Geo-Environmental Impact Assessment of Urbanization on Top Soil in Okene Metropolis, North Central, Nigeria

Geo-Environmental Impact Assessment of Urbanization on Top Soil in Okene Metropolis, North Central, Nigeria
Geo-Environmental Impact Assessment of Urbanization
on Top Soil in Okene Metropolis, North Central, Nigeria
*1Gideon, Yomi B., 2Fatoye, Felix B. and 3Omada, Joseph I.
1Department of Earth Science, Faculty of Natural Sciences, Kogi State University, Anyigba, Nigeria
2Department of Mineral and Petroleum Resources Engineering, Kogi State Polytechnic, Lokoja, Nigeria
3National Open University of Nigeria, Lokoja, Kogi State, Nigeria
The impact of urbanization on top soil within Okene metropolis was evaluated using geochemical
mapping tools. Methods of investigation involved urban studies, sampling, standard laboratory
analyses and data evaluation. A total of one hundred and twenty-four (124) composite soil
samples were systematically collected from different regions of the metropolis. Heavy metals
composition of the soil samples was determined using Energy Dispersion X-ray Fluorescence
Spectrometer (EDXRF). The mean concentrations of Cu (153.84 ppm), Fe (78680.70 ppm), Ni
(163.84 ppm) and Zn (476.50 ppm) contents in the urban soil are higher than maximum allowable
limit for agricultural and residential standards. As (5.47 ppm), Cd (0.91 ppm) and Cr (44.00 ppm)
are within the allowable limits, while Pb was found at its threshold of 100.00 ppm. The pairs of As
and Pb (r = 0.938), Fe and Cr (r = 0.685), and Ni and Cu (r = 0.689) was observed to be governed
by similarity in origins, lithologic processes and anthropogenic activities. Based on soil pollution
index, 85.48% of the top soil in Okene metropolis is polluted at varying degrees. Soil within Okene
central, Ogaminana, and the nucleated parts between Adavi-Eba and Agassa regions are highly
impacted. These areas have relatively higher population density, ineffective sanitary system, poor
wastes management services and higher level of urbanization activities. Awareness on
consequences of polluted environments should be made public. Systematic remediation of the
urban soil by suitable means is recommended.
Keywords: Geo-environmental, Impact, Urbanization, Urban-soil, Heavy-metals, Spatial-distribution, Pollution, Okene.
INTRODUCTION
Nigerian cities are witnessing high rate of environmental
deterioration and consequently rated among urban areas
with lowest liveability index in the world (Adedeji and Eziyi,
2010). Humans, animals and plants depend on the land,
water and air within their immediate environment in their
daily lives (Thornton et al.,1994). Thus, trace elements in
the soil we cultivate, find their way into the human body
directly from the soils and/or the underlying bedrock or
through the food chain (Faibridge, 1972).Thus, the
distribution of elements either by natural and/or
anthropogenic sources poses potential health danger to
man and therefore require great attention. Increase in
population without proper environmental practices will
overtime lead to degradation and deterioration of the
quality of the environment (Fordyce et al., 2004). Heavy
metals emanate from urbanization processes like traffic or
vehicular movements, agricultural practice, industrial
activities and waste disposal, which possess a risk to the
health of human, animals and plants (Galadima et al.,
2011).Worldwide interest in evaluation of urban
geochemical environments in order to identify polluted
regions and assess risk to health is on the increase. This
is because environmental problems are mostly due to
developmental processes and are of local, regional and
global effects. In Nigeria, Geochemical Baseline Survey
of Environment (G-BASE) has not been given adequate
attention by the relevant authorities despite the rapid rate
*Corresponding Author: Gideon, Yomi B., Geo-
Environmental Impact Assessment of Urbanization on Top
Soil in Okene Metropolis, North Central, Nigeria. Email:
yommex76@yahoo.co.uk; Tel: +2348033778895
Research Article
Vol. 5(3), pp. 287-296, October, 2019. © www.premierpublishers.org. ISSN: 3019-8261
International Journal of Geology and Mining

Gideon et al. 288
of population growth (Lar, 2013). The direct consequences
of this, among others are that, post-catastrophe impact
cannot be assessed or understood, and the link between
geo-environmental impacts resulting from urbanization
and severe illnesses or sudden deaths of humans in
Nigeria cannot be ascertained (Adedokun et al., 1989).
The life expectancy in Nigeria is, unfortunately, the lowest
in all of West Africa. It is about 53.7years for men and 55.4
years for women (WHO, 2015). This short life span can be
attributed to a lot of health issues hinged on the
geochemistry of our environment. This study therefore, is
to establish the impact of urbanization on the geochemical
environment of Okene metropolis, North central, Nigeria.
Geography of the Study Area
Okene metropolis covers three Local Government Areas,
namely: Adavi, Okehi and Okene (Figure 1) with a total
landmass of 1,707km2 and estimated population of
989,629 (NBS, 2015). It has an area of 54.28 km2 and
perimeter of 93. 11km2.The area is situated between
latitudes 70 30ʹ 15ʺ and 70 38ʹ 25ʺ N and longitudes 60 7ʹ
25ʺ and 60 16ʹ 48ʺ E (Figure 2) and influenced by two
climatic conditions of rain and dry seasons. Annual rainfall
of about 1,500 mm has been recorded by Ogbonna et al.,
(2006). Relative humidity of the area is lowest during the
dry season and highest during the wet season. The pattern
of settlement of Okene metropolis could be described as
nucleated at the centre and linear towards the suburbs.
The relief of the land played primary role in the type of
houses built in the metropolis.
Figure 1: Location map of the study area (modified from
map of Nigeria)
Urbanization
World Urbanization Prospects (WUP) prepared by the
United Nations in 2001 reported that the world’s population
was expected to grow from 6.1 billion in 2000 to 8.3 billion
in 2030 (Table 1 and Figure 2). In Nigeria, human
population quadrupled from 45.21 million in 1960 to 182.20
million in the year 2015, and estimated to be about 262.59
million by 2030 (NBS, 2015). The population of Kogi State
was 3,314,043 in year 2006 and expected to hit 6.10
million in 2030. According to UN (2006) reports, an
estimated 50% of the world’s population were already
living in urban areas as at 2005 and, the urban population
will exceed 61% by 2030. This statistic indicates that
nearly all of the expected growth in population for three
decades (2000-2030) will take place in urban areas, with
almost no growth in the rural population (UN, 2006). These
undeniably suggest that the urban environment will soon
become the most dominant human habitat for the first time
in history. According to National Bureau of Statistics
projections (NBS, 2015), the population of people in
Okene metropolis will increase from 988,268 in year 2015
to 1,413530 by the year 2030 (Table 1 and Figure3a). This
implies an increase in population density from 579 in 2015
to 828 by the year 2030 (Table 1 and Figure 3b) based on
the landmass of 1,707 km2.These increases in numerical
figures and density of people call for environmental
monitoring exercise.
Table 1: Population growth and projection in Nigeria, Kogi
State and study area
Year
Nigeria Kogi State Study Area
Population
Den-
sity Population
Den-
sity Population
Den-
sity
2006 140,431,790 152 3,314,043 119 766,416 449
2011 159,424,742 173 3,730,936 134 864,132 506
2015 182,201,962 197 4,266,906 154 988,268 579
2030 262,599,107 284 6,102,955 220 1,413,530 828
Source: Adapted from NBS (2015)
Geology of the Study Area
Nigeria is made up of three major geological components
which includes the Pre-Cambrian Basement Complex (≥
600 million years), the Jurassic Granites (200- 140 million
years) and Sedimentary Basins which are of Cretaceous
to recent in age (≤ 145 million years).The regional rock in
the study area is migmatite gneiss complex comprising
relics of ancient meta-sedimentary sequences of biotite-
gneiss, calc-silicate rock, quartzite and quartz schist, all of
which had been migmatized and strongly deformed
(Figure 3). Migmatite and biotite gneiss are the most wide
spread rock type. They are well exposed as high hills and
seen in cuts across rivers channels. The gneiss is
segregated into the leucosome and melanosome bands.
The rocks strike in NW-SE direction and dip to the west.
The migmatite and gneisses rocks represent
metamorphosed products of fractionated igneous bodies
as suggested by Odigi et al., (1993). Other rocks
encountered within the metropolis are Granite,
Charnockite, and minor dykes of pegmatite.

Int. J. Geol. Min. 289
(a) (b)
Figure 2: Chart showing population growth and density of study area (NBS, 2015)
Figure 3: Map showing Basement Complex Geology of Nigeria (after Obaje, 2009)
MATERIALS AND METHODS
Sample Collection
Sampling of top soil was based on Geochemical Surveys
of Urban Environments (GSUE) method by Fordyce et al.,
(2004).The satellite imagery of study area was
downloaded, adapted to topographic map of Sheet 246
(Scale 1: 100,000) and gridded to aid collections of top soil
(0 cm to 10 cm) samples at the centre of each cell. A total
of four hundred and ninety-six (496) sub-samples, which
yielded one hundred and twenty-four (124) composite soil
samples were collected from Okene metropolis. Handheld
Dutch auger, sample bags, GPS, permanent ink marker,
field notebook, topographic map, plastic container and
stainless-steel spoons were used during soil sampling. At
each sampling cell, about 200g of 3 to 5 sub-samples were
obtained within a minimum distance of not less than 20
meters apart. Thereafter, the sub-samples in each of the
cell were perfectly homogenized to a composite sample.
The control samples were collected from seemingly
pristine environment outside the demarcated boundaries
of the metropolis, in an area having the same geological
terrain. The geographic coordinates of the sample points
ware taken, recorded and represented on the metropolitan
map (Figure 4).

Gideon et al. 290
Figure 4: Soil sample locations map (Modified from Goggle Map, 2015)
Analytical Methods
Soil samples were separately air-dried and ground using
agate mortal. Each ground sample was subdivided by
quartering, and ground again into fine powder to yield
homogeneous material. Each ground sample was
pulverized, sieved through 60 µm sieve, pressed into pellet
with de-ionized water and air-dried. Chemical composition
of soils was determined using Energy Dispersion X-ray
Fluorescence Spectrometer (EDXRF), Model EDS3600B
(USA) at Centre for Nanotechnology and Advanced
Material, National Agency for Science and Engineering
Infrastructure (World Bank Assisted Project), Akure, Ondo
State, Nigeria.
Environmetric Techniques
Anthropogenic Factor
Anthropogenic factor has been employed by many
workers to quantitatively determine the level of contribution
from lithogenic processes and anthropogenic activities. It
is the ratio of concentration of individual metal in an
environmental media to the concentration of the metal in
its control sample, and it is usually rated to Percent. When
AF value is equal to 1, it implies no anthropogenic
contribution, but when AF is greater than 1 (AF >1), it
means that, anthropogenic contributions are present.
Index of Geo-accumulation (Igeo)
Geo-accumulation index was based on Muller (1979)
method. It has been widely used since the late 1960’s for
assessment and quantification of heavy metals in pollution
studies. Igeo contamination assessment is by comparing
the levels of heavy metals obtained at a site to the
background level in the environment. Igeo is expressed as
follows:
Igeo= Log2 [Cn] /1.5Bn
Where: Cn is the concentration of the metal in the sample,
Bn is the geochemical background/ control value of the
metal and, the constant 1.5 is introduced to minimize the
effect of possible variations in the background values
which may be attributed to natural/Lithologic variations in
the soil sediments. According to Muller (1979), seven
contamination classes are used to define the degree of
metal pollutants in soils:

Table 2: Geo-accumulation indices classes of heavy
metals
Igeo Index value Pollution Intensity
< 0 Practically unpolluted
0-1 unpolluted to moderately polluted
1-2 moderately polluted
2-3 moderately to highly polluted
3-4 highly polluted
4-5 highly to very highly polluted
>5 very highly polluted
Contamination Factor (CF)
Contamination factor was developed by Hakanson (1980).
It is used to evaluate the level or degree of deterioration or
otherwise in the quality of environmental media such as
soil or sediments. The CF of a particular metal in an
environment is the ratio of the concentration of such metal
in the sample to the concentration of the metal in the
control or background sample. CF values indicate the
individual impact of each metal on the sample. Table 3
shows the degrees of contamination that could be
assumed by metals in an environmental media.
CF= C metal / C control;
Cmetal is the concentration of pollutant in the soil or
sediments and Ccontrol is the control value for the metal.
Table 3: Classification of contamination factor indices
Contamination Factor
(CF) Indices
Degree of Contamination
CF < 1.0 Low contamination
1 ≥ CF ≤ 3 Moderate contamination
3 ≥ CF ≤ 6 Considerable contamination
CF > 6 Very high contamination
Pollution Load Index (PLI)
Pollution Load Index was developed to measure the
degree of soil pollution for each metal in a single site. PLI
provides simple but comparative means for assessing a
site quality(Prasad and Kumaris, 2008). PLI is calculated
using the formula proposed by Tomlinson et al., (1980),
which is given as:
PLI= [(CF1) x (CF2) x (CF3)… (CFn)]1/n
Where n is the number of selected metals for the
assessment of PLI and CF is the contamination factor
defined by CF= C metal / Ccontrol; Cmetal is the concentration
of pollutant in the soil or sediments and Ccontrol is the
background value for the metal. PLI< 1 denotes perfection;
PLI = 1 denotes that only baseline levels of pollutants are
present, and PLI>1, indicates deterioration in quality of the
environment/ site. In order words, the PLI for a single site
is the nth root of n number multiplying the contamination
factor (CF values) together. The CF is the quotient
obtained as:
CF= Cmetal concentration / Ccontrol point concentration of same metal;
and; PLI= nth √CF1 x CF2 x CF3 x CFn
Where n is the number of metals studied and CF is
contamination factor.
Correlation Analysis
With aid of Special package for statistics (SPSS) version
20.0, Pearson’s correlation coefficient was utilized for
displaying relationships between variables. High
correlation coefficient between pair of element or groups
of elements is indicative of similar geochemical processes,
factor and reactions which may have influenced metal
distribution while marked differences in element
correlations may indicate dissimilar source materials,
leaching or physico-chemical depositional characteristics
(Kronberg et al., 1979).
Hierarchical Cluster Analysis
Cluster analysis is a series of multivariate methods. It was
employed to define true groups of data such that similar
objects fall into the same class. It joins the most similar
observations and successively the next most similar
observations. The levels of similarity at which observations
are merged are displayed as dendrogram. Low distance
shows that the two objects are similar or close together
whereas a large distance indicates dissimilarity (Praveena
et al., 2007; Sekabira et al., 2010; Harikumar and Jisha,
2010).
RESULTS AND DISCUSSION
Heavy Metals Distribution
The geochemical data of heavy metals in urban soils
(Table 20) plotted by interpolation of geographical data
using Inverse Distance Weighted (IDW) revealed the
spatial distribution of the metals in the metropolis (Figures
5 and 6). The distribution map of As and Pb in urban soil
of Okene metropolis ranged from < 0.01 ppm to 142.55
ppm and < 0.01 ppm to 1,172 ppm, respectively (Figures
5a and 6c). Arsenic and lead have low values in top soils
from Agassa, Okaito, Kuroko, Obangede, Adavi-Eba and
part of Ogaminana regions and relatively higher values in
Okene-Anyigba road flank (Figures 5a and 6c). These
correlating geochemical phenomena strongly suggest that
the metals have similar sources of introduction into the top
soils of the regions involved. The concentration of Cu
distribution ranged from 23.98 ppm to 280.64 ppm. Most
parts of Agassa, Okaito, FCE and Kuroko regions have
greater than 126.66 ppm Cu content in their top soil (Figure
5d). These areas have higher Cu content above the
maximum permissible level in soils for residential and
agricultural purposes of 100.00 ppm by WHO (2015). The
concentrations of Cr and Fe in the urban soil are
predominantly more than 10.10 ppm and 58,326 ppm,
respectively. Higher values between 40 ppm and 157 ppm
contaminate Adavi, Obangede, Ogaminana, Okene, Otete
and Kuroko regions (Figure 5b), while Fe content of at
least 83,589 ppm dominate the same parts of the
metropolis (Figure 6a), indicating similarity in geochemical
pathways of Cr and Fe in the environment. Ni distribution

Gideon et al. 292
in the soils ranged between 17.29 ppm to 227.55 ppm
(Figure 6b) with most part of the metropolis having
concentration value greater that157.48 ppm, which is
much higher compared to the maximum allowable limit of
Ni in urban soils (Table 4). Zn distribution ranged from
18,046 ppm to 192,144 ppm in Okene metropolis soils
(Figure 6d). With maximum allowable limit of 300 ppm in
soils for residential and agricultural purposes, top soils in
Okene metropolis generally have Zn content far above the
stipulated limit.
a) b)
c) d)
Figure 5: Spatial distribution of arsenic, cadmium, chromium and copper in urban soils of Okene metropolis
a) b)
Figure 6: Spatial distribution of iron, nickel, lead and zinc in urban soils of Okene metropolis

c) d)
Figure 6 continued: Spatial distribution of iron, nickel, lead and zinc in urban soils of Okene metropolis
Table 4: Descriptive Statistics of heavy metals in urban soils
Heavy metals
(ppm)
Min. Max. Mean Control soil Maximum Permissible level in
soil (WHO, 2015)n = 124
As 0.00 143.90 5.47 0.05 20
Cd 0.00 4.80 0.91 0.03 3
Cr 0.00 159.00 44.40 35.80 100
Cu 23.00 281.00 153.84 126.00 100
Fe 17601.00 197034.00 78680.70 40471.50 50,000
Ni 16.00 228.00 163.84 159.70 50
Pb 0.00 1181.00 99.29 62.00 100
Zn 91.00 1096.00 731.12 476.50 300
Source: This study
Geochemistry of Urban Soil
The mean concentrations of heavy metals in top soils of
Okene metropolis are higher when compared to the
concentrations found in the control soil (Table 4). Fe is the
most abundant heavy metal in the urban soil. It ranged
from 17601 ppm to 197034 ppm with a mean concentration
of 78680.70 ppm. The trend of abundance of the heavy
metals in the urban topsoil samples (Fe > Zn > Ni > Cu >
Pb > Cr >As > Cd) is similar to the trend of heavy metals
values in the background soil samples (Fe > Zn > Ni > Cu
> Pb >Cr > As > Cd), indicating that urban soil samples
and the control point sample were derived from similar
underlain geology. The average concentrations of Cu
(153.84 ppm), Fe (78680.70 ppm), Ni (163.84 ppm) and
Zn (476.50 ppm) in soils from Okene metropolis are above
the maximum allowable limit for soils usable for agricultural
and residential purposes (WHO, 2015). While As (5.47
ppm), Cd (0.91 ppm) and Cr (44.00 ppm) are below their
maximum limits. Pb (99.29 ppm) concentration was found
to be at its threshold of 100.00 ppm (Table 4).
Environmentric Data Evaluation Methods
Anthropogenic Factor (AF)
The anthropogenic factor of the urban soils revealed that
nearly all the As (99.09%) and Cd (96.81%) contents in the
soils are from anthropogenic sources. Conversely, Fe,
which has 16.28% AF and 83.72% geogenic factor (Table
5), indicated that the concentration of Fe in the soil is
mainly a result of geological (lithological) processes. Both
anthropogenic activities and lithologic processes are
significantly responsible for the concentrations of Cr, Cu,
Ni, Pb and Zn as indicated by their AF and geogenic values
in Table 41 and Figure 74. For example, 55.36% of Cr
concentration in the soils was derived from anthropogenic
activities, while the remaining 44.64% came from
geological processes.
Table 5: The anthropogenic factor of heavy metals in
urban soils
Heavy
metal
Mean
value, Cm
Cp value
AF
value
AF (%)
Geogenic
(%)
As 5.47 0.05 109.40 99.09 0.91
Cd 0.91 0.03 30.33 96.81 3.19
Cr 44.39 35.80 1.24 55.36 44.64
Cu 307.64 293.00 1.05 51.22 48.78
Fe 7868 40471.50 0.19 16.28 83.72
Ni 311.11 297.00 1.05 51.16 48.84
Pb 99.28 62.00 1.60 61.56 38.44
Zn 731.16 476.50 1.53 60.54 39.46
The AF = Cm/Cp; where Cm = measured concentration;
Cp = control point concentration

Gideon et al. 294
Index of Geo-accumulation (Igeo)
The average Igeo index values of the heavy metals show
that, the urban soils are unpolluted with Cr, Cu, Fe, Ni, Pb
and Zn; and highly polluted with As and Cd. The pollution
intensity of the heavy metals in soils is in the order As >
Cd > Fe > Zn > Cr > Ni > Cu (Figure 6)on the average.
Table 6: Summary of geo-accumulation index of heavy
metals in urban soils
Heavy
metals
Range of Igeo index
values
Average
Igeo values
Pollution
Intensities
Min. Max.
As 0.00 - 10.91 4.25 Highly polluted
Cd 0.00 - 6.74 3.11 Highly polluted
Cr -5.33 - 1.56 -0.48 unpolluted
Cu -4.24 - -0.65 -1.58 unpolluted
Fe -1.79 - 1.70 0.18 Unpolluted
Ni -4.77 - -0.97 -1.52 unpolluted
Pb -7.25 - 3.67 -0.36 unpolluted
Zn -2.97 - 0.62 -0.01 unpolluted
Pollution Load Index
The PLI of soils from Okene metropolis ranged from 0.55
to 4.35 with about 85.48% of the metropolis having PLI >
1.0, indicating that the pollution level of soil in most part of
the metropolis is progressively deteriorating in quality
(Figure 7). The highly polluted areas identified fall within
the oldest parts of the city and are with high population
density, where very ineffective sanitary and poor wastes
management services are eminent. These areas include
Okene central, Ogaminana, and the nucleated part
between Adavi-Eba and Agassa (Figure 7). According to
Tomlinson et al., (1980), areas with PLI < 1.0 are less
populated and fall at the outskirt of the city in most cases.
Heavy metal soil pollution of the soils must have been
preceded by enrichment and accumulation processes of
the heavy metals in the soils by geological and
anthropogenic activities. Geologically, rocks from the
metropolis consist of some heavy metals which could be
released into the soils by weathering processes. The use
of fertilizers, biosolids and manures, pesticides and
fungicides which consists some heavy metals meant to
improve crop yields in mini farms within the city may
contribute to enrichment and pollution of the soils.
Figure 7: Soil pollution index map of Okene metropolis
Statistical Data Evaluation
Correlation and Hierarchical Cluster Analyses
At 0.01 significance level, As has moderate to strong
positive correlation coefficient with Cu, Ni, Pb and Zn.
Highest similarity exists between As and Pb (r = 0.938).
Moderate correlation of r = 0.685 exists between Fe and
Cr. Copper (Cu) has moderate correlation with Ni and Pb.
According to Kronberg et al., (1979), the high positive
correlation between As and Pb as well as Fe and Cr
suggests similar sources of geochemical processes,
factors and reactions which have influenced their
distribution. Cd has very low correlation coefficients with
all other heavy metals in the soils as indicated by their low
correlation values (Table 7), indicating that it has dissimilar
geochemical pathway of its introduction into the soils.
R-mode hierarchical cluster analysis performed on the
geochemical data of urban soils extracted two clusters and
two independent variables (Figure 8). Cluster one (1) is an
association of As-Pb-Cr-Fe with highest similarity between
As and Pb, followed by Cr and Fe. This association
indicated a relative homogenous grouping as observed in
correlation analysis. Cd and Zn are standing as
independent and separate variables. They separately
linked clusters one and two at the largest Euclidean
distance which implies maximum level of independency
and dissimilarities in origin. Cluster two is an association
of Cu and Ni.
Table 7: Pearson correlation matrix of heavy metals in urban soils
Variables As Cd Cr Cu Fe Ni Pb Zn
As 1
Cd -.132 1
Cr -.090 .083 1
Cu .572**
.052 -.330** 1
Fe .128 .013 .685**
-.403** 1
Ni .637**
.056 -.173 .689**
-.374** 1
Pb .938**
-.127 -.020 .589**
.196* -.710** 1
.660**
.087 .066 -.126 .017 .002 -.632** 1
*.Correlation is significant at the 0.05 level (2-tailed) ** Correlation is significant at the 0.01 level (2-tailed).

Figure 8: R-mode cluster analysis of urban soils
The mean concentrations of As, Cd, Cr, Cu, Fe, Ni, Pb and
Zn in top soil of Okene metropolis are higher than the
control value, indicating that the surface soil has been
influenced by anthropogenic activities. The similarity in the
trend of average abundances of heavy metals in urban
topsoil and control soil samples: Fe > Zn > Ni > Cu > Pb >
Cr > As > Cd (Table 4), strongly suggests similarity in
geology. The spatial distribution maps for the heavy metals
(Figures 5 and 6) revealed different patterns of elemental
distribution as influenced by the lithological processes and
anthropogenic activities. Although, the primary source of
heavy metals is geological through weathering,
transportation, and other processes. Secondary sources
and enrichment processes by anthropogenic activities is
also a major influence in the distribution of heavy metals in
soils. Human influence could be through emission and
deposition of particulate from fossil fuel combustion,
leachates from wastes dump soils, among others.
Statistically, the association of heavy metals in the urban
soil of the metropolis controls their spatial distribution. For
example, very strong association which exists between
As-Pb (r = 0.938) and Fe-Cr (0.685) in the urban soils as
indicated in the correlation matrix (Table 7) and
hierarchical clustering (Figure 8) of the pairs of metals,
governed the correspondingly high and low concentration
of As (Figure5a) and Pb (Figures5a and 6c) in urban soils
of similar regions in the metropolis. Similar
correspondence also affects Cr (Figure5b) and Fe
(Figure6a) distribution in the urban soil.AF values of the
heavy metals revealed that, nearly all the concentrations
of As (99.09%) and Cd (96.81%) contents in the soils were
from anthropogenic sources. Fe which has 16.28% AF and
83.72% geogenic factors, indicated that its concentration
in the soils is mainly due to geological processes.
However, both anthropogenic activities and lithologic
processes are significantly responsible for the
concentrations of Cr (55.36% anthropogenic and 44.64%
geogenic), Cu (51.22% and 48.78% geogenic) and Ni
(51.16% anthropogenic and 48.84% geogenic). Pb and Zn
have slightly higher contributions from anthropogenic
activities compared to their geogenic contributions. The
urban soils are unpolluted with Cr, Cu, Fe, Ni, Pb and Zn;
moderately polluted with As and highly polluted with Cd
(Table 6). According to Campbell (2006), cadmium (Cd)
and arsenic (As) are mainly found in the earth crust due to
application of agricultural inputs such as fertilizers,
pesticides, biosolids, bush burning. Also, incineration,
deposition of atmospheric contaminants, burning of fossil
fuel, oil spillage, domestic wastes, effluents and leachates
from waste dumps are sources of As and Cd. Furthermore,
the PLI of the soil shows that 85.48% of the sites have PLI
> 1.0, indicating that the pollution level of soil in most part
of the metropolis is progressively deteriorating in quality
(Figure 7). The polluted areas identified fall within the
oldest parts of the city which have high population density,
very ineffective sanitary system and poor wastes
management services. These areas include Okene
central, Ogaminana, and the nucleated part between
Adavi-Eba and Agassa (Figure7).
CONCLUSIONS
i. Heavy metals content in top soil in Okene metropolis
has been influenced by anthropogenic activities
through urbanization to the extent that, the
concentrations of Cu, Fe, Ni and Zn in the urban soils
are above the maximum allowable limit for soils usable
for agricultural and residential purposes (WHO, 2015).
ii. The spatial distribution of heavy metals revealed
different patterns of elemental distribution as influenced
by the underlying rocks, geochemical processes and
anthropogenic activities through urbanization events.
iii. About 85% of the top soil within the study area is
progressively deteriorating at an alarming and varying
degree, while Okene central, Ogaminana, and the
nucleated part between Adavi-Eba and Agassa are
highly polluted.
iv. Highly impacted areas fall the oldest parts of the city
with high population and population density, very
ineffective sanitary system and poor wastes
management services.
RECOMMENDATIONS
i. Policies and laws regarding wastes disposal
management system should be enforced
ii. Awareness on the need for clean environment and the
risks associated with environmental pollution should be
held across the metropolis through formal education,
community workshops and indigenous media system
iii. Remediation of soil already polluted by heavy metals in
order to reduce the associated risk to the ecosystem
and land resource is needful.
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Accepted 1 October 2019
Citation: Gideon YB, Fatoye FB, Omada JI (2019). Geo-
Environmental Impact Assessment of Urbanization on Top
Soil in Okene Metropolis, North Central, Nigeria.
International Journal of Geology and Mining 5(3): 287-296.
Copyright: © 2019: Gideon et al. This is an open-access
article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.

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