Research Journal of Environmental and Earth Sciences 4(12): 1079-1084, 2012
ISSN: 2041-0492
© Maxwell Scientific Organization, 2012
Submitted: September 08, 2012
Accepted: October 19, 2012
Published: December 20, 2012
Assessment of Zn Bioavailability in Maize and Soils Using Cold Extraction Technique
S.S. Mohammed, I.A. Abdulmalik and F.M. Abdulkadir
Department of Applied Science, College of Science and Technology, Kaduna Polytechnic,
Kaduna, Nigeria
Abstract: A study on the bioavailability of zinc in maize and soil samples from selected agricultural areas of
Kaduna Metropolis Nigeria was conducted. The objective of the study was to determine the concentration of zinc in
the maize and soil samples. Wet ashing method was used for Zn analysis in the maize. Zn metal from soil samples
was extracted using cold extraction technique employing different digestion and extraction reagents. The Zn
concentration in both the maize and soil samples were analyzed using Flame Atomic Absorption Spectrometry
(FAAS). The results indicated that the soil samples collected from various locations contain varying amounts of zinc
and were distributed between residual, oxide, Fe and Mn oxide and carbonate/organically bound phases. The result
of the study also showed that in all the sampling locations, the zinc concentration in the soil was below the tolerable
limit of 300 mg/kg and ANOVA (p = 0.468>0.05) showed no significant difference in the zinc concentrations across
the various maize crops. Similarly, the ANOVA (p = 0.002<0.05) also indicated a significant difference in the zinc
concentrations across various maize grown soils.
Keywords: AAS, bioavailability, cold extraction, maize, soil, zinc
INTRODUCTION
Zinc influences growth rate and bone development,
the integrity of the skin, the development and function
of the reproductive organs. It also helps in wound
healing capacity (Hodel and Chang, 2004). Zinc
deficiency syndrome manifests itself by growth
retardation, anorexia, lesions of the skin and
appendages, impaired development and function of
reproductive organs (Stoepler, 1991). Zn is an essential
trace element and hence affects the normal functions of
plants, animals and man either by its deficiency or
surplus (Stoepler, 1991).
Zinc contamination in soils and vegetation is
derived from several anthropogenic activities (Ahmad
and Bouhadjera, 2010). Soils are the receptacles for
metals released from industrial activities, municipal
waste sludge, urban composts, road traffics,
atmospheric deposits and agrochemicals (Khairah et al.,
2004).
Heavy metals are persistent in the environment and
are non biodegradable thus readily accumulate to toxic
levels (Sharma et al., 2007). The heavy metal content
alonedoes not provide predictive insight on the
bioavailability, mobility and fate of heavy metal
contaminant (Albores et al., 2000). It is the chemical
form or specie of the heavy metals that is a factor in
assessing their impacts on the environment because it is
their chemical forms that control its bioavailability or
mobility (Norvel, 1984).
The approach to soil speciation is to separate the
soil into different chemical reagents or solvent fractions
and analyze in each fraction the amount of element
combined or associated with each fraction or phase
(Uba et al., 2008). Research on nutrient intake has
shown that low dietary Zn poses a potential nutritional
problem (Reddy et al., 2010). Therefore, the accurate
Zn determination in food and soil is very important.
In the research work, Zn concentrations in maize
and soil samples are determined by Flame Atomic
Absorption Spectrometry (FAAS) using cold extraction
technique.
MATERIALS AND METHODS
The soil samples were dissolved by using the
chemical reagents such as mixture of HNO3/H202,
(COOH)2, Na2 EDTA, C6H807 and CH3COOH. The
relation between the maize contents and the Zn contents
of soil extracts was also investigated. In the digestion
and extraction procedures, concentrated HNO3, H202,
1.0 M (COOH)2, 0.05 M Na2 EDTA, 1.0 M CH3COOH
and Citric acid (C6H807) were used. Stock solution of
Zn (1000 mg/L) was prepared by dissolving Zn (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),
Corresponding Author: S.S. Mohammed, Department of Applied Science, College of Science and Technology, Kaduna
Polytechnic, Kaduna, Nigeria
1079
Res. J. Environ. Earth Sci., 4(12): 1079-1084, 2012
Fig. 1: Map of Kaduna metropolis
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 maize 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
Science, College of Science and Technology, Kaduna
Polytechnic, Kaduna-Nigeria.
Wet ashing of maize: Five grams of oven dried
crushed and sieved maize sample was weighed into an
evaporating dish and ashed at 480°C 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. 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 Zn 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 m, model pH 210. Ten 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/dm3 nitric acid was added and centrifuged and
diluted to 60 cm3 with water and filtered. The clear
digest was analyzed for Zn using FAAS model 8010
Young Lin. A blank digest was carried out in the same
way.
1080 Res. J. Environ. Earth Sci., 4(12): 1079-1084, 2012
Table 1: Results of Zn concentrations of maize and soil samples at Kabala
Cold extraction
-----------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Acetic acid
Metal conc in soil sample EDTA
Oxalic acid
Citric acid
site
pH
sample HNO3/H2O2 (2+1)
1.0 M
HNO3/H2O2 (2+1)
0.05 M
1.0 M
1.0 M
KB1
5.16
38.76±0.70
10.44±0.7
9.69±0.7
13.42±0.7
2.98±0.70
11.93±0.7
KB2
5.46
234.22±0.7
2.24±0.70
2.98±1.5
12.67±0.7
8.94±1.50
3.73±0.70
KB3
5.36
245.96±7.5
2.98±0.70
3.73±1.5
12.67±0.7
9.69±0.70
3.73±1.50
KB4
5.26
39.50±0.70
11.18±1.5
10.43±1.5
14.16±0.7
3.73±0.70
12.67±1.5
KB5
5.66
240.00±0.7
2.98±0.70
3.73±0.7
13.42±0.7
9.69±0.70
4.47±0.70
KB6
6.12
240.75±1.5
3.73±0.70
4.47±1.5
14.16±0.7
10.43±0.7
5.22±0.70
KB7
6.12
240.00±0.7
3.73±0.70
4.47±0.7
13.42±0.7
10.43±1.5
4.47±0.70
KB8
6.12
240.00±0.7
3.73±0.70
4.47±1.5
14.16±1.5
10.43±0.7
6.46±1.60
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 2: Results of Zn concentrations of maize and soil samples at Nasarawa
Cold extraction
------------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Metal conc in soil sample
EDTA
Oxalic acid
Citric acid
Acetic acid
site
pH
sample HNO3/H2O2 (2+1) HNO3/H2O2 (2+1)
0.05 M
1.0 M
1.0 M
1.0 M
NS1
5.49
11.93±0.70
8.20±1.5
9.69±0.70
9.24±2.20
11.93±0.7
9.69±0.70
NS2
6.12
245.52±1.4
2.24±1.5
30.56±0.7
40.25±1.5
53.66±1.5
33.54±0.7
NS3
5.33
242.24±0.7
2.98±0.7
31.30±0.7
40.25±0.7
52.92±0.7
33.54±0.7
NS4
5.92
13.42±0.70
8.94±0.7
10.43±0.7
11.18±0.7
12.67±0.7
10.43±0.7
NS5
6.12
242.24±0.7
2.98±0.7
31.30±0.7
40.99±0.7
54.41±0.7
34.29±1.5
NS6
6.45
242.98±0.7
3.73±0.7
32.05±0.7
41.74±0.7
55.16±0.7
35.03±0.7
NS7
6.45
242.98±1.5
2.98±0.7
31.30±0.7
41.74±0.7
54.41±1.5
35.03±0.7
NS8
6.45
242.98±0.7
4.47±0.7
31.30±0.7
41.74±0.7
55.16±0.7
35.03±1.5
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 3: Results of Zn concentrations of maize and soil samples at Mando
Cold extraction
---------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Metal conc in soil sample EDTA
Oxalic acid
Citric acid
Acetic acid
site
pH
sample HNO3/H2O2(2+1)
HNO3/H2O2 (2+1)
0.05 M
1.0 M
1.0 M
1.0 M
4.15
11.93±0.70
11.93±0.7
16.40±0.7
14.16±0.7
11.93±0.7
14.16±0.7
MD1
MD2
4.45
204.46±1.6
20.87±0.7
16.40±1.5
20.12±1.5
26.83±1.5
29.07±0.7
MD3
4.56
205.71±0.7
21.61±0.7
17.14±0.7
20.12±1.5
27.58±1.5
29.81±7.5
MD4
4.35
13.42±1.50
12.67±1.5
17.14±0.7
15.65±0.7
13.91±1.6
15.65±0.7
MD5
4.26
207.20±0.7
207.20±0.7
17.14±0.7
20.87±0.7
27.58±0.7
29.81±0.7
MD6
4.75
207.95±1.5
22.36±0.7
17.89±0.7
21.61±0.7
28.32±1.5
30.56±0.7
MD7
4.75
207.20±0.7
22.36±1.5
17.14±0.7
21.61±1.5
28.32±1.5
29.81±0.7
MD8
4.75
210.43±5.0
22.36±0.7
17.89±0.7
21.61±0.7
28.32±0.7
30.56±0.7
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 4: Results of Zn concentrations of maize and soil samples at Kakuri
Cold extraction
-------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Metal conc in soil sample EDTA
Oxalic acid
Citric acid
Acetic acid
site
pH
sample HNO3/H2O2 (2+1)
HNO3/H2O2 (2+1)
0.05 M
1.0 M
1.0 M
1.0 M
5.08
10.44±0.70
11.18±0.7
14.16±0.7
11.93±0.7
9.42±7.60
12.67±0.7
KK1
KK2
4.98
259.15±1.6
27.58±1.5
24.60±1.5
24.60±1.5
29.57±1.6
24.60±0.7
KK3
5.14
258.63±1.5
28.32±0.7
26.83±0.7
25.34±0.7
29.07±0.7
25.34±1.5
KK4
5.14
13.42±1.50
12.67±1.5
17.14±0.7
15.65±0.7
13.91±1.6
15.65±0.7
KK5
4.34
207.20±0.7
207.20±0.7
17.14±0.7
20.87±0.7
27.58±0.7
29.81±0.7
KK6
5.15
207.95±1.5
22.36±0.7
17.89±0.7
21.61±0.7
28.32±1.5
30.56±0.7
KK7
4.50
207.20±0.7
22.36±1.5
17.14±0.7
21.61±1.5
28.32±1.5
29.81±0.7
KK8
4.50
258.63±0.7
28.32±0.7
26.83±0.7
26.09±0.7
29.07±0.7
26.09±0.7
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 5: Results of Zn concentrations of maize and soil samples at T/Wada
Cold extraction
---------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Oxalic acid
Citric acid
Acetic acid
Metal conc in soil sample
EDTA
site
pH
sample HNO3/H2O2 (2+1) HNO3/H2O2 (2+1)
1.0 M
1.0 M
1.0 M
0.05 M
TW1
5.07
10.44±0.70
11.18±0.7
14.16±0.7
11.93±0.7
9.42±7.60
12.67±0.7
TW2
5.12
176.39±1.7
27.58±1.5
24.60±1.5
24.60±1.5
29.57±1.6
24.60±0.7
TW3
5.25
181.86±0.7
49.19±0.7
40.25±1.5
32.80±0.7
41.74±1.5
26.09±1.5
TW4
5.27
15.65±0.70
13.42±0.7
16.40±0.7
14.91±7.5
20.87±0.7
20.12±1.5
TW5
5.17
175.16±0.7
175.16±0.7
40.25±0.7
33.54±0.7
41.74±0.7
26.09±1.5
TW6
5.49
175.90±0.7
49.94±0.7
40.99±0.7
34.29±0.7
42.48±1.5
26.83±0.7
TW7
5.49
175.90±0.7
49.19±0.7
40.25±0.7
34.29±1.5
41.74±0.7
26.83±0.7
TW8
5.49
174.41±0.7
47.70±0.7
26.09±0.7
36.27±1.6
33.54±0.7
29.81±0.7
Results of mean values (mg/kg) ±S.D. (n = 3)
1081 Res. J. Environ. Earth Sci., 4(12): 1079-1084, 2012
Table 6: Results of Zn concentrations of maize and soil samples at S/Tasha
Cold extraction
-----------------------------------------------------------------------------------------------------------Sample
Oxalic acid
Citric acid
Acetic acid
Metal conc in maize
Metal conc in soil sample
EDTA
site
1.0 M
1.0 M
1.0 M
pH
sample HNO3/H2O2 (2+1) HNO3/H2O2 (2+1)
0.05 M
ST1
5.14
20.87±0.70
16.40±0.7
16.64±4.4
20.12±0.7
17.89±0.7
18.63±0.7
ST2
5.20
233.89±1.6
24.60±0.7
17.14±1.5
18.63±1.5
20.87±1.5
12.67±0.7
ST3
5.25
235.53±1.5
25.34±0.7
17.14±0.7
19.38±1.5
19.38±0.7
12.67±0.7
ST4
5.82
22.36±7.50
20.62±1.6
22.36±7.5
26.91±1.5
23.85±2.0
20.87±1.5
ST5
5.25
235.53±0.7
25.34±0.7
17.89±0.7
19.38±0.7
21.61±0.7
13.42±0.7
ST6
6.10
236.27±0.7
26.09±0.7
18.63±0.7
20.12±1.5
22.36±0.7
14.16±1.5
ST7
6.10
236.27±1.5
25.34±1.5
17.89±0.7
20.12±0.7
21.61±1.5
14.16±1.5
ST8
6.10
235.53±0.7
25.34±0.7
18.63±0.7
19.38±0.7
22.36±1.5
14.16±0.7
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 7: Results of Zn concentrations of maize and soil samples at U/Muazu
Cold extraction
-----------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Acetic acid
Metal conc in soil sample
EDTA
Oxalic acid
Citric acid
site
pH
sample HNO3/H2O2 (2+1) HNO3/H2O2 (2+1)
1.0 M
0.05 M
1.0 M
1.0 M
UM1
4.01
20.12±0.70
17.89±0.7
20.12±0.7
24.65±0.7
15.43±11.4
18.63±0.7
UM2
4.10
176.66±1.6
163.98±7.5
8.94±0.70
15.65±0.7
11.18±0.7
10.43±1.5
UM3
4.22
177.39±0.7
17.14±0.7
17.14±0.7
16.40±0.7
11.93±0.7
43.98±0.7
UM4
5.82
23.11±0.70
20.87±1.5
23.11±0.7
27.58±1.5
24.60±1.5
20.87±0.7
UM5
4.11
177.39±0.7
17.14±0.7
17.14±0.7
15.65±0.7
11.93±1.5
11.18±0.7
UM6
4.54
178.14±1.5
17.89±0.7
17.14±0.7
17.14±0.7
12.67±1.5
11.93±1.5
UM7
4.54
178.14±0.7
17.14±0.7
17.14±0.7
17.14±0.7
11.93±0.7
11.93±0.7
UM8
4.54
177.39±0.7
17.89±0.7
17.14±0.7
16.40±0.7
12.67±0.7
11.93±0.7
Results of mean values (mg/kg) ±S.D. (n = 3)
Table 8: Results of Zn concentrations of maize and soil samples at Kachia
Cold extraction
------------------------------------------------------------------------------------------------------------Sample
Metal conc in maize
Metal conc in soil sample
EDTA
Oxalic acid
Citric acid
Acetic acid
site
pH
sample HNO3/H2O2 (2+1) HNO3/H2O2 (2+1)
0.05 M
1.0 M
1.0 M
1.0 M
6.16
164.72±0.75
1.49±0.75
2.24±1.49
8.94±0.75
7.45±0.75
2.98±0.75
KC1
KC2
6.24
166.96±0.7
2.24±1.50
15.65±0.7
20.12±1.5
26.83±0.7
17.14±0.7
KC3
6.15
161.74±0.7
10.43±0.7
8.20±0.70
10.43±1.5
13.42±0.7
14.16±1.5
KC4
6.08
161.74±0.7
10.43±0.7
8.20±0.70
10.43±1.5
13.42±0.7
14.16±1.5
KC5
6.07
158.01±0.7
36.52±0.7
23.11±0.7
25.34±0.7
24.60±0.7
22.36±0.7
KC6
6.14
163.23±0.7
20.87±0.7
13.42±1.5
14.91±0.7
15.65±0.7
7.45±0.70
KC7
6.01
158.01±0.7
13.42±0.7
11.18±0.7
13.42±0.7
7.45±0.70
7.45±0.70
Results of mean values (mg/kg) ±S.D. (n = 3)
Extraction of soil: Soil extracts were obtained by
shaking separately, 5g of soil samples with 10 cm3 of
0.05 mol/dm3Na2EDTA (for carbonate and organically
bound phases), 1.0 mol/dm3 oxalic acid (for oxide
phases), 1.0 mol/dm3 acetic acid (for carbonate phases)
and 1.0 mol/dm3 citric acid (Fe and Mn oxide phase) at
room temperature and centrifuged after stirring for 5
min. This procedure is referred to as cold extraction
(Yaman et al., 2005). The digest was diluted to 60 cm3
with water and analyzed for Zn using FAAS model
8010 Young Lin. A blank digest was carried out in the
same way.
Content of Zn in maize and soil: The Zn content for
the samples collected from the eight different locations
in Kaduna is shown in Table 1 to 8.
The results of the Zn concentrations both in hot and
cold extractions indicate higher concentrations of the
metal in maize than the corresponding soil samples.
Similar observations were reported by other
investigators (Gworek and Mocek, 2003; Wieczorek
et al., 2005; Khairah et al., 2004; Yaman et al., 2005;
Ana-Irina et al., 2008; Takac et al., 2009). The lower
Zn values for some soil sites compared to other may be
due to the impact of anthropogenic sources of pollution
in these locations. These results are in agreement with
the results reported by other investigators in different
parts of the world (Kashem and Singh, 1998; Yusuf,
2007). The higher Zn values in maize samples could be
attributed to the various agricultural practices in the
sampling sites (Kashem and Singh, 1998). The Zn
concentration in the soil is least at site KC1 and highest
at KK5 and MD5. In all the sampling locations, the Zn
concentration is within the range (10-300 mg/kg)
(Lindsay and Norvell, 1978).
The ANOVA (p = 0.468>0.05) showed no
significant difference in the Zinc concentrations across
the various maize crops. Moreover, the mean plots
1082 Res. J. Environ. Earth Sci., 4(12): 1079-1084, 2012
said to be carbonate species in cold extraction (Yaman
and Bakirdere, 2002).
In T/Wada (TW), cold extractions, the Zn
concentration bound to the residual fraction is highest.
Thus, Zn is said to be residual species in this area and is
available, for plant uptake (Yaman et al., 2005). Similar
observations were observed in the other sampling
locations.
The pH of the soil samples from the sampling
locations is acidic, which could increase the solubility
and mobility of the metal in the soils (Kashem and
Singh, 1998; Baranowski et al., 2002; Chamon et al.,
2005; Urunmatsoma et al., 2010).
The ANOVA (p = 0.002<0.05) indicated a
significant difference in the Zinc concentrations across
the various maize grown soils. The real differences in
Zinc concentrations can be deduced by a post-hoc test
using the Duncan Multiple range test where the means
of homogeneous subgroups are clearly displayed.
Moreover, the mean plots that follow depict the mean
values of the Zinc concentrations across the various
maize grown soils.
The Duncan multiple range tests showed that
Nasarawa and Kabala West had the least Zinc
concentration in maize grown soils. While Ungwan
Muazu, Mando, among others had the highest Zinc
concentration as depicted in Fig. 3.
Fig. 2: Mean plot for zinc concentration in maize crops
CONCLUSION
Fig. 3: Mean plot for zinc concentration in maize soil
clearly depict the mean values of the Zinc
concentrations across the various maize crops as shown
in Fig. 2.
Metal speciation: The Zn distribution in soil samples
from the locations showed that the metal exists in the
forms; residual, oxide, carbonate/organic and Fe-Mn
oxide. In both hot and cold extractions, the
concentration of the metal bound to oxide fraction is
highest at Kabala (KB). Therefore, the metal in these
soils was oxide species, bioavailable and mobile. Hence
it is available for plant uptake. Similar results were
reported elsewhere (Sposito et al., 1982; Hickey and
Kittrick, 1984). In hot extraction, the concentration of Zn bound to
carbonate/organic fraction is highest in Nasarawa (NS),
while in cold extraction, the metal concentration bound
to Fe-Mn oxide is highest. The metal is said to be
carbonate species or organically bound in hot extraction
and Fe-Mn oxide species in cold extraction. This is in
agreement with the results from other investigators
(Yaman and Bakirdere, 2002; Gworek and Mocek,
2003; Takac et al., 2009).
In Mando (MD), the Zn concentration in cold
acetic acid extracts was highest. Therefore, the metal is
Different selective chemical reagents and the
modified sequential extraction procedures used in this
work were found useful in determining the mobility and
chemical forms of zinc in soil. The result obtained
showed that the metal is distributed between residual,
oxide, Fe-Mn oxide and carbonate fractions.
ACKNOWLEDGMENT
The authors acknowledge the assistance of Kaduna
Polytechnic, Nigeria for providing the laboratory
facilities.
REFERENCES
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