Asian Journal of Agricultural Sciences 4(2): 102-107, 2012
ISSN: 2041-3890
© Maxwell Scientific Organization, 2012
Submitted: September 13, 2011
Accepted: October 15, 2011
Published: March 26, 2012
Evaluation of Heavy Metals from Soil and Lettuce Grown in Irrigated Farmlands
of Kaduna Metropolis Nigeria
1
W.L.O. Jimoh and 2Mahmud Imam Mohammed
Department of Pure and Industrial Chemistry, Bayero University, Kano Nigeria
2
Department of Applied Science, College of Science and Technology, Kaduna Polytechnic
1
Abstract: The aim of this research study is to determine the level of heavy metal such as cadmium, copper and
lead were investigated in soil and lettuce grown in irrigated farmlands of Kaduna metropolis so as to ascertain
the extent of pollution. Concentrations of heavy metals were determined using atomic absorption
spectrophotometer. The results obtained were compared with limit recommended by FAO/WHO (2007)
Allimentarius standard so as to ascertain the extent of their pollution. The level of cadmium in lettuce ranged
from 0.03-1.37 :g/g. The concentrations of lead was found to be in range of 0.96-3.81 :g/g, were above the
limit stipulated by WHO while copper concentration ranged from 0.27-4.97 :g/g were within the recommended
limit given by the FAO/WHO (2007) standard. This suggests that the lettuce grown in the studied areas were
prone to lead and cadmium toxicity as at the time of this research work. Pearson correlation shows positive
correlation between soil and vegetable (lettuce) in these irrigation sites.
Key words: Atomic absorption spectrophotometer, heavy metals, Kaduna metropolis, lettuce, Nigeria, soil
typically eaten cold and raw in salads, hamburgers, tacos
and many other dishes. The lettuce plant has short stem
initially (a rosette growth habit), but when it blooms the
stem lengthens and branches and it produce many flower
heads that look like those of dandelions, but smaller,
which is called botting. When grown to eat, lettuce is
harvested before it bolt.
The aim of this research study is to determine the
level of heavy metal (Cu, Pb and Cd) in soil and lettuce
grown in irrigated farmlands of Kaduna metropolis so as
to ascertain the extent of pollution.
INTRODUCTION
Heavy metals are ubiquitous in the environment, as
a result of both natural and anthropogenic activities, and
humans are exposed to them through various pathways
(Wilson and Pyatta, 2007). In general, wastewater
contains substantial amounts of beneficial nutrients and
toxic heavy metals, which are creating opportunities and
problems for agricultural production, respectively (Chen
et al., 2005; Singh et al., 2004).
Heavy metals have been excessively released into the
environment due to rapid industrialization and have
created a major global concern (Wan Ngah and Hanafiah,
2007).
Heavy metals have been excessively released into the
environment due to rapid industrialization and have
created a major global concern (Wan Ngah and Hanafiah,
2007).
Contamination and consequent pollution of the
environment by toxic heavy metals have become an issue
of global concern due to their sources, widespread
distribution and multiple effects on the ecosystem
(Nriagu, 1990).
Vegetable constitute an important part of the human
diet since they contain carbohydrates, proteins, as well as
vitamins, minerals and trace elements (Dastane, 1987).
Lettuce (Lactuca sativa) is a temperate annual or
biennial plant of the daisy family asteracease. It is most
often grown as a leaf vegetable. In many countries, it is
MATERIALS AND METHODS
Sample and sampling: Lettuce samples were collected
from October 2009 to February 2010 from twenty one
(21) different irrigation site of the farmlands of the
Kaduna metropolis where they were irrigated with water
from the river or pond which are sometimes contaminated.
Soil samples were also randomly collected from the farm
where these vegetables were grown and irrigated with
water. These samples were then stored in polythene bags
and taken to the laboratory and dried in an oven at 100ºc.
The dried samples were ground with mortar and
pestle and sieved with 2 mm sieve.
Description of the sampling sites: Soil samples for
heavy metal determination were collected from twenty
one (21) irrigation sites of the Kaduna metropolis. These
Corresponding Author: Mahmud Imam Mohammed, Department of Applied Science, College of Science and Technology,
Kaduna polytechnic
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Asian J. Agric. Sci., 4(2): 102-107, 2012
Table 1: Distribution of cadmium in soil from different irrigation sites of the Kaduna metropolis
Sampling sites
SL (KBL)
SL (DMN)
SL (RGS)
SL (BNW)
SL (MKR)
SL (KKR)
SL (BDK)
SL (NAS)
SL (MAL)
SL (KUD)
SL (KKN)
SL (KWO)
SL (URM)
SL (UNS)
SL (TDW)
SL (DKA)
SL (UDS)
SL (CTA)
SL (KMS)
SL (ABK)
SL (RCK) Control
Mean Concentration (:g/g)
1.35
1.02
0.04
2.23
1.95
0.73
1.27
1.80
1.25
2.18
1.55
0.12
0.00
0.03
0.20
1.25
1.57
1.55
1.47
1.18
1.32
S.D.
0.30
0.08
0.06
1.47
0.28
0.60
0.10
0.70
0.31
0.86
0.14
0.03
0.00
0.03
0.25
1.75
0.23
0.23
0.20
0.24
0.44
S.E.
0.17
0.04
0.04
0.85
0.16
0.35
0.06
0.40
0.18
0.50
0.08
0.02
0.00
0.02
0.14
1.01
0.13
0.13
0.12
0.14
0.25
95% Confidence interval for mean
------------------------------------------------Lower bound
Upper bound
0.61
2.09
0.83
1.21
0.12
0.19
0.43
5.89
1.26
2.64
0.76
2.22
1.01
1.53
0.06
3.54
0.47
2.03
0.05
4.32
1.20
1.89
0.05
0.20
0.00
0.00
0.04
0.11
0.41
0.82
0.10
5.60
1.01
2.13
0.98
2.12
0.96
1.97
0.60
1.77
0.23
2.40
Table 2: Distribution of cadmium in lettuce from different irrigation sites of the Kaduna metropolis
Sample sites
LT (KBL)
LT(DMN)
LT(RGS)
LT (BNW)
LT (MKR)
LT (KKR)
LT (BDK)
LT (NAS)
LT (MAL)
LT (KUD)
LT (KKN)
LT (KWO)
LT (URM)
LT (UNS)
LT(TDW)
LT (DKA)
LT (UDS)
LT (CTA)
LT (KMS)
LT (ABK)
LT (RCK) (Control)
Mean concentration (:g/g)
0.09
0.00
0.09
0.47
0.73
0.03
0.47
0.47
1.27
1.13
1.13
0.80
0.67
0.27
0.20
1.37
0.60
0.53
0.67
1.00
0.63
S.D.
0.10
0.00
0.07
0.41
0.23
0.06
0.42
0.46
0.23
0.31
0.42
0.40
0.23
0.46
0.25
0.21
0.00
0.58
0.31
0.20
0.47
S.E.
0.06
0.00
0.04
0.23
0.13
0.03
0.24
0.27
0.13
0.18
0.24
0.23
0.13
0.27
0.14
0.12
0.00
0.33
0.18
0.12
0.27
sites were Kabala (KBL), Danmani (DMN), Rigasa
(RGS), Barnawa (BNW), Makera (MKR), Kakuri (KKR),
Badiko (BDK) Nasarawa (NAS, Malali (MAL), Kudende
(KUD), Kinkinau (KKN), Kawo (KWO), Unguwan Rimi
(URM), Unguwan Sanusi (UNS), Tudun Wada (TDW),
Doka (DKA), Unguwan Dosa (UDS), Kabala Costain
(CTA), Kurmin Mashi (KMS) and Abakpa (ABK). In this
research work soil sample from Rigachikun (RCK)
irrigation site was taken as control site.
95% Confidence interval for mean
-----------------------------------------------Lower bound
Upper bound
0.00
0.34
0.00
0.00
0.00
0.25
0.00
1.48
0.16
1.31
0.00
0.18
0.00
1.50
0.00
1.61
0.69
1.84
0.37
1.89
0.10
2.17
0.00
1.79
0.09
1.24
0.00
1.41
0.00
0.82
0.85
1.88
0.60
0.60
0.00
1.97
0.00
1.43
0.50
1.50
0.00
1.81
The digested residues were dissolved with 50 cm of
distilled water and filtered in 50 cm3 volumetric flask.
Soil sample: 20 g of the finely ground soil samples was
mixed with 60 cm3 (5:5:1) H2SO4/HNO3/HCl acid
mixtures and the content were refluxed for 12 h. The
sample was washed with 1M HNO3 and 100 cm3 of
deionized water was also added and centrifuged. The
elements (Cd Cu & Pb) were determined using bulk
scientific model VPG 210 model atomic absorption
spectrophotometer (AAS).
In order to investigate the ratio of the concentration
of heavy metal in a plant to the concentration heavy metal
in soil, the transfer factor was calculated based on the
Sample preparation:
Lettuce samples: 5 g of the ground Lettuce samples were
ashed in a muffle furnace at a temperature of 550ºC for
five hours and digested with 20 cm3 of HNO3/H2O2 (2:1).
103
Asian J. Agric. Sci., 4(2): 102-107, 2012
Table 3: Distribution of copper in soil from different irrigation sites of the Kaduna metropolis
Sampling sites
SL (KBL)
SL (DMN)
SL (RGS)
SL (BNW)
SL (MKR)
SL (KKR)
SL (BDK)
SL (NAS)
SL (MAL)
SL (KUD)
SL (KKN)
SL (KWO)
SL (URM)
SL (UNS)
SL (TDW)
SL (DKA)
SL (UDS)
SL (CTA)
SL (KMS)
SL (ABK)
SL (RCK) (Control)
Mean Concentration (:g/g)
3.21
5.05
3.19
42.94
8.33
17.28
4.55
7.52
4.07
7.97
6.33
20.14
20.86
8.22
24.41
14.59
5.05
3.98
5.43
3.53
3.53
S.D.
0.11
3.13
1.82
28.01
0.26
14.25
0.91
3.08
1.53
3.90
3.13
15.94
15.35
4.78
24.09
13.63
0.67
0.91
0.38
0.58
0.95
S.E.
0.06
1.81
1.05
16.17
0.15
8.23
0.53
1.78
0.88
2.25
1.80
9.20
8.86
2.76
13.91
7.87
0.39
0.52
0.22
0.33
0.55
95% Confidence interval for mean
--------------------------------------------------Lower bound
Upper bound
2.94
3.49
0.74
12.84
0.33
7.71
0.63
112.51
7.70
8.97
0.12
52.67
2.28
6.82
0.12
15.16
0.26
7.87
1.72
17.66
1.43
14.10
8.47
59.74
7.27
58.98
3.66
20.10
5.45
84.26
9.26
48.44
3.38
6.72
1.73
6.24
4.50
6.37
2.10
4.97
1.17
5.89
Table 4: Distribution of copper in lettuce from different irrigation sites of the Kaduna metropolis
Sampling sites
LT (KBL)
LT (DMN)
LT (RGS)
LT (BNW)
LT (MKR)
LT (KKR)
LT (BDK)
LT (NAS)
LT (MAL)
LT (KUD)
LT(KKN)
LT (KWO)
LT (URM)
LT (UNS)
LT (TDW)
LT (DKA)
LT (UDS)
LT (CTA)
LT (KMS)
LT (ABK)
LT (RCK) (Control)
Mean Concentration (:g/g)
2.41
1.00
2.50
2.47
2.67
0.27
2.50
4.07
4.77
3.87
3.20
2.67
2.33
0.67
2.67
4.97
3.20
3.53
3.47
3.43
4.20
S.D.
2.33
0.87
4.05
2.19
0.47
0.31
2.18
1.53
0.75
0.83
1.18
0.72
0.75
1.15
2.36
1.86
0.89
1.70
0.55
1.19
3.64
S.E.
1.34
0.50
2.34
1.27
0.27
0.18
1.26
0.88
0.43
0.48
0.68
0.42
0.43
0.67
1.36
1.07
0.51
0.98
0.32
0.69
2.10
method described by (Oyedele et al., 1995 and Harrison
and Chirgawi, 1989).
95% Confidence interval for mean
-----------------------------------------------Lower bound
Upper bound
0.36
8.19
0.17
3.17
0.56
12.56
0.98
7.92
1.49
3.84
0.49
1.03
0.91
7.91
0.26
7.87
2.90
6.63
1.80
5.94
0.27
6.13
0.87
4.46
0.47
4.20
0.20
3.54
0.20
8.54
0.35
9.58
0.99
5.41
0.70
7.77
2.10
4.83
0.47
6.40
0.85
13.25
Kaduna metropolis. The result shows that some sampling
sites had more concentration of Cadmium than of the
control site (1.32:g/g). Sharma et al. (2009) reported
concentration of cadmium as 2.3:g/g in the soil which is
higher than the concentration obtained in the present
study.
From Table 2, for Cadmium concentration in lettuce,
the mean concentration obtained in the present study were
far above FAO/WHO (2007) standard of 0.2 :g/g. This
implies that, the concentration of Cadmium in lettuce are
above the tolerable limit in most of the sampling sites.
However, there are isolated cases in Kabala, Danmani,
Rigasa, and Tudun Wada etc., where the Cadmium
concentration are within the WHO limit.
TF = Ps (:g/g/ St (:g/g)
where Ps is the plant metal content originating from the
soil and St is the total content in the soil.
RESULTS AND DISCUSSION
The mean concentration of cadmium, copper and lead
in soil and lettuce at various irrigation sites of the Kaduna
metropolis are summarized in Table. Table 1-6. shows
Cadmium distribution of soil in the irrigation site of the
104
Asian J. Agric. Sci., 4(2): 102-107, 2012
Table 5: Distribution of lead in soil from different irrigation sites of the Kaduna metropolis
Sampling sites
SL (KBL)
SL (DMN)
SL (RGS)
SL (BNW)
SL (MKR)
SL (KKR)
SL (BDK)
SL (NAS)
SL (MAL)
SL (KUD)
SL (KKN)
SL (KWO)
SL (URM)
SL (UNS)
SL (TDW)
SL (DKA)
SL (UDS)
SL (CTA)
SL (KMS)
SL (ABK)
SL (RCK) (Control)
Mean Concentration (:g/g)
4.17
4.00
13.23
35.46
3.20
36.47
2.17
4.67
3.80
4.95
3.47
39.78
16.47
9.60
5.16
30.36
3.67
2.53
2.60
3.47
3.67
S.D.
2.88
2.84
6.64
14.26
0.20
12.57
0.96
1.89
1.64
2.23
1.00
13.64
2.22
7.21
6.35
20.50
1.36
0.61
0.60
1.50
2.02
S.E.
1.66
1.64
3.84
8.23
0.12
7.26
0.55
1.09
0.95
1.29
0.58
7.88
1.28
4.17
3.67
11.84
0.79
0.35
0.35
0.87
1.17
95% Confidence interval for mean
-----------------------------------------------Lower bound
Upper bound
0.98
11.33
0.05
11.04
1.27
29.73
0.03
70.88
2.70
3.70
5.24
67.70
0.22
4.55
0.03
9.36
0.27
7.87
0.59
10.49
0.98
5.95
5.90
73.66
10.96
21.97
2.32
27.53
1.63
20.94
2.57
81.28
1.28
7.05
1.02
4.05
1.11
4.09
1.26
7.20
1.36
8.69
Table 6: Distribution of lead in lettuce from different irrigation sites of the Kaduna metropolis
Sampling sites
LT (KBL)
LT (DMN)
LT (RGS)
LT (BNW)
LT (MKR)
LT (KKR)
LT (BDK)
LT (NAS)
LT (MAL)
LT (KUD)
LT (KKN)
LT (KWO)
LT (URM)
LT (UNS)
LT (TDW)
LT (DKA)
LT (UDS)
LT (CTA)
LT (KMS)
LT (ABK)
LT (RCK) (Control)
Mean Concentration (:g/g)
3.44
0.96
3.57
1.51
2.37
3.81
0.00
2.87
2.33
3.67
1.73
2.13
3.40
1.27
2.47
2.73
1.80
1.80
2.17
3.33
3.27
S.D.
3.14
0.84
1.71
0.37
0.24
2.97
0.00
1.70
0.31
0.92
0.76
1.01
1.56
0.12
2.19
0.64
0.35
0.35
0.85
1.97
1.90
S.E.
1.81
0.48
0.99
0.21
0.14
1.71
0.00
0.98
0.18
0.53
0.44
0.58
0.90
0.07
1.27
0.37
0.20
0.20
0.49
1.14
1.10
95% Confidence interval for mean
------------------------------------------------Lower bound
Upper bound
0.36
11.24
0.11
3.04
0.69
7.83
0.58
2.43
1.77
2.97
0.57
11.19
0.00
0.00
0.37
7.10
1.57
3.09
1.37
5.96
0.15
3.61
0.37
4.63
0.48
7.28
0.98
1.55
0.98
7.92
1.14
4.33
0.94
2.66
0.94
2.66
0.05
4.28
0.57
8.23
0.46
7.99
below FAO/WHO (2007) standard of 40.00 :g/g. This
implies that, the concentration of Copper in lettuce are
within the tolerable limit in all the sampling sites.
However, there are no isolated cases in any of the
sampling site.
The results for copper in lettuce recorded in the
present study were lower than 6.54 :g/g for vegetable
sample given by Serife and Fatma (2010).
Okoye (2001) recorded 0.3 :g/g for lettuce sample
which is lower than that obtained in the present research
work.
Table 5 shows lead distribution of soil in the
irrigation site of the Kaduna metropolis. The
concentrations obtained in the analysed samples were
In the present study, cadmiun concentration of some
lettuce samples from Malali, Kawo, Kinkinau and Abakpa
and others were higher than the concentrations for
vegetables (lettuce) reported by Demirezen and Aksoy
(2006) given as 1.01 :g/g.
Table 3 shows Copper distribution of soil in the
irrigation site of the Kaduna metropolis. Some sampling
sites had more concentration of Copper than the control
site (3.53 :g/g). Krishna and Govil (2007) also reported
137.7 :g/g for copper in the soil which is higher than
concentration of copper obtained from all sampling sites
in this research work.
Table 4, shows Copper concentration in lettuce, the
mean concentrations obtained in this research study were
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Asian J. Agric. Sci., 4(2): 102-107, 2012
Table 7: Correlation coefficients for cadmium
Vegetable type
Lettuce
Cadmium concentration in soil sample (ug/g)
Table 8: Correlation coefficients for copper
Vegetable type
Lettuce
Copper concentration in soil sample (ug/g)
Table 9: Correlation coefficients for lead
Vegetable type
Lettuce
Lead concentration in soil sample (:g/g)
Pearson correlation
Sig. (2-tailed)
Cadmium concentration in vegetable sample (ug/g)
0.685
0.004
Pearson correlation
Sig. (2-tailed)
Copper Concentration in vegetable sample (ug/g)
0.636
0.002
Pearson correlation
Sig. (2-tailed)
more than that of the control sites (3.67 :g/g). Oyedele
et al. (2008) reported 37.9-42 :g/g for lead in soil which
were higher than the concentration obtained in this
research work.
Lead concentration for most of the soil samples
analyzed in this research study were found to be higher
than 2.95 and 3.58 :g/g for the soil from Alau dam and
Gongulon (Maiduguri. Nigeria) as reported by Uwah et
al. (2009), in contrast with Badiko, costain and Kurmin
mashi samples had lower concentrations.
From table 6 shows lead concentration in lettuce, the
obtained mean concentration for the analyzed samples
were higher than FAO/ WHO standard of 0.3 :g/g. This
implies that, the concentrations of lead in lettuce are
above the tolerable limit in most of the sampling sites.
However, from the results obtained in this research work
consumers of such vegetables are liable to lead toxicity.
Table 7 shows correlation coefficient for cadmium in
soil and lettuce with p = 0.004<0.05 for lettuce. This
shows that there is significant correlation between
Cadmium concentrations in soil and Cadmium
concentrations in the vegetables. The correlation is
strongly positive with the value of r = 0.685. This implies
that both Cadmium concentrations in soil and Cadmium
concentrations in the vegetables increase and decrease
together in the same direction. As Cadmium
concentrations in soil increases, the Cadmium
concentrations in lettuce also increases and vice versa.
Table 8, indicates correlation coefficient for copper
in soil and lettuce with p = 0.002<0.05 for lettuce, which
shows that there is significant correlation between Copper
concentrations in soil and Copper concentrations in
lettuce sample. The correlation is moderately positive
with the value of r = 0.636. This implies that both Copper
concentrations in soil and Copper concentrations in
lettuce increase and decrease together in the same
direction. As Copper concentrations in soil increases,
Copper concentrations in lettuce also increases and vice
versa.
Table 9 shows the correlation coefficient for lead in
soil and lettuce with p = 0.007<0.05 for lettuce. This
shows that there is significant correlation between lead
concentrations in soil and lead concentrations in lettuce
Lead concentration in vegetable sample (ug/g)
0.687
0.007
sample. The correlation is strongly positive with the
value of r = 0.687. This implies that both lead
concentrations in soil and lead concentrations in lettuce
increase and decrease together in the same direction. As
lead concentrations in soil increases, lead concentrations
in lettuce also increases and vice versa.
CONCLUSION
In the present study, the concentration of cadmium,
copper and lead were determined in the soil and lettuce
obtained from irrigation sites of Kaduna Metropolis,
Nigeria. The result revealed that the concentration of lead
and cadmium from some samples were above the
recommended limit stipulated by FAO/WHO (2007)
allimentarius but copper was found to be within such
limit. Therefore consumption of lettuce from the study
areas might result to lead and cadmium toxicity and
thereby dangerous to human health.
ACKNOWLEDGMENT
The Authors were grateful to the management of
Kaduna Polytechnic for sponsoring this research study.
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