International Journal of Advancements in Research & Technology, Volume 2, Issue4, April-2013
ISSN 2278-7763
215
HEAVY METALS CONTAMINATION OF TEA ESTATES SOIL IN
SIVASAGAR AND DIBRUGARH DISTRICTS OF ASSAM, INDIA
T.N. Nath
Associate Professor , Department of Chemistry, Moran College, Sivasagar,
Assam, India. taranathnath@yahoo.co.in
K.G.Bhattachayya
Professor, Department in Chemistry, Gauhati University, Guwahati, Assam, India.
Abstract: The aim was to determine the concentration of heavy metals in tea estates
soil in the Dibrugarh and Sivasagar districts of Assam, India. Soil samples from twenty
tea estates and a control site were analysed for selected heavy metals namely: Cd, Cr,
Cu, Fe, Pb, Mn, Ni and Zn. Soil samples were obtained triplicates and at depths of 0 to
15(surface), 15 to 30(subsurface I) and 30 to 60(subsurface II) cm respectively in the
month of December every year from 2007 to 2009. According to the results, Cd, Cr, Cu,
Fe, Pb, Mn, Ni and Zn contents of soils ranged from 1.52 to 2.83, 1.28 to 2.80 and 1.19
to 2.69 mg/kg; 68.73 to 102.02, 56.0 to 94.07 and 46.58 to 88.93 mg/kg; 16.73 to 36.33,
15.35 to 31.73 and 13.17 to 29.13 mg/kg; 4.933 to 10.766, 4.405 to 9.962 and 3.206 to
8.531 mg/g; 25.17 to 52.88, 20.17 to 41.67 and 16.97 to 33.70 mg/kg; 118.53 to 420.53,
103.73 to 390.33 and 92.07 to 377.50 mg/kg; 34.40 to 65.37, 30.67 to 60.00 and 19.13
to 46.27 mg/kg and 21.43 to 65.20, 21.07 to 56.47 and 17.70 to 48.87 mg/kg for the
surface, subsurface (I) and subsurface (II) soil respectively. Evidence of contamination
of these soils was obvious when these values were compared to the control soil. The
results revealed that the concentration of the heavy metals were below the typical
agricultural soil critical level but higher the soil control. Among these Cu, Fe, Mn and
Zn are micronutrients and Cd, Cr, Ni and Pb are soil pollutants. Heavy metals can create
some harmful effects on the eco- system and cause the environmental pollution due to
their toxic impacts on plants, animals and human beings.
Keywords: Heavy metal, micronutrients, soil pollutants, eco-system, environmental
pollution and toxic impacts.
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Introduction: Soil testing is a key weapon in assessing the fertility of soil [40]. Soil
testing results can be effectively used for assessing plant nutrient requirement [53]. To
increase the tea production, a huge amount of fertilizers are applied in the tea estates
soil. Fertilizers can enhance the soil fertility and also yield the productivity of tea. But
fertiligers itself contain sufficient amount of heavy metals. Therefore, the heavy metal
concentrations in soils gradually increased.
Soil is a medium of acting as a sink for natural and anthropogenic pollutants [18].
Humans are introducing heavy metals into the environment. Heavy metals were no
longer restricted to local area but were distributed over a wide area by means of air,
water and soil. When the heavy metals are carried into the soil, they will accumulate
there with time and enter into the ecosystem or the food chain causing harm to human
health [27], [82]. Soil heavy metal contamination has occurred since prehistoric times,
but the extent of contamination has increased by the geogenic, rate of urbanization and
several
anthropogenic
activities.
The
anthropogenic
activities
such
as
mining and smelting operation, application of sewage sludge, inorganic fertilizers
animal wastes and pesticides [4], [55] ,[38], [54]. Anthropogenic contamination with
heavy metals is a worldwide problem that causes massive water and soil pollution [16],
[66]. Heavy metals that have contaminated industrialized areas, roadside soils,
riverbanks, and urban areas are among the most serious environmental hazards [45].
The management of metal-polluted soils is now of major concern for most industrialized
countries because of the ubiquity of the metals, their environmental persistence and
their hazardous effects for the environment and human health [28], [20], [64], [23].
Various remediation methods, such as soil excavation and land filling, may be very
helpful to contribute to restore metal-polluted soils [52]. These methods are usually
expensive and some of them have unfortunately induced adverse effects on the
biological activity, the structure and the fertility of soils. An alternative stagedy is the
use of plant species to stabilize or remove pollutants from soils, defined as
phytoremediation [69]. Phytoextraction technology is defined as the use of plants to
remove metals from soils into the harvestable part of their biomass [21]. Heavy metal
uptake and accumulation by plants depends on metal speciation, mixed contamination,
soil factors (pH and CEC) and plant characteristics (root depth, species, age etc.) [9],
[15]. One of the key steps in phytoextraction remains the selection of plant species [52]
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Unlike other heavy metals such as Cu, Zn, Mn and Fe that are essential to living cells at
low concentrations, Pb does not have any known biological role [67]. While the
introduction of unleaded gasoline has contributed to the decrease of lead emissions into
the environment, lead pollution is still significant due to historical loads as well as to the
continuing deposition from other sources including, mining, smelters, and batteries
disposal [1]. A debate exists among researchers whether absorbed metals are
bioavailability, while some claim that only soluble metals are available [1], [33], [65].
Others demonstrated that some metals e.g. Cd and Pb are bioavailable even when
absorbed to particulate matter [34], [13]. Such discrepancies on the need, scale, costs,
and clean up goals of contaminated soils [12]. Numerous studies on contaminated soil
suggest that physiochemical soil properties such as pH and clay and organic matter
content are the major factors controlling heavy metal toxicity and bioavailability [36],
[61], [60]. It was demonstrated that only desorbed Pb is bioavailable, while bound Pb is
not [45]. Because of their enormous adsorption capacity, organic matter and Fe-oxide
are capable of taking up very large amounts of Pb and do not release any detectable Pb
to solution, diminishing the bioavailability of Pb [25], [71], [31]. The bioavailability of
Pb depends on the type of the soil and the components it contain. Arid and semiarid
soils which contain large amount of carbonates and have little organic matter will effect
differently the solubility of Pb and hence its bioavailability compared with temperate
soils which usually lack pedogenic carbonate but have large amount of organic matter
[45].
Sewage sludge, an envitable by product of waste-water treatment, contains high
proportions of organic matter and plant nutrients [79] [49], [70]. The use of it improve
the physical and chemical properties of soil is recommended [46], [74]. It contains
contaminants, and excessive salts, which much also be considered in its agricultural use
[58]. Heavy metals in sewage sludge may enter the food chain through crops and affect
human health [75]. The physicochemical effects of the long-term use of sewage sludge
in the amendment of topical soils are still uncertain [48], [56],[77].
The accumulation of heavy metals in plants has been a serious environmental
concern because their uptake by plants from contaminated soils is the principal
processes by which heavy metals enter the food chain and then to men and animals and
are relatively toxic at levels slightly above than those required for maintaining normal
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metabolic activities of body [32], [62], [24], [18], [36]. The uptake of heavy metals by
plants from soil depends on their concentration in soil, organic matter, soil, clay content
and on their specific geochemical properties [8]. Plants species differ not only in heavy
metals’ uptake but also with respect to the translocation of metals to various plant
organs [42] which influence heavy metal concentration in food chain and food stuffs
[43]. The degree of toxicity depends upon the form in which they are present. Thus,
organo-lead is much more poisonous than the inorganic form. The oxidation state of
metals also plays an important role in this regard. So, the hexavalent chromium is more
toxic than its trivalent forms [6]. The present work is an attempt to study the census of
heavy metal concentration of tea estates soils in Dibrugarh and Sivasagar district.
Materials and Methods:
The studies were conducted in twenty tea estates soil which covers approx 7000
hectares of land in Dibrugarh and Sivasagar districts. Sivasagar district is one of the
most important historic and industrial City of Assam. The Sivasagar district is located
from 25 045 / to 27 015 / N latitude and 94025/ to 95 025 / E longitude. It has elevation of
86.6 Mts. above the sea level. It is surrounded by Lakhimpur district and Dibrugarh
district in the north, Arunachal Pradesh and Dibrugerh district in the east, Arunachal
Pradesh and Nagaland in the south and Jorhat in the west. The geographical area
covered by sivasagar district is 2668 sq km.
The physiography of Sivasagar district is mainly valley. The tributaries of
Brahmaputra River like dimow, Darika, Disang, Dikhow etc. flows through this district.
Sivasagar district carries a pleasant weather throughout the year. The temperature
ranges from 80C to 180C in winter and 150C to 35 0C during summer. The district is
characterized by highly humid atmosphere and abounded rains. The average rainfall is
about 230 cm. The regular rains of the summer generally prevent the prevalence of the
hot weather.
There are 119 tea estates in Sivasagar district which covered the area of 88008
Hectares land. Besides these tea estates, 80 registered small tea growers and 4004 small
tea growers, this covers the 5356 Hectares of land in this district.
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International Journal of Advancements in Research & Technology, Volume 2, Issue4, April-2013
ISSN 2278-7763
Fig.1 Location of study area and soil sampling stations.
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Dibrugarh, the head quarter of Dibrugarh district is famous as the “Tea City of
India”. Dibrugarh district is situated in the eastern part of Assam. The Dibrugarh district
extends from 27 005.38/ N to 27 042.30 / N Latitude and 94 033.46/ E to 95029.80/ E
Longitude. It is surrounded by Dhemaji district and a part of Lakhimpur district in the
North, Tirap district of Arunachal Pradesh and a part of Sivasagar district in the South,
Tinsukia district in the East, and Sivasagar district in the West. The geographical area
covered by Dibrugarh district is 3381 sq km.
The physiography of Dibrugarh district is mainly valley. The Dibrugarh district is
located in the north eastern corner of the Upper Brahmaputra valley south with an
altitude ranging between 99 and 474 meters. A major part of it is and extensive plain
formed by the Brahmaputra and its major south bank tributary –the Buri-Dihing. Being
located on the north of the 270N latitude and with its unique physiographic elements, the
area experiences subtropical monsoon climate with mild winter, warm and humid
summer. Rainfall decreases from south to north and east to west in the area. The
average annual rainfall of the Dibrugarh city in the north is 276 cm with a total number
of 193 rainy days, while at Naharkatia in the south; it is 163 cm with 147 rainy days.
The temperature generally decreases from south to north. The average annual
temperature in Dibrugarh and Naharkatia is 23.9 0C and 24.30C respectively.
There are 139 tea estates in Dibrugarh district which covered the area of 120489
Hectares land. Besides these tea estates, there are 104 registered small tea growers and
6530 small tea growers, which covering the 11798 Hectares land.
In the plains of Dibrugarh and Sivasagar districts, the soil is Alluvial. The soil in
adjacent to the river banks is sandy and away from the bank is muddy. The main crops
grown in this district are tea and rice. Tea is the most important cultivation in this area.
The districts are the largest producer of tea in Assam (about 70% of the total
production). The productivity of tea is about 1850 kg per hectare. The tea estates which
are selected for studies (Figure 1) are
(1)Sepon tea estate: 27007.105 / N and 0940 50.466/ E
(2) Moran tea estate: 27007.391/ N and 094052.943/E
(3) Doomar Dullung tea estate: 27007.609 /N and 094 052.903 / E
(4) Hingrijan tea estate: 27008.618 / N and 094056.628 / E
(5) Khumtai tea estate: 27009.548 / N and 094056.236 / E
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(6) Teloijan tea estate: 27013.596/ N and 094057.759/ E
(7) Thowra tea estate: 27007.222/ N and 094049.922 / E
(8) Mahkhooti tea estate: 27006.498/ N and 094048.459/ E
(9) Maskara tea estate: 270 07.298/ N and 094043.647 / E
(10) Rajmai tea estate: 27005.975 / N and 094042.789 / E
(11)Amarawati tea estate: 27016.276/ N and 094055.761/E
(12)Borboruah tea estate: 27024.554 /N and 094 053.237/E
(13)Bamunbari tea estate: 27014.415/ N and 094059.018/ E
(14)Khowang tea estate: 27014.936 /N and 094053.311 /E
(15)Duliabam tea estate: 27016.364 /N and 094055.277/E
(16) Diksam tea estate: 27012.710/N and 095001.684/E
(17)Ghoorania tea estate: 27021.378 /N and 094 052.188 /E
(18)Durgapur tea estate: 27023.506/N and 094052.443 /E
(19) Dirai tea estate: 27 012.070 / N and 095 002.030 / E
(20)Lepetkata tea estate: 27022.649 /N and 094 052.139/E
A total of 60 surface soil samples (0-15) cm, corresponding 60 subsurface (I) soil
samples (15-30) cm and 60 subsurface (II) soil samples (30-60) cm were collected from
the different area of the twenty tea estates. Soil samples were collected every year at the
same time, in the months of January and February, because no fertilization or compost
was applied during these months in the tea estates. Soil control sample was equally
collected from the nearby the tea estate area with no fertilization.
The collection of soil samples is done by using a soil auger. Several samples are
collected from a single station from three grids (7×10 m) within each field and these are
then mixed together to obtain a composite representative samples.
The effective size reduction was done by coning and quartering method. Preliminary
treatment of the soil samples after collection, preservation and analysis are carried out
by following standard procedures [35], [10], [30].
The total organic matter was estimated by Walkley-Black method [78]. For heavy
metals, about 1g of the sieved air dried soil samples were transferred
to 100 ml
beaker. A triacid mixture [63] about 25-30 ml consisting of Conc.H2SO4, Conc. HCl
and Conc. HNO3 in the ratio of 4:2:1 was added to each beaker.The mixture was heated
on a hot plate gently at first and then more strongly until white fumes were no longer
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evolved. The digested soil was treated with hot dilute HCl (1:1) and kept overnight and
filtered through a Whatman No 42 filter paper and washed several times with distilled
water.The filtrates were diluted so as to get an adequate volume of solution for analysis.
The dilution factor was noted. The digested extracts were then analyzed for the
concentration of heavy metals (Cd, Cr, Cu, Fe, Pb, Mn, Ni and Zn) by atomic
absorption spectrophotometer (Varian Spectra 220).
Result and Discussion:The experimental results of the analysis at three depths (0-15)
cm, 15-30) cm and (30-60) cm are presented in table 1 to 11 for the tea estate soils.
Table 1. Total organic carbon content (%)
of the soil samples at three depths.
Sample Surface Subsurface I
Subsurface II
1
2.3
1.52
1.2
2
2.81
1.53
1.48
3
2.8
1.98
1.65
4
2.72
1.9
1.61
5
2.22
1.49
1.12
6
2.07
1.31
0.97
7
3.05
2.27
1.92
8
3.23
2.41
2.11
9
2.02
1.28
0.96
10
2.97
2.14
1.81
11
2.16
1.47
1.09
12
3.6
2.81
2.46
13
1.91
1.27
0.9
14
3.21
2.4
2.08
15
2.96
2.14
1.71
16
1.87
1.19
0.88
17
2.64
1.85
1.54
18
2.12
1.4
1
19
2.15
1.44
1.02
20
2.76
1.96
1.63
Control
1.34
1.2
0.8
Values are means of three measurements.
Table 2. Cadmium content (mg/kg) of
the soil samples at three depths.
Sample Surface Subsurface I Subsurface II
1
2.19
1.9
1.83
2
2.48
2.3
2.29
3
2.4
2.25
2.14
4
2.31
2.11
1.97
5
2.11
1.86
1.71
6
1.78
1.57
1.44
7
2.73
2.51
2.47
8
2.82
2.69
2.61
9
1.65
1.51
1.4
10
2.67
2.45
2.4
11
2.06
1.79
1.62
12
2.83
2.8
2.69
13
1.61
1.43
1.26
14
2.8
2.59
2.54
15
2.57
2.38
2.33
16
1.52
1.28
1.19
17
2.27
2.06
1.87
18
1.86
1.66
1.5
19
1.98
1.76
1.56
20
2.35
2.16
2.06
Control
1.42
1.06
0.96
Values are means of three measurements.
The percentage of total organic matter ranged from 1.87 to 3.60%, 1.19 to 2.81% and
0.88 to 2.46% for the surface, subsurface (I) and subsurface (II) soil respectively. The
organic carbon of the soil samples were higher in tea estate soil, this may be due to
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addition of fertilizers, animal wastes, tea leaves and branches into the soil. The
percentage of organic carbon decreased as soil depth increased. Similar evidences have
been reported by many researchers [8] that organic carbon was more in the top soils and
decreased as depth increased. It was found that the percentage of total organic matter of
the tea estate soil increases during the study period from 2007 to 2009.
Table3. Chromium content (mg/kg) of
soil samples at three depths.
Sample Surface Subsurface I
Subsurface II
1
82.42
72.92
63.7
2
91.9
82.43
74.07
3
90.53
80.53
72.5
4
86.38
76.33
68.17
5
80.92
70.83
61.57
6
74.58
63.97
54
7
96.93
89.13
82.4
8
99.8
92.67
87.77
9
72.18
60.38
50.38
10
95.28
87.9
80.53
11
79.83
68.5
59.03
12 102.02
94.07
88.93
13
70.97
58.3
48.83
14
98.3
91.1
84.87
15
93.6
85.83
78.13
16
68.73
56
46.58
17
84.5
75.03
66.13
18
76.23
64
55.5
19
78.1
66.47
56.72
20
88.37
78.37
71.07
Control
42.2
34.6
28.4
Values are means of three measurements.
Table4. Total copper content of the soil
samples at three depths.
Sample Surface Subsurface I Subsurface II
1 24.12
20.6
17.2
2 27.89
23.83
21.23
3
27.4
23.17
20.03
4 25.97
22.23
18.88
5 23.93
20.37
16.93
6
21.5
17.33
14.53
7 30.77
27.53
24.6
8 34.52
29.9
26.83
9 19.93
16.4
13.9
10 30.03
26.73
23
11
23.5
19.87
16.27
12 36.33
31.73
29.13
13 18.67
15.77
13.43
14
31.9
28.07
25.33
15 28.85
25.23
22.07
16 16.73
15.35
13.17
17 25.03
21.83
17.9
18 22.57
19.13
15.27
19
23.2
19.77
15.87
20 26.75
22.93
19.33
Control
12.8
10.5
8.4
Values are means of three measurements.
The concentration of Cd, Cr, Cu, Fe, Pb, Mn, Ni and Zn were varied from 1.52 to 2.83,
1.28 to 2.80 and 1.19 to 2.69 mg/kg; 68.73 to 102.02, 56.0 to 94.07 and 46.58 to 88.93
mg/kg; 16.73 to 36.33, 15.35 to 31.73 and 13.17 to 29.13 mg/kg; 4.933 to 10.766, 4.405
to 9.962 and 3.206 to 8.531 mg/g; 25.17 to 52.88, 20.17 to 41.67 and 16.97 to 33.70
mg/kg; 118.53 to 420.53, 103.73 to 390.33 and 92.07 to 377.50 mg/kg; 34.40 to 65.37,
30.67 to 60.00 and 19.13 to 46.27 mg/kg and 21.43 to 65.20, 21.07 to 56.47 and 17.70
to 48.87 mg/kg for the surface, subsurface (I) and subsurface (II) soil respectively.
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The heavy metals fraction of the soil showed largest variation from metal to metal and
tea estate to tea estate. The heavy metals can enter the soil by a number of pathways and
their behaviors and fate in soils differ according to their sources and species. Once
heavy metals are introduced into the soil they accumulate in the soil system.
Table 5. Iron content (mg/g) of the soil
samples at three depths.
Sample Surface Subsurface I Subsurface II
1
7.475
6.6
5.115
2
9.366
8.436
6.964
3
8.952
8.069
6.625
4
8.108
7.194
5.705
5
7.194
6.352
4.897
6
6.051
5.182
3.687
7 10.232
9.281
7.808
8 10.632
9.775
8.358
9
5.582
4.623
3.533
10
9.975
9.122
7.636
11
6.808
5.963
4.521
12 10.766
9.962
8.531
13
5.197
4.415
3.287
14 10.485
9.592
8.138
15
9.755
8.86
7.407
16
4.933
4.405
3.206
17
7.809
6.945
5.404
18
6.437
5.579
4.116
19
6.56
5.605
4.156
20
8.615
7.715
6.275
Control
4.052
3.68
3.022
Values are means of three measurements.
Table 6. Manganese content(mg/kg) of the
soil samples at three depths.
Sample Surface Subsurface I Subsurface II
1 260.33
238.63
210.13
2 333.2
307.93
277.73
3 318.5
288.63
267.93
4 288.73
260.27
235.4
5 245.93
223.53
197.8
6
174
157
144.2
7 373.7
357.4
328.73
8 404.6
383.6
356.8
9 153.4
144.8
123.3
10
360
349.53
310.87
11 230.67
207.3
185.6
12 420.53
390.33
377.5
13 138.07
120.3
101.8
14 390.13
373.13
343.07
15 347.33
322.8
290.47
16 118.53
103.73
92.07
17 274.07
248.3
225.3
18 196.1
183
158.8
19 215.23
191.57
171.53
20 302.47
276.27
247.07
Control 98.04
86.28
78.8
Values are means of three measurements.
The content of solid-phase humic substances is greatly affecting the adsorption capacity
for heavy metals by cation exchange and formation of chelate complexes. Carboxy
groups play a predominant role in metal binding in both humic and fulvic acid [3].
Presence of dissolved organic matter, may, on the contrary, also decrease heavy metal
adsorption, as found for copper by some workers [51]. It was investigated that the
sorption of heavy metals (including Cu, Cr, Pb and Zn) to humic acid at different pH
values and found that Pb was adsorbed to the highest extent in the pH range 2.4 to 5.8
and Zn to the least extent [72]. The influence from organic matter on the overall
adsorption is dependent on the actual heavy metal [57]. Different mechanisms are
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responsible for the adsorption and retention of heavy metals in polluted soils such as
specific adsorption, cation exchange capacity, organic complexation and coprecipitation [2], [3]. The affinity of different heavy metals for adsorption to different
soil particles is a highly complex
Table 7. Nickel content(mg/kg) of the soil
samples at three depths.
Sample Surface Subsurface I Subsurface II
1
49.63
44.43
33
2
57.9
45.13
38.3
3
56.6
48.07
37.2
4
52.8
46
35.43
5
48.7
43.27
31.8
6
43.1
37.07
27.4
7
61.1
51.83
41.63
8
63.67
55.27
44.47
9
40.43
36.13
25.33
10
60.07
50.77
40.53
11
46.93
41.93
31
12
65.37
60
46.27
13
36.9
33
22.5
14
62.5
53.07
43.03
15
59.13
49.73
39.3
16
34.4
30.67
19.13
17
51.33
45.33
34.6
18
44.9
39.67
28.93
19
45.87
41
30.27
20
55.1
46.97
36.5
Control
26.54
24.2
23.8
Values are means of three measurements.
Table 8. Lead content (mg/kg) of the soil
samples at three depths.
Sample Surface Subsurface I Subsurface II
1 36.77
29.4
24.83
2 44.08
30.07
28.7
3 42.17
33.78
28.2
4 39.77
31.77
26.82
5 35.98
28.05
23.97
6 30.58
24
20.23
7 47.85
37.8
30.93
8
50.9
40.55
32.97
9
28.4
22.73
19.23
10 46.73
36.87
30.33
11 34.97
27.03
23.13
12 52.88
41.67
33.7
13 26.67
20.95
17.83
14 49.22
38.5
31.97
15
45.4
36
29.6
16 25.17
20.17
16.97
17 38.53
30.52
25.83
18 32.22
25.03
21.13
19 34.02
25.95
22.6
20 41.28
32.53
27.53
Control 20.34
18.8
17.12
Values are means of three measurements.
matter [57]. Lead adsorbed to a high extent as the only heavy metal to iron oxides,
whereas, e.g., Cd, Cr, Cu, Ni, Pb and Zn all adsorbed to vermiculite in a study of
different heavy metals to individual soil components [19]. Uptake of Cadmium depends
upon the content of Zinc in the soil, and plants generally take up more Cadmium if Zinc
content is low [41]. The retention of heavy metals in a specific soil depends on the soil
composition as well as on the actual heavy metal [57]. It was also investigated the
relation between pH and Zn solubility in spiked acid and calcareous soils [68]. Zinc was
solubilised at a slightly higher pH in the calcareous soils than in the acid soils [47].
Lead and nickel occur at the highest concentrations, usually near the roadsides,
Copyright © 2013 SciResPub.
International Journal of Advancements in Research & Technology, Volume 2, Issue4, April-2013
ISSN 2278-7763
226
associated with Zinc and Cadmium [14], their amounts decrease with increasing
distances from the road and with increasing depth in soil [59], [76].
Table 9. Zinc content (mg/kg) of the soil
samples at three depths.
Sample Surface Subsurface I
Subsurface II
1
41.97
39.53
29.83
2
51
49.27
37.93
3
47.8
46.27
36.3
4
45.53
43.53
33.3
5
40.57
37.83
27.73
6
33.03
30.07
22.93
7
58.27
52.13
41.73
8
62.8
55.07
46.4
9
30.9
27.17
20.8
10
55.77
50.73
40.27
11
38.4
36.37
26.6
12
65.2
56.47
48.87
13
25.57
22.67
19.47
14
60.43
53.5
44.2
15
52.87
50.1
39
16
21.43
21.07
17.7
17
44.23
41.57
31.77
18
34.97
31.47
23.9
19
37.1
34.33
25.47
20
46.6
44.6
34.8
Control
20.82
18.68
16.9
Values are means of three measurements.
Table 10. Probable background levels and typical
concentration of some heavy metals in soils
Heavy
metal
Cd
Cr
Cu
Ni
Pb
Zn
Background
concentration(mg/kg)
0.1 to 40
80 to 200
6 to 60
1 to 100
12 to 20
17 to 125
Source: [14],[6], [33] [2],[47]
Copyright © 2013 SciResPub.
Typical
concentration (mg/kg)
0.1 to 50
5 to 1500
2 to 250
2 to 1000
2 to 300
10 to 300
International Journal of Advancements in Research & Technology, Volume 2, Issue4, April-2013
ISSN 2278-7763
Table 11.
Maximum and minimum measured values of heavy metals contents(mg/kg) of soils
Sample
Measured limits
1 Max.
Min.
2 Max.
Min.
3 Max.
Min.
4 Max.
Min.
5 Max.
Min.
6 Max.
Min.
7 Max.
Min.
8 Max.
Min.
9 Max.
Min.
10 Max.
Min.
11 Max.
Min.
12 Max.
Min.
13 Max.
Min.
14 Max.
Min.
15 Max.
Min.
16 Max.
Min.
17 Max.
Min.
18 Max.
Min.
19 Max.
Min.
20 Max.
Min.
Control Max.
Min.
Cd
Cr
Cu
Fe(mg/g)
Mn
227
Ni
Pb
Zn
2.19
82.42
24.12
7.475
260.33
49.63
36.77
41.97
1.83
2.48
2.29
2.4
63.7
91.9
74.07
90.53
17.2
27.89
21.23
27.4
5.115
9.366
6.964
8.952
210.13
333.2
277.73
318.5
33
57.9
38.3
56.6
24.83
44.08
28.7
42.17
29.83
51
37.93
47.8
2.14
2.31
1.97
2.11
72.5
86.38
68.17
80.92
20.03
25.97
18.88
23.93
6.625
8.108
5.705
7.194
267.93
288.73
235.4
245.93
37.2
52.8
35.43
48.7
28.2
39.77
26.82
35.98
36.3
45.53
33.3
40.57
1.71
1.78
1.44
2.73
61.57
74.58
54
96.93
16.93
21.5
14.53
30.77
4.897
6.051
3.687
10.232
197.8
174
144.2
373.7
31.8
43.1
27.4
61.1
23.97
30.58
20.23
47.85
27.73
33.03
22.93
58.27
2.47
2.82
2.61
1.65
82.4
99.8
87.77
72.18
24.6
34.52
26.83
19.93
7.808
10.632
8.358
5.582
328.73
404.6
356.8
153.4
41.63
63.67
44.47
40.43
30.93
50.9
32.97
28.4
41.73
62.8
46.4
30.9
1.4
2.67
2.4
2.06
50.38
95.28
80.53
79.83
13.9
30.03
23
23.5
3.533
9.975
7.636
6.808
123.3
360
310.87
230.67
25.33
60.07
40.53
46.93
19.23
46.73
30.33
34.97
20.8
55.77
40.27
38.4
1.62
2.83
2.69
1.61
59.03
102
88.93
70.97
16.27
36.33
29.13
18.67
4.521
10.766
8.531
5.197
185.6
420.53
377.5
138.07
31
65.37
46.27
36.9
23.13
52.88
33.7
26.67
26.6
65.2
48.87
25.57
1.26
2.8
2.54
2.57
48.83
98.3
84.87
93.6
13.43
31.9
25.33
28.85
3.287
10.485
8.138
9.755
101.8
390.13
343.07
347.33
22.5
62.5
43.03
59.13
17.83
49.22
31.97
45.4
19.47
60.43
44.2
52.87
2.33
1.52
1.19
2.27
78.13
68.73
46.58
84.5
22.07
16.73
13.17
25.03
7.407
4.933
3.206
7.809
290.47
118.53
92.07
274.07
39.3
34.4
19.13
51.33
29.6
25.17
16.97
38.53
39
21.43
17.7
44.23
1.87
1.86
1.5
1.98
66.13
76.23
55.5
78.1
17.9
22.57
15.27
23.2
5.404
6.437
4.116
6.56
225.3
196.1
158.8
215.23
34.6
44.9
28.93
45.87
25.83
32.22
21.13
34.02
31.77
34.97
23.9
37.1
1.56
2.35
2.06
56.72
88.37
71.07
42-2
15.87
26.75
19.33
12.8
4.156
8.615
6.275
4.052
171.53
302.47
247.07
98.04
30.27
55.1
36.5
26.54
22.6
41.28
27.53
20.34
25.47
46.6
34.8
20.82
28.4
8.4
3.022
78.8
23.8
17.12
16.9
1.42
0.96
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Table12 Range of concentration of heavy metals in some fertilizers and lime materials
in mg/kg.
Elements
Cd
Cr
Cu
Ni
Pb
Zn
Na
.05—8.5
0.3—2.9
1--15
7--34
2--27
1--42
Pb
0.1--170
66--245
1--300
7--38
7--225
50--1450
NPK b
1--10
20--72
4--38
9--20
10--130
22--350
Lime a
0.1—24
10—15
2—125
10—20
20—250
10--450
a= [39]
b=[29]
If the contaminats are bound strongly to the soil and their desorption does not occur,
ground water pollution may not be a problem. On the other hand, if desorption takes
place easily, the contaminants could become mobile and contaminate water supplies.
The concentration of heavy metals Cd, Cr, Cu, Fe, Pb, Mn, Ni and Zn increases with
increase in organic matter content in the soil [80] The soil samples showing high levels
of heavy metal concentration had high organic matter content. A complexation reaction
occurs between heavy metals and organic matter content and results in the retention of
heavy metal in the soil [50], [44]. Increase in pH in the soil results in increase heavy
metal concentration in the soil. Even though the higher pH favors the heavy metal
retention in soil, it limits the heavy metal uptake by plants. The heavy metal uptake by
plants decreases as the pH value increases. The acidic pH favors the uptake and causes
harmful effect to the living beings through the food chain. The pH value of the tea estate
soil was found to be acidic. This indicates that the uptake by plants was high and the
biological system was contaminated by the heavy metals. Soil pH and high total organic
matter content have a higher retention capacity of heavy metal in soil. The present
studies agree with the findings of workers [81], [8] ,[80]. All the heavy metals
decreased in concentration as soil depth increased. It was found that the concentration of
heavy metals of the tea estate soil increases during the study period.
According to the following workers [73], [22] a good correlation is predicted if the
linear regression co-efficient “r” is ≥ .7. A positive and significant correlation between
total organic matter and available heavy metals Cd to Zn are 0.95, 0.96, 0.96, 0.96, 0.97,
0.96, 0.96 and 0.96 respectively.
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229
The movement of heavy metals within a region is influenced by wind, water and
gravity. The movement of heavy metals within the soil mass will be principally in the
solution phase [17]. The movement of heavy metal or potentially toxic element in the
soil is of concern due to potential impact on the environment through contamination of
ground water by leaching.
The degree of soil pollution by heavy metals from various anthropogenic activities, such
as application of inorganic fertilizers, animal wastes and pesticides [38], [54]. A large
amount of heavy metals enrich in the tea estates soil by fertilizers. The range of
concentration of heavy metals in some fertilizers and lime material in mg/kg is given in
the table 12 [29], [47].
Conclusion
The results indicate that the soil had slightly increasing trends of heavy metal
concentration but still within tolerable levels. However, the obtained mean values of
heavy metals in the study sites are higher that found in the control site.Among these
heavy metals Ni, Cr, Pb and Cd are soil pollutants and Cu, Zn, Mn and Fe, and are
known as micronutrients or trace elements as these are required in small quantities. The
micronutrient elements in minute quantities produce optimum effects. On the other
hand, even a slight deficiency or excess is harmful to the plants. By the application of
fertilizers, animal wastes and fungicides into the soil not only supply the essential
nutrients but also enrich the soil with the heavy metals. These are capable of interfering
with biological activities, persistent toxicants within ecosystems and create acute health
hazards for humans, animals and plant kingdoms. Therefore, there is a need for
optimization of fertilizers, animal wastes and fungicides for improvement of the soil
productivity without creating environmental problems.
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ISSN 2278-7763
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