Elmer optima8000). The calibration curves for Cd and Pb is shown in
42
Fig-5 and the correlation coefficient, r2 =0.9997 and r2 = 0.9996 showed respectively which
were greater than the acceptable limit. This showed that there is a good correlation between
concentration and absorbance indicating good calibration of the instrument for the
calibration curves of elements analyzed indicating that the sensitivity of the method is
statistically accepted. The effectiveness of the methods used was tested by using spiked
samples. One of the fertilizers samples, NPSB, were spiked with 1.623 mg/kg, 1.510 mg/kg
of standard solutions of Cd and Pb respectively. The percentage recovery of the metals
were 92.6%,97.6% respectively and for soil 96.9% soil were spiked with 0.978mg/kg .
This indicated that the analytical method used were valid.
43
5. CONCLUTION AND RECOMENDATION
5.1. CONCLUTION
Generally the presence of heavy metal Cadmium and Lead in relatively low concentrations
in fertilizers and soil can be toxic to soil and plant threatening food production and the
environment; and consequently to the animal-human health and productivity .Long term
applications of such impure fertilizers in to soil may lead to accumulation of lead and
cadmium in the soil and crop produced. Over use or misuse of fertilizers with Poor quality
in agriculture contributes to environmental deterioration from nonpoint source pollution
and is therefore of great concern nationally and internationally.
The high concentration of toxic heavy metals in fertilizers may lower the value of crop
produced by and may cause poison effects to soil, animal-human health and productivity.
Thus, the quality of fertilizers used ones country has to be regulated periodically for both
soil and food production. The concentration of Pb and Cd in soil, fertilizers in Arsi Zone
Sire Woreda Oromia region was determined by ICP-OES. The study indicated that the soil
content of Pb metal concentration is bellow Ewers and FAO/WHO. The absence of heavy
metal Cd in soil may be due to the Analytical Error, absorption by plants from the soil or
below the detection limits. The presence of heavy metal in soil may be due to the
application of fertilizers, pesticide in the vegetable (plants) farming area. The soil studied
were not harm for Agricultural because soil heavy metal concentration is bellow Ewers and
FAO/WHO and The mean values of soil pH content of the soil sample are shown in Table
11. From this table, we can see that pH of the Cirao < Shameda < Bale < Michika. The
highest pH of the relative samples at Michika may be due to the more concentration
of metals in that particular area. metals concentration and pH values decreased with
increased horizontal distance from the site .And the pH values were ranged from 6.89 -
7.25 as shown in Table 5. It is reported that the pH is an essential factor that influences the
cations mobility and regulates the solubility of heavy metals in soil. In relation to alkaline
soil, solubility of metal is more in acidic soils. Therefore, the soil samples tested all are
normal and is an indication for the absence Cd and low concentration of heavy metals
Pb in the area. The pH for optimum crop production is between 6.5-7.5 [26]. The gradual
44
application of fertilizer, pesticide, herbicide other chemical to soil increases the
concentration of Cd and Pb in soil.
5.2. RECOMENDATION
So attention should be given by concerned body accordingly for Fertilizers used. Ethiopia
have to establish regulation with respect to maximum input rates of trace elements (heavy
metal) into agricultural soils and maximum concentration limits in fertilizers. Especially
NPSB which manufactured by OPC of Morocco and supplied by YARA SWITZERLAND LTD.
(country of origin Morocco) have high Cd and Pb concentration. Because maximum
concentration of trace elements (heavy metal) as impurities is from phosphates inorganic
fertilizers in countries.
One major problem that Ethiopia faced pertinent to the agricultural soils was the
lack of soil fertility database according area and crop specific fertilizer recommendation.
It has not been possible to delineate the key soil fertility limitations and nutrient shortages
that impact on crop yield in the country. So in order to solve this problem, the Ministry of
Agriculture should designed the way approach conducting soil and plant nutrient survey in
each areas.
Ethiopia must formulate appropriate agricultural policies at a national level and strict
regulations to the quality of fertilizers used in agricultural systems and educate the
extension services and farmers to reduce fertilizer application which can degrade
sustainable development.
45
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