Research Journal of Applied Sciences, Engineering and Technology 3(3): 202-209, 2011
ISSN: 2040-7467
© Maxwell Scientific Organization, 2011
Received: January 16, 2011
Accepted: February 15, 2011
Published: March 30, 2011
Speciation of Nickel in Soils and Cereal
1
1
J.T. Ayodele and 2S.S. Mohammed
Department of Pure and Applied Chemistry, Bayero University, Kano, Nigeria
2
Department of Applied Science, College of Science and Technology,
Kaduna Polytechnic, Kaduna, Nigeria
Abstract: The levels of trace elements in food and agricultural samples have been shown to influence human
and plant metabolism. The study of heavy metal speciation is of interest for the evaluation of their mobility,
bioavailability and ecotoxicity. In this study, the Nickel concentrations of the cereal and soil samples were
determined using Flame Atomic Absorption Spectrometry (FAAS). The soil samples related to the cereal were
digested and extracted using different digestion and extraction reagents. The results indicate that the soil
samples collected from various locations, contain varying amounts of the metals, and it was distributed between
Residual, Oxide and Carbonate fractions. The results of the study also showed that the lowest value of total Ni
concentration in soil was in sampling point KC4 (2.93 mg/kg) and the highest value was in points ST6 and ST7
(105.37 mg/kg). In some of the sample locations, the Ni concentration was above the tolerable limit value of
50 mg/kg. The relationship between the cereal Ni and soil-extractable Ni concentrations was significant
(p<0.05).
Key words: Cereal, flame atomic absorption spectrometry, Nickel, soil, speciation
surface or on inorganic cations exchange surfaces, watersoluble, and free-ion or chelated metal complexes in soil
solution (Bennett, 1982).
Much research has been conducted on heavy metals
contamination in soils from various anthropogenic sources
such as industrial wastes (Yusuf, 2006; Adeniyi and
Okedeyi; 2004; Kakula and Osibanjo, 1988), automobile
emissions (Arowolo et al., 2000; Ma and Rao, 1997),
mining activity (Kabala and Singh, 2001; Ramos et al.,
1994), street dusts (Ayodele and Gaya, 1994) and
agricultural practice (Chlopecka et al., 1996; Gzyl, 1990).
The total heavy metal content in soils provide a
convenient means of expressing a measure of pollution,
numerous reports have highlighted that such measures are
deficient in predicting toxicity of metal pollutants
(Yusuf, 2006). Heavy metals may be distributed among
many components 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 nature of the
association is referred to as speciation. The general
approach for the soil speciation studies has been to
separate the soil using different chemical reagents or
solvents fractions and, by analyzing each fraction, to
determine the amount of element combined or associated
with each soil fraction or phase (Yaman et al., 2000).
Therefore, the identification of the chemical form or
phases of Nickel in soil is necessary for estimating its
biological availability, physico-chemical reactivity and
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).
Nickel and Nickel compounds have many industrial
and commercial uses, and the progress of industrialization
has led to increased emission of pollutants into
ecosystems. Although Nickel is vital for the function of
many organisms, concentrations in some areas from both
anthropogenic release and naturally varying levels may be
toxic to living organisms (Diagomanolin et al., 2004).
Inhalation exposure in occupational settings is a primary
route for nickel-induced toxicity, and may cause toxic
effects in the respiratory tract and immune system
(Bennett, 1982). The general exposure to nickel mainly
concerned oral intake, primarily through waste and food,
as a contaminant in drinking water or as both a constituent
and contaminant of food (Haber et al., 2000).
Nickel is generally distributed uniformly through the
soil profile but typically accumulates at the surface from
disposition by industrial and agricultural activities.
Nickel may present a major problem in land near towns,
in industrial areas, or even in agricultural land receiving
wastes such as sewage sludge. Nickel can exist in soils in
several forms such as inorganic crystalline minerals or
precipitates, complexes and absorbed on organic cations
Corresponding Author: S.S. Mohammed, Department of Applied Science, College of Science and Technology, Kaduna
Polytechnic, Kaduna, Nigeria
202
Res. J. Appl. Sci. Eng. Technol., 3(3): 202-209, 2011
Fig. 1a: Map of Nigeria showing Kaduna state
Fig. 1b: Map of Kaduna state showing Kaduna metropolis
Air flow rate (L/min) - 5.0
Shit width (nm) - 0.2
HCl current (mA) - 8.0
transport in the environment and into the food chain
(Yaman and Yusuf, 2002).
In this research, Ni concentrations in maize and soil
samples were determined by Flame Atomic Absorption
Spectrometry (FAAS). The soil samples were dissolved
by using the chemical reagents such as the mixture of
HNO3/H2O2, oxalic acid, Na2 EDTA and Acetic acid. The
relation between the maize Ni contents and the Ni
contents of the soil extracts was also investigated.
In the digestion and extraction procedures,
concentrated nitric acid, hydrogen peroxide, 1.0M oxalic
acid, 0.05M Na2EDTA and 1.0M acetic acid were used.
Stock solution of Ni (1000 mg/L) was prepared by
dissolving Ni (NO3)2 in 1.0 mol/L nitric acid.
MATERIALS AND METHODS
Preparation of samples: The research covered seven
agricultural sites in Kaduna, Nigeria. The sites are:
Nasarawa (NS), Sabon Tasha (ST), Unguwar Muazu
(UM), Tudun Wada (TW), Kakuri (KK), Mando (MD),
Kabala (KB) west and Kachia (KC). The samples were
collected during the harvest season (Oct-Nov., 2008, 2009
and 2010). The soil samples were collected from the
different areas enumerated at a depth of about 10 cm
A flame atomic absorption spectro-photometer model
8010 Young Lin was used for the Ni determination. The
optimum conditions for FAAS are given as below:
Wave length (nm) - 232
Acetylene flow rate (L/min) - 1.8
203
Res. J. Appl. Sci. Eng. Technol., 3(3): 202-209, 2011
Fig. 1c: Map of Kaduna Metropolis
nitric acid was then added and centrifuged. 60 cm³ water
was added to the clear digest and was filtered. This was
analysed for Ni using FAAS model 8010 Young Lin. A
blank digest was carried out in the same way.
below the surface (Yaman et al., 2005). The cereal
samples were collected at each of the locations. Maize
was chosen for the purpose of this research work as it is
the staple food being produced and consumed in these
areas. Kachia, a town situated about 130 km away from
Kaduna was taken as a control Fig. 1(a, b, c). The cereal
was thoroughly washed with water and allowed to drain
on a filter paper. Both the cereal and soil samples were
dried at 85ºC. All the analyses were carried out in the
analytical laboratory of the department of Applied
Science, College of Science and Technology, Kaduna
Polytechnic, Kaduna - Nigeria
Digestion and extraction of soil: Soil pH was measured
(1:5, w/v) by digital pH meter.
A modified Tessier et al. (1979) extraction method
developed by Yaman et al. (2005) was used. 10 cm³ of a
mixture of nitric acid-hydrogen peroxide (2+1) was added
to 5g of soil sample and dried with occasional shaking on
a hot plate and cooled. 4 cm³ of 1.5 mol/L nitric acid was
added to the remainder, centrifuged and diluted to 60cm³
with water and filtered. The clear digest was analysed for
Ni using FAAS model 8010 Young Lin. A blank digest
was carried out in the same way. 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
Wet ashing of cereal: Five (5) g of oven dried maize
sample was accurately weighed into an evaporating dish
and ashed at 480ºC in an ashing furnace for 4 h. 10 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, 4 cm³ of 1.5 mol/L
204
Res. J. Appl. Sci. Eng. Technol., 3(3): 202-209, 2011
Table 1: Results of Ni contents of maize and soil samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc
Total metal conc
in maize sample
in soil sample
Sample site
maize
HNO3/H2O2
metals
samples
(2+1)
5.85±2.9
5.85±2.9
KB1
KB2
38.05±17.8
14.63±2.9
KB3
58.54±29.3
17.56±2.9
KB4
5.85±2.9
8.78±2.9
KB5
29.27±2.9
17.56±2.9
KB6
35.12±2.9
20.49±5.9
KB7
32.20±2.9
20.49±5.9
KB8
38.05±2.9
22.44±6.1
Hot extraction
---------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
2.93±0.0
14.63±2.9
26.34±2.9
8.78±2.9
11.71±2.9
14.63±2.9
8.78±2.9
14.63±5.9
17.56±5.9
6.15±3.0
17.56±5.9
26.34±5.9
11.71±2.9
14.63±5.9
17.56±2.9
14.63±2.9
17.56±2.9
17.56±5.9
11.71±2.9
17.56±5.9
17.56±2.9
14.63±2.9
17.56±5.9
20.49±5.9
Table 2: Results of Ni contents of maize and soil samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc.
Total metal conc.
in maize sample
in soil sample
Sample site
maize
HNO3/H2O2
metals
samples
(2+1)
11.71±5.9
11.71±2.9
NS1
NS2
29.27±2.9
11.71±2.9
NS3
43.90±2.9
14.63±5.9
NS4
14.63±5.9
11.71±2.9
NS5
32.20±2.9
14.63±2.9
NS6
38.05±2.9
17.56±2.9
NS7
11.71±2.9
11.71±5.9
NS8
32.20±2.9
14.63±2.9
Hot Extraction
-------------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
14.63±2.9
43.90±2.9
26.34±2.9
11.71±5.9
23.41±2.9
17.56±5.9
11.71±5.9
36.10±19.5
17.56±2.9
14.63±2.9
46.83±2.9
29.27±2.9
14.63±5.9
26.34±2.9
20.49±5.9
17.56±5.9
29.27±2.9
23.41±2.9
23.41±2.9
11.71±5.9
35.12±2.9
14.63±5.9
29.27±2.9
23.41±2.9
pH
5.49
6.12
5.33
5.92
6.12
6.45
6.45
6.45
Table 3: Results of Ni contents of maize and soil samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc.
Total metal conc.
in maize sample
in soil sample
Sample site
maize
HNO3/H2O2
metals
samples
(2+1)
MD1
8.78±2.9
23.41±2.9
MD2
32.20±2.9
8.78±2.9
MD3
35.12±2.4
11.71±2.4
MD4
14.63±2.9
29.27±2.9
MD5
35.12±2.9
35.12±2.9
MD6
35.08±2.9
17.56±2.9
MD7
35.12±2.9
17.56±2.9
MD8
32.20±2.9
8.78±2.9
Hot extraction
-------------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
11.71±5.9
61.46±2.9
43.90±2.9
8.78±2.9
8.78±2.9
11.71±2.9
11.71±4.8
11.71±2.4
14.63±2.4
17.56±5.9
67.61±3.4
49.76±5.9
11.71±2.9
11.71±5.9
14.63±5.9
17.56±2.9
20.29±5.9
14.63±2.9
17.56±5.9
26.34±5.9
23.41±2.9
8.78±2.9
11.71±2.9
11.71±2.9
pH
4.15
4.45
4.56
4.35
4.26
4.75
4.75
4.75
oxide phases) and 1.0 mol/L acetic acid (for carbonate
phases). The mixture was evaporated with occasional
shaking on a hot plate. 4 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 60cm³ and
analyzed for Ni using FAAS model 8010 Young Lin. A
blank digest was carried out in the same way.
pH
5.16
5.46
5.36
5.26
5.66
6.12
6.12
6.12
agricultural activities, soils from main roads and the
various anthropogenic activities within the locations.
This is in agreement with the result from other
investigators (Kashem and Singh, 1998; Chamon
et al., 2009; Hickey and Kittrick, 1984; Ana-Irina
et al., 2008; Aydinalp and Marinova, 2003; Pei-Fang
et al., 2008; Kashem et al., 2007; Khairah et al., 2004;
Chamon et al., 2005).
The lower Ni values obtained for some soil sites
compared to other may be due to the lesser impact of
anthropogenic sources of pollution in the locations.
Similar findings were also observed by other investigators
(Blom, 1986; Yusuf, 2007) reported a very drastic
decrease in metal concentration away from the source
point. The decreasing tendency with distance indicates
the accumulation of metals by the anthropogenic activities
within the locations.
The pH of the soil samples from the various locations
is acidic (Table 1-8). This could possibly increase the
RESULTS AND DISCUSSION
Total content of Ni in samples: The total content of Ni
for the samples collected from the eight different
agricultural locations at Kaduna, Nigeria are shown in
Table 1 to 8.
In general, the maize samples from KB, NS, MD,
KK, UM, and KC had higher Ni concentrations than the
corresponding soil samples. Maize sample obtained from
site UM3 had the highest enrichment in Ni (107 mg/kg)
compared to all the sites. This could be attributed to
205
Res. J. Appl. Sci. Eng. Technol., 3(3): 202-209, 2011
Table 4: Results of Ni contents of maize and soil samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc
Total metal conc
in maize sample
in soil sample
maize
HNO3/H2O2
Sample site metals
samples
(2+1)
KK1
5.85±2.9
5.85±2.9
KK2
29.27±2.9
5.85±2.9
KK3
35.12±2.9
8.78±2.9
KK4
11.71±2.9
11.71±2.9
KK5
32.20±2.9
32.20±2.9
KK6
35.12±2.9
11.71±2.9
KK7
32.20±2.9
11.71±2.9
KK8
35.12±2.9
11.71±5.9
Hot extraction
-------------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
17.56±2.9
46.83±2.9
20.49±2.9
20.49±5.9
29.27±2.9
40.98±5.9
20.49±5.9
35.12±2.9
43.90±2.9
23.41±2.9
52.68±2.9
26.34±2.9
23.41±2.9
29.27±2.9
43.90±5.9
26.34±5.9
35.12±5.9
46.83±2.9
26.34±5.9
35.12±2.9
43.90±2.9
26.34±5.9
32.20±2.9
46.83±5.9
pH
5.08
4.98
5.14
5.14
5.18
5.58
5.08
4.98
Table 5: Tesults of Ni Contents of Maize and Soil Samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc
Total metal conc
in maize sample
in soil sample
maize
HNO3/H2O2
Sample site metals
samples
(2+1)
TW1
8.78±2.9
9.76±3.4
TW2
67.32±5.9
73.00 ±2.9
TW3
73.00 ±2.9
102.44±2.9
TW 4
70.24±2.9
76.10±2.9
TW 5
14.63±2.9
14.63±5.9
TW 6
70.24±2.9
70.24±2.9
TW 7
73.17±2.9
79.02±2.9
TW 8
73.17±5.9
76.10±2.9
Hot extraction
----------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
23.41±2.9
52.68±2.9
46.83±2.9
87.80±29.3
90.73±2.9
79.02±5.9
102.44±2.9
110.93±3.4
93.66±5.9
90.73±2.9
93.66±2.9
81.95±5.9
23.41±2.9
29.27±2.9
88.78±4.5
90.73±2.9
93.66±2.9
83.90±6.1
93.66±2.9
96.59±5.9
84.88±5.9
93.66±2.9
93.66±5.9
84.88±5.9
pH
5.07
5.12
5.25
5.27
5.17
5.49
5.49
5.49
Table 6: Results of Ni Contents of Maize and Soil Samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc
Total metal conc
in maize sample
in soil sample
maize
HNO3/H2O2
Sample site metals
samples
(2+1)
ST1
8.78±0.0
9.76±2.9
ST2
93.66±5.9
99.51±2.9
ST3
96.59±2.9
99.51±5.9
ST4
8.78±2.9
29.27±2.9
ST5
70.24±2.9
70.24±2.9
ST6
99.51±2.9
105.37±5.9
ST7
100.49±4.5
105.37±2.9
ST8
96.59±5.9
102.44±2.9
Hot extraction
------------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
23.41±2.9
52.68±2.9
46.83±2.9
90.73±2.9
93.66±2.9
81.95±2.9
90.73± 2.9
96.59±5.9
84.88±2.9
29.27±2.9
49.76±2.9
35.12±2.9
90.73±2.9
93.66±2.9
83.90±6.1
96.59±5.9
99.51±2.9
87.80±5.9
93.66±2.9
99.51±5.9
84.88±2.9
93.66±2.9
96.59±2.9
87.80±2.9
pH
5.14
5.20
5.24
5.82
5.25
6.10
6.10
6.10
Table 7: Results of Ni contents of Maize and soil samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc
Total metal conc
in maize sample
in soil sample
maize
HNO3/H2O2
Sample site metals
samples
(2+1)
UM1
5.85± 2.9
14.63±2.9
UM2
99.51±2.9
90.73±2.9
UM3
107.32±4.5
93.66±2.9
UM4
17.56±2.9
26.34±5.9
UM5
102.44±2.9
93.66±2.9
UM6
105.37±2.9
93.66±2.9
UM7
105.37±2.9
93.66±2.9
UM8
99.51±2.9
93.66±2.9
Hot extraction
------------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
17.56±2.9
52.68±2.9
30.24±4.5
93.66±5.9
81.95±5.9
81.95±2.9
93.66±5.9
81.95±2.9
84.88±5.9
29.27±2.9
64.39±2.9
40.98±2.9
96.59±2.9
84.88±2.9
84.88±5.9
99.51±2.9
87.80±5.9
87.80±2.9
99.51±5.9
84.88±5.9
87.80±5.9
96.59±2.9
84.88±5.9
84.88±5.9
pH
4.01
4.10
4.22
4.74
4.11
4.54
4.54
4.54
solubility and mobility of the metal in the soils. Such
increase in solubility of the metal is likely to lead to
increased availability of the metal for plant uptake, and it
might cause Ni toxicity. The results indicate that
appreciable soil acidification has taken place in the
vicinity of the locations. Similar results were also
reported by many authors (Baranowski et al., 2002;
Kashem and Singh, 1998; Chamon et al., 2005).
Metal speciation: The distribution of Ni in the soil
samples collected from Kabala showed that the metal
exists in three forms; the residual, oxide and carbonate
phases (Table 1). The concentration of the metal bound
to carbonate (CH3COOH) is higher than in the oxide
[(COOH)2], EDTA or residual (HNO3/H2O2) except in
KB6, KB7 and KB8, where its concentration is higher in
residual fraction than the other two fractions. This shows
206
Res. J. Appl. Sci. Eng. Technol., 3(3): 202-209, 2011
Table 8: Results of Ni Contents of Maize and Soil Samples
The results are mean values (mg/kg) ± standard deviation n = 3
Total metal conc
Total metal conc
in maize sample
in soil sample
maize
HNO3/H2O2
Sample site metals
samples
(2+1)
KC1
14.63± 2.9
73.17±5.9
KC 2
17.56±5.9
5.85±0.0
KC 3
17.56±2.9
5.85±2.9
KC 4
17.56±2.9
2.93±0.0
KC 5
49.76±2.9
38.05±2.9
KC 6
46.83±2.9
49.76±2.9
KC 7
49.76±5.4
43.90±5.9
Hot extraction
------------------------------------------------------------------------EDTA
Oxalic acid
Acetic acid
0.05 M
1.0 M
1.0 M
5.85±2.9
5.85±2.9
73.17±2.9
5.85±2.9
11.71±2.9
8.78±2.9
5.85±2.9
5.85±2.9
5.85±2.9
11.71±2.9
14.63±5.9
20.49±2.9
43.90±2.9
46.83±2.9
40.98±2.9
46.83±5.9
46.83±2.9
40.98±2.9
46.83±2.9
40.98±5.9
40.98±2.9
Table 9: Correlation Matrix for maize and different Ni extractable species in soil
EDTA
Oxalic acid
Acetic acid
Components
Maize sample
HNO3/H2O2
(a)
Maize sample
1
0.743*
0.566
- 0.197
- 0.807
1
0.951**
0.314
- 0.718*
HNO3/H2O2
EDTA
1
0.405
- 0.621
Oxalic acid
1
0.355
Acetic acid
1
- 0.474
pH
1
(b)
Maize sample
1
0.625
-0.441
- 0.020
- 0.747*
1
-0.037
- 0.068
- 0.397
HNO3/H2O2
EDTA
1
- 0.559
0.841**
Oxalic acid
1
- 0.139
Acetic acid
1
0.323
pH
1
(c)
Maize Sample
1
-0.367
-0.044
- 0.918**
- 0.883**
1
0.398
0.493
0.524
HNO3/H2O2
EDTA
1
0.432
0.504
Oxalic Acid
1
0.995**
Acetic Acid
1
- 0.509
PH
1
(d)
Maize sample
1
0.284
0.586
- 0.857**
0.995**
1
0.321
- 0.334
0.310
HNO3/H2O2
EDTA
1
- 0.282
0.645
Oxalic acid
1
- 0.855**
Acetic acid
1
0.216
pH
1
(e)
Maize sample
1
0.962**
0.994**
0.939**
0.605
1
0.982**
0.959**
0.632
HNO3/H2O2
EDTA
1
0.967**
0.581
Oxalic acid
1
0.401
Acetic acid
1
0.489
pH
1
(f)
Maize sample
1
0.991**
0.998**
0.999**
0.985**
1
0.996**
0.984**
0.955**
HNO3/H2O2
EDTA
1
0.995**
0.976**
Oxalic acid
1
0.990**
Acetic acid
1
0.203
pH
1
(g)
Maize sample
1
0.995**
0.993**
0.959**
0.992**
1
0.999**
0.978**
0.998**
HNO3/H2O2
EDTA
1
0.982**
0.999**
Oxalic acid
1
0.986**
Acetic acid
1
0.075
pH
1
*: Correlation is significant at the 0.05 level (2-tailed); **: Correlation is significant at the 0.01 level (2-tailed)
207
pH
6.16
6.24
6.15
6.08
6.07
6.14
6.01
pH
0.372
0.878**
0.917**
0.557
- 0.287
0.261
0.578
- 0.660
0.693
- 0.632
0.224
- 0.526
0.199
0.186
0.337
0.035
0.656
0.532
0.616
0.526
0.223
0.285
0.250
0.233
- 0.040
0.021
0.044
0.195
Res. J. Appl. Sci. Eng. Technol., 3(3): 202-209, 2011
Table 9: Continued
Components
Maize sample
HNO3/H2O2
EDTA
Oxalic acid
Acetic acid
(h)
Maize sample
1
0.284
0.586
- 0.857**
0.995**
1
0.321
- 0.334
0.310
HNO3/H2O2
EDTA
1
- 0.282
0.645
Oxalic acid
1
- 0.855**
Acetic acid
1
0.216
pH
1
*: Correlation is significant at the 0.05 level (2-tailed); **: Correlation is significant at the 0.01 level (2-tailed)
pH
0.199
0.186
0.337
0.035
different forms have different mobilities, bioavailabilities
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.
that Ni in soils occurs in the carbonate, oxide and residual
fractions with highest concentration coming from the
carbonate fraction (KB1, KB4). Similar results were also
reported by many authors (Yaman and Bakirdere, 2002;
Hickey and Kittrick, 1984; Sposito et al., 1982).
The Nickel concentration in the soil from Nasarawa
(NS), showed that the metal exists also in three forms;
that is residual, oxide and carbonate. The predominance
of the oxide fraction in these areas is in agreement with
the results reported by Hickey and Kittrick (1984) and
Sposito et al. (1982). The carbonate fraction is the highest
in NS7. This is in agreement with the result from other
investigators (Yaman and Bakirdere, 2002). Similar
observations were made in the other agricultural locations
with respect to nickel concentration in soil fractions.
In case of total Ni concentration in the soil, the
lowest value was in point KC4 and the highest was in the
sampling points ST6 and ST7. In some of these sampling
locations, the Nickel concentration is above the tolerable
limit value of 50 mg/kg (Baralkiewicz and Siepak, 1999).
The highest concentration of Ni and the metals in the
areas is not only a problem with respect to plant nutrition
and the food chain, they may constitute a direct health
hazards as well. The highest concentration of total and
extractable Ni could be attributed to agricultural
processes, heavy traffic and other anthropogenic activities
within the locations (Kashem and Singh, 1998).
HNO3/H2O2 extractable, EDTA extractable,
CH3COOH extractable and (COOH)2 extractable Ni have
been considered as available Ni (Lindsay and
Norvell, 1978). These Ni species should measure
available concentration of Ni in the soil samples of the
agricultural locations.
The results of correlation calculations (Table 9)
shows that the HNO3/H2O2, EDTA, (COOH)2 and
CH3COOH3 extractable and total Ni content in maize
positively and significantly correlate with each other at
0.05 and 0.01 levels. Hence it could be deduced that the
various reagents used were efficient for the extraction of
this metal from the soil at these levels.
ACKNOWLEDGMENT
The authors show great appreciation to Kaduna
Polytechnic, Nigeria for providing facilities to analyze the
samples and to Nasiru Musa, Kabiru Shehu, Dr. A.O.
Lawal, Yusuf Abdul-raheem, Sarkiyayi Shehu and
Nuruddeen for the help in sample collection, metal and
statistical analyses.
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