Environ Geochem Health (2012) 34:55–69 DOI 10.1007/s10653-011-9412-4
ORIGINAL PAPER
Mercury contamination in agricultural soils from abandoned metal mines classified by geology and mineralization Han Sik Kim • Myung Chae Jung
Received: 25 August 2010 / Accepted: 25 January 2011 / Published online: 4 August 2011 Ó Springer Science+Business Media B.V. 2011
Abstract This survey aimed to compare mercury concentrations in soils related to geology and mineralization types of mines. A total of 16,386 surface soils (0*15 cm in depth) were taken from agricultural lands near 343 abandoned mines (within 2 km from each mine) and analyzed for Hg by AAS with a hydride-generation device. To meaningfully compare mercury levels in soils with geology and mineralization types, three subclassification criteria were adapted: (1) five mineralization types, (2) four valuable ore mineral types, and (3) four parent rock types. The average concentration of Hg in all soils was 0.204 mg kg-1 with a range of 0.002–24.07 mg kg-1. Based on the mineralization types, average Hg concentrations (mg kg-1) in the soils decreased in the order of pegmatite (0.250) [ hydrothermal vein (0.208) [ hydrothermal replacement (0.166) [ skarn (0.121) [ sedimentary deposits (0.045). In terms of the valuable ore mineral types, the concentrations decreased in the order of Au–Ag–base metal mines & base metal mines [ Au–Ag mines [ Sn–W– Mo–Fe–Mn mines. For parent rock types, similar concentrations were found in the soils derived from sedimentary rocks and metamorphic rocks followed by heterogeneous rocks with igneous and metamorphic
H. S. Kim M. C. Jung (&) Department of Energy and Mineral Resources Engineering, Sejong University, Seoul 143-747, South Korea e-mail:
[email protected]
processes. Furthermore, farmland soils contained relatively higher Hg levels than paddy soils. Therefore, it can be concluded that soils in Au, Ag, and base metal mines derived from a hydrothermal vein type of metamorphic rocks and pegmatite deposits contained relatively higher concentrations of mercury in the surface environment. Keywords Mercury Agricultural soil Mining in Korea Geology Mineralization
Introduction Among contaminants, mercury (Hg) is a major concern due to its significant impact on ecological system and human health (Alloway 1995; Adriano 2001). Although Hg can be derived from various natural processes (e.g., Kim et al. 2002), the dominant fraction of Hg in the environment results from human activities including industry, mining and smelting, land filling, and many livelihood activities (Fergusson 1990; Kim and Kim 1999, 2002; KabataPendias and Mukherjee 2007). Lamborg et al. (2002), for example, have estimated that the anthropogenic input of Hg into the environment is as much as 3 9 106 kg per year. In addition, mercury by-product emission from anthropogenic sources in the world was 1.48 9 106 kg in 2005 (AMAP/UNEP 2008). Arctic Monitoring and Assessment Programme and UNEP (AMAP/UNEP 2008) also estimated mercury
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by-product emission from anthropogenic sources in the world to be 1.85 9 106 kg in 2020, which was calculated by status quo scenario. On a global scale, coal combustion in China and India is the main Hg sources. Another important anthropogenic source of Hg emission to the environment is mining and refining of metals, together with grinding, concentrating ores, and disposal of tailings, which account for 12% of the global emission of Hg into the air (Han et al. 2006). Thus, special attention has been paid to the environmental effects of Hg related to Hgbearing mining areas from various countries: Australia (Dhindsa et al. 2003), Brazil (Requelmea et al. 2003), China (Qiu et al. 2006; Li et al. 2009), Czech Republic (Hojdova´ et al. 2009), Korea (Lee et al. 2008), Italy (Covelli et al. 2009), Slovenia (Biester and Scholz 1997), Spain (Loredo et al. 2005; Milla´n et al. 2006), UK (Yang 2010), and USA (Dreher and Follmer 2004). For example, Hg concentrations in soils from Chatian Hg mining deposits in southwestern China averaged 85.45 mg kg-1 with a range of 0.87–424.00 mg kg-1 (Qiu et al. 2006). In addition, Hg contents in soils from the Almade´n mining areas, Spain, ranged from 5.0 to 1,710 mg kg-1 (Milla´n et al. 2006). Furthermore, increased Hg loading into the environment is due to its use in Au mines for amalgamation process, especially in the Amazonian and Siberian regions as well as other countries in the world (Kabata-Pendias and Mukherjee 2007). There are over 900 metalliferous mines in Korea, and most of them are abandoned or closed due to the increases in labor costs, loss of profits, and the exhaustion of ore reserves (Susaya et al. 2010). After closing the mines, large amount of mine waste materials including tailings were left behind without proper remediation work, and consequently, they have become an important point source of trace elements including Hg in the surface environment (Jung and Thornton 1997; Lee et al. 2001; Jung 2008). Furthermore, the extent and degree of heavy metal contamination derived from the mining activities may vary according to the type of mineralization, composition of ore minerals, geology, topography, method of mining, and smelting. For example, mine wastes occurring in hydrothermal deposits with sulfide minerals contained elevated levels of heavy metals (Lee et al. 2001, 2008). Jung (2008) also reported that metal concentrations in mine waste varied depending upon geology and
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mineralization type of each mine. In case of the Au–Ag mines, mine wastes from hydrothermal vein type with sulfide minerals contained relatively higher concentrations of Cd, Cu, Pb, and Zn. However, relatively low concentrations of the metals were found in mine wastes from the hydrothermal vein type with carbonate minerals and skarn deposits. In addition to base metal mines, mine wastes with large amount of sulfide minerals contained elevated levels of the metals. Thus, Jung (2008) suggested that mineralization type of each mine is one of the most important factors affecting metal concentrations in mine wastes and nearby soils. Various mineral-forming processes occurred in Korea, which included hydrothermal replacement, hydrothermal vein type, contact metasomatic type (so-called skarn), pegmatite, and sedimentation. Among these processes, mineralization of the mines as a hydrothermal vein type associated with Au–Ag bearing quartz vein and to a lesser extent of base metals (Geological Society of Korea (GSK) 1988) occurs highly frequently. The hydrothermal deposits include (1) the presence of hot water (so-called hydrothermal solution) to dissolve and transport minerals, (2) the presence of interconnected openings in the rock to allow the solutions to move, (3) an availability of sites for the deposits, and (4) a chemical reaction that will result in deposition. Although hydrothermal deposits may form an array of parent rocks, the deposition is preferentially influenced or localized by certain kinds of rock. Of the deposits, the hydrothermal vein type associated with porphyry base metal deposits appears to form at lower temperatures during a later mineralization event (GSK 1988). The other important mineralization type is a pegmatite that is a coarse-grained igneous rock with a grain size of 3 cm or more. Most pegmatite is found in granitic layers. Thus, it is mainly composed of granite and its constituents like quartz, feldspar, and mica. For this reason, a study related to metal contamination in soils derived from various geology and mineralization types is strongly needed to understand the extent and degree of Hg contamination in the surface environment. In this study, therefore, a nationwide survey of Hg concentrations in agricultural soils contaminated by metal mining activities in Korea has been carried out. The study also examines a comparison of Hg concentrations in the soils as various mineralization
Environ Geochem Health (2012) 34:55–69
types, productive and/or target metals, and parent rocks of each mine.
57 Table 1 Classification of soils as mineralization type, valuable ore minerals, and parent rocks Mineralization types
Materials and methods Classification of geology and mineralization In this study, 343 representative abandoned or closed metal mines of over 900 mines in Korea were selected due to following conditions: (1) operated on large scales, (2) large amount of mine wastes including tailings, (3) creating heavy metal contamination from mining activities, and (4) major or representative mines in the various mineral deposits classified as geological evidence in a literature survey by GSK (1988). In order to classify the geology and mineralization types of each mine, three major classification items were adapted: (1) mineralization type, (2) productive metals, and (3) parent rocks. In case of mineralization type, five types of major mineralization in Korea were classified as follows: 1. 2. 3. 4. 5.
Hydrothermal vein type Hydrothermal replacement type Contact metasomatic type (so-called skarn) Pegmatite type Sedimentary type
In addition to classify the productive metals, four types of major metal production were adapted as follows: A. Mines associated with Au and Ag only B. Mines associated with Au, Ag, and base metals including Cu, Pb, Zn, etc. C. Mines associated with base metals D. Mines associated with Sn, W, Mo, Fe, and Mn Finally, parent rocks were classified as four types as follows, adapted as follows: a. Igneous rock origin b. Metamorphic rock origin c. Sedimentary rock origin d. Heterogeneous rocks (co-mineralization with igneous and metamorphic activities) In this study, three digits of grouping as geology and mineralization types were adapted. For example, group ID of ‘1Aa’ was used to define soil samples
1
Hydrothermal vein
2
Hydrothermal replacement
3
Contact metasomatic (so-called skarn)
4
Pegmatite deposits
5
Sedimentary deposits
Productive metals (valuable ore minerals) A
Au and Ag only
B
Au, Ag, and base metals (Cu, Pb, Zn, etc.)
C
Base metals (Cu, Pb, Zn, etc.)
D Sn, W, Mo, Fe, and Mn Parent rocks a
Igneous rock
b
Metamorphic rock
c
Sedimentary rock
d
Heterogeneous rocks with igneous and metamorphic processes
from Au–Ag mines mineralized by hydrothermal vein deposits underlain by igneous rocks. Table 1 explains the classification criteria for the selected mines stated above. Sampling and chemical analysis Over 3 years, from 2007 to 2009, surface soils (0–15 cm in depth) in agricultural areas including both paddy fields and farmlands were sampled by hand auger (3.0 cm in diameter) in and around selected 343 mining sites within 2 km downstream from each mining site. In order to reduce the sampling bias, over 5 kg of soil samples was taken with a composite of over nine subsamples in and around mines. After air-drying at room temperature for 7 days, the samples were disaggregated, sieved to \2 mm, and then ground to a fine powder (\180 lm) in a ceramic pestle and mortar. The finely milled sample was used for the chemical analysis of Hg. In accordance with the Korean Standard Method for Soils, total concentrations of Hg were determined by digesting with a 3:1 ratio of concentrated HCl and HNO3 (aqua regia) and analyzed by atomic absorption spectrometry (AA-240, Varian, Australia) with a hydride-generation (HG) device (Ure 1995). A rigorous quality control program was implemented, which included reagent blanks (average values
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0.005 mg L-1 for Hg), replicate samples, and certified international reference material of SRM2710 and SRM2711 (Montana soils, National Institute of Standards and Technology, USA). The detection limit of the chemical analysis for Hg in this study was 0.004 mg L-1. Thus, half of the detection limit value (0.002 mg kg-1) was used for the ‘not detected’ data of the chemical analysis. The accuracy of the laboratory result was within the 95% confidential intervals of the stated reference values. The calculations for mean, median, and box plot were obtained by the statistical package, and the Student’s unpaired t test was also employed to evaluate significant differences between means using the package.
Results and discussions Hg concentration in soils as mineralization types The classified group, numbers of samples and mines, and Hg concentrations in soil samples are listed in Table 2. Because of large size of the data set, the average concentrations in the mines were used for the comparison of Hg levels in soils as geology and mineralization types. A wide range of Hg concentrations in the soils was found, and these variations are mainly influenced by extent and degree of mineralization of the mines. The maximum concentration of Hg in the 16,386 soil samples was 24.07 mg kg-1, which is about six times higher than the environmental guideline for Hg of 4 mg kg-1 in agricultural soils under the Soil Conservation Act in Korea (KMoE 2009b). Surface soils taken in the vicinity of the Silim Au–Ag mine (ID = 140) contained the maximum concentrations of Hg. According to its history, the mine was known for the usage of an amalgamation process for Au extraction during the mine operation time. Other mines used the amalgamation method, including the Hongsung mine (ID = 47), Hwajeon-Daemyeong mine (ID = 60), Gongju-Daeheung mine (ID = 101), Jeoneu mine (ID = 110), Daeheung-Seonggeo mine (ID = 116), and Ado mine (ID = 227), where soils also contained elevated levels of Hg. Thus, the main sources of Hg in agricultural soils may be caused by the weathering products in the amalgamation processes of each mine.
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Kabata-Pendias and Mukherjee (2007) also reported that increased Hg loading into the environment is, in addition, due to its use in Au mines for the amalgamation process, which became a real risk of its transfer to the food chain. This is a serious threat in the Amazonian and Siberian regions as well as other countries. A great deal of other research also reported the dispersion of Hg from the process in the world (Fergusson 1990; Dhindsa et al. 2003; Qiu et al. 2006; Milla´n et al. 2006; Lee et al. 2008; Hojdova´ et al. 2009). The data for Hg concentrations in soils (classified as geological and mineralized activities) are summarized in Table 3. In addition, box plot for Hg concentrations in soils classified as mineralization types of mines is shown in Fig. 1. Among the 343 investigated mines, 91.8% of the mines were classified as a hydrothermal vein (type 1), which is one of the most frequent occurrences in Korea. About 3% of the mines were classified as hydrothermal replacement deposits (type 2) and contact metasomatic deposits (type 3). Pegmatite deposits (type 4) and sedimentary deposits (type 5), however, were limited in Korea. According to Table 3 (Fig. 1), the average concentrations (mg kg-1) decreased in the order of soils mineralized by pegmatite (0.250) [ hydrothermal vein (0.208) [ hydrothermal replacement (0.166) [ skarn (0.121) [ sedimentary deposits (0.045). The high average Hg concentrations in soils influenced by pegmatite deposits may be due to the soil data from the Geumjung Au–Ag mine (ID = 140), which is one of the largest Au–Ag mines in Korea. In 2003, the tailings dam of the mine was corrupted by a typhoon and large amount of mine waste materials including the tailings contained elevated levels of heavy metals were dispersed into downstream by the heavy rain, eventually settling down to the agricultural lands. In comparison with the hydrothermal deposits, relatively low concentrations of Hg in soils were found in the contact metasomatic deposits and sedimentary deposits. In case of the contact metasomatic deposits, the parent rocks of the mines are the limestone with high pH values. Therefore, low concentrations of Hg in the soils may be due to the low solubility of the elements under high pH conditions. In addition to sedimentary deposits, low concentrations of Hg may be due to the washing out of the Hg in the surface environment.
Environ Geochem Health (2012) 34:55–69
59
Table 2 Statistical summary of Hg concentration in soils from 343 metal mines in Korea ID
Group
Numbers of samples
Hg (mg kg-1)
Paddy
ID
Farm
Total
Mean
Min
Max
Group
Numbers of samples
Hg (mg kg-1)
Paddy
Total
Mean
Min
Max
Farm
1
1Aa
27
0
27
0.604
0.113
3.483
66
1Ab
9
0
9
0.002
0.002
0.002
2
1Aa
19
0
19
0.050
0.002
0.178
67
1Ab
21
4
25
0.003
0.002
0.011
3
1Aa
40
15
55
0.196
0.002
2.982
68
1Ab
42
19
61
0.003
0.002
0.117
4
1Aa
3
95
98
0.101
0.002
1.100
69
1Ab
10
58
68
0.018
0.002
0.260
5
1Aa
30
24
54
0.138
0.002
1.667
70
1Ab
14
27
41
0.002
0.002
0.002
6
1Aa
28
17
45
0.023
0.002
0.304
71
1Ab
2
4
6
0.031
0.020
0.060
7
1Aa
41
20
61
0.159
0.002
1.758
72
1Ab
15
62
77
0.253
0.081
0.471
8
1Aa
1
51
52
0.218
0.032
1.737
73
1Ab
2
13
15
0.207
0.125
0.318
9
1Aa
22
34
56
0.003
0.002
0.007
74
1Ab
13
14
27
0.257
0.124
0.494
10
1Aa
26
44
70
0.003
0.002
0.003
75
1Ab
8
32
40
0.049
0.004
0.200
11
1Aa
23
22
45
0.144
0.027
1.247
76
1Ab
11
35
46
0.071
0.017
0.143
12
1Aa
27
29
56
0.037
0.002
0.146
77
1Ab
0
2
2
0.037
0.002
0.074
13
1Aa
12
1
13
0.205
0.096
0.342
78
1Ab
3
42
45
0.710
0.002
1.892
14
1Aa
8
35
43
0.178
0.083
0.302
79
1Ab
35
44
79
0.063
0.002
0.737
15 16
1Aa 1Aa
9 1
11 14
20 15
0.141 0.159
0.013 0.010
0.718 0.936
80 81
1Ab 1Ab
2 0
76 95
78 95
0.037 0.059
0.002 0.012
0.206 1.155
17
1Aa
18
35
53
0.045
0.007
0.250
82
1Ab
12
32
44
0.047
0.002
0.143
18
1Aa
33
17
50
0.239
0.072
0.987
83
1Ab
10
28
38
0.178
0.023
1.390
19
1Aa
3
62
65
0.063
0.027
0.200
84
1Ab
0
61
61
0.110
0.010
0.548
20
1Aa
0
6
6
0.037
0.011
0.112
85
1Ab
3
32
35
0.036
0.021
0.105
21
1Aa
17
5
22
0.056
0.005
0.113
86
1Ab
16
86
102
0.045
0.002
0.209
22
1Aa
0
6
6
0.037
0.011
0.112
87
1Ab
8
28
36
0.074
0.020
0.302
23
1Aa
73
77
150
0.044
0.005
0.377
88
1Ab
19
110
129
0.073
0.018
0.517
24
1Aa
23
41
64
0.153
0.002
0.794
89
1Ab
8
3
11
0.031
0.007
0.060
25
1Aa
42
13
55
0.040
0.002
0.323
90
1Ab
4
68
72
0.103
0.013
0.707
26
1Aa
4
5
9
0.092
0.002
0.484
91
1Ab
4
34
38
0.037
0.002
0.412
27
1Aa
23
4
27
0.033
0.002
0.186
92
1Ab
11
53
64
0.050
0.018
0.144
28
1Aa
2
13
15
0.080
0.002
0.292
93
1Ab
4
19
23
0.094
0.002
0.354
29
1Aa
37
51
88
0.058
0.014
0.343
94
1Ab
16
5
21
0.550
0.142
0.929
30 31
1Aa 1Aa
77 29
138 43
215 72
0.239 0.091
0.002 0.002
6.604 0.549
95 96
1Ab 1Ab
25 32
31 6
56 38
0.415 0.071
0.017 0.025
6.205 0.284
32
1Aa
10
10
20
0.174
0.002
0.953
97
1Ab
4
61
65
0.048
0.002
0.857
33
1Aa
4
0
4
1.910
0.082
7.365
98
1Ab
12
21
33
0.047
0.016
0.158
34
1Aa
10
3
13
0.103
0.004
0.419
99
1Ab
6
4
10
0.078
0.014
0.239
35
1Aa
0
113
113
0.122
0.021
0.352
100
1Ab
12
55
67
0.039
0.002
0.483
36
1Aa
25
26
51
0.049
0.002
0.125
101
1Ab
19
27
46
2.538
2.385
2.769
37
1Aa
1
44
45
0.018
0.002
0.206
102
1Ab
34
4
38
0.030
0.002
0.160
38
1Aa
9
86
95
0.032
0.002
0.182
103
1Ab
18
32
50
0.034
0.002
0.225
39
1Aa
0
40
40
0.066
0.027
0.124
104
1Ab
12
56
68
0.070
0.003
0.573
40
1Aa
4
42
46
0.091
0.030
0.614
105
1Ab
5
60
65
0.026
0.003
0.160
41
1Aa
0
77
77
0.025
0.002
0.118
106
1Ab
15
36
51
0.155
0.019
1.114
42
1Aa
3
76
79
0.050
0.016
0.151
107
1Ab
11
9
20
0.307
0.024
3.610
43
1Aa
0
80
80
0.039
0.015
0.089
108
1Ab
26
43
69
0.166
0.015
0.486
123
60
Environ Geochem Health (2012) 34:55–69
Table 2 continued ID
Group
Numbers of samples
Hg (mg kg-1)
Paddy
Farm
Total
Mean
Min
ID
Group
Max
Numbers of samples
Hg (mg kg-1)
Paddy
Farm
Total
Mean
Min
Max
44
1Aa
5
95
100
0.586
0.024
1.589
109
1Ab
15
17
32
0.066
0.020
0.209
45
1Aa
25
90
115
0.337
0.002
2.000
110
1Ab
3
35
38
2.579
2.317
7.214
46
1Aa
11
40
51
0.040
0.012
0.157
111
1Ab
61
29
90
0.020
0.005
0.053
47
1Aa
13
66
79
0.687
0.008
112
1Ab
10
11
21
0.054
0.026
0.091
48
1Aa
3
30
33
0.064
0.032
0.187
113
1Ab
28
83
111
0.020
0.002
0.106
49
1Aa
7
26
33
0.311
0.023
1.517
114
1Ab
22
19
41
0.145
0.046
0.479
50
1Aa
12
46
58
0.041
0.002
0.287
115
1Ab
8
0
8
0.072
0.012
51
1Aa
15
31
46
0.032
0.010
0.267
116
1Ab
30
4
34
2.978
0.002
52
1Aa
8
37
45
0.003
0.002
0.033
117
1Ab
22
7
29
0.146
0.002
1.727
53
1Ab
48
0
48
0.040
0.016
0.086
118
1Ab
0
54
54
0.131
0.028
2.712
54
1Ab
28
3
31
0.223
0.122
0.901
119
1Ab
13
29
42
0.139
0.008
0.791
55
1Ab
5
0
5
0.036
0.025
0.060
120
1Ab
22
41
63
0.056
0.002
0.674
56
1Ab
73
0
73
0.188
0.006
1.484
121
1Ab
8
23
31
0.629
0.208
0.678
57
1Ab
45
33
78
0.067
0.002
0.730
122
1Ab
5
5
10
0.044
0.016
0.125
58 59
1Ab 1Ab
53 13
17 0
70 13
0.052 0.116
0.002 0.009
0.269 0.326
123 124
1Ab 1Ab
10 0
0 11
10 11
0.111 0.014
0.052 0.002
0.287 0.049
60
1Ab
28
28
56
1.485
0.639
125
1Ab
27
20
47
0.056
0.013
0.333
61
1Ab
54
20
74
0.562
0.068
126
1Ab
19
41
60
0.053
0.007
0.333
62
1Ab
26
2
28
0.689
0.137
3.697
127
1Ab
2
1
3
0.406
0.027
0.890
63
1Ab
38
22
60
0.361
0.130
0.887
128
1Ab
10
16
26
0.154
0.018
0.757
64
1Ab
8
27
35
0.024
0.002
0.230
129
1Ab
2
45
47
0.380
0.047
5.599
65
1Ab
11
0
11
0.008
0.002
0.087
130
1Ab
10
27
37
0.048
0.013
0.145
131
1Ac
14
0
14
0.294
0.220
0.339
196
1Ba
12
54
66
0.084
0.002
1.550
132
1Ac
45
0
45
0.147
0.012
1.702
197
1Ba
14
12
26
0.037
0.013
0.089
133
1Ac
13
0
13
0.039
0.015
0.146
198
1Ba
8
9
17
0.101
0.024
0.653
134
1Ac
8
64
72
0.128
0.073
0.953
199
1Bb
36
0
36
0.024
0.012
0.120
135
1Ac
15
54
69
0.026
0.002
0.415
200
1Bb
22
23
45
0.025
0.008
0.306
136
1Ac
0
80
80
0.144
0.025
2.638
201
1Bb
6
0
6
0.030
0.002
0.066
137
1Ac
0
65
65
2.483
2.155
2.735
202
1Bb
22
33
55
0.056
0.002
0.736
138 139
1Ac 1Ac
13 4
5 37
18 41
0.043 0.041
0.013 0.003
0.090 0.130
203 204
1Bb 1Bb
39 35
27 5
66 40
0.294 0.002
0.113 0.002
3.112 0.002
140
1Ad
36
58
97
0.046
0.002
205
1Bb
23
3
26
0.014
0.002
0.107
141
1Ad
24
0
24
0.727
0.178
3.500
206
1Bb
15
35
50
0.004
0.002
0.014
142
1Ad
6
0
6
0.343
0.083
0.600
207
1Bb
12
54
71
0.003
0.002
0.017
143
1Ad
15
0
15
0.350
0.335
0.367
208
1Bb
33
32
65
0.054
0.002
0.460
144
1Ad
21
0
21
0.126
0.015
1.041
209
1Bb
35
14
49
0.002
0.002
0.002
145
1Ad
14
2
16
0.309
0.031
3.543
210
1Bb
26
31
57
0.002
0.002
0.002
146
1Ad
19
5
24
0.054
0.013
0.274
211
1Bb
12
106
118
0.020
0.002
0.232
147
1Ad
20
14
34
0.269
0.063
2.638
212
1Bb
5
45
50
0.176
0.098
0.337
148
1Ad
24
28
52
0.003
0.002
0.039
213
1Bb
0
30
30
0.754
0.103
0.949
149
1Ad
21
26
47
0.003
0.002
0.041
214
1Bb
3
14
17
0.183
0.002
1.501
150
1Ad
0
6
6
0.016
0.008
0.045
215
1Bb
17
33
50
0.118
0.002
2.351
151
1Ad
43
37
80
0.109
0.062
0.739
216
1Bb
8
47
55
0.036
0.013
0.200
123
16.74
17.48 3.583
24.07
0.156 23.39
Environ Geochem Health (2012) 34:55–69
61
Table 2 continued ID
Group
Numbers of samples
Hg (mg kg-1)
Paddy
ID
Farm
Total
Mean
Min
Max
Group
Numbers of samples
Hg (mg kg-1)
Paddy
Farm
Total
Mean
Min
Max
152
1Ad
3
25
28
0.032
0.014
0.070
217
1Bb
8
46
54
0.026
0.010
0.087
153
1Ad
2
53
55
0.065
0.002
0.408
218
1Bb
3
50
53
0.291
0.002
5.895
154
1Ba
15
0
15
1.127
0.543
2.128
219
1Bb
2
74
76
0.034
0.002
0.358
155
1Ba
24
19
43
0.473
0.002
3.307
220
1Bb
0
103
103
0.219
0.051
0.794
156
1Ba
36
31
67
0.004
0.002
0.067
221
1Bb
5
51
56
0.087
0.022
0.493
157
1Ba
13
37
51
0.003
0.002
0.011
222
1Bb
2
87
89
0.384
0.002
2.092
158
1Ba
17
51
68
0.003
0.002
0.032
223
1Bb
0
4
4
0.039
0.018
0.067
159
1Ba
7
3
10
0.189
0.090
0.500
224
1Bb
7
69
76
0.040
0.002
0.216
160
1Ba
49
16
65
0.132
0.080
0.480
225
1Bb
9
11
20
0.035
0.002
0.282
161
1Ba
0
43
43
0.011
0.002
0.033
226
1Bb
4
29
33
0.026
0.002
0.168
162
1Ba
19
2
21
0.247
0.051
1.884
227
1Bb
12
43
55
2.429
1.454
6.735
163
1Ba
0
152
152
0.057
0.011
0.364
228
1Bb
26
22
48
0.065
0.002
0.704
164
1Ba
0
24
24
0.018
0.002
0.033
229
1Bb
7
44
51
0.044
0.016
0.140
165
1Ba
3
63
66
0.414
0.151
3.685
230
1Bb
26
59
85
0.405
0.002
2.110
166 167
1Ba 1Ba
1 0
87 21
88 21
0.012 0.078
0.002 0.050
0.033 0.466
231 232
1Bb 1Bb
4 2
5 39
9 41
0.348 0.798
0.273 0.247
0.429 2.068
168
1Ba
30
34
64
0.140
0.013
0.436
233
1Bb
15
0
15
0.104
0.010
0.903
169
1Ba
43
12
55
0.124
0.026
0.885
234
1Bb
1
45
46
0.083
0.002
0.650
170
1Ba
2
20
22
0.014
0.002
0.033
235
1Bb
1
2
3
0.087
0.067
0.104
171
1Ba
16
44
60
0.246
0.002
1.551
236
1Bb
10
63
73
0.197
0.056
1.390
172
1Ba
24
39
63
0.167
0.051
1.026
237
1Bb
20
16
36
0.111
0.012
0.764
173
1Ba
74
30
104
0.136
0.080
0.463
238
1Bb
8
55
63
1.165
0.002
9.920
174
1Ba
1
161
162
0.007
0.002
0.267
239
1Bb
2
55
57
0.049
0.002
0.263
175
1Ba
1
88
89
0.425
0.002
2.525
240
1Bc
14
0
14
0.387
0.138
1.002
176
1Ba
0
4
4
0.005
0.002
0.015
241
1Bc
13
0
13
2.133
1.116
5.346
177
1Ba
6
1
7
0.042
0.006
0.076
242
1Bc
11
123
134
0.217
0.002
1.490
178
1Ba
0
6
6
0.119
0.088
0.140
243
1Bc
1
69
70
0.069
0.021
0.432
179
1Ba
3
11
14
0.109
0.076
0.172
244
1Bc
60
21
81
0.086
0.005
1.028
180
1Ba
2
15
17
0.201
0.117
0.297
245
1Bc
3
22
25
0.003
0.002
0.018
181 182
1Ba 1Ba
2 36
23 3
25 39
0.108 0.270
0.081 0.002
0.431 2.578
246 247
1Bc 1Bc
1 0
5 31
6 31
0.634 0.514
0.002 0.002
1.414 2.191
183
1Ba
0
6
6
0.002
0.002
0.002
248
1Bc
14
21
35
0.350
0.002
0.003
184
1Ba
2
55
57
0.049
0.023
0.193
249
1Bc
19
38
57
1.190
0.435
3.827
185
1Ba
1
7
8
0.081
0.002
0.192
250
1Bc
21
65
90
0.007
0.002
0.567
186
1Ba
22
9
31
0.376
0.012
2.300
251
1Bc
7
0
7
0.003
0.002
0.004
187
1Ba
4
7
11
0.055
0.005
0.100
252
1Bd
42
6
48
0.905
0.002
8.428
188
1Ba
49
0
49
0.325
0.024
6.752
253
1Bd
42
3
45
1.011
0.002
6.762
189
1Ba
4
2
6
0.037
0.013
0.077
254
1Bd
11
0
11
0.172
0.126
0.269
190
1Ba
19
2
21
0.303
0.002
1.060
255
1Bd
4
14
18
0.148
0.041
0.337
191
1Ba
3
7
10
0.223
0.077
0.679
256
1Bd
15
1
16
0.168
0.086
0.294
192
1Ba
16
57
73
0.136
0.026
0.974
257
1Bd
7
142
149
0.169
0.070
0.299
193
1Ba
4
0
4
0.002
0.002
0.002
258
1Bd
0
91
91
0.188
0.034
0.789
194
1Ba
15
5
20
0.049
0.021
0.107
259
1Bd
0
71
71
0.013
0.002
0.033
123
62
Environ Geochem Health (2012) 34:55–69
Table 2 continued ID
Group
Numbers of samples
Hg (mg kg-1)
Paddy
ID
Farm
Total
Mean
Min
Max
Group
Numbers of samples
Hg (mg kg-1)
Paddy
Mean
Farm
Total
Min
Max
195
1Ba
32
6
38
0.167
0.016
0.574
260
1Bd
2
99
101
0.011
0.002
0.152
261
1Bd
24
47
71
0.146
0.016
0.564
303
1Dc
24
0
24
0.073
0.006
0.606
262
1Bd
16
168
184
0.337
0.068
1.212
304
1Dc
50
0
50
0.040
0.002
0.257
263
1Bd
0
29
29
0.002
0.002
0.002
305
1Dc
9
86
95
0.184
0.002
4.069
264
1Bd
0
82
82
0.590
0.002
1.932
306
1Dc
2
56
58
0.048
0.015
0.413
265
1Bd
5
64
69
0.069
0.002
0.167
307
1Dc
15
4
19
0.024
0.010
0.077
266
1Bd
2
101
103
0.059
0.002
0.348
308
1Dc
9
0
9
0.002
0.002
0.002
267
1Bd
2
70
72
0.943
0.002
2.709
309
1Dc
4
0
4
0.021
0.006
0.036
268
1Bd
0
61
61
0.016
0.002
0.067
310
1Dd
23
0
23
0.002
0.002
0.002
269
1Ca
2
68
70
0.110
0.018
0.298
311
1Dd
45
89
134
0.152
0.003
1.214
270
1Ca
20
10
30
0.174
0.079
0.915
312
1Dd
16
6
22
0.123
0.016
1.445
271
1Ca
0
27
27
0.016
0.002
0.033
313
1Dd
60
7
67
0.130
0.002
1.594
272
1Ca
16
80
96
0.117
0.071
0.831
314
1Dd
68
24
92
0.068
0.003
0.214
273
1Ca
20
25
45
0.168
0.026
0.436
315
1Dd
9
73
82
0.278
0.014
3.931
274 275
1Ca 1Ca
44 8
207 2
251 10
0.264 0.087
0.002 0.019
7.417 0.262
316 317
2Ad 2Bb
32 13
21 174
53 187
0.002 0.407
0.002 0.114
0.002 1.175
276
1Ca
15
32
47
0.088
0.017
0.733
318
2Bc
29
0
29
0.082
0.009
0.256
277
1Ca
10
27
37
0.144
0.021
1.197
319
2Bd
4
19
23
0.050
0.026
0.218
278
1Ca
5
36
41
0.041
0.020
0.303
320
2Ca
0
9
9
0.011
0.002
0.033
279
1Cb
9
0
9
0.004
0.002
0.002
321
2Cd
5
2
7
0.032
0.023
0.046
283
1Cb
0
6
6
0.049
0.009
0.182
322
2Da
19
17
36
0.221
0.028
0.878
284
1Cb
10
49
59
1.101
0.002
2.513
323
2Dc
27
34
61
0.034
0.002
0.179
285
1Cb
19
63
82
0.003
0.002
0.133
324
2Dc
44
56
100
0.013
0.002
0.068
280
1Cd
1
63
64
0.015
0.002
0.067
325
2Dd
18
10
28
0.026
0.002
0.667
281
1Cd
0
6
6
0.053
0.007
0.226
326
2Dd
2
36
38
0.065
0.021
0.463
282
1Cd
59
7
66
0.494
0.008
2.866
327
3Ad
24
19
43
0.030
0.011
0.060
286
1Da
41
0
41
0.092
0.004
1.483
328
3Ad
7
18
25
0.056
0.005
0.323
287
1Da
6
16
22
0.254
0.003
0.387
329
3Bb
23
11
34
0.212
0.111
0.915
288
1Da
2
70
72
0.143
0.064
0.320
330
3Bb
5
54
59
0.151
0.002
0.713
289 290
1Da 1Da
8 4
19 34
27 38
0.078 0.274
0.018 0.027
0.161 2.693
331 332
3Bd 3Bd
1 3
3 0
4 3
0.017 0.048
0.002 0.002
0.033 0.082
291
1Da
32
11
43
0.047
0.010
0.405
333
3Bd
5
9
14
0.077
0.062
0.087
292
1Da
45
1
46
0.095
0.002
0.631
334
3Bd
19
44
63
0.059
0.002
0.129
293
1Da
5
54
59
0.040
0.007
0.087
335
3Cd
6
0
6
0.561
0.135
1.265
294
1Da
12
0
12
0.307
0.026
1.077
336
3Da
19
5
24
0.215
0.096
1.043
295
1Da
19
0
19
0.002
0.002
0.002
337
3Db
20
41
61
0.022
0.002
0.256
296
1Da
12
0
12
0.047
0.013
0.165
338
3Dd
43
0
43
0.285
0.002
3.967
297
1Db
24
29
29
0.558
0.028
3.197
339
4Ba
32
0
32
0.311
0.019
2.917
298
1Db
31
38
69
0.416
0.058
3.587
340
4Ba
10
0
10
0.234
0.002
0.794
299
1Db
3
29
32
0.201
0.038
1.392
341
4Ba
33
0
33
0.195
0.012
3.201
300
1Db
5
59
64
0.463
0.002
1.912
342
5Ab
19
11
30
0.069
0.008
0.365
301
1Db
9
54
63
0.176
0.011
1.703
343
5Db
7
8
16
0.002
0.002
0.002
123
Environ Geochem Health (2012) 34:55–69
63
Table 2 continued ID
Group
302
1Db
Numbers of samples
Hg (mg kg-1)
Paddy
Farm
Total
Mean
Min
Max
56
0
56
0.040
0.005
0.167
ID
Group
Total
–
Numbers of samples
Hg (mg kg-1)
Paddy
Farm
Total
Mean
Min
Max
5,356
11,040
16,386
–
–
–
See Table 1 for explanation of group Table 3 Mean and range of Hg in soils in relation to geology and mineralization type of mines
Type
Number of mines
Number of samples
Mean mg kg-1
Range mg kg-1
1
Hydrothermal vein
315
15,315
0.208
0.002*24.07
2
Hydrothermal replacement
11
571
0.166
0.002*4.175
3
Contact metasomatic (skarn)
12
379
0.121
0.002*3.967
Classification of soils as geological activity Mineralization types
4
Pegmatite deposits
3
75
0.250
0.002*3.201
5
Sedimentary deposits
2
46
0.045
0.002*0.365
Au and Ag only
157
7,413
0.201
0.002*24.07
B
Au, Ag, and base metals
127
6,215
0.222
0.002*9.920
C
Base metals
20
968
0.221
0.002*7.417
Sn, W, Mo, Fe, and Mn
39
1,790
0.144
0.002*4.069
Igneous rock
124
5,946
0.147
0.002*16.74
Productive metals (valuable ore minerals) A
D Parent rocks a b
Metamorphic rock
135
6,379
0.241
0.002*23.39
c
Sedimentary rock
31
1,429
0.282
0.002*5.346
d
Heterogeneous rocks with igneous and metamorphic processes
53
2,632
0.204
0.002*24.07
343
16,386
0.204
0.002*24.07
Total
Hg in soils (mg kg -1)
10
Hg concentration in soils as productive metals (valuable ore minerals)
1
0.1
0.01
0.001 1
2
3
4
5
Classifications of soils in relation to mineralization types
Fig. 1 Box plot for Hg concentrations in soils in relation to mineralization types of mines (see Table 1 for explanation of mineralization type 1, 2, 3, 4, and 5)
The number of mines and samples classified as valuable ore minerals is also shown in Table 2 for all the mines and in Table 3 as a summary. Among the 343 mines, 45.8% of the mines were exploited Au and Ag (type A) and 37.0% of the mines were produced Au, Ag, and base metals (type B). Thus, 82.3% (284 of 343 mines) of the mines were targeted in Au and Ag, and about 5.8% of the total mines were base metal mines (type C), mainly producing Cu, Pb, and Zn. In addition, about 11.4% of the mines produced high-temperature minerals including Sn, W, Mo, Fe, and Mn (type D).
123
64
Environ Geochem Health (2012) 34:55–69
1
0.1
0.01
0.001 A
B
C
D
Classifications of soils in relation to variable ore minerals
Fig. 2 Box plot for Hg concentrations in soils in relation to valuable ore minerals of mines (see Table 1 for explanation of productive metal type A, B, C, and D)
As shown in Table 3 and Fig. 2, the average concentrations of Hg in soils were 0.201, 0.222, 0.221, and 0.144 mg kg-1 around mines that produced Au and Ag only; Au, Ag, and base metals; and base metals and high-temperature minerals, respectively. In general, Hg minerals such as cinnabar can be produced at low temperatures caused by the volatile characteristics of both Hg and S; pure HgS itself sublimes at 584°C (GSK 1988). According to a national survey on mineralization of mining activities in Korea, there are no records for Hg mines. A few Au–Ag and base metal mines, however, contained a small amount of Hg minerals such as cinnabar (HgS) as associated minerals with the other sulfide minerals (GSK 1988). In some cases, furthermore, cinnabar can be formed under the middle range of hydrothermal solution (100*300°C) associated with other sulfide minerals including pyrite (FeS2), galena (PbS), and sphalerite (ZnS). Thus, relatively high concentrations of Hg in soils were derived from weathering of mine waste materials from base metal mines. However, relatively low concentrations of Hg in soils were found in Sn, W, Mo, Fe, and Mn mines, which may be due to a lack of Hg mineralization under the high temperature, or the character of the respective ores rather occurring as oxides.
granite (so-called the Daebo Orogeny) is distributed in the middle part of the Korean Peninsula, and Bulguksa granite is covered in the south part of the Korean Peninsula (GSK 1988). The Daebo granite was the most severe in intensity, so that all previous formations were intensely deformed and a great many rocks were metamorphosed. As a result, there is a wide distribution of metamorphic rocks including granitic schist and gneiss in Korea. Thus, 39.4% of all the mines were underlain by the metamorphic rocks (type b). Furthermore, 15.5% of the mines were composed by a combination of various rocks. However, a relatively small amount of mines were underlain by sedimentary rocks (type c) such as sandstone, shales, limestone, and mudstone. The number of mines and samples classified as parent rocks is presented in Table 2 for all the mines and in Table 3 for a summary. As shown in Table 3 (Fig. 3), the average concentrations of Hg in soils were 0.147, 0.241, 0.282, and 0.204 mg kg-1 underlain by igneous, metamorphic, sedimentary, and the heterogeneous rocks with igneous and metamorphic processes, respectively. Fergusson (1990) assessed that Hg concentrations in various rocks were 0.012, 0.08, and 0.19 mg kg-1 in basalt, granite, and sedimentary rocks, respectively. Similar patterns were also found in this study. Mercury concentrations in soils derived from igneous rocks are relatively lower than the other rocks. In Korea, there are numerous Au–Ag mines, and most of them were embedded in igneous origins (Jung 2008). During the mineralization, granite, formed under high temperature and pressure, was the dominant rock. Under this 10
Hg in soils (mg kg -1)
Hg in soils (mg kg -1)
10
1
0.1
0.01
0.001
Hg concentration in soils as parent rocks
a
b
c
d
Classifications of soils in relation to parent rocks
There are two major igneous activities in Korea: Daebo granite formed at Jurassic period and Bulguksa granite formed at Cretaceous period. The Daebo
123
Fig. 3 Box plot for Hg concentrations in soils in relation to parent rocks of mines (see Table 1 for explanation of parent rock type a, b, c, and d)
Environ Geochem Health (2012) 34:55–69
condition, volatile metals such as Hg in the rocks can get out from parent rocks along the small fissure and crack. As a result, limitations of Hg mineralization in these rocks were found in Korea (GSK 1988). This study confirmed lower concentrations of Hg in soils derived from weathering products of igneous rocks. However, volatile metals derived from volcanic rocks formed at relatively lower temperature and pressure may be concentrated as sulfide minerals. The GSK (1988) confirmed that small amounts of cinnabar were identified as associated and accessory minerals with common sulfide minerals such as pyrite, galena, and sphalerite. According to the geological survey of Korea, the weathered cinnabar was found in the southern part of the Korean Peninsula underlain by volcanic rocks including tuff, andesite, and trachyte (GSK 1988). According to compiled data for mining environment in Korea surveyed from 2007 to 2009, Hg concentrations in soils sampled from southern part of Korea with dominant volcanic activity were higher than those from middle part of Korea with dominant granitic composition (KMoE 2007, 2008, 2009a). Several types of sedimentary rocks occur in the Korean Peninsula. The most frequent sedimentary rocks are sandstone, shale, and limestone, and they are found in the middle and southern part of the peninsula (GSK 1988). In general, sedimentation resulted from weathered rocks of various types formed enrichment of heavy metals in the surface environment. As a consequence, relatively high levels of Hg were found in soils derived from sedimentary rocks (Table 2). In comparison with Hg in igneous rocks (0.012 mg kg-1 in basaltic and 0.08 mg kg-1 in acidic rocks), the relatively higher average Hg concentration in sedimentary rocks of 0.19 mg kg-1 was reported by Fergusson (1990), and this study also showed a similar trend with enrichment of soil Hg concentrations originated from sedimentary rocks. There is wide range of metal concentrations in soils derived from the weathering process of rocks. This is mainly due to a variation of metal in existence in the rocks. High-temperature minerals such as Sn, W, Mo, Fe, and Mn can be enriched under the high metamorphic alteration. However, volatile metals can be formed at low grade of metamorphic activities (GSK 1988). As mentioned before, there are the two major metamorphic activities interacted with old parent rocks and igneous activities by the Daebo
65
Orogeny and the Bulguksa granite. As a result, this study showed a wide range of Hg concentrations in soils influenced by metamorphic rocks, which can be controlled by temperature of metamorphism at each mine. A higher altered rock zone by the Daebo Table 4 Group, numbers of mines and samples, and mean and range of Hg in soils in relation to geology and mineralization type of mines Group1
Number of mines
Number of samples
Mean mg kg-1
Range mg kg-1 0.002*16.75
1Aa
52
2,849
0.146
1Ab
78
3,491
0.233
0.002*23.39
1Ac
9
417
0.474
0.002*2.735
1Ad
14
505
0.120
0.002*24.07
1Ba
45
1,908
0.143
0.002*6.752
1Bb 1Bc
41 12
2,032 563
0.231 0.310
0.002*9.920 0.002*5.346
1Bd
17
1,221
0.279
0.002*8.428
1Ca
10
654
0.169
0.002*7.417
1Cb
4
156
0.420
0.002*2.513
1Cd
3
136
0.249
0.002*2.866
1Da
11
391
0.115
0.002*2.693
1Db
6
313
0.301
0.002*3.587
1Dc
7
259
0.095
0.002*4.069
1Dd
6
420
0.145
0.002*3.931
2Ad
1
53
0.002
0.002*0.002
2Bb
1
187
0.407
0.114*1.175
2Bc
1
29
0.082
0.009*0.256
2Bd
1
23
0.050
0.026*0.218
2Ca
1
9
0.011
0.002*0.033
2Cd
1
7
0.032
0.023*0.046
2Da 2Dc
1 2
36 161
0.221 0.021
0.028*0.878 0.002*0.179
2Dd
2
66
0.049
0.002*0.667
3Ad
2
68
0.040
0.016*0.384
3Bb
2
93
0.173
0.002*0.915
3Bd
4
84
0.060
0.002*0.129
3Cd
1
6
0.561
0.135*1.265
3Da
1
24
0.215
0.096*1.043
3Db
1
61
0.022
0.002*0.256
3Dd
1
43
0.285
0.002*3.967
4Ba
3
75
0.250
0.002*0.794
5Ab
1
30
0.069
0.008*0.365
5Db
1
16
0.002
0.002*0.002
343
16,386
0.204
0.002*24.07
Total 1
See Table 1 for explanation of group
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66 10
Hg in soils (mg kg-1)
Fig. 4 Box plot for Hg concentrations in soils classified as mineralization types of mines (see Table 2 for explanation of geology and mineralization types)
Environ Geochem Health (2012) 34:55–69
1
0.1
0.01
0.001 1Aa
1Ab
1Ac
1Ad
-
1Ba
1Bb
1Bc
1Bd
-
1Ca
1Cb
1Cd
-
1Da
1Db
1Dc
1Dd
Classifications of soils as geology and mineralization types
Orogeny, especially in the middle part of the Korean Peninsula, contained relatively lower levels of Hg in soils with the range of 0.05–0.25 mg kg-1. However, lesser altered rock zone by the Bulguksa granite, especially in the southern part of the Korean Peninsula, contained relatively high levels of Hg in soils with the range of 0.12–0.53 mg kg-1. Thus, it can be suggested that soils derived from the weathering process of low-grade alteration in metamorphic activities can be enriched in volatile metals including Hg. Comparison of Hg in soils due to geology and mineralization types As discussed before, Hg concentrations in soils can be influenced by a variety of geological conditions and mineralization types. Of those mineralization types, the average Hg concentrations (mg kg-1) decreased in the order of soils in mines mineralized by pegmatite (0.250) [ hydrothermal vein (0.208) [ hydrothermal replacement (0.166) [ skarn (0.121) [ sedimentary deposits (0.045). In case of the group with productive metals, the concentrations decreased in the order of Au, Ag, and base metal mines [ base metal mines [ Au and Ag mines [ Sn, W, Mo, Fe, and Mn mines. In addition to parent rocks, the concentrations decreased in the order of sedimentary rocks [ metamorphic rocks [ heterogeneous rocks with igneous and metamorphic processes [ igneous rocks in origin. The mean and range of Hg in soils classified as various geology and mineralization types are shown in detail in Table 4. Of the hydrothermal vein type, groups of 1Ac (Au–Ag mines) mineralized by hydrothermal vein in sedimentary rocks and 1Cb
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(base metal mines) mineralized by hydrothermal vein in metamorphic rocks. Groups of 1Bc, 1Dd, to a less extent, 1Ab, 1Bb, 1Bd, and 1Cd contained relatively higher Hg contents in the soils (for abbreviations, see Table 1). However, soils taken from 1Dc (Sn, W, Mo, Fe, and Mn mines mineralized by hydrothermal vein in the sedimentary rocks) contained relatively lower Hg levels. Furthermore, groups of 1Ad, 1Da, and to a lesser extent, 1Aa, 1Ba, and 1Dd contained relatively lower levels of Hg. A box plot for Hg concentrations in soils influenced by hydrothermal vein types is shown in Fig. 4, in which Hg concentrations are high in soils derived from Au, Ag, and base metal mines underlain by metamorphic and sedimentary rocks. For the other mineralization types, groups of 3Cd (base metal mines mineralized by skarn in the combination of limestone and igneous rocks) and 2Bb (Au, Ag, and base metal mines mineralized by hydrothermal replacement in metamorphic rocks) contained high levels of Hg. In addition, groups of 2Da, 3Da, 3Dd, and 4Ba also contained relatively higher levels of Hg. Groups of 2Ad, 2Bd, 2Ca, 2Cd, 2Dc, 2Dd, 3Bd, 3Db, 5Ab, and 5Db, however, contained below natural background values for paddy soils in Korea of 0.09 mg kg-1 reported by NIER (National Institute of Environmental Research) (1999). Thus, in summary, Hg concentrations are high in soils derived from Au, Ag, and base metal mines underlain by metamorphic and sedimentary rocks.
Comparison of Hg in paddy soils and farmland soils A box plot for Hg concentrations in paddy and farmland soils from each mine type mineralized by
Environ Geochem Health (2012) 34:55–69 100 1Aa-P : sampled at paddy field classified as '1Aa' 1Aa-F : sampled at farm land classified as '1Aa'
Hg in soils (mg kg-1)
Fig. 5 Box plot for Hg concentrations in paddy and farmland soils classified as mineralization types of mines (see Table 2 for explanation of geology and mineralization types)
67
10
1
0.1
0.01
0.001 1Aa-P1Aa-F1Ab-P1Ab-F1Ac-P1Ac-F1Ad-P1Ad-F
-
1Ba-P1Ba-F1Bb-P1Bb-F
-
1Ca-P 1Ca-F
-
1Dd-P1Dd-F
Classifications of soils as geology and mineralization types
Table 5 Mercury contents in various soil, water, and crop plants in Korea (NIER 1999)
Area
Soil (mg kg-1)
Water (lg L-1)
Crop plant (lg kg-1)
Paddy field (unpolluted)
0.09 (0.02*0.33)a
0.015 (NDb*2.0)
Rice grain: 3.0 (ND*14.0)
Paddy field (industrial)
0.08 (0.01*0.73)
11.0
–
Paddy field (urban) Paddy field (coal mine)
0.15 (0.03*0.86) 0.11 (0.04*0.20)
– –
– –
Paddy field (Cu mine)
0.43 (0.02*9.18)
–
Rice grain: 11.0 (3*60)
1.90
–
Paddy field (Pb, Zn mine)
–
a
Farmland (vegetable)
0.11 (0.02*1.13)
–
–
0.22 (0.01*2.44)
–
–
b
Farmland (municipal waste)
Figure in parenthesis is the range of Hg contents Not detected
hydrothermal veins is shown in Fig. 5. According to NIER (1999), national background levels for Hg in farmland soils and paddy soils were 0.11 and 0.09 mg kg-1, respectively (Table 5). As shown in the figure, this study also confirmed that Hg concentrations from farmland contained relatively higher levels than those from paddy fields. This may be due to the conditions of the two soils, including extent and degree of Hg holding capacity, particle size, organic matter contents, sorption ability, and redox potential (Fergusson 1990; Adriano 2001). Jung and Thornton (1997) reported that water irrigation in paddy field is one of the most important factors governing the heavy metals in paddy soils. During irrigation, relatively lower concentrations were found in soils and rice stalks sampled in the vicinity of a Pb–Zn mine in Korea. Lee et al. (2001) also found that heavy metals in rice stalks sampled during the dry season (no irrigating time) contained relatively higher than those during the wet season (irrigating time).
Conclusions This study focused on the evaluation of Hg concentrations in agricultural soils influenced by various metal mining activities in Korea. A total of 16,386 surface soils at 343 metal mines were sampled and classified as geology and mineralization type of the mines. The results of this study can be summarized as follows: 1.
According to mineralization types, the average Hg concentrations (mg kg-1) decreased in the order of soils mineralized by pegmatite [ hydrothermal vein [ hydrothermal replacement [ skarn [ sedimentary deposits. This order is greatly influenced by temperature and pressure under rock-forming conditions. 2. In terms of productive metals, the average concentrations decreased in the order of Au, Ag, and base metal mines [ base metal mines [ Au and Ag mines [ Sn, W, Mo, Fe, and Mn
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68
3.
Environ Geochem Health (2012) 34:55–69
mines. Relatively higher Hg in soils from Au, Ag, and base metal mines were mainly controlled by sulfide mineralization under low temperature. An elevated level of Hg is additionally due to its use in Au mines for the amalgamation process. In addition to parent rocks, the concentrations decreased in the order of sedimentary rocks [ metamorphic rocks [ heterogeneous rocks with igneous and metamorphic processes [ igneous rocks in origin. In detail, Hg concentrations are high in soils derived from Au, Ag, and base metal mines underlain by metamorphic and sedimentary rocks. This study also confirmed that Hg concentrations from farmland contained relatively higher levels than those from paddy fields, which may be due to various conditions including extent and degree of Hg holding capacity, particle size, organic matter contents, and sorption ability. The study also suggested that water irrigation in the paddy field is one of the most important factors governing heavy metal levels and availability in paddy soils.
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