Heavy Metals Contents and Their Mobility in Various Land Uses for Horticulture in Bali, Indonesia.
Heavy Metals Contents and Their Mobility in Various Land Uses
for Vegetables Cultivating in Bali, Indonesia
I Made Adnyana1* and I Made Siaka2
1.
Agricultural Soil Department of Agricultural Faculty, Udayana University, Jl. P.B. Sudirman Denpasar-Bali, Indonesia
2.
Chemistry Department of Maths and Sciences Faculty, Udayana University, Bukit Jimbaran Campus -Bali, Indonesia.
Abstract: A study on the mobility of heavy metals in various types of land uses for vegetables cultivating at Candi Kuning, Bedugul, Bali
has been carried out. Heavy metals contaminating agricultural soils could contaminate the vegetables growing on the lands. The movements
of heavy metals to the vegetables depend on their mobility and the land characteristics. This study was aimed to determine the mobility of
heavy metals being available in the lands uses by investigating the most bioavailable fractions of the metals under study. Digestion and
sequential extraction methods were applied to establish the mobility of heavy metals. All metals measurements were carried out with the
use of AAS. The results showed that the concentrations of total Pb, Cu, Cd, Cr, and Zn were in the range of 27.952-102.248, 112.759179.664, 4.593-16.201, 5.512-36.473, and 110.289-238.498 mg/kg, respectively. The mobility of each metal in the soils was varied. The
mobility of Pb (the highest) was found in the soil for cultivating potatoes (37.13%), Cu and Zn in soil for lettuce (25.68 and 36.65%), Cd
and Cr in soil for tomatoes (31.61 and 42.38%). Statistically, the mobility of the metals was significantly different (p lettuce soil > potato soil > carrots soil > spring onion soil. In general, the average concentration of Cd in
soils investigated was above the range for both common value (0.2 - 1 mg/kg) and range for agricultural soils (0.01 2.4 mg/kg )[1]. This revealed that Cd could be a threat to health, if it in high availability therefore, it could contaminate
the vegetables grown in the soils. In addition, Cd can also compete with Zn or in the absence of Zn, Cd substitutes this
metal resulting in malfunctions in metabolic processes. Cd is located in the same group with Zn in the periodic table of
elements, so that the metals have similar properties[33]. Absorption of Cd by plants including vegetables is highly
dependent on the bioavailability of the metal. The introduction of Cd into agricultural lands could be derived from the
use of synthetic pesticides, inorganic fertilizers and manure[1-7] intensively in the area.
Chromium found in the vegetable lands in Bedugul area ranged from 5.512 to 36.473 mg/kg. These
concentrations were below the lowest common value Cr range in agricultural soils, i.e. 70-100 mg/kg[1]. The highest Cr
concentration was found in the soil for tomato while the lowest concentration was in lettuce soil. Although Cr content
was low enough, but a preliminary research found that the content of Cr in 8 out of 10 types of vegetables exceeded the
maximum limit allowed by FAO/WHO[32]. This indicated that the chromium in the soil has a high bioavailability so that
at high concentration this metal could be absorbed by the vegetables.
Zinc was the highest metal contained in soils investigated. The average concentration of Zn in five types of
vegetable soils in Bedugul area was in the range of 110.289-238.498 mg/kg. This range was within the range
concentration of Zn in agricultural soils (10 – 300 mg/kg), but exceeds the common value (50 mg/kg)[1]. The highest
content of Zn was found in the soil for lettuce while the lowest was in the soil for carrots. The high content of zinc in
the soil can be alarming because it can inhibit the absorption of Cu by the plants causing Cu deficiency[34]. Fertilizers
and pesticides used in agricultural in this area is the major source of Zn contamination. Although Zn in soil was
relatively high, but its accumulation in plants is not necessarily high, as the results of the preliminary research reported
that the zinc contents in 10 types of vegetables analyzed were below the maximum limit allowed by FAO/WHO
regulation[32].
Table 2 The average of total heavy metals containing in various vegetable soils
3.2
Soils for
cultivating
Tomato
Pb
(mg/kg)
27.952
Lettuce
Spring onion
SD
0.088
Cu
(mg/kg)
112.759
102.248
0.014
34.928
0.024
Potatoes
29.596
Carrot
31.198
SD
0.223
Cd
(mg/kg)
16.201
SD
Cr
(mg/kg)
36.473
0.224
156.126
0.077
9.462
174.871
0.005
4.593
0.338
179.664
0.681
0.059
119.421
0.018
SD
0.143
Zn
SD
(mg/kg)
212.545
0.620
0.165
5.512
0.008
238.498
0.831
0.005
20.612
0.057
183.808
0.367
8.387
0.681
16.587
0.091
129.487
1.103
4.916
0.018
18.046
0.022
110.289
0.019
Fractionation of heavy metals in different types of lands for vegetable cultivation
Fractionation results of Pb, Cu, Cd, Cr, and Zn in soil cultivated with tomato, lettuce, spring onion, potatoes,
and carrots are presented in Table 3. Fractionation of the metals is the result of a sequential extraction of four steps in
accordance with the strength of the metal bonding to the soil particles. From the table, it can be seen that the tomatoes
soil had the highest Zn and Cr extracted in F1, while the other metals, Pb, Cu, and Zn in F1 were found to be the
highest in lettuce soil. F1 is the fraction that has the weakest bond so that the metals in this fraction are easily separated
from the bonding in soil particles. Heavy metals in this fraction are classified as dissolved metals or ionic forms, metals
bound to carbonate, and exchangeable metals[29-31]. Therefore, these metals are very unstable so they can be readily
available for the plants growing on the soil. It was evident that the soils showing the highest total metal contents they
also showed the highest bioavailable fractions, except that Cu showed the highest total metal content in the soil for
potatoes.
Fraction 2 and 3 are the fractions of the heavy metals that are more tightly bound to the soil particles than that
of in fraction 1 and they bound to Fe/Mn oxides (F2) and organic and sulfide (F3). The metals in these
fractions/bonding are more stable than those in F1, this causes the metals are less bioavailable but they can potentially
change becoming bioavailable as the conditions of the soils changes, such as pH decreases (for F2) and increased
oxidation of soil (for F3). The soil for tomatoes was dominated by Cu, Cd, Zn, and Cr those were potentially
bioavailable, while lettuce soil was dominated by Pb and Zn. Spring onion and potato soils were dominated by Cr and
Cu that were potentially bioavailable. Evidently, the soil for carrot did not show a metal that dominates each other.
Several factors that can affect the entry of heavy metals into plants including soil pH, cation exchange capacity (CEC),
organic matter content, soil texture, and interaction between elements of the target (soil pH, cation exchange capcity,
organic matter content, soil texture, and interaction among the targets elements)[35].
The remaining fraction F4 is a solid residue whose main contents are minerals of primary and secondary that
may bound to trace metals in their crystal structure[36]. Therefore, the heavy metals may not be extracted in the previous
steps of the extraction. The metals contained in the remaining fraction is inert metals and they tend to be non
bioavailable, so their presence in the soils are very safe and in a normal state of nature they are not absorbed by the
plants grown on the soils. In general, the average concentrations of Pb, Cu, Cd, Cr, and Zn in all soils were 9.235,
44.472, 2.435, 3.60, and 32.428 mg/kg. The higher the content of heavy metals in this phase F4, the more secure the
plants that grow on the soils to heavy metals contamination.
Tabel 3 Fracionation of heavy metal Pb, Cu, Cd, Cr, dan Zn on vegetables soil
Tomato
Pb
6.321
Fraction 1 (mg/kg)
Cu
Cd
Cr
19.651
5.121
15.457
Zn
63.716
Pb
4.477
Fraction 2 (mg/kg)
Cu
Cd
Cr
31.325
2.311
3.722
Zn
47.449
Lettuce
35.058
40.087
1.308
2.047
87.416
13.288
11.694
1.447
0.665
57.458
Spring onion
8.260
33.141
1.369
8.646
36.695
11.858
15.013
0.423
4.265
44.238
Potatoes
10.989
18.811
0.887
1.641
14.163
3.034
5.603
3.160
1.393
25.767
Carrot
4.916
30.042
1.518
2.732
38.326
7.601
12.869
1.457
3.331
16.088
Soils for
Cultivating
Residual Fraction* (mg/kg)
Fraction 3 (mg/kg)
8.978
36.551
4.247
13.500
42.405
8.175
25.175
4.375
3.581
57.609
Lettuce
39.711
53.268
2.171
1.352
77.691
14.118
51.010
4.396
1.447
15.060
Spring onion
10.497
78.174
1.846
6.336
65.086
4.306
48.543
0.955
1.362
37.788
Potatoes
6.192
83.960
2.272
7.766
19.588
9.339
71.279
2.065
5.771
21.761
Carrot
8.437
50.145
1.557
6.138
25.953
10.236
26.355
0.384
5.846
29.923
Tomato
3.3
*
Residual fraction: non-extractable
Mobility of heavy metals in different types of lands for vegetable cultivation
The mobility of Pb, Cu, Cd, Cr, and Zn in the soils for cultivating of vegetables investigated is the ratio of the
concentration of heavy metals extracted at the first fraction to the total concentration of the metals. The mobility of an
element is hard to predict quantitatively in the environment surface, so it should be considered as a relative matter by
comparing the behavior of the elements under environmental conditions changes empirically[18]. The mobility of each
metal in each area including the land for cultivating tomatoes, lettuce, spring onion, potatoes, and carrots showed
different levels as illustrated in Figure 1. The average mobilities of Pb, Cu, Cd, Cr, and Zn in all types of the vegetable
soils were 15.76 to 37.13, 10.47 to 25.68, 10.57 to 31.61, 9.90 to 42.38, and 10.94 to 36.65 %. Statistically, the mobility
of each metal in each field was significantly different at p < 0.05 or at confidence limit of 95% (as shown in Table 4).
The most mobile Pb was found in the soil for cultivating potatoes and the lowest was in the land for carrots.
Lead mobility in the soils decreased as follows: potato soil > lettuce soil > spring onion soil > tomato soil > carrots soil.
The high mobility of Pb in the potatoes soil may be due to lack of Fe/Mn oxides (% F2) and organic matter or sulfides
(% F3) that can bind these metals so that they tend to stay in the form of ions or easily dissolved in the soil solution.
Likewise, the presence of Cr is high enough on the soil (as shown in Table 2) allowing Pb to precipitate chromium in
the form of Cr2O72- and CrO42- as PbCrO4 which is in the soil solution ( pH < 7 ) likely to dissolve as Pb2+ (pH soil =
6.20, recorded).
Figure 1 shows that the mobility of Cu in the range of 10-27 % and can be ordered from the highest value to
the lowest as follows : lettuce soil > carrots soil > spring onion soil > tomato soil > potatoes soil. Like Pb, Cu also was
less bound by oxide Fe/Mn and organic matter in the lettuce soil, so it tends to be in the carbonate phase, exchangeable,
and dissolved matter. It can also be proved by the mobility of Cu in carrots soil (2nd highest), where the sum
percentages of F2 and F3 in carrot soil was slightly higher than that of in lettuce soil. This resulted in the mobility of Cu
in carrots soil was only slightly lower than that of in the lettuce soil. The lowest Cu mobility was found in the soil of
potatoes while the organic phase/sulphide (% F3) was the highest in this soil. This causes the lowest mobility of Cu as
the affinity of Cu is very strong to the organic matter in the soil[36] .
Table 4 Analysis statistic for heavy metals in different vegetable soils
Soils for
cultivating
Tomato
Lettuce
Spring onion
Potatoes
Carrot
Mean Square
Sig.
The highest percentage heavy metal
Mobility (%)
*
50
40
30
20
10
0
Cr
42.3767*
37.1333
41.9467
9.8967
15.1400
0.181
1.000
Zn
29.9800
36.6633*
19.9633
16.7500
34.7500
0.060
1.000
Significant for Cr in tomato and spring onion soils was 0.244
37.13
34.29
23.65
22.61
15.76
Pb
50
40
30
20
10
0
50
40
30
20
10
0
17.43
31.61
25.16
18.95
10.47
Vegetable Soils
30.89
29.81
13.82
25.68
Cu
Ӯ = 19.54%
Vegetable Soils
Mobility (%)
Ӯ = 26.69%
Heavy Metals (%)
Cd
31.6100*
13.8233
29.8067
10.5733
30.8833
0.022
1.000
Cu
17.4267
25.6767*
18.9533
10.4700
4.1167
0.005
1.000
Mobility (%)
Duncanabc
Pb
22.6467
34.3033
23.6700
37.0633*
15.7467
0.026
1.000
10.57
Cd
50
40
30
20
10
0
42.38
37.13
Vegetable Soils
41.95
9.90
Mobility (%)
Mobility (%)
Ӯ = 23.34%
15.14
50
40
30
20
10
0
29.98
36.65
34.75
19.96
10.94
Cr
Ӯ = 29.30%
Vegetable Soils
Zn
Ӯ = 26.46%
Vegetable Soils
Ӯ = the average mobility of metal
Figure 1 Mobility of Pb, Cu, Cd, Cr, and Zn in various cultivating lands
The mobility of Cd in all types of soils found in this study ranged between 10.57 and 31.61 % and the highest
mobility was found in tomatoes soil, while the lowest was in potatoes soil. The high mobility of Cd in tomato soil can
be explained by considering the sum percentages of Fe/Mn oxides phase (% F2) and the organic or sulphide phase
(%F3). The sum of both fractions in the tomato soil was the smallest fraction compared to those in other soils. This
indicated that Cd mostly presents in carbonates, exchangeable, and dissolved phases, so cadmium has the highest
mobility in that soil. Cadmium mobility decreased sequence in the order of: tomato soil > carrot soil > spring onion soil
> lettuce soil > potatoes soil.
In contrast to Pb, Cu, and Cd, Chromium has a fairly large mobility (37.13 to 42.38%) in three types of soils
that were tomato, lettuce and spring onion soils. The mobility of Cr in tomatoes soil was the highest, followed by spring
onion soil, lettuce soil and decreased sharply in carrots soil (15.14%), while the lowest was found in potatoes soil. The
level of Cr mobility in these cases can not be explained by the existence of the second and third factions, because it can
not explain consistently as the discussions of Pb, Cu, and Cd. This is probably because of Cr has very different
properties with the other four metals. For example, Cr can form anion compounds with other elements such as CrO42and Cr2O72-. Likewise, Cr has two oxidation numbers which are +3 and +6 with its ionic radius of the smallest (75.5
and 58 pm) among other metals. The ionic radii of Pb+2, Cu+1, Cu+2, Cd+2, and Zn+2 are 133, 91, 87, 109, and 88 pm
respectively. Theoritically, the smaller the atomic radius, the more mobile the metal is[18]. Therefore, it is reasonable
that chromium was the most mobile metals among the five metals under study. It was supported by the average of the
mobility percentage of Cr on all soils was the highest i.e. 29.30 %. The average of the mobility percentages of Pb, Zn,
Cd, and Cu were 26.69, 26.46, 23.24, and 19.54 % respectively.
Zinc was the metal that showed the third highest mobility after Cr and Pb, as presented in Figure 1. The
mobility of Zn was quite high in the three soil types including: lettuce, carrots, and tomatoes soils. Mobility of Zn was
found to be the highest in the lettuce soil, while the lowest was in the potatoes soil. The mobilities of Zn in vegetable
soils were found in the range of 10.94 to 36.65 % with the average of 26.46 %. This metal mobility in vegetable soils
can be arranged as following the order of lettuce soil > carrots soil > tomato soil > spring onion soil > potatoes soil.
In general, the results of this study indicated that Cr metal mobility was the highest, followed by Pb, Zn, and
Cd, and the lowest was Cu. The soils for tomatoes and lettuce had four metals with relatively high mobilities, namely
Pb, Cd, Cr, and Zn in tomatoes soil and Pb, Cu, Cr, and Zn in lettuce soil. The soil for carrot had 3 metals with high
enough mobility, i.e. Cu, Cd and Zn, while spring onion soil had two metals with relatively high mobilities. Potatoes
soil was the only had one metal with high mobility, i.e. Pb and the other metals were relatively low (< 11 %). This
suggested that the soil for potatoes was the most secure land for cultivating all types of vegetables.
4
Conclusion
Based on the above discussions, it can be concluded that the range of total heavy metals including Pb, Cu, Cd,
Cr, and Zn in various soil types for cultivating vegetables were: 27.952 - 102.248, 112.759 - 179.664, 4.593 - 16.201,
5.512 - 36.473, and 110.289 - 238.498 mg/kg, respectively. The highest Pb and Zn contained in the soil for cultivating
lettuce, while the highest concentrations of Cd and Cr were found in soils for tomato. The highest Cu content was found
in the soil for cultivating potatoes. The mobilities of all heavy metals were significantly different between metals and
the soils. The average mobilities of Pb, Cu, Cd, Cr, and Zn in all types of the vegetable lands were 15.76 - 37.13; 10.47
- 25.68; 10.57 - 31.61; 9.90 - 42.38; and 10.94 -36.65%, respectively. Statistically, the mobility of each metal in each
field was significantly different at 95% confidence limit (p Pb > Zn > Cd > Cu.
5
Acknowledgements
The authors would like to thank Mr. Wayan Ada as the leader of farmer’s group in Candi Kuning VillageBedugul and Mrs. Emmy Sahara for their helps and supports for making this possible.
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for Vegetables Cultivating in Bali, Indonesia
I Made Adnyana1* and I Made Siaka2
1.
Agricultural Soil Department of Agricultural Faculty, Udayana University, Jl. P.B. Sudirman Denpasar-Bali, Indonesia
2.
Chemistry Department of Maths and Sciences Faculty, Udayana University, Bukit Jimbaran Campus -Bali, Indonesia.
Abstract: A study on the mobility of heavy metals in various types of land uses for vegetables cultivating at Candi Kuning, Bedugul, Bali
has been carried out. Heavy metals contaminating agricultural soils could contaminate the vegetables growing on the lands. The movements
of heavy metals to the vegetables depend on their mobility and the land characteristics. This study was aimed to determine the mobility of
heavy metals being available in the lands uses by investigating the most bioavailable fractions of the metals under study. Digestion and
sequential extraction methods were applied to establish the mobility of heavy metals. All metals measurements were carried out with the
use of AAS. The results showed that the concentrations of total Pb, Cu, Cd, Cr, and Zn were in the range of 27.952-102.248, 112.759179.664, 4.593-16.201, 5.512-36.473, and 110.289-238.498 mg/kg, respectively. The mobility of each metal in the soils was varied. The
mobility of Pb (the highest) was found in the soil for cultivating potatoes (37.13%), Cu and Zn in soil for lettuce (25.68 and 36.65%), Cd
and Cr in soil for tomatoes (31.61 and 42.38%). Statistically, the mobility of the metals was significantly different (p lettuce soil > potato soil > carrots soil > spring onion soil. In general, the average concentration of Cd in
soils investigated was above the range for both common value (0.2 - 1 mg/kg) and range for agricultural soils (0.01 2.4 mg/kg )[1]. This revealed that Cd could be a threat to health, if it in high availability therefore, it could contaminate
the vegetables grown in the soils. In addition, Cd can also compete with Zn or in the absence of Zn, Cd substitutes this
metal resulting in malfunctions in metabolic processes. Cd is located in the same group with Zn in the periodic table of
elements, so that the metals have similar properties[33]. Absorption of Cd by plants including vegetables is highly
dependent on the bioavailability of the metal. The introduction of Cd into agricultural lands could be derived from the
use of synthetic pesticides, inorganic fertilizers and manure[1-7] intensively in the area.
Chromium found in the vegetable lands in Bedugul area ranged from 5.512 to 36.473 mg/kg. These
concentrations were below the lowest common value Cr range in agricultural soils, i.e. 70-100 mg/kg[1]. The highest Cr
concentration was found in the soil for tomato while the lowest concentration was in lettuce soil. Although Cr content
was low enough, but a preliminary research found that the content of Cr in 8 out of 10 types of vegetables exceeded the
maximum limit allowed by FAO/WHO[32]. This indicated that the chromium in the soil has a high bioavailability so that
at high concentration this metal could be absorbed by the vegetables.
Zinc was the highest metal contained in soils investigated. The average concentration of Zn in five types of
vegetable soils in Bedugul area was in the range of 110.289-238.498 mg/kg. This range was within the range
concentration of Zn in agricultural soils (10 – 300 mg/kg), but exceeds the common value (50 mg/kg)[1]. The highest
content of Zn was found in the soil for lettuce while the lowest was in the soil for carrots. The high content of zinc in
the soil can be alarming because it can inhibit the absorption of Cu by the plants causing Cu deficiency[34]. Fertilizers
and pesticides used in agricultural in this area is the major source of Zn contamination. Although Zn in soil was
relatively high, but its accumulation in plants is not necessarily high, as the results of the preliminary research reported
that the zinc contents in 10 types of vegetables analyzed were below the maximum limit allowed by FAO/WHO
regulation[32].
Table 2 The average of total heavy metals containing in various vegetable soils
3.2
Soils for
cultivating
Tomato
Pb
(mg/kg)
27.952
Lettuce
Spring onion
SD
0.088
Cu
(mg/kg)
112.759
102.248
0.014
34.928
0.024
Potatoes
29.596
Carrot
31.198
SD
0.223
Cd
(mg/kg)
16.201
SD
Cr
(mg/kg)
36.473
0.224
156.126
0.077
9.462
174.871
0.005
4.593
0.338
179.664
0.681
0.059
119.421
0.018
SD
0.143
Zn
SD
(mg/kg)
212.545
0.620
0.165
5.512
0.008
238.498
0.831
0.005
20.612
0.057
183.808
0.367
8.387
0.681
16.587
0.091
129.487
1.103
4.916
0.018
18.046
0.022
110.289
0.019
Fractionation of heavy metals in different types of lands for vegetable cultivation
Fractionation results of Pb, Cu, Cd, Cr, and Zn in soil cultivated with tomato, lettuce, spring onion, potatoes,
and carrots are presented in Table 3. Fractionation of the metals is the result of a sequential extraction of four steps in
accordance with the strength of the metal bonding to the soil particles. From the table, it can be seen that the tomatoes
soil had the highest Zn and Cr extracted in F1, while the other metals, Pb, Cu, and Zn in F1 were found to be the
highest in lettuce soil. F1 is the fraction that has the weakest bond so that the metals in this fraction are easily separated
from the bonding in soil particles. Heavy metals in this fraction are classified as dissolved metals or ionic forms, metals
bound to carbonate, and exchangeable metals[29-31]. Therefore, these metals are very unstable so they can be readily
available for the plants growing on the soil. It was evident that the soils showing the highest total metal contents they
also showed the highest bioavailable fractions, except that Cu showed the highest total metal content in the soil for
potatoes.
Fraction 2 and 3 are the fractions of the heavy metals that are more tightly bound to the soil particles than that
of in fraction 1 and they bound to Fe/Mn oxides (F2) and organic and sulfide (F3). The metals in these
fractions/bonding are more stable than those in F1, this causes the metals are less bioavailable but they can potentially
change becoming bioavailable as the conditions of the soils changes, such as pH decreases (for F2) and increased
oxidation of soil (for F3). The soil for tomatoes was dominated by Cu, Cd, Zn, and Cr those were potentially
bioavailable, while lettuce soil was dominated by Pb and Zn. Spring onion and potato soils were dominated by Cr and
Cu that were potentially bioavailable. Evidently, the soil for carrot did not show a metal that dominates each other.
Several factors that can affect the entry of heavy metals into plants including soil pH, cation exchange capacity (CEC),
organic matter content, soil texture, and interaction between elements of the target (soil pH, cation exchange capcity,
organic matter content, soil texture, and interaction among the targets elements)[35].
The remaining fraction F4 is a solid residue whose main contents are minerals of primary and secondary that
may bound to trace metals in their crystal structure[36]. Therefore, the heavy metals may not be extracted in the previous
steps of the extraction. The metals contained in the remaining fraction is inert metals and they tend to be non
bioavailable, so their presence in the soils are very safe and in a normal state of nature they are not absorbed by the
plants grown on the soils. In general, the average concentrations of Pb, Cu, Cd, Cr, and Zn in all soils were 9.235,
44.472, 2.435, 3.60, and 32.428 mg/kg. The higher the content of heavy metals in this phase F4, the more secure the
plants that grow on the soils to heavy metals contamination.
Tabel 3 Fracionation of heavy metal Pb, Cu, Cd, Cr, dan Zn on vegetables soil
Tomato
Pb
6.321
Fraction 1 (mg/kg)
Cu
Cd
Cr
19.651
5.121
15.457
Zn
63.716
Pb
4.477
Fraction 2 (mg/kg)
Cu
Cd
Cr
31.325
2.311
3.722
Zn
47.449
Lettuce
35.058
40.087
1.308
2.047
87.416
13.288
11.694
1.447
0.665
57.458
Spring onion
8.260
33.141
1.369
8.646
36.695
11.858
15.013
0.423
4.265
44.238
Potatoes
10.989
18.811
0.887
1.641
14.163
3.034
5.603
3.160
1.393
25.767
Carrot
4.916
30.042
1.518
2.732
38.326
7.601
12.869
1.457
3.331
16.088
Soils for
Cultivating
Residual Fraction* (mg/kg)
Fraction 3 (mg/kg)
8.978
36.551
4.247
13.500
42.405
8.175
25.175
4.375
3.581
57.609
Lettuce
39.711
53.268
2.171
1.352
77.691
14.118
51.010
4.396
1.447
15.060
Spring onion
10.497
78.174
1.846
6.336
65.086
4.306
48.543
0.955
1.362
37.788
Potatoes
6.192
83.960
2.272
7.766
19.588
9.339
71.279
2.065
5.771
21.761
Carrot
8.437
50.145
1.557
6.138
25.953
10.236
26.355
0.384
5.846
29.923
Tomato
3.3
*
Residual fraction: non-extractable
Mobility of heavy metals in different types of lands for vegetable cultivation
The mobility of Pb, Cu, Cd, Cr, and Zn in the soils for cultivating of vegetables investigated is the ratio of the
concentration of heavy metals extracted at the first fraction to the total concentration of the metals. The mobility of an
element is hard to predict quantitatively in the environment surface, so it should be considered as a relative matter by
comparing the behavior of the elements under environmental conditions changes empirically[18]. The mobility of each
metal in each area including the land for cultivating tomatoes, lettuce, spring onion, potatoes, and carrots showed
different levels as illustrated in Figure 1. The average mobilities of Pb, Cu, Cd, Cr, and Zn in all types of the vegetable
soils were 15.76 to 37.13, 10.47 to 25.68, 10.57 to 31.61, 9.90 to 42.38, and 10.94 to 36.65 %. Statistically, the mobility
of each metal in each field was significantly different at p < 0.05 or at confidence limit of 95% (as shown in Table 4).
The most mobile Pb was found in the soil for cultivating potatoes and the lowest was in the land for carrots.
Lead mobility in the soils decreased as follows: potato soil > lettuce soil > spring onion soil > tomato soil > carrots soil.
The high mobility of Pb in the potatoes soil may be due to lack of Fe/Mn oxides (% F2) and organic matter or sulfides
(% F3) that can bind these metals so that they tend to stay in the form of ions or easily dissolved in the soil solution.
Likewise, the presence of Cr is high enough on the soil (as shown in Table 2) allowing Pb to precipitate chromium in
the form of Cr2O72- and CrO42- as PbCrO4 which is in the soil solution ( pH < 7 ) likely to dissolve as Pb2+ (pH soil =
6.20, recorded).
Figure 1 shows that the mobility of Cu in the range of 10-27 % and can be ordered from the highest value to
the lowest as follows : lettuce soil > carrots soil > spring onion soil > tomato soil > potatoes soil. Like Pb, Cu also was
less bound by oxide Fe/Mn and organic matter in the lettuce soil, so it tends to be in the carbonate phase, exchangeable,
and dissolved matter. It can also be proved by the mobility of Cu in carrots soil (2nd highest), where the sum
percentages of F2 and F3 in carrot soil was slightly higher than that of in lettuce soil. This resulted in the mobility of Cu
in carrots soil was only slightly lower than that of in the lettuce soil. The lowest Cu mobility was found in the soil of
potatoes while the organic phase/sulphide (% F3) was the highest in this soil. This causes the lowest mobility of Cu as
the affinity of Cu is very strong to the organic matter in the soil[36] .
Table 4 Analysis statistic for heavy metals in different vegetable soils
Soils for
cultivating
Tomato
Lettuce
Spring onion
Potatoes
Carrot
Mean Square
Sig.
The highest percentage heavy metal
Mobility (%)
*
50
40
30
20
10
0
Cr
42.3767*
37.1333
41.9467
9.8967
15.1400
0.181
1.000
Zn
29.9800
36.6633*
19.9633
16.7500
34.7500
0.060
1.000
Significant for Cr in tomato and spring onion soils was 0.244
37.13
34.29
23.65
22.61
15.76
Pb
50
40
30
20
10
0
50
40
30
20
10
0
17.43
31.61
25.16
18.95
10.47
Vegetable Soils
30.89
29.81
13.82
25.68
Cu
Ӯ = 19.54%
Vegetable Soils
Mobility (%)
Ӯ = 26.69%
Heavy Metals (%)
Cd
31.6100*
13.8233
29.8067
10.5733
30.8833
0.022
1.000
Cu
17.4267
25.6767*
18.9533
10.4700
4.1167
0.005
1.000
Mobility (%)
Duncanabc
Pb
22.6467
34.3033
23.6700
37.0633*
15.7467
0.026
1.000
10.57
Cd
50
40
30
20
10
0
42.38
37.13
Vegetable Soils
41.95
9.90
Mobility (%)
Mobility (%)
Ӯ = 23.34%
15.14
50
40
30
20
10
0
29.98
36.65
34.75
19.96
10.94
Cr
Ӯ = 29.30%
Vegetable Soils
Zn
Ӯ = 26.46%
Vegetable Soils
Ӯ = the average mobility of metal
Figure 1 Mobility of Pb, Cu, Cd, Cr, and Zn in various cultivating lands
The mobility of Cd in all types of soils found in this study ranged between 10.57 and 31.61 % and the highest
mobility was found in tomatoes soil, while the lowest was in potatoes soil. The high mobility of Cd in tomato soil can
be explained by considering the sum percentages of Fe/Mn oxides phase (% F2) and the organic or sulphide phase
(%F3). The sum of both fractions in the tomato soil was the smallest fraction compared to those in other soils. This
indicated that Cd mostly presents in carbonates, exchangeable, and dissolved phases, so cadmium has the highest
mobility in that soil. Cadmium mobility decreased sequence in the order of: tomato soil > carrot soil > spring onion soil
> lettuce soil > potatoes soil.
In contrast to Pb, Cu, and Cd, Chromium has a fairly large mobility (37.13 to 42.38%) in three types of soils
that were tomato, lettuce and spring onion soils. The mobility of Cr in tomatoes soil was the highest, followed by spring
onion soil, lettuce soil and decreased sharply in carrots soil (15.14%), while the lowest was found in potatoes soil. The
level of Cr mobility in these cases can not be explained by the existence of the second and third factions, because it can
not explain consistently as the discussions of Pb, Cu, and Cd. This is probably because of Cr has very different
properties with the other four metals. For example, Cr can form anion compounds with other elements such as CrO42and Cr2O72-. Likewise, Cr has two oxidation numbers which are +3 and +6 with its ionic radius of the smallest (75.5
and 58 pm) among other metals. The ionic radii of Pb+2, Cu+1, Cu+2, Cd+2, and Zn+2 are 133, 91, 87, 109, and 88 pm
respectively. Theoritically, the smaller the atomic radius, the more mobile the metal is[18]. Therefore, it is reasonable
that chromium was the most mobile metals among the five metals under study. It was supported by the average of the
mobility percentage of Cr on all soils was the highest i.e. 29.30 %. The average of the mobility percentages of Pb, Zn,
Cd, and Cu were 26.69, 26.46, 23.24, and 19.54 % respectively.
Zinc was the metal that showed the third highest mobility after Cr and Pb, as presented in Figure 1. The
mobility of Zn was quite high in the three soil types including: lettuce, carrots, and tomatoes soils. Mobility of Zn was
found to be the highest in the lettuce soil, while the lowest was in the potatoes soil. The mobilities of Zn in vegetable
soils were found in the range of 10.94 to 36.65 % with the average of 26.46 %. This metal mobility in vegetable soils
can be arranged as following the order of lettuce soil > carrots soil > tomato soil > spring onion soil > potatoes soil.
In general, the results of this study indicated that Cr metal mobility was the highest, followed by Pb, Zn, and
Cd, and the lowest was Cu. The soils for tomatoes and lettuce had four metals with relatively high mobilities, namely
Pb, Cd, Cr, and Zn in tomatoes soil and Pb, Cu, Cr, and Zn in lettuce soil. The soil for carrot had 3 metals with high
enough mobility, i.e. Cu, Cd and Zn, while spring onion soil had two metals with relatively high mobilities. Potatoes
soil was the only had one metal with high mobility, i.e. Pb and the other metals were relatively low (< 11 %). This
suggested that the soil for potatoes was the most secure land for cultivating all types of vegetables.
4
Conclusion
Based on the above discussions, it can be concluded that the range of total heavy metals including Pb, Cu, Cd,
Cr, and Zn in various soil types for cultivating vegetables were: 27.952 - 102.248, 112.759 - 179.664, 4.593 - 16.201,
5.512 - 36.473, and 110.289 - 238.498 mg/kg, respectively. The highest Pb and Zn contained in the soil for cultivating
lettuce, while the highest concentrations of Cd and Cr were found in soils for tomato. The highest Cu content was found
in the soil for cultivating potatoes. The mobilities of all heavy metals were significantly different between metals and
the soils. The average mobilities of Pb, Cu, Cd, Cr, and Zn in all types of the vegetable lands were 15.76 - 37.13; 10.47
- 25.68; 10.57 - 31.61; 9.90 - 42.38; and 10.94 -36.65%, respectively. Statistically, the mobility of each metal in each
field was significantly different at 95% confidence limit (p Pb > Zn > Cd > Cu.
5
Acknowledgements
The authors would like to thank Mr. Wayan Ada as the leader of farmer’s group in Candi Kuning VillageBedugul and Mrs. Emmy Sahara for their helps and supports for making this possible.
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