Research Journal of Environmental and Earth Sciences 4(2): 186-195, 2012
ISSN: 2041-0492
© Maxwell Scientific Organization, 2012
Submitted: November 10, 2011
Accepted: November 18 , 2011
Published: February 01, 2012
Geochemical Characteristics of Soils from Selected Districts in the Upper East
Region, Ghana: Implications for Trace Element Pollution and Enrichment
1
Gordon Foli, 2 Prosper M. Nude and 3Ohene B. Apea
1
Department of Geological Engineering, College of Engineering, Kwame Nkrumah University of
Science and Technology, Kumasi, Ghana
2
Department of Earth Science, University of Ghana, Legon-Accra, Ghana
3
Department of Applied Chemistry and Biochemistry, University for Development Studies
(UDS), Navrongo Campus, Navrongo, Ghana
Abstract: This study assessed the major and selected trace elements i.e., vanadium (V), chromium (Cr), cobalt
(Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), lead (Pb), tin (Sn), strontium (Sr), zirconium (Zr),
barium (Ba), gallium (Ga), yttrium (Y) concentrations in soils sampled from the B-horizon from selected
communities in the Upper East region of Ghana. The area which is mostly underlain by granitoids, is
characterized by extensive agricultural activities, soil erosion, land degradation and artisanal mining at places.
The objectives were to determine the sources of these elements, and to evaluate the levels of trace element
enrichments, pollution and potential risks in the area. The concentration values of the elements in the soils were
compared to their respective background reference values to establish possible enrichments and pollution. The
relative enrichments of the trace elements were evaluated using Enrichment Factor (EF) and geo-accumulation
index (Igeo), while Pollution Load Index (PLI) was used to compare enrichments within the east and west zones
of the study area. The results show that while the major elements reflect the bedrock compositions, the trace
elements were derived from both natural sources such as weathering of underlying bedrocks, and anthropogenic
sources such as mining and other land use activities. Elements such as Cr, Zn, As, Pb, Sn, Sr, Zr, Ba and Y were
enriched by various degrees while V, Co, Ni, Cu and Ga were not. The results also show that the east side of
the study area was relatively more polluted in trace elements than the west.
Key words: Anthropogenic, enrichment factor, geo-accumulation index, major elements, pollution load index
et al., 2007). In the right doses, some trace metals can be
essential nutrients for plant growth as well as plant and
animal health value to organisms (McBride, 1995).
In the Upper East region of Ghana, land cultivation,
animal husbandry, annual bushfires and over-harvesting
of wood have hugely contributed to environmental
degradation (EPA, 2002). Unsustainable land cultivation
in these areas have also resulted in soil nutrient depletion
(CSIR, 1974), while overgrazing by animals which are
normally raised by the free range type of animal
husbandry is another source of land degradation in the
area (Blanjan, 1991). The high livestock population
density in the Upper East region has exacerbated the
above problems (EPA, 2002; Blench, 2006). For example,
Pal et al. (2007) showed that droppings of cattle that
drank from contaminated mine water may contain high
levels of As. Incidentally, artisanal gold mining with its
attendant environmental impacts have been well noted in
some communities in the area and beyond to the frontiers
of the Burkina-Ghana border. Relating to specific climatic
conditions, the impacts of trace metals-laden particulate
INTRODUCTION
Soils constitute an important location for the transfer,
retention and sedimentation of pollutants in the
environment (Aswathanarayana, 1999) and the contents
of these pollutants in soils are becoming higher by the day
due to increasing anthropogenesis (Collin and Melloul,
2003). Weathering of rocks often mobilizes elements into
soils, and when these soils become exposed to agents of
erosion, the elements can be transported and distributed
into the larger environment. Trace elements distribution
in soils depends on factors such as the nature of parent
material, weathering processes, human activity and
climatic conditions (Martínez et al., 2003). Trace metals
such as As, Pd, Cd have been noted to be characterized by
long periods of residual, high invisibility, little transfer,
high toxicity, and complexity of chemical behaviors
(Alloway, 1995). These metals are capable of entering the
food chain (Wenzel and Jockwer, 1999), where exposure
to elevated levels can pose threat to health and life
(Nriagu and Pzcyna, 1988; Qian et al.,1996; Agbozu
Corresponding Author: Gordon Foli, Department of Geological Engineering, College of Engineering, Kwame Nkrumah University
of Science and Technology, Kumasi, Ghana
186
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
Fig. 1: Geological sketch map of the study area showing the lithological distributions
matter sometimes flux into the Upper regions of Ghana
from the Sahara desert during the hamarttan period
(Breuning-Madsen and Awadzi, 2005).
Rainstorm activities and seasonal flooding of most
parts of the area are also common means of element
mobilization and distribution in the environment.
In this study we determined the concentrations of the
major and selected trace elements in soils sampled from
the B-horizon from selected districts in the Upper East
region, Ghana. We used the data to assess the distribution
of the major and trace elements in the soils relative to the
underlying rocks, and evaluate the levels of trace metal
enrichment and the potential ecological risks in the soils
from the area.
Birimian granitoids interspersed with minor pyroclastic
and volcaniclastic rocks (Fig. 1). The north-east trending
Bole-Nangodi gold belt occurs to the south-eastern
portion of the area (Kesse, 1985; Leube et al., 1990;
Taylor et al., 1992; Hirdes et al., 1992). Typical soils in
the area include ochrosols, made up of moderately
shallow to moderately deep, concretionary and/or
gravelly, and heavy to medium textured soils that overlie
weathered granitic rocks. According to Obeng (2000) and
Blench (2006), hydromorphic soils are normally
concentrated in valley bottoms while vegetation is made
up of the Sudan savanna type and characterized by an
anthropogenic landscape that is prone to wind erosion.
Also, rainy and dry seasons in the area span May-October
and October-April respectively, mean annual rainfall is
about 700-1200 mm, temperatures range from about 45oC
in March/April to 12oC in December, while annual
evaporation range and aridity index are 1652-1720 mm
and 0.60, respectively.
METHODOLOGY
The study area: is located in the Upper East region of
Ghana; the area is underlain by Paleo-Proterozoic
187
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
Fig. 2: Sketch map of study area showing sampling points
or sediments were used to evaluate the trace element
concentrations in the soils. Detailed computation and
interpretation of the above indices have been described by
Nude et al. (2011). The EF is the relative abundance of a
chemical element in soils compared with the background;
it is used to measure geochemical trends for comparison
between areas, and also to express anthropogenic
pollution (Hernandez et al., 2003; Praveena et al., 2007;
Mohiuddin et al., 2010). The Igeo assesses pollution by
quantifying metal accumulation in sediments (Olatunji et
al., 2009), while the PLI is also a measure of pollution of
an area, based on the ratio of the determined metal
concentration to the background value of the metal at
specific points within the area of assessment (Mohiuddin
et al., 2010).
In the assessment of the pollution indices for the trace
elements in this study, Cesium (Cs) was used as reference
element (Loska et al., 2003) for estimating the EF; crustal
or background values for V, Cr, Ni, Cu, Zn, As and Pb are
from Mohiuddin et al. (2010); Co is from McLennan and
Taylor (1999), while Sn, Cs, Sr, Ba, Ga and Y, are from
Jefferson Laboratory report (2007). Pollution Load Index
(PLI) was estimated for only the enriched parameters. The
Spearman rank correlation was used to compare all the
trace elements to determine possible interrelationships and
chemical associations between the trace elements
(Forstner, 1981; Jaquet et al., 1982). The mean
concentration values of parameters were also compared
with crustal values to evaluate their relative enrichments
or depletions. The mean concentrations of the major
elements in the soils from the east and west cluster areas
Sampling: Nineteen representative soil samples were
taken from locations covering seven communities within
the study area (Fig. 2). The communities are; Paga,
Navrongo, Chuchuliga and Sandema, forming the west
cluster of sampling points (SP 1, 2, 3, 4, 5, 6, 7 and 8),
while Bolgatanga, Zuarungu and Bongo form the east
cluster (SP 9, 10, 11, 12, 13, 14, 15, 16, 17 18 and 19)
(Fig. 2). 2 kg composite samples were collected from the
B-horizon at depths of 30-40 cm at each sampling point.
The samples were air dried, disaggregated and sieved
through 2 mm passing to remove pebbles and debris, and
the samples analyzed for major and trace elements at the
Ghana Geological Survey laboratory.
Sample analyses: 4.0 g of the soil samples were
weighed and mixed with 0.9 g of Fluxana Licowax C
Micropowder PM (Hoechstwax) and transferred into
sample caps. The samples were homogenized at
automated frequency of 15 rev/sec for 3 min and pressed
into pellets. The pressed pellets were then analysed by
X-Ray Fluorescence (XRF) Spectrometer. Major element
concentrations were determined for SiO2, Al2O3 MgO,
MnO, Fe2O3, K2O, Na2O, CaO, TiO2 and P2O5, and
concentrations of selected trace elements were determined
for V, Cr, Co, Ni, Cu, Zn, As, Pb, Sn, Sr, Zr, Ba, Ga, Y,
and Cs.
Pollution evaluation and correlation of major and
trace
elements:
Enrichment
Factor
(EF),
Geoaccumulation index Igeo and Pollution Load Index
(PLI) which are methods of expressing pollution in soils
188
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
during weathering in well-aerated soils that have acidic
pH (5.0-5.5), while elements such as Co, Ni, Cu, Zn, and
Pb are depleted under the same conditions (Marques
et al., 2003). Considering the rock types in the area, and
nature of the soil types and their pH range (pH = 4.7-6.3,
average 5.6, Apea, 2010), elements such as Zr, Cr, Y, Sr,
and Ba, are probably accumulated in the soils as a result
of weathering of the underlying rocks. For example Zr
which exists in soils mainly in zircon, is highly resistant
to weathering and thus can persist and be accumulated
while, Cr and Y can also be accumulated by incorporating
into octahedral sites in the structures of clay mineral
fractions such as kaolinite and gibbsite during prolonged
weathering activity (Marques et al., 2003; Shannon and
Prewitt, 1969). Sr and Ba are enriched in granitic rocks,
and as the area is mostly underlain by granitoids, their
enrichment in the soils is not surprising. The depletion of
elements such as Co, Ni and Cu could be due to the
assumption that, being monovalent or divalent elements,
they could be lost during long periods of weathering since
they cannot be incorporated into the structures of the clay
mineral fractions without producing charge imbalances
were also used to determine whether the concentrations
vary with the basement geology and rock types over
which they occur.
RESULTS AND DISCUSSION
Trace element variations: Trace element the major
element concentrations are shown in Table 1 and 2
respectively, while Table 3 presents the correlation
between the trace elements. Table 4 and 5 presents the CF
and the Igeo values of the trace elements at the specific
sampling points respectively, whereas Table 6 shows the
PLI of the enriched elements at the east and west sides of
the study area. Fig. 3 is a histogram showing the
comparison of the concentrations of the means of trace
metals with crustal values at the east and west sides of the
study area.
From Fig. 3, the mean concentrations of Cr, Zn, Pb,
Sn, Sr, Zr, Ba and Y are higher than their respective
crustal values at both sides, while those of V, Co, Ni, Cu,
and Ga are lower at both sides. Except for Cr and Y, the
soils from the east side record higher concentrations of the
trace elements than the west side. Arsenic (As) and Cs in
the soils are found to be higher than crustal values at the
east but lower at the west side. In Fig. 4 the PLI of the
enriched trace elements from both sides have been
compared; the east cluster indicate relatively more intense
contamination than the west cluster. Again from the PLI
values of the nine elements assessed, only Cr and Y
recorded higher contamination at the west side than the
east. Yttrium has the highest PLI value at both sides while
As also has the least in both cases.
L og concentration (ppm )
10000.0
West side
East side
Crustal values
1000.0
100.0
10.0
1.0
V Cr Co Ni Cu Zn As Pb Sn Cs Sr Zr Ba Ga Y
Major element concentrations: Figure 5 shows the
comparison between the means of selected major elements
concentration in the east and west sides of the area. SiO2,
Al2O3, Fe2O3, K2O, and Na2O are dominant in the soils in
that decreasing order, while TiO2, P2O5 and MnO are
relatively very low. These trends appear to conform to the
compositions of the bedrocks, considering that these rocks
are predominantly granitoids; these rocks are acid rocks
of quartzo-feldspathic composition and chemically
evolved. The observed concentrations of the major
elements in the soils are however, relatively lower than
Fig. 3: Histogram showing the comparison of concentration
(log ppm) of the means of trace elements from the east
and west sides of the study area
6.0
East side
West side
PLI (value)
5.0
that of average granitoids because the soils may have
undergone dilution effects due to the redistribution and
probable transportation after weathering. Notably all the
major elements have relatively higher concentrations in
soils from the east side than the west, and these conform
to the pattern observed for the trace elements.
4.0
3.0
2.0
1.0
0.0
Cr
Zn
As
Sr
Y
Zr
Enriched metals
Sn
Ba
Pb
Fig. 4: Histogram showing comparison of Pollution load index
of enriched elements from the east and west sides of the
study area
Sources and distributions of the metals: Trace elements
such as Zr, Cr, Y, V and Ga are noted to accumulate
189
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
Table 1: Trace elements concentrations (ppm) in the soils from the sampling sites, and respective crustal values
West side sampling results
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------SP
V
Cr
Co
Ni
Cu
Zn
As
Pb
Sn
Cs
Sr
Zr
Ba
Ga
Y
1
103.0
66.8
18.0
12.9
37.7
214.0
1.5
110.0 14
5.9
725.0 673.0
1944.0 15.0
18.0
2
58.0
289.0 19.0
18.0
33.1
103.0
0.6
18.0
8.2
1.5
164.0 560.0
440.0
9.5
19.0
3
75.0
996.0 12.0
33.8
16.5
28.0
0.5
10.0
3.3
1.5
27.6
340.0
591.0
1.6
13.0
4
76.0
59.5
15.0
12.4
24.9
95.0
1.9
29.0
5.4
1.5
818.0 597.0
1353.0 13.0
13.0
5
41.0
221.0 18.0
15.0
13.9
17.0
0.8
20.0
1.0
2.9
299.0 733.0
1167.0 11.0
15.0
6
59.0
236.0 19.0
12.7
30.4
105.0
1.1
16.0
5.1
3.6
251.0 791.0
402.0
9.4
13.0
7
76.0
80.2
15.0
13.1
32.7
72.0
2.2
15.0
2.8
1.5
296.0 975.0
352.0
12.0
14.0
8
56.0
837.0 12.0
17.7
13.5
25.0
0.7
10.0
3.7
1.7
375.0 577.0
480.0
15.0
14.0
MW
68.0
348.2 16.0
17.0
25.3
82.4
1.2
28.5
5.4
2.5
369.5 655.8
841.1
10.8
14.9
East side sampling results
9
120.0
553.0 36.0
12.0
33.5
48.0
0.6
7.8
2.0
1.8
265.0 181.0
360.0
14.0
20.0
10
46.0
442.0 17.0
13.2
21.3
81.0
0.7
34.0
5.9
2.9
951.0 176.0
2150.0 15.0
13.0
11
67.0
648.0 16.0
14.5
31.3
134.0
1.0
50.0
5.6
3.7
411.0 611.0
1126.0 13.0
12.0
12
74.0
529.0 15.0
13.3
33.7
131.0
1.3
52.0
5.7
2.0
398.0 653.0
1062.0 14.0
12.0
13
85.0
458.0 13.0
14.7
33.1
145.0
4.3
35.0
8.0
3.9
675.0 804.0
1830.0 15.0
17.0
14
67.0
64.1
15.0
10.3
17.4
68.0
0.4
14.0
3.8
1.2
740.0 1109.0 982.0
15.0
15.0
15
102.0
137.0 21.0
13.5
23.9
367.0
4.7
70.0
6.3
3.8
867.0 751.0
2288.0 16.0
13.0
16
77.0
133.0 16.0
17.3
42.0
272.0
1.8
40.0
4.0
2.0
311.0 573.0
476.0
12.0
16.0
17
46.0
572.0 17.0
53.4
52.4
411.0
1.3
15.0
5.7
2.0
398.0 653.0
1062.0 9.1
12.0
18
85.0
458.0 13.0
14.7
33.1
145.0
4.3
72.0
8.0
3.9
67.0
804.0
1830.0 15.0
17.0
19
60.0
498.0 12.0
9.7
14.9
23.0
0.6
28.0
7.6
4.3
704.0 1131.0 2290.0 14.0
19.0
ME
75.4
408.4 17.4
17.0
30.6
165.9
1.9
38.0
5.7
2.9
526.1 676.9
1405.1 13.8
15.1
MTW
72.3
383.0 16.8
17.0
28.4
130.7
1.63
4.0
5.6
2.7
460.1 668.0
1167.6 12.6
15.0
Vc’stal 135.0
100.0 29.0
75.0
55.0
70.0
1.8
12.5
2.3
3.0
375.0 165.0
425.0
19.0
3.2
SP: Sampling point; MW: Mean at west side; ME: Mean at east side; MTW: Weighted total of the means from the west and east sides; V c’stal: Crustal
value (Values in ppm)
Table 2: Major elements concentration (wt. %) from east and west sides of the study area
West side sampling results
----------------------------------------------------------------------------------------------------------------------------------------------------------------------SP
Na2O
MgO
Al2O3
SiO2
P2O5
K2O
CaO
TiO2
MnO
Fe2O3
1
2.17
1.73
11.99
51.01
0.59
4.18
1.11
0.63
0.09
4.71
2
0.58
2.13
8.70
52.96
0.96
1.13
2.64
0.89
0.08
3.35
3
2.16
2.08
8.66
47.34
0.17
1.09
1.28
0.65
0.07
3.59
4
1.67
1.60
8.57
40.56
0.43
2.74
6.03
0.54
0.08
3.39
5
2.51
1.92
10.16
60.42
0.24
2.69
0.87
0.67
0.06
2.55
6
2.38
2.20
7.91
53.44
0.42
1.19
1.12
0.49
0.06
3.10
7
2.16
2.08
8.66
47.34
0.17
1.09
1.28
0.65
0.07
3.59
8
3.05
2.12
11.24
51.68
0.21
1.05
2.63
0.46
0.04
2.88
Mw
2.09
1.98
9.49
50.59
0.40
1.90
2.12
0.62
0.07
3.40
East side sampling results
9
1.98
3.08
11.46
41.00
0.18
0.8
2.85
0.79
0.18
6.6
10
1.96
1.74
17.18
48.61
0.58
4.42
1.72
0.77
0.05
3.53
11
2.81
1.93
11.24
54.5
0.36
2.94
1.36
0.48
0.09
3.26
12
1.85
1.83
11.72
58.16
0.50
3.07
0.75
0.47
0.06
3.27
13
2.22
1.80
10.96
50.27
0.35
4.23
2.38
0.71
0.06
3.73
14
1.92
1.80
11.55
50.82
0.24
1.78
1.38
0.53
0.06
2.66
15
2.30
1.79
12.43
52.63
0.32
5.11
1.15
0.69
0.09
4.29
16
2.65
2.43
10.87
52.55
0.66
1.58
2.09
0.56
0.09
4.14
17
1.06
2.34
7.79
49.25
0.91
1.24
8.09
0.95
0.08
3.56
18
2.36
1.85
12.59
54.38
0.25
1.78
1.38
0.53
0.06
2.66
19
1.89
1.87
12.98
65.28
0.25
5.19
0.32
0.88
0.03
2.57
ME
2.09
2.04
11.89
52.50
0.42
2.92
2.13
0.67
0.08
3.66
SP: Sampling point; MW: Mean at west side; ME: Mean at east side; (Values in wt %)
(Marques et al., 2003). The enrichment of Zn, and Pb in
the soils contrary to expectation seems to suggest that
they were to some extent mobilized from wider
environment, and probably through anthropogenic
activities. Zinc and Pb being divalent elements are
capable of forming strong complexes with soil organic
matter (Marques et al., 2003), probably within the
hydromorphic soil zones from where they may be
190
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
Table 3: Correlation matrix of the weighted mean concentrations of the trace elements from all the sampling sites
Metal
V
Cr
Co
Ni
Cu
Zn
As
Pb
Sn
Cs
Sr
Cr
- 0.15
Co
0.50
- 0.14
Ni
- 0.30
0.44
- 0.12
Cu
0.18
- 0.12
0.24
0.42
Zn
0.18
- 0.20
0.07
0.50
0.70
As
0.44
- 0.26
- 0.12
- 0.11
0.26
0.49
Pb
0.29
- 0.15
- 0.17
- 0.30
0.27
0.44
0.50
Sn
0.24
0.02
- 0.33
- 0.08
0.24
0.31
0.44
0.53
Cs
0.03
0.04
- 0.06
- 0.26
- 0.06
0.22
0.48
0.75
0.50
Sr
- 0.03
- 0.40
- 0.07
- 0.30
- 0.19
0.16
0.16
0.21
0.24
0.21
Zr
- 0.14
- 0.43
- 0.46
- 0.22
- 0.12
0.03
0.25
0.09
0.21
0.22
0.15
Ba
0.09
- 0.07
- 0.25
- 0.18
- 0.23
0.21
0.48
0.62
0.57
0.69
0.67
Ga
0.25
- 0.34
0.12
- 0.60
- 0.02
0.08
0.38
0.47
0.29
0.33
0.59
Y
0.40
- 0.07
0.34
- 0.32
- 0.03
- 0.23
0.00
0.09
0.16
0.24
- 0.18
Table 4: Contamination factors of the trace elements from all the sampling points
SP
V
Cr
Co
Ni
Cu
Zn
As
Pb
1
1.1
19.9
0.8
0.9
0.6
0.8
0.6
1.6
2
0.5
8.6
0.9
1.1
1.4
8.8
1.1
1.8
3
0.7
14.8
0.7
0.4
0.4
0.6
0.7
1.4
4
1.5
9.2
2.1
0.3
1.0
1.1
0.6
1.0
5
0.9
5.8
1.3
0.5
1.2
2.9
0.7
2.9
6
0.3
3.5
0.3
0.1
0.2
0.2
0.2
1.6
7
1.2
1.6
1.3
0.3
0.8
2.4
0.6
2.8
8
0.6
1.1
0.6
0.1
0.3
4.1
2.1
4.4
9
0.5
3.5
0.3
0.2
0.5
1.6
1.8
4.4
10
0.4
0.3
0.3
0.1
0.3
1.6
0.4
4.5
11
0.4
4.6
0.6
0.2
0.4
1.2
0.4
2.8
12
0.9
2.0
0.8
0.3
1.1
5.8
1.5
4.8
13
0.4
2.0
0.5
0.1
0.5
1.3
0.5
1.1
14
1.1
1.6
1.0
0.3
1.2
2.1
2.4
2.4
15
0.4
5.3
0.4
0.2
0.5
1.6
0.5
3.2
16
0.8
7.9
0.8
0.3
0.9
2.8
1.1
6.2
17
0.5
3.5
0.3
0.2
0.5
1.6
1.8
2.2
18
1.1
1.2
1.0
0.3
0.9
2.7
2.1
4.6
19
0.3
2.3
0.6
0.2
0.3
0.3
0.5
1.7
SP: Sampling point
Table 5: Geo-accumulation indices of the trace elements from all the sampling points
SP
V
Cr
Co
Ni
Cu
Zn
As
Pb
1
-1.4
2.7
-1.9
-1.7
-2.3
- 1.9
- 2.4
- 0.9
2
-2.1
1.9
-1.4
-1.1
-0.7
2.0
- 1.1
- 0.3
3
-1.9
2.5
-1.9
-2.7
-2.6
- 2.1
- 1.9
- 0.9
4
-0.8
1.9
-0.3
-3.2
-1.3
- 1.1
- 2.2
- 1.3
5
-1.8
0.9
-1.2
-2.6
-1.3
0.0
- 2.2
- 0.1
6
-1.8
1.7
-1.9
-3.5
-2.5
- 2.2
- 2.2
0.6
7
-1.6
- 1.2
-1.5
-3.4
-2.2
- 0.6
- 2.8
- 0.4
8
-1.0
- 0.1
-1.1
-3.1
-1.8
1.8
0.8
1.9
9
-1.3
1.6
-1.7
-2.9
-1.3
0.5
0.7
1.9
10
-1.0
- 1.2
-1.3
-3.1
-1.1
1.0
- 0.8
2.6
11
-2.1
1.6
-1.4
-3.1
-2.0
- 0.4
- 1.9
0.9
12
-1.4
- 0.2
-1.4
-2.7
-1.0
1.4
- 0.6
1.1
13
-1.8
0.7
-1.2
-3.1
-1.4
0.0
- 1.3
- 0.2
14
-1.4
- 0.9
-1.5
-3.1
-1.3
- 0.5
- 0.3
- 0.3
15
-1.6
2.1
-1.4
-3.0
-1.4
0.4
- 1.4
1.4
16
-1.5
1.8
-1.5
-3.1
-1.3
0.3
- 1.1
1.5
17
-1.3
1.6
-1.7
-2.9
-1.3
0.5
0.7
0.9
18
-1.4
- 1.3
-1.5
-3.2
-1.7
- 0.1
- 0.5
0.6
19
-2.3
0.6
-1.3
-2.9
-2.6
- 2.6
- 1.8
0.1
SP: Sampling point
C
distributed in the area. Other factors apart from pedogenic
effects that are likely to affect the extent of metals
distribution in soils include:
191
Sn
2.9
3.7
2.8
1.4
7.1
2.3
4.1
2.2
2.7
3.1
2.7
2.6
1.8
2.4
2.0
3.7
2.7
4.7
0.4
Sr
0.1
1.6
1.8
1.2
0.9
1.3
4.9
1.8
0.1
1.0
2.6
1.2
0.6
1.6
0.9
1.6
1.4
4.4
0.8
Sn
- 0.1
0.7
0.1
- 0.8
1.2
1.1
0.1
0.9
1.2
2.0
0.8
0.2
0.6
- 0.3
0.7
0.7
1.2
0.6
- 1.8
Sr
- 4.3
- 0.5
- 0.6
- 1.1
- 1.8
0.3
0.4
0.6
- 3.1
0.4
0.8
- 0.9
- 1.2
- 0.9
- 0.5
- 0.5
0.3
0.5
- 0.9
Zr
4.1
5.9
6.2
1.8
6.8
4.8
16.8
3.6
3.7
2.1
1.1
5.2
4.0
11.8
3.0
5.9
3.7
7.2
4.6
Zr
0.5
1.4
1.2
- 0.5
1.2
2.2
2.2
1.6
1.7
1.4
- 0.5
1.2
1.7
2.0
1.3
1.4
1.7
1.3
1.6
Zr
0.21
0.25
0.07
Ba
Ga
0.49
- 0.001 0.22
Ba
2.8
3.7
2.0
1.4
2.1
3.8
5.8
4.3
3.3
2.3
5.2
1.7
0.8
1.7
2.1
3.7
3.3
6.4
2.8
Ga
0.2
0.7
1.4
1.2
1.0
0.5
2.0
0.7
0.6
0.4
0.8
0.9
0.4
1.3
0.6
1.1
0.6
1.4
0.6
Y
8.1
5.6
7.7
10.4
11.9
4.1
11.7
3.2
4.1
2.9
4.2
7.5
3.4
8.8
3.0
5.6
4.1
8.1
4.8
Ba
- 0.1
0.7
- 0.4
- 0.8
- 0.5
1.8
0.6
1.8
1.5
1.6
1.8
- 0.4
- 0.7
- 0.9
0.8
0.7
1.5
1.1
0.9
Ga
-4.2
-1.6
-0.9
-1.0
-1.6
-1.0
-0.9
-0.8
-0.9
-0.9
-0.9
-1.2
-1.6
-1.2
-1.1
-1.0
-0.9
-1.1
-1.4
Y
1.4
1.3
1.5
2.1
2.0
2.0
1.6
1.4
1.8
1.9
1.4
1.7
1.4
1.5
1.3
1.3
1.8
1.4
1.6
Artisanal gold mining activities and accompanying
unregulated mine spoil disposal (Wang et al.,
2004)
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
Table 6: Pollution Load Index of enriched trace elements from the east
and west sides of the study area
Enriched elements
East side
West side
Cr
2.2
3.7
Zn
1.5
1.0
As
0.9
0.5
Sr
1.0
0.8
Y
4.5
4.8
Zr
3.6
3.3
Sn
2.2
2.0
Ba
2.5
2.0
Pb
2.9
1.3
Log mean composition (wt. %)
10000.0
Zn/Ni/Cu (0.50-0.70), Ba/Pb/Sn/Cs/Sr (0.57-0.69),
Ba/Ga/Sr (0.49-0.59) and Pb/Sn/Cs (0.50-0.75) all
indicate moderate associations from similar sources.
Enrichment of trace metals and environmental
concerns: Metal enrichment as well as excessive
exposure to particulate matter trace elements in the
environment can have serious health consequences and
potential health risks (Lu et al., 1992; Gao et al., 2005).
Considering both the EF and the Igeo values (Table 3
and 4), V, Co, Ni, Cu and Ga are generally depleted at all
the sampling points probably due to weathering under
acidic and aerated conditions while V and Ga, which
should have been enriched under the same geochemical
conditions, were not enriched probably due to
mineralogical variations in the area rocks. The correlation
between Cu/Ni/Zn (0.50; 0.70); Ga/Sr/Ba (0.59; 0.67),
Cs/Sn/Pb (0.50; 0.75) seems to suggest that Ni, Cu, Cs
and Ga, although not mobilized have the potential for
doing so under changing environmental conditions.
Yttrium (Y) is generally enriched moderately or
significantly at all the sites. The element is more
commonly found in household items; it correlated weakly
with all the elements determined, thus confirming its
source in the area as probably due to anthropogenesis.
Excessive inhalation of Y can cause lung embolism, lung
cancer and liver problems when bio-accumulated
(Lenntech, 1998-2011). Generally As is moderately
enriched at only one site (SP 8), but measured values at
sampling points 7, 13, 15 and 18 exceeded the crustal
value of 1.8 mg/kg. Arsenic may commonly be mobilized
from arsenopyrite, a mineral which is often associated
with gold mineralization in the Birimian rocks in the
south eastern side of the study area. Prolonged exposure
of humans to As contamination can have serious health
consequences. Tin (Sn) and Zr are generally enriched at
all except two sampling points each, SP 4 and 19 for Sn
and SP 4 and 11 for Zr respectively. Although the effects
from Sn exposure have not been widely documented, the
possibility of such effects exists (Lenntech, 1998-2011).
Also, Sr (enriched at SP 7, 11 and 18), occurs
naturally in rocks, soil, water and air, but also in
anthropogenic form and can accumulate in biological
samples (Lenntech, 1998-2011). The stable form of Sr has
tremendous health benefits (Dean, 2004). Significant
enrichments of Zn are recorded at SP 2, 8, 12 and16. Zinc
occurs naturally in rocks, air, water and easily
accumulates in soils as well (Malle, 1992). Though of
immerse benefits to all organisms (Van Assche et al.,
1996), Zn pollution may affect human health (ANL,
2005), some farm animals and plant species, fish, wildlife
and invertebrates (Munkittrick et al., 1991; Eisler, 1993).
West side
East side
1000.0
100.0
Na O MgO L O3 SiO
P O5
K O CaO TiO
Fe O3
10.0
MnO
1.0
Fig. 5: Histogram showing comparison of the concentrations
of the means of the major elements (log wt %).
C
C
Sand and gravel winning which often result in the
breakdown of the soil structure (EPA, 2002)
Use of agrochemicals including pesticides and
herbicides on farmlands and the annual flooding of
the area often accompanied by sheet-wash erosion
Other factors such as the influx of dust laden northeast trade winds during the harmattan season have been
documented to often deposit fine dust which could
possibly be associated with air-borne metal pollutants
in the area (Breuning-Madsen and Awadzi, 2005; He
et al., 2007).
According to these authors, the harmattan dust has
high mineralogical assemblages of kaollinite, illite,
smectite and chlorite; these minerals have the possibility
of adsorbing trace metals and transporting them as
particulate matter. For example Schulthess and Huang
(1990), Matini et al. (2011) and Usman et al. (2004)
reported the enrichment of trace metals such as Ni,
Cd, Zn, Pb, As and Cu in soil s dominated by clay
minerals. The common use of livestock manures on
farms is anothe r possible sources of contamination of
the soils in the study area ( Li and Chen, 2005).
On the correlations in trace element concentrations,
weak values and in some instances negative values were
obtained particularly between V, Cr, Co and Y. The
correlation values between Zn/Pb/As (0.44-0.50),
192
Res. J. Environ. Earth Sci., 4(2): 186-195, 2012
Although not enriched, Ni, Cu, Cs and Ga may easily
become mobilized under changing conditions. The
concentrations of Zn, Pb, As, Cu, Cr, Ni and/or their
combinations could be of danger to health. Measures to
minimize degradation of the environment, such as
improved farming practices, regulating artisanal mining
procedures, preservation of natural resources among
others may help minimize the effects of these pollutants
in the environment. The major elements however, appear
to reflect the basement rock compositions.
The effect of Zn-Cu combination has also been shown to
be quite lethal to aquatic life (Finlayson and Ashuckian,
1979; Finlayson and Verrue, 1980). Although Cu was not
enriched in the area, the high correlation of 0.70 with Zn
may suggest the probable increase of Cu contents under
favorable conditions, and this may in turn affect aquatic
life in dams which are numerous in the area. Enrichment
of Pb is relatively dominant in the eastern side and its
contamination in the environment may lead to serious
public health problems, particularly for children (ATSDR,
1988). From the present data variable, enrichments of Cr
and Pb have been noted and together with As, the
combinations of these elements could be of serious health
issues in the area. For example, ATSDR (2004) stated
serious human toxic health effects associated with
combinations of As-Pb-Cr orally ingested from soils. As
an isolated element, Cr has positive health benefits
(Cefalu and Hu, 2004).
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