International Conference on:
“New Role for the World Sugar Economy in a Changed Political and
Economic Environment ”
Environmental Impact Assessment of Heavy Metal Pollution
in Soil from Assiut Fertilizer Plant, Egypt
Thabet A. Mohameda, Ragab ElS. Rabeiyb,
Mohamed Abuel – Kassem Mohamedb,Mahmoud A. Gandourc
a National Institute of Occupational Safety and Health (NIOSH), Assiut.
b Mining and Metallurgical Engineering Dept. Faculty of Engineering, Assiut University.
c Chemistry Dept., Faculty of Science, Assiut University.
Abstract:
The Phosphate fertilizer industry is considered as one of the main sources
of pollution to air, water, soil and vegetations. A phosphate fertilizer plant is
located near Assiut city, Egypt, has strong negative environmental impacts on the
adjacent area. A soil sampling network was developed around the plant to assess
these harmful effects. 72 Soil samples were taken and analyzed to represent the
spatial distribution of 5 trace elements. The soil samples have been analyzed
using SEM- EDS method to evaluate the heavy metal elements of Cd, Pb, Zn,
Hg, and As in the soil. The obtained results gave evidence of soil pollution on the
study area caused by the emissions which released from the phosphate fertilizer
plant. The average values of heavy metals concentrations (%) in the soil is
18.96%, 6.06%, 7.89%, 29.77% and 5.92% for Hg, Zn, As, Pb and Cd
respectively. These values exceed much more than the permissible levels. Five
control soil samples were taken upwind the fertilizer plant to compare them with
the polluted area. The average values of the control samples were 1.31% for Hg,
0.08% for Zn, and 0.05% for Pb. While the elements As and Cd are not detected
in the soil located upwind the plant. This comparison refers that the soil
contaminations by heavy metals are caused only by the pollutants emitted from
Assiut fertilizer plant.
Key words: Soil Pollution, SEM- EDS Analysis, Heavy Metal Contaminations,
Phosphate Fertilizer Industry.
1. Introduction:
Heavy metals are important trace elements in nutrition of plants, animals,
and human (e.g. Zn, Cu, Mn, Cr, Ni), while others are not known to have positive
nutritional effects (e.g. Cd, Pb, Hg, As). However, all of these elements may
cause toxic effects (some of them at a very low content level), if they occur
excessively. Previous studies revealed that heavy metals have negative effects on
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the microbial activity, composition of soil, inhibition of the germination of seeds
and growth of plants [3]. Other effects of pollutants can be described as
inhibitory effects by blocking the uptake of other elements and hence depriving
the plant from absorbing essential elements from the soil [4]. The
bioaccumulation of heavy metals over large territories and long time periods may
result in the gradual damage of living organisms, and the functionality of the soil
[1].
Assiut phosphate fertilizer plant, under consideration is located 9 km south
of Assiut city, is processing phosphate rock for the production of Single
Superphosphate SSP and Granulated Superphosphate GSP fertilizers. The
production of the plant was 960,000 tons on 2009 [1.1]. Huge amounts of dust
and gases are liberating from industrial units, bearing heavy metals that
atmospherically dispersed and deposited in the nearby area producing a high
degree of pollution in the air, soil, and aquatic system [2]. 72 soil samples were
collected from the study area to determine the extent of heavy metal pollutants in
contaminated soils. SEM-EDS technique was used for the quantitative estimation
of elements Cd, Pb, Zn, Hg, and As in soil samples. Also micro quantitative
analysis helps in technological measures to prevent heavy metals transfer to food
chain.
The objective of this study is to: (1) analyze the effect of atmospheric
deposition of heavy metals from Assiut fertilizer plant in its surrounded soil, (2)
determine to what extent the pollutants dispersed on the study area, and (3) study
the effects of heavy metals on the growing vegetations.
2. Materials and Methods
2.1
Study Area
The superphosphate fertilizer plant is located at 9 km north of Assiut city
(27 N and 31○ E). The Plant lies between Nile river (East) and Ibraheemia canal
(West). The area around the factory is cultivated with some main crops such as
wheat, faba bean and clover in winter and sorghum, maize and cotton in summer.
In addition, some fruit orchards like grapes, banana, jawava and figs are found in
the area. The area under investigation is an agricultural land of 25 km2 and
inhabited with 5000 individuals in three scattering villages.
○
2.2
Sample Collection and Preparation
72 Soil samples were obtained using a stainless steel auger; disposable
trowel at each location to a depth of 6 inches below the soil surface; any grass or
other vegetative materials were removed and excluded from the collected soil
sample. Each soil sample is composed of five subsamples which taken from a
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circle of 5 meters diameter. One subsample was taken from the center and rests
were taken from the circumference of the circle. Sample locations are illustrated
in Figure 1. The collected soil samples were placed in provided containers, stored
in coolers which containing ice, and shipped to the Electron Microscope Unit in
Assiut University [5]. The soil samples were collected from the investigated area
in both Winter (W) and Summer (S) seasons of the year 2010. Also, five control
soil samples were taken from an unpolluted area; 3km up wind the fertilizer
processing units. The reference samples were specified according to the
specifications of the National Institute of Standards and Technology (NIST) [6 &
7]. All soil samples were dried in oven at 60 ºC for four hours to remove moisture
content. Dried samples were grinded into fine powder using agate mortar [8].
These samples are analyzed be the Scanning Electron Microscope-Energy
Dispersive Spectrometer (SEM-EDS).
Figure 1: Location of the study area and soil samples
2.3
SEM-EDS Technique
The micrographs were recorded using SEM JEOL model, JSE-5610LV
with an accelerating voltage of 20 kv, at High Vacuum (HV) mode and secondary
Electron Image (SEI). The maximum magnification possible in this equipment is
300000 times with resolution of X500 for all samples. The semi quantification
elemental analysis to identify the weight percentage of major and minor elements
present in the samples was done using the OXFORD INA Energy Dispersive xray spectrometer (SEM-EDS). This technique is used in numerous applications
for environmental science and technology [6, 8].
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Energy dispersive x-ray spectrometer is a popular method for the
determination of trace elements in geological and environmental samples. With
the morphological characters obtained from SEM, supported by Energy
Dispersive x-ray EDS micro analysis device, it is possible to identify the
elements Cd, Pb, Zn, Hg and As that present in soil samples.
3. Results and Discussion
3.1
Morphology of Soil Samples
The SEM microstructure and corresponding EDS spectrum were obtained
for all soil samples and one typical micrographs and spectrum of soil samples are
given in Figure 2 (a, b). The weight percentages of elements in typical five
sample locations with control sample for soil obtained from EDS are given in
Table 1.
For quantitative electronic microscopic investigation preparations of
samples becomes very important and, besides, such a procedure combines two
particular actions: selection of very low concentration fine dispersive fraction to
maximum separate particles into monomineral aggregates on the surface, and
coating of conductive layer in order to reduce charge effect. The morphology of
fine-dispersive fraction of sample soil appears as a selection of scaly aggregates
with wide dispersion of dimensions from 0.5 to 5-7 μm. Apparently, electrolytic
properties, when the sample was being formed, caused aggregation of illite and
vermiculite in flakes of asymmetric shape [8]. The fact that particles are
composed of plane aggregates (scales), may be explained by no uniformity of
optical plane particles- there are darker and lighter portions.
Figure 2 (a) Example of SEM spectrum of a soil sample
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Figure 2 (b) Example of SEM microstructure of the sample
The results of x-ray phase analysis and study of soils fine-dispersive
fractions by SEM makes possible to identify separate minerals and to assess their
sizes and shapes. Nevertheless, unambiguous visual identification and
confirmation of the presence of the all minerals in a sample was quite
probabilistic. Most likely, without separation of fine dispersive fraction for
sufficiently narrow in sizes fraction, cover of larger particles upon the fine ones
and total adherence into aggregates will shade the identification of morphologic
characters of mineral particles. Morphological analysis by SEM of fine dispersive
fraction has shown that there does not occur any evident division of particles into
separate identifiable minerals. Only quartz particles may be identified
unambiguously, Illite, smectite and vermiculite from asymmetric flake like
aggregates of various sizes.
3.2
Statistical Analysis
Table (1) Statistical Analysis of the soil samples in the investigated area
Minimum
Average
Maximum
Permissible
Limit
Element
Control
Control
Control
Soil
Soil
Soil
%
Samples Samples Samples Sample Samples Sample
References
Cd
0.510
N.D
3.990
0.002
9.01
0.006
0.00002
Adriano.,1986
Pb
6.270
0.480
20.745
0.786
57.65
1.02
0.02
"
Zn
0.080
0.050
7.044
0.552
72.58
1.49
0.03
"
Hg
7.570
1.020
16.593
1.390
26.92
2.28
-
As
0.540
N,D
5.360
0.002
18.98
0.007
0.004
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"
Adriano.,1986
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Economic Environment ”
From Table 1 the data obtained from SEM-EDS microanalysis for soil
samples showed that the percentages of heavy metal contents are different,
especially Cd and Pb. Metal contents are ranged from 9.01% - 0.510%, 57.65% –
6.27%, 72.58% – 0.08%, 26.92% - 7.57%, and 18.98% - 0.540% for Cd, Pb, Zn,
Hg As respectively.
Figure 3: Concentration of heavy metals compared with control and guideline values
Comparing the average values of heavy metal contents with that of both
the control sample and the permissible levels it was found from Fig. 3 that the
average value of Pb content equals 13 times that of the control sample, where it
reached 313.5 times to Pb present in permissible level. But for Cd average value
equals 25500 times to that of the permissible level and Cd in control sample is
not detected. For Zn, the average value reached 1.6 times of that of the control
sample and 2.6 of the permissible levels. For Hg, the average value is 7.4 times to
that of the control sample. At last for As average value equals 135 times to that of
the permissible level where As and Cd are not detected in control sample.
As samples have been taken in the two seasons, winter and summer, it
revealed that the average concentration values of heavy metal pollutants increase
than that of summer. The temperature degree in this region is relatively high in
summer and this enhances dispersion of pollutants, so the deposited atmospheric
matter is decreased. But in winter where temperature degree is moderately low,
the average concentration of pollutants is localized and is precipitated in the area
under investigation. Also it was found that the average concentrations of heavy
metal pollutants decrease faraway the plant location.
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4. Conclusion and Recommendations
4.1
Conclusion
The phosphate fertilizer plant brings about serious heavy metal pollution
problem. The soil is seriously polluted by heavy metals. The contents of Cd, Pb,
Zn, Hg and As in soil reached a dangerous level where their concentration values
surpassed those of the reference sample by significant values [10]. Cd and As are
not detected in control sample and this refers that almost concentrations of the
two elements do harm to the environment.
As the estimation of pollutants in soil samples are highly affected by heavy
metals, these metals can be absorbed by plant and in turn transfer to the food
chain causing environmental risk. It is noticed that the leaves of the plant have
covered with fine dust that hinders photosynthesis processes which refer that the
area is affected by air pollution by the atmospheric emission from industries. The
plants seem to have no exclusion mechanism in leaf structure [7], and hence, they
seem to absorb Pb and Cd from atmosphere during the photosynthesis process.
This phenomenon has support from visual evidence that the plants in the study
area suffer due to small leaves, lesser number of leaves and deformed growth of
plants. Hence, it may be concluded that the area which we studied suffer more
from air pollution than from the soil pollution. If the atmospheric emissions from
chimneys are governed by the standard pollution norms, the area may be saved
from future pollution problems.
4.2
Environmental Recommendations
Analysis of soil sampling data indicates that all obtained samples taken
around the phosphate fertilizer plant contained toxic heavy metals in
concentration which exceed the soil screening levels [9]. So the unacceptable
concentration levels of these heavy metals can cause a human health risk to the
people living in the concerned area. Based on what has been mentioned above,
the following may be recommended:
 The concerned agency should delineate further surface and subsurface
extent of soil contamination in the area surrounding the fertilizer plant.
 Egyptian Environmental Affairs Agency (EEAA) should develop and
implement a soil and other contaminated media remedial plan to address
the community exposure situation .
 Phosphate Fertilizer Plant should apply the control measures to reduce the
fugitive and stack emissions of heavy metals in order to reduce community
exposure.
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Economic Environment ”
Acknowledgment
The authors would like to acknowledge Dr. Atif Abu El Wafa, dean of
Sugar Technology Research Institute (STRI), for his support in the analysis of the
soil samples. Also, the acknowledgement is extended to the team of Electron
Microscopy Unit (EMU), Assiut University for their efforts in SEM-EDS
microanalysis.
References
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Met. Soc. China, 2008, 18, 207- 211.
6- Prosycevas, I., Vaisvalavicius, U., Grigaliunas, V. Application of Screening
Electron Microscopy in soil fine-dispersive fraction investigations. Material
Science, 2003,9(1).
7- Peavy, H.S., Rowe,D., R.and Teccobanologus, G. “Environmental
engineering”, McGrow- Hill Book Company, 1986 .
8- Kiekens, “Biological and analytical aspects of soil pollution”, lab. of Anal. &
Argo, 1982.
9- Hannigan, R., Nassef, M., El-Sayed, K. A., and El Tahawy, M.S.,
“Determination of some heavy metals in the environment of Sadat industrial
city”, Proceedings of the 2nd Environmental Physics Conference, Egypt, 2006.
10- Mohamed, A-K., M., “Pollution and Environmental Control”, Assiut
University Book, Publishing Unit, 2006.
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