British Journal of Pharmacology and Toxicology 3(6): 267-272, 2012
ISSN: 2044-2459; E-ISSN: 2044-2467
© Maxwell Scientific Organization, 2012
Submitted: September 08, 2012
Accepted: October 19, 2012
Published: December 25, 2012
Use of Sequential Extraction Technique to Estimate Nickel Bioavailability in Guinea
Corn and Soils of Kaduna Metropolis, Nigeria
S.S. Mohammed, A.A. Orukotan and H.K. Yahaya
Department of Applied Science, College of Science and Technology,
Kaduna Polytechnic, Kaduna, Nigeria
Abstract: An estimation of Nickel bioavailability in guinea corn and soils from Kaduna metropolis was carried out.
The objective of the study was to determine the bioavailable Nickel in guinea corn and soil samples by Flame
Atomic Absorption Spectrometry (FAAS) using sequential extraction technique. The results indicated that the soil
samples collected from various locations contain varying amounts of Nickel and were distributed between residual,
oxide and carbonate/organically bound phases. The results also indicated that in all the sampling sites, Nickel
concentration is below the tolerance limit value of 50 mg/kg and the ANOVA (p = 0.070>0.05) indicated no
significant difference in the Nickel concentration across the various guinea corn crops. Similarly the ANOVA (p =
0.004<0.05) showed a significant difference in the Nickel concentration across the various guinea corn soils.
Keywords: Bioavailability, guinea corn, nickel, sequential extraction, soil
of HNO3/H2O2, oxalic acid, Na2EDTA and acetic acid.
The relation between the guinea corn Ni contents and
Ni content of the soil extracts was also investigated.
INTRODUCTION
Nickel is a nutritionally trace metal for at least
several animal species, micro-organisms and plants and
therefore either deficiency or toxicity symptoms can
occur when respectively, too little or too much Nickel is
taken up (Bencko, 1983; Scott-Fordsmand, 1997).
The accumulation of heavy metals in soil from
different sources such as atmospheric deposition,
agricultural practices, urban-industrial activities, etc is
of great environmental concern because of metal
persistence and toxicity. In this sense, there is a
consensus in the literature that the estimation of the
bioavailable heavy metals in soil is a preferable tool to
determine potential risks from soil contamination than
the total contents (Yusuf, 2006).
Heavy metals may be distributed among many
component of the soil or sediment and may be
associated with them in different ways (Harrison et al.,
1981; Chlopecka et al., 1996; Kabala and Singh, 2001;
Khairah et al., 2009). The general approach for soil
speciation studies has been to separate the soil using
different chemical reagents or solvents fraction and by
analyzing each fraction to determine the amount of
element combined or associated with each soil fraction
or phase (Yaman et al., 2000).
In this research, Nickel concentrations in guinea
corn and soil samples were determined by Flame
Atomic Absorption Spectrometry (FAAS) using
sequential extraction technique. The soil samples were
extracted using chemical reagents such as the mixture
MATERIALS AND METHODS
The soil samples were dissolved by using the
chemical reagents such as mixture of HNO3/H202,
(COOH)2, Na2EDTA and CH3COOH. The relation
between the guinea corn contents and the Ni contents of
soil extracts was also investigated. In the digestion and
extraction procedures, concentrated HNO3, H202, 1.0 M
(COOH)2, 0.05M Na2EDTA and 1.0 M CH3COOH
were used. Stock solution of Ni (1000 mg/L) was
prepared by dissolving Ni (NO3)2 in 1.0 mol/L nitric
acid.
Preparation of samples: The study covered seven
agricultural sites in Kaduna, Nigeria (Fig. 1). The sites
are: Nasarawa (NS), Sabon Tasha (ST), Unguwar
Mu’azu (UM), Tudun Wada (TW), Kakuri (KK),
Mando (MD) and Kabala West (KB). The samples were
collected during the harvest season (Oct-Nov., 2008,
2009 and 2010). The soil samples were collected from
different areas enumerated at the depth of 10 cm below
the surface (Yaman et al., 2005). The guinea corn
samples were collected at each of the locations. Kachia
a town situated about 130 km away from Kaduna was
taken as control. The sample was washed with water
and allowed to dry on filter papers. Both samples were
dried at 85°C. All the analyses were carried out in the
analytical laboratory of the Department of Applied
Corresponding Author: S.S. Mohammed, Department of Applied Science, College of Science and Technology, Kaduna
Polytechnic, Kaduna, Nigeria
267
Br. J. Pharmacol. Toxicol., 3(6): 267-272, 2012
Fig. 1: Map of Kaduna metropolis
Science, College of Science and Technology, Kaduna
Polytechnic, Kaduna -Nigeria.
Wet ashing of guinea corn: Five grams of oven dried
crushed and sieved guinea corn sample was weighed
into an evaporating dish and ashed at 480°C for 4 h.
Ten cm3 of a mixture of nitric acid-hydrogen peroxide
(2+1) was added to the ashed sample and dried with
occasional shaking on a hot plate and cooled. Four cm3
of 1.5 mol/dm3 nitric acid was then added and
centrifuged. The digest was diluted to 60 cm3 of water
and filtered. This was analyzed for Ni using FAAS
model 8010 Young Lin. A blank digest was carried out
in the same way.
Digestion of soils: Soil pH was measured (1:5, w/v)
using microprocessor pH meter, model pH 210. 10 cm3
of mixture of nitric acid-hydrogen peroxide (2+1) was
added to 5 g soil sample and dried with occasional
shaking on a hot plate and cooled. Four cm3 of 1.5 mol
268 Br. J. Pharmacol. Toxicol., 3(6): 267-272, 2012
Table 1: Results of Ni concentrations in G/corn and soil samples at Kabala
Hot extraction
------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1) EDTA 0.05 M
Oxalic acid 1.0 M Acetic acid 1.0 M
4.45
ND
ND
0.46±0.1
ND
0.46±0.1
KB1
KB2
4.60
ND
ND
0.41±0.1
0.39±0.1
ND
5.45
0.13±0.10
ND
0.26±0.1
0.06±0.1
0.1320±0.1
KB3
4.45
10.87±2.1
12.09±2.6
0.06±0.0
ND
7.62±1.1
KB4
5.15
2.58±0.80
3.44±1.00
2.25±0.4
2.12±0.3
2.58±0.5
KB5
KB6
5.25
2.12±0.70
2.12±0.70
2.65±0.8
2.71±0.9
1.45±0.4
KB7
4.55
11.73±2.1
5.63±1.10
5.37±1.0
12.86±2.5
9.14±2.0
4.55
1.72±0.70
1.98±0.80
3.77±1.1
4.17±1.3
3.44±1.0
KB8
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 2: Results of Ni concentrations in G/corn and soil samples at Nasarawa
Hot extraction
--------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1)
sample HNO3/H2O2 (2+1) EDTA 0.05 M
Oxalic acid 1.0 M
Acetic acid 1.0 M
NS1
4.50
ND
0.53±0.1
0.07±0.0
0.07±0.0
ND
NS2
5.50
ND
8.28±0.3
10.60±2.4
0.06±0.0
7.29±0.2
NS3
5.45
0.13±0.1
ND
6.62±1.5
0.39±0.1
0.06±0.1
5.45
8.08±1.3
7.09±1.1
2.71±0.4
4.97±0.6
6.89±1.8
NS4
NS5
5.25
3.57±1.0
1.52±0.8
2.58±0.9
4.42±1.0
2.05±0.8
NS6
5.35
11.26±2.2
10.62±2.1
2.58±0.8
1.45±0.4
2.58±0.8
NS7
5.15
7.81±1.7
6.39±1.1
9.52±2.4
13.12±3.0
6.03±1.1
NS8
4.45
3.38±1.1
1.26±0.4
2.38±0.7
2.65±0.8
1.12±0.7
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 3: Results of Ni concentrations in G/corn and soil samples at Mando
Hot extraction
--------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1) EDTA 0.05 M
Oxalic acid 1.0 M
Acetic acid 1.0 M
4.46
ND
ND
0.27±0.01
6.62±1.3
ND
MD1
MD2
ND
ND
11.87±3.2
6.61±1.1
ND
5.25
ND
ND
1.99±0.3
ND
0.06±0.1
MD3
MD4
4.47
5.43±1.1
7.09±1.3
5.37±1.0
3.38±0.9
8.68±2.0
MD5
5.35
4.17±1.1
4.17±1.1
1.85±0.9
4.24±1.2
4.30±1.4
MD6
5.20
2.18±0.7
2.98±0.9
2.18±0.7
1.45±0.4
2.12±0.7
MD7
4.55
14.25±2.8
12.06±2.5
8.88±2.0
10.67±2.4
6.89±1.6
MD8
4.55
4.64±1.2
1.06±0.2
3.18±1.0
4.30±1.2
2.58±0.9
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 4: Results of Ni concentrations in G/corn and soil samples at kakuri
Hot extraction
--------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample Site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1) EDTA 0.05 M
Oxalic acid 1.0 M
Acetic acid 1.0 M
4.45
ND
3.44±0.8
1.32±0.7
6.17±0.90
0.06±0.0
KK1
KK2
4.45
ND
ND
1.06±0.1
0.26±0.10
0.06±0.1
4.50
ND
ND
1.32±0.2
132.00±8.5
0.26±0.1
KK3
KK4
5.15
0.43±0.1
5.17±1.0
4.11±1.2
6.82±1.60
3.02±0.9
KK5
4.34
1.92±0.7
2.98±0.9
2.38±0.8
11.26±2.4
7.29±1.9
5.15
1.43±0.5
22.53±4.0
3.31±1.0
2.12±0.70
2.32±0.7
KK6
KK7
4.50
7.02±1.4
12.86±2.5
2.679±0.9
10.40±2.4
8.68±2.0
KK8
4.50
0.27±0.1
0.45±0.2
0.23±0.1
0.31±0.10
0.34±0.1
Results of mean values (mg/kg) ±S.D. (n = 3)
/dm3 nitric acid was added and centrifuged and diluted
to 60 cm3 with water and filtered. The clear digest was
analyzed for Ni using FAAS model 8010 Young Lin. A
blank digest was carried out in the same way.
269 Br. J. Pharmacol. Toxicol., 3(6): 267-272, 2012
Table 5: Results of Ni concentrations in G/corn and soil samples at T/Wada
Hot extraction
-------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1) EDTA 0.05 M
Oxalic acid 1.0M Acetic acid 1.0 M
TW1
4.60
ND
0.46±0.10
ND
0.39±0.1
0.33±0.1
TW2
5.15
ND
18.22±3.5
ND
ND
2.66±0.1
TW3
4.50
ND
ND
0.26±0.1
126.00±11.1
0.13±0.1
5.10
4.70±1.2
4.37±1.0
6.03±1.8
4.57±1.3
3.58±1.0
TW4
4.55
3.11±1.0
4.30±1.4
3.97±1.1
4.04±1.3
8.48±2.0
TW5
4.50
2.22±0.7
2.85±0.8
1.85±0.5
2.12±0.7
1.98±0.5
TW6
4.55
2.38±0.9
1.70±0.7
8.34±2.0
8.55±2.1
11.9±2.3
TW7
4.15
1.65±0.6
2.45±0.9
3.84±1.1
1.85±0.6
2.32±0.7
TW8
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 6: Results of Ni concentrations in G/corn and soil samples at S/Tasha
Hot extraction
--------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1)
EDTA 0.05 M
Oxalic acid 1.0 M Acetic acid 1.0 M
5.10
ND
4.64±0.80
ND
3.97±0.90
1.33±0.8
ST1
ST2
4.50
ND
10.60±2.1
0.19±0.10
ND
ND
5.45
ND
ND
1.32±12.1
ND
ND
ST3
4.50
0.72±0.50
7.49±1.80
3.31±0.80
5.76±1.00
4.30±0.9
ST4
4.45
3.43±1.40
11.92±2.6
3.31±1.20
4.83±1.50
9.80±2.3
ST5
5.15
11.92±2.4
3.38±1.20
1.59±0.50
1.45±0.40
2.18±0.9
ST6
5.10
12.39±2.2
12.26±2.2
11.33±2.1
12.86±2.5
9.54±2.0
ST7
4.10
2.64±0.70
2.78±0.70
2.98±0.90
3.18±1.10
4.24±1.2
ST8
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 7: Results of Ni concentrations in G/corn and soil samples at U/Muazu
Hot extraction
--------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1)
EDTA 0.05 M
Oxalic acid 1.0 M Acetic acid 1.0 M
UM1
5.05
ND
ND
ND
2.65±0.1
1.59±1.2
UM2
5.50
ND
ND
7.29±1.7
2.65±0.3
1.32±0.7
5.25
ND
ND
1.32±0.7
0.06±0.0
1.32±0.7
UM3
4.45
2.02±0.7
6.49±1.3
7.22±1.8
6.03±1.4
4.70±1.0
UM4
5.60
3.77±1.4
3.57±1.2
3.24±1.1
3.11±1.1
3.04±1.0
UM5
5.60
1.06±0.4
1.52±0.6
2.71±0.9
1.98±0.7
3.31±1.1
UM6
5.60
15.64±3.5
6.03±1.3
14.85±2.5
3.84±1.1
10.34±2.1
UM7
5.65
2.45±0.7
2.71±0.9
2.05±0.6
2.05±0.6
4.77±1.4
UM8
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 8: Results of Ni concentrations in G/corn and soil samples at Kachia
Hot extraction
--------------------------------------------------------------------------------------------------------Metal conc in G/corn
Metal conc in soil
Sample site pH
sample HNO3/H2O2 (2+1) sample HNO3/H2O2 (2+1)
EDTA 0.05 M
Oxalic acid 1.0 M Acetic acid 1.0 M
KC1
4.55
0.16±0.1
1.22±0.3
0.27±0.1
0.25±0.1
0.40±0.2
KC2
4.55
1.20±0.3
0.02±0.0
0.01±0.0
0.36±0.2
0.37±0.2
5.15
0.25±0.1
0.36±0.1
0.25±0.1
0.36±0.1
0.25±0.1
KC3
4.50
0.37±0.1
0.24±0.1
0.51±0.1
0.02±0.0
0.14±0.1
KC4
4.55
0.49±0.3
0.38±0.1
0.13±0.1
0.01±0.0
0.38±0.1
KC5
5.10
0.38±0.1
0.26±0.1
0.27±0.1
0.01±0.0
1.33±0.5
KC6
5.15
0.37±0.1
0.37±0.1
0.13±0.0
0.00±0.0
0.13±0.0
KC7
Results of mean values (mg/kg) ±S.D. (n = 3)
Extraction of soil: Soil extracts were obtained by
shaking separately, 5 g of soil samples with 10 cm³ of
0.05 mol/L Na2EDTA (for carbonate and organically
bound phases), 1.0 mol/L oxalic acid (for oxide phases)
and 1.0 mol/L acetic acid (for carbonate phases). The
mixture was evaporated with occasional shaking on a
hot plate. Four cm³ of 1.5 mol/L nitric acid was added
to the remainder and centrifuged. This is referred to as
hot extraction. The digest was diluted to 60 cm³ and
analyzed for Ni using FAAS model 8010 Young Lin. A
blank digest was carried out in the same way.
Nickel content in guinea corn and soils: The Ni
content for the samples from the eight different
agricultural locations in Kaduna are shown in Table 1
to 8.
270 Br. J. Pharmacol. Toxicol., 3(6): 267-272, 2012
The results of the Ni concentration in guinea corn
and soil varied from one location to another. The Ni
concentrations from Kabala (KB) indicate higher
concentration of the metal in soil than the
corresponding guinea corn samples. Similar
observations were reported by Bennett (1982), Hickey
and Kittrick (1984) and Krishna et al. (2010). However,
the guinea corn samples from NS (Nasarawa) had
higher Ni concentrations than the corresponding soils
samples. This could be attributed to agricultural
activities, heavy traffic, various anthropogenic activities
within the locations and the species of guinea corn
grown on the land. This is in agreement with the results
from other investigators (Kashem and Singh, 1998;
Aydinalp and Marinova, 2003; Ana-Irina et al., 2008;
Pei-Fang et al., 2008; Chamon et al., 2009; Khairah
et al., 2009). Similar observations were also observed
in other sampling sites in both cold and hot extractions
as in KB and NS.
The low Ni values for some soil sites compared to
other may be due to lesser impact of anthropogenic
sources of pollution in these locations. Similar findings
were also observed by other investigators (Chamon
et al., 2005; Yusuf, 2006).
The ANOVA
0.070 0.05 indicated no
significant difference in the Nickel concentrations
across the various guinea corn sampled sites. Moreover,
the mean plots depict the mean values of the Nickel
concentrations across the various guinea corn grown
soils as shown in Fig. 2.
Metal speciation: The Ni distribution in the soil
samples at Kabala (KB) varied from one sampling site
to another. The metal existed in the residual, oxide, FeMn oxide and carbonate/organic phases. The
concentration of the metal bound to carbonate/organic
phase is higher in KB2 and KB3 than either the residual
or oxide fractions while the concentration of the metal
bound to the residual fraction is higher in KB4 than in
the other two fractions. The Ni concentration bound to
the oxide fraction is higher in KB6, KB7, KB8 than in
other fractions. The Ni concentration from KB1 bound
to carbonate/organic phases is highest. Similar results
were reported by many authors (Sposito et al., 1982;
Hickey and Kittrick, 1984). Similar observations were
observed in NS, MD, KK, TW, ST, UM and KC. The
Ni concentration in soil is least in KC2. In all the
sampling locations, the Nickel concentration is below
the tolerable limit value of 50 mg/kg (Baralkiewicz
and Siepak, 1999). The higher Ni concentration in
guinea corn and extractable Ni in some of the sampling
sites could be attributed to agricultural processes, heavy
traffic and other anthropogenic activities in these areas
(Kashem and Singh, 1998). HNO3/H2O2, EDTA,
CH3COOH and (COOH) 2 extractable Ni was
considered as available Ni in these locations. Fig. 2: Mean plot for nickel concentration in guinea corn
crops
Fig. 3: Mean plot for nickel concentration in guinea corn
grown soil
The poor uptake of the metal by guinea corn from
the soil at some sites could be attributed to the
formation of high molecular weight metal complexes,
which may decrease metal uptake by plants as a result
of steric hindrance (Dunemann et al., 1991).
The pH of the soil samples from the various
locations is acidic. This could be due to the various
agricultural activities in the sampling sites (Kashem and
Singh, 1998; Chamon et al., 2009; Khairah et al.,
2009).
The ANOVA
0.004 0.05 indicated a
significant difference in the Nickel concentrations
across the various guinea corn grown soils. The
differences in Nickel concentrations can further be
deduced by a post-hoc test using the Duncan Multiple
range test where means of homogeneous subgroups are
displayed. Moreover, the mean plots depict the mean
values of the Nickel concentrations across the various
guinea corn soils.
271 Br. J. Pharmacol. Toxicol., 3(6): 267-272, 2012
The Duncan multiple range tests showed that
Kachia had the least Nickel concentration in their soils
while Nasarawa, Kakuri, among others had the highest
Nickel concentration (Fig. 3).
CONCLUSION
Total trace metal composition of soil is of little
importance in determining its uptake by plants and
consequently, in contaminating the food chain since the
different forms have different mobility’s, bioavailability
and potential environmental contamination potential.
The results on heavy metal speciation in the study
indicated that the soil samples collected from various
areas contain varying amounts of the metal. The metal
was distributed between residual, oxide and carbonate
fractions. An increase of the metal concentration in
some areas suggests that heavy use of agrochemical
materials for planting activities could cause increase in
the content of heavy metals in the soil.
ACKNOWLEDGMENT
The authors acknowledge the assistance of Kaduna
Polytechnic, Nigeria for providing the laboratory
facilities.
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