DSpace at VNU: Arsenic and Heavy Metal Concentrations in Agricultural Soils Around Tin and Tungsten Mines in the Dai Tu district, N. Vietnam

Water Air Soil Pollut (2009) 197:75–89
DOI 10.1007/s11270-008-9792-y

Arsenic and Heavy Metal Concentrations
in Agricultural Soils Around Tin and Tungsten Mines
in the Dai Tu district, N. Vietnam
Kien Chu Ngoc & Noi Van Nguyen &
Bang Nguyen Dinh & Son Le Thanh & Sota Tanaka &
Yumei Kang & Katsutoshi Sakurai & Kōzō Iwasaki

Received: 17 March 2008 / Accepted: 29 June 2008 / Published online: 20 July 2008
# Springer Science + Business Media B.V. 2008

Abstract This study assessed the arsenic and heavy
metal contaminations of agricultural soils around the
tin and tungsten mining areas in Dai Tu district in
northern Vietnam. Among the examined elements,
high total contents of As and Cu were found in the
agricultural fields at both tin and tungsten mining
sites. Although the major part of the accumulated As
and Cu were bound by various soil constituents such
as Fe and Mn oxides, organic matter, and clay
minerals, increases in water soluble As and Cu were
observed, especially for the paddy fields. The results
suggest that, in the studied area, As and Cu dispersion
from their pollution sources into farmlands is mainly
via fluvial transportation of mine waste through
streams that cross the paddy fields around the tin

K. Chu Ngoc
United Graduate School of Agricultural Sciences,

Ehime University,
Ehime 790-8566, Japan
N. Van Nguyen : B. Nguyen Dinh : S. Le Thanh
Faculty of Chemistry, Hanoi University of Science,
Hanoi, Vietnam
S. Tanaka
Graduate School of Kuroshio Science, Kochi University,
Kochi 783-8502, Japan
Y. Kang : K. Sakurai : K. Iwasaki (*)
Faculty of Agriculture, Kochi University,
Kochi 783-8502, Japan
e-mail:

mining area, and soil erosion at the tea fields located
at lower positions of the slope in the tungsten mining
area.
Keywords Arsenic . Heavy metal . Soil
contamination . Tin mine . Tungsten mine . Vietnam

1 Introduction
Mining can be a significant source of metal contamination of the environment owing to activities such as
mineral excavation, ore transportation, smelting and
refining, disposal of the tailings and waste water
around mines (Adriano 2001; Jung 2001; Razo et al.
2004; Chopin and Alloway 2007). Due to discharge
and dispersion of mine wastes from the metalliferous
mines, agricultural soils, food crops and stream
systems are often contaminated by elevated levels of
toxic metals (McGowen and Basta 2001; Jung 2001;
Lee 2006). With growing public concern throughout

the world over health hazards caused by polluted
agricultural products, many studies have been conducted on metal and metalloid contamination in soils,
water and sediments from metalliferous mines
(Merrington and Alloway 1994; Iwasaki et al. 1997;
Jung et al. 2002; Lee 2006; Chopin and Alloway
2007; Anawar et al. 2008). According to these
studies, metal contaminations of agricultural soils
should be evaluated based on the results of metal
speciation as well as their total contents, because only


76

soluble, exchangeable and chelated metal species in
the soils are the available fractions for plant uptake
(Kabata-Pendias and Pendias 1992; Chen et al. 2007).
The proportion of a metal which is mobile and bioavailable will provide more practical information for
evaluating its potential environmental risks. In Vietnam, however, only few studies on the forms and
distributions of heavy metals and metalloids have
been carried out for the agricultural soils affected by
mining activities.
Vietnam is well endowed with a wide range of
mineral resources located mainly in the northern
regions. The Dai Tu district, situated in northern
Vietnam, is one of the largest areas rich in ferrous and
non-ferrous ore deposits in the country. The mines
have produced ores containing Fe, Ti, Zn, Sn, W, Cu,
and Pb (Thai Nguyen Department of Planning and
Investment 2005) and the common minerals are pyrite
(FeS2), chalcopyrite (CuFeS2), wolframite [(Fe, Mn)

WO4], accessory galena (PbS) with minor amounts of
arsenopyrite (FeAsS), and bismuthinite (Bi2S3; Jung
et al. 2002; Chopin and Alloway 2007). Recently,
involvement of foreign companies has been accelerating the development of export-orientated minerals
with high values, and several important ore deposits
were newly discovered in this district. Besides such
large-scale exploitation, traditional mining operations
are still continued by local farmers living in the
vicinity of the mine although many of the mines have
been abandoned due to the lack of modern mining
technologies.
In the Dai Tu district, over the last few decades,
traditional manual mining has been operated through
small adits and open pits. Unfortunately, this mining
operation has potential for releasing toxic elements
such as As, Cd, Cr, Cu, Ni, and Pb to the surrounding
environment during digging and washing ores because small quantities of these elements are present as
minor constituents and impurities in the ores. In
addition, the abandoned mines, without appropriate
measures, can become important point sources of the
toxic element contaminations. Further, allocations of
mines and farmlands may pose a potential health risk
from intake of heavy metals derived from soils and
irrigated water from the mines, because settlements
and farmlands of rural communities are located as
close as hundreds of meters from the mine sites.
It is therefore of prime importance to assess
potential environmental risks originating from the

Water Air Soil Pollut (2009) 197:75–89

mining activities in order to establish a proper
pollution management plan. Therefore, in this study,
we focused on the tin and tungsten mining areas in
Dai Tu district, about 1.5 km from each other across
the valley, where the ores have been mined using
traditional methods. The aims of this study were (1) to
evaluate the degree of contamination in agricultural
soils and waters by toxic elements (As, Cd, Cr, Cu,
Mn, Ni, Pb and Zn) and to clarify the contaminant
pathways from the tin and tungsten mining areas, and
(2) to determine the distribution of As and Cu among
various soil chemical fractions in order to assess the
potential risks.

2 Materials and Methods
2.1 Study Area
The survey was conducted around tin and tungsten
mining areas at Hung Son commune (21°38′33″ N,
105°38′58″ E) in Dai Tu district, Thai Nguyen
province, situated in northern Vietnam on 18–20
February, 2006 (Fig. 1). This area is located in a
monsoon tropical climate zone with two distinct
seasons. The rainy season is from May to September
with an annual average temperature of 27–29°C, and
the dry season is from November to March with an
annual average temperature of 16–20°C. The average
precipitation is approximately 1,700–1,800 mm per
year, and the annual evaporation is about half of the
annual precipitation (The Hydrometeorological Data

Center, Vietnam 2005).
The main agricultural practices in the study area
include lowland rice cultivation and tea plantation.
The rice cultivation system involves two rice croppings per year; from February to June and from July
to October. Before crop establishment, the fields are
shallowly submerged, plowed, and puddled. After
puddling, the fields are left flooded for several days
with the water depth of 10–15 cm. After transplanting
rice seedlings, the soils are kept submerged until 1–2
weeks before harvest. The depth of the standing water
is normally 5–10 cm. As a basal dressing, N–P–K
fertilizers (6–11–2) are supplied at the rate of
approximately 0.5 Mg ha−1. Sometimes, farmers also
apply limes or composts (e.g. green manures) before
transplanting. During crop growth, urea and potassium chloride fertilizers are supplied additionally at the


Water Air Soil Pollut (2009) 197:75–89

77

Fig. 1 The location of sampling sites

Legend
180 Altitude line
18
Mining cavity

Thai Nguyen
Vietnam

▲

Forest soil

■

Paddy soil

River, stream

●

Tea field soil
Stream
tream water

■

Standing water

140

T2
T5 T4
T6 ●
T7

T1

(Tungsten)

P4

T3

160
120

P5

P6

100

P1
80

P2
P3
160

ng
Co
e
riv

rate of 0.05–0.1 Mg ha−1. In contrast, the tea
plantations are usually located on the hilly area. The
common fertilizers supplied to the tea field are N–P–

K fertilizers (16–8–4). The dosages vary largely upon
each field and year by year. In addition, water for tea
plantation is mostly supplied by rainfall.

(Tin)

180

200 m

200

chosen. Three paddy fields (P4−P6) located in the
valley below the slope of the mountain were also
investigated. At each site, surface (0–5 cm) and
subsurface (20–25 cm) soils were sampled. In
addition, water samples were taken from the stream
running through the tin mining area (Sw) and the
standing water of the paddy fields (P1w−P6w).

2.2 Sampling
2.3 Soil and Water Analysis
Agricultural lands were selected around the mining
areas based on toposequential location (Fig. 1). At the
tin mining area, three paddy fields (P1−P3) were
selected. They were located along a stream running
through the tin mine area at different distances from
the main adit, and were irrigated with water from the
stream. A natural forest (F) on the mountain slope
near the main adit of the mine was also selected. At

the tungsten mining area, seven tea fields located at
different elevations of the slope (T1−T3, located
at higher positions; T4−T7, at lower positions) were

Soil samples were air-dried at room temperature, and
crushed to pass through a 2-mm mesh sieve. Soil
particle size distributions were determined with a
pipette method (Gee and Bauder 1986). The electrical
conductivity (EC) and pH (H2O) values were determined using a platinum and glass electrode at 1:5 (w/
v) ratio of soil to water, respectively. Exchangeable
(Ex-) cations were extracted with 1 mol l−1 ammonium acetate at pH 7.0 and the contents were
determined using an atomic absorption spectrometer


78

Water Air Soil Pollut (2009) 197:75–89

(AAS; AA-6800, Shimadzu, Kyoto, Japan). After
removing the excess NH4+, the soil was extracted with
100 g l−1 NaCl solution and the supernatant was used
to determine the cation exchangeable capacity (CEC)
with the Kjeldaghl distillation and titration method
(Rhoades 1982). The contents of total carbon (TC) and
total nitrogen (TN) were analyzed on an NC analyzer
(Sumigraph NC-80, Sumitomo Chemical, Osaka,
Japan). The organic matter contents (OM) were
calculated by multiplying the TC values by 1.724
(Nelson and Sommers 1982), as it was assumed that
the amounts of carbonate salts would be negligible

under the relatively acidic nature of the soils.
For the analysis of total As content, the soil sample
was digested in a mixture of HClO4–HNO3–HF
(2:3:5) with the addition of 20 g l−1 KMnO4 in a
teflon vessel at 100°C. The standard reference
materials (JSO-1 and JSO-2 from the Geological
Survey of Japan) were used to verify the accuracy
of As determination. The recovery rates of As were
within 90–95%. The chemical forms of As were
evaluated using a sequential extraction method
according to Keon et al. (2001) with some modifications (Van et al. 2006; Table 1). Briefly, five kinds of
extracting solution were sequentially employed to
divide the total As into water soluble (Ws-), MgCl2
extractable (Mg-), NaH2PO4 extractable (P-), HCl
extractable (HCl-), and residual (Res-) fractions. The
As in these operationally defined fractions was

Table 1 Methods for the sequential extraction of As from soil
Fractions

Reagents

Soil/
Solution
Ratio

Condition

Water
soluble

(Ws-)
MgCl2
extractable
(Mg-)
NaH2PO4
extractable
(P-)
HCl
extractable
(HCl-)
Residual
(Res-)

Water

1:100

Shaken
2h

1.0 mol l−1 MgCl2
(pH 7.0)

1:100

Shaken
2h

1.0 mol l−1 NaH2PO4
(pH 5.0)

1:100

Shaken
24 h

1.0 mol l−1 HCl

1:100

Shaken
1h

HClO4–HNO3–HF–
KMnO4 digestion

assumed to correspond to water soluble As (Ws-),
ionically bound As (Mg-), As strongly bound by
monodentate or bidentate ligand exchange (P-), As
specifically adsorbed or occluded by Mn oxides and
amorphous Fe oxides (HCl-), and As occluded by
crystalline Fe oxides, organic matter and secondary
minerals (Res-), respectively. The concentration of As
in the acid digests and in the fractions were
determined by using an inductively coupled plasma
atomic emission spectrometer (ICP-AES; ICPS1000IV, Shimadzu, Kyoto, Japan) equipped with a
hydride vapor generator (HVG-1, Shimadzu, Kyoto,
Japan). The averaged ratio of sum amounts of As in
each fraction to the total As content for all the
selected soil samples was 101%.

For the analysis of total contents of heavy metals
(Cd, Cr, Cu, Mn, Ni, Pb and Zn), the soil samples
were digested in a mixture of HNO3 and HF (9:1) by
microwave heating (Multiwave, Perkin-Elmer, Yokohama, Japan). The accuracy of the method was
assessed using the certificated reference soils (JSO1) and marine sediment (NIES No.12, provided by the
National Institute for Environmental Studies, Japan).
The recoveries of Cd, Cr, Cu, Mn, Ni, Pb, and Zn
were in the ranges 92.6–117%, 96.7–101%, 96.6–
101%, 96.2–104%, 84.2–95.6%, 92.5–100% and
92.9–96.2%, respectively. Chemical forms of Cu were
estimated by the sequential extraction method
reported by Iwasaki et al. (1997) with some modifications. The reagents employed and shaking period
for the extraction of seven different fractions of soil
Cu are summarized in Table 2. The respective
fractions were designated as water soluble (Ws-),
exchangeable (Ex-), acid soluble (Aci-), Mn oxideoccluded (MnO-), organically bound (OM-), Fe
oxide-occluded (FeO-), and residual (Res-) fractions.
The total concentration of heavy metals (Cd, Cr, Cu,
Mn, Ni, Pb and Zn) in the acid digests and in the Cu
fractions were measured by AAS. After fractionation,
the average recovery of Cu for all selected soil
samples was 92%.
Water samples were filtered through a 0.45 μm
membrane filter and divided into two portions. One
portion was acidified with HNO3 (0.2% v/v) for the
analysis of As and heavy metal concentrations, while
the other was left un-acidified for pH and EC
measurements. Water samples were stored in a
refrigerator at 4°C until physical-chemical analyses.
The total concentration of As and heavy metals (Cd,

Water Air Soil Pollut (2009) 197:75–89

79

Table 2 Methods for the sequential extraction of Cu from soil
Fractions

Reagents

Soil/
solution
ratio

Condition

Water
soluble (Ws-)
Exchangeable
(Ex-)
Acid soluble
(Aci-)
Mn-oxide
occluded
(MnO-)
Organically bound
(OM-)
Fe-oxide occluded
(FeO-)

Residual (Res-)

Water

1:5

Shaken 1 h

1.0 mol l−1 CH3COONH4 (pH 7.0)

1:10

Shaken 2 h

25 g l−1 CH3COOH (pH 2.6)

1:10

Shaken 6 h

0.1 mol l−1 NH2OH.HCl (pH 2.0)

1:50

Shaken 0.5 h

0.1 mol l−1 Na4P2O7 (pH 10.0)

1:50

Shaken 24 h

0.175 mol l−1 (NH4)2C2O4 +0.1 mol l−1 H2C2O4 +0.1
mol l−1 ascorbic acid (pH 3.1)
HClO4–HNO3–HF digestion

1:50

Shaken 4 h, then stirred occasionally in
boiling water for 0.5 h

Cr, Cu, Mn, Ni, Pb and Zn) were determined by ICPAES and AAS, respectively.
2.4 Statistical Analysis
Using data on the physicochemical properties, total
contents of As and heavy metals, and amounts of As
and Cu in different chemical forms in each soil layer,
Tukey’s multiple comparisons were performed on
three kinds of the fields (paddy fields around the tin
mining area, tea fields, and paddy fields around the
tungsten mining area). Student’s t-tests were conducted between surface and subsurface soils in each
soil group. The SPSS (Statistics Program for Social
Science) statistical program package (Release 13.0 for
Windows; SPSS Inc.) was used for these statistical
analyses.

3 Results and Discussion
3.1 General Characteristics of Soils
General physicochemical properties of soils are given
in Table 3. Based on the USDA classification system,
the soils in the forest and tea fields were classified

into Typic Haplustults (Soil Survey Staff 2006). Due
to the use of irrigation water during the growing
season, soil profile description could not be carried

out at the paddy fields of the studied areas. However,
based on the general characteristics of the paddy soils,
it was assumed to be classified as Typic Endoaquents
or its relatives. At the tin and tungsten mining areas,
the soils collected at the forest and tea fields showed
relatively clayey texture while those at the paddy
fields had a sandy texture (Gee and Bauder 1986). TC
and OM contents tended to be higher in the tea field
soils than in the paddy soils. Soil pH ranged from
about 4 to 5, with the forest and tea field soils being
slightly more acidic than those of the paddy soils. The
values of TC, OM, pH and EC showed significant
differences between the paddy soils around the tin
mining area and the tea field soils around the tungsten
mining area (p<0.05). Both for the surface and
subsurface soils, the amounts of Ex–Ca in the paddy
soils were significantly higher than in the tea field
soils (p<0.05). The same tendency was observed for
the amounts of Ex–Mg and Ex–Na. These results can
be ascribed to the application of liming materials
containing CaCO3 and MgCO3 for neutralization of
soil acidity. No distinct differences in general properties were observed between the paddy soils around
the tin and tungsten mining areas.
3.2 As and Heavy Metals in Soils
Total contents of As and heavy metals (Cd, Cr, Cu,
Mn, Ni, Pb and Zn) in the collected soils and their

pH

EC
(dS m−1)

Soils from the tin mining area
Forest soil
4.18
0.60
Fua
4.29
0.40
Flb
Paddy fields
P1u
5.44
1.40
P1l
6.09
0.30
P2u
5.21
1.10
P2l
4.94
0.30
P3u
5.49

1.00
P3l
5.16
0.90
Soils from the tungsten mining area
Tea fields
T1u
4.14
0.60
T1l
3.97
0.60
T2u
4.07
0.50
T2l
4.36
0.20
T3u
4.46
0.40
T3l
4.28
0.30
T4u
4.72
0.40
T4l
4.68
0.20

T5u
4.75
0.40
T5l
4.60
0.20
T6u
4.71
0.40
T6l
4.59
0.20
T7u
5.02
0.20
T7l
4.92
0.10

Symbol

1.44
1.48
0.90
0.37
0.67
0.38
1.03
0.86

1.80
0.72
0.97
0.58
1.25
1.54
1.87
0.59
1.54
0.65
0.96
1.40
1.05
0.60

8.14
1.81
7.50
1.72
10.8
7.15

17.1
9.68
11.8
7.34
13.2
9.59
15.7
6.74

13.6
7.90
16.5
8.54
10.2
6.53

TN

27.5
11.9

(g kg−1)

TC

2.95
1.67
2.03
1.27
2.28
1.65
2.71
1.16
2.34
1.36
2.84
1.47
1.76
1.13

1.40
0.31
1.29
0.30
1.86
1.23

4.74
2.05

OM (%)

0.07
0.03
0.03
0.01
0.11
0.05
0.18
0.05
0.18
0.05
0.17
0.05
0.09
0.05

0.18
0.09

0.20
0.05
0.21
0.15

0.18
0.04

(cmolc kg−1)

Ex–K

0.05
0.02
0.03
0.02
0.03
0.02
0.03
0.02
0.03
0.03
0.03
0.02
0.03
0.02

0.06
0.05
0.09

0.04
0.10
0.06

0.05
0.03

Ex–Na

0.10
0.02
0.05
0.02
0.22
0.02
0.12
0.01
0.22
0.05
0.36
0.03
0.14
0.06

1.74
1.61
1.35
0.36
2.03
1.57

0.31
0.02

Ex–Ca

Table 3 Physicochemical properties of soil sampled close to tin and tungsten mines (Dai Tu district, N. Vietnam)

0.06
0.02
0.03
0.01
0.12
0.03
0.09
0.03
0.10
0.02
0.09
0.02
0.07
0.02

0.23
0.26
0.26
0.10
0.45
0.29

0.12
0.03

Ex–Mg

12.6
13.2
10.7
11.2
8.55
9.60
7.20
6.55
7.20
7.00
8.25
7.65
4.80
5.25

4.88
3.45
3.98
2.10
5.60
4.10

23.3
19.1

CEC

40
46
38
44
36
41
24
26
22
24
24
25
16
19

9
11
12
9
14
13

39
46

Clay (%)

SC

C
SC
C
SC
SC
SCL
SCL
SCL
SCL
SCL
SCL
SL
SL

LS
SL
SL
LS
SL
SL

SC
C

Texture

80
Water Air Soil Pollut (2009) 197:75–89

pH

EC
(dS m−1)

0.87 A
0.54 a

1.35 A
0.87 a
1.03 A
0.87 a

14.0 A**
8.05 a
10.7 AB
7.73 ab

0.84
1.20
1.60
0.95
0.66
0.46

TN

8.11 B*
3.56 b

12.2
11.8
12.8
5.96
7.14
5.44

(g kg−1)

TC

1.85 AB
1.33 ab

2.42 A**
1.39 a

1.52 B*
0.61 b

2.10
2.03
2.21
1.03
1.23
0.94

OM (%)

0.18 A

0.07 a

0.12 A**
0.04 a

0.20 A
0.10 a

0.22
0.13
0.25
0.05
0.06
0.02

(cmolc kg−1)

Ex–K

0.10 A*
0.05 a

0.03 B*
0.02 b

0.08 A
0.05 a

0.10
0.06

0.11
0.05
0.09
0.04

Ex–Na

1.14 B
0.75 a

0.17 C**
0.03 b

1.71 A
1.18 a

1.40
0.99
1.35
0.74
0.67
0.51

Ex–Ca

0.19 AB
0.13 a

0.08 B**
0.02 b

0.31 A
0.22 a

0.21
0.16
0.25
0.11
0.10
0.11

Ex–Mg

7.02 A
5.76 ab

8.47 A
8.64 a

4.82 A**
3.22 b

6.75
6.00
10.7
7.55
3.60
3.73

CEC

18 AB
17 ab

28 A
32 a

12 B
11 b

21
17
21
18
12
15

Clay (%)

SCL
SL
SCL
SL
SL
SL

Texture

b

a

l: subsurface soil (20–25 cm)

u: surface soil (0–5 cm)

**Averages that are significantly different from the average values for the surface and subsurface soils in each soil group at 1% level

*Averages that are significantly different from the average values for the surface and subsurface soils in each soil group at 5% level

Average values followed by the same capitalized letter are not significantly different at a 5% level for surface soil, and those followed by the same small letter are not significantly
different at a 5% level for subsurface soil, according to a Tukey’s method.

Paddy fields
P4u
4.98
0.80
P4l
4.99
0.60
P5u
4.96
1.50
P5l
5.16
0.20
P6u
4.75
1.00
P6l

5.25
0.20
Average values
Soils from the tin mining area
Paddy fields (n=3)
u
5.38 A
1.17 A
l
5.40 a
0.50 a
Soils from the tungsten mining area
Tea fields (n=7)
u
4.55 B
0.41 B**
l
4.49 b
0.26 a
Paddy fields (n=3)
u
4.90 AB
1.10 A
l
5.13 ab
0.33 a

Symbol

Table 3 (continued)

Water Air Soil Pollut (2009) 197:75–89
81


82

Water Air Soil Pollut (2009) 197:75–89

Table 4 Total As and heavy metal contents in soils close to the tin and tungsten mines (Dai Tu district, N. Vietnam)
Symbol

As

Cd

Cr

Cu

Mn

Ni

Pb

Zn

82.9
77.3

330
272

156
159

16.8
10.9

266
254

104
121

22.1
27.2
19.2
16.2
21.1
25.9

267
57.1
165
21.0
104
69.3

303
379
191
176
207
159

6.35
7.65
6.25
4.40
5.70
4.95

49.3
49.7
45.7
43.2
57.2
52.1

89.5
83.3
83.8
69.1
79.7
69.4

56.0
51.5

43.5
49.5
51.0
35.1
35.4
38.6
35.1
16.2
45.4
41.4
23.4
20.2

88.3
96.4
82.5
72.5
57.0
46.9
82.8
68.2
30.4
31.6
29.3
27.4
15.7
16.2

124
155

288
224
215
197
280
289
265
315
316
302
355
323

15.3
17.2
14.2
19.0
14.2
20.2
15.0
15.8
13.7
17.0
16.3
15.2
12.1
9.10

155
269

76.1
71.4
61.8
69.0
67.1
40.0
52.2
46.9
44.3
43.2
34.1
27.7

94.4
114
99.5
95.2
87.0
88.8
105
106
89.9
109
104
89.8
87.0
80.5

28.9
26.0

30.5
26.2
22.5
24.6

37.6
23.8
34.7
14.2
17.8
13.9

309
290
305
335
417
406

8.50
7.45
8.30
7.25
5.65
7.05

40.3
34.7
58.4
37.3

33.9
32.5

103
89.5
98.2
102
71.6
72.9

20.8 B
23.1 a

179 A
49.1 a

234 A
238 a

6.10 B
5.67 b

50.7 A
48.3 a

84.3 A
73.9 b

41.4 A
36.1 a

55.1 B
51.3 a

263 A
258 a

14.4 A
16.2 a

70.1 A
81.0 a

95.3 A
97.6 a

27.3 AB
25.6 a

30.0 B
17.3 a

344 A
344 a

7.48 B
7.25 b

44.2 A
34.8 a

90.9 A
88.1 ab

(mg kg−1)
Soils from the tin mining area
Forest soil
Fua
431
2.15
Flb
545
3.25
Paddy fields
P1u
37.6
1.35
P1l
66.0
1.25
P2u
63.2
1.45
P2l
16.3
0.85
P3u
56.6
0.75
P3l

43.0
0.55
Soils from the tungsten mining area
Tea fields
T1u
927
1.90
T1l
1,010
2.30
T2u
531
0.60
T2l
866
1.10
T3u
312
1.00
T3l
409
0.40
T4u
39.3
0.35
T4l
36.7
0.95
T5u
21.0

1.10
T5l
18.8
1.85
T6u
98.3
0.90
T6l
37.1
1.10
T7u
25.9
0.50
T7l
18.8
0.90
Paddy fields
P4u
80.0
1.70
P4l
64.8
1.60
P5u
49.6
1.80
P5l
26.2
1.55
P6u

28.4
2.40
P6l
21.0
1.15
Average values
Soils from the tin mining area
Paddy fields (n=3)
u
52.5 A
1.18 AB
l
41.8 a
0.88 a
Soils from the tungsten mining area
Tea fields (n=7)
u
279 A
0.91 B
l
342 a
1.23 a
Paddy fields (n=3)
u
52.7 A
1.97 A
l
37.3 a
1.43 a

Average values followed by the same capitalized letter are not significantly different at a 5% level for surface soil, and those followed
by the same small letter are not significantly different at a 5% level for subsurface soil, according to a Tukey’s method.
There is no significant difference from the average values for the surface and subsurface soils in each soil group at 5% or 1% level.
a

u: surface soil (0–5 cm)

b

l: subsurface soil (20–25 cm)


Water Air Soil Pollut (2009) 197:75–89

83

Table 5 pH, EC and concentrations of As and heavy metals in water sampled around the tin and tungsten mines (Dai Tu district, N.
Vietnam)
pH

EC

As

Cd

(dS m−1) (μg l−1)
Water from the tin mining area
Sw
P1w

P2w
P3w
Water from the tungsten mining area
P4w
P5w
P6w
Vietnamese standard limitation
for surface water (TCVN 5942-1995)
a

Not detected

b

Cr (VI)

Cr

Cu

Ni

Pb

Mn

Zn

0.108
0.100

–
0.003

1.72
0.71
–
–

4.59
0.71
–
–

(mg l−1)

Stream water
3.22
Standing water 4.23
7.01
7.09

4.70
1.71
2.14
1.04

153
120
22.0
10.0

32.0
6.00
–a
–

16.0
6.00
3.00
–

15.800
2.150
0.040
0.015

0.012
0.004
–
–

Standing water 7.18
7.18
6.45
10.0
10.0

0.95
2.07
1.08

50 b

32.0
124
15.0
0.1

–
–
–
0.1

4.00
3.00
3.00
0.05

0.020
0.022
0.005
0.10

–
–
–
–
0.015 0.003 0.61 –
–
0.003 0.46 –
1.00

concentrations in the water samples are shown in
Tables 4 and 5, respectively. Among the examined
elements, contamination by As and Cu in the
agricultural soils was more marked than other
elements. Therefore, the spatial distributions of their
total contents in the studied area were investigated.
They are provided in Fig. 2. Sequential extraction
procedures (vide supra) were applied in order to
identify the chemical forms of As and Cu and their
mobility. The amounts of these elements in various
soil chemical fractions are given in Figs. 3 and 4,
respectively.
3.2.1 Soils Around the Tin Mining Area
Extremely high levels of As, Cd, Cu, and Pb were
recorded in both surface and subsurface layers of the
natural forest soil. These values were roughly comparable to the previously reported values for the soils
in mining areas; Lee et al. (2001) reported elevated
levels of Cd, Cu and Pb, in the range of 0.80–2.20,
13.6–6.00 and 33.0–708 mg kg−1, respectively, for
forest soil around a Au–Ag–Pb–Zn mine area in
Korea. O’Neill (1990) showed that the surface soils
(0–5 cm) of a mineralized area in Southwest England
contained 424 mg kg−1 of As. However, the contents
of Cr, Mn, Ni, and Zn in the forest soil of the present
study were roughly within the ranges for uncontaminated soils reported by Bowen (1979). In addition,

there was no substantial difference in the contents of
As and heavy metals between the surface and
subsurface forest soil.

In the surface forest soil, the results of sequential
extraction showed that more than 80% of total As was
extracted in the Res-fraction, followed by the P- and
HCl-fractions. The amounts of Cu in the Res-, FeO-,
and OM-fractions of the surface soil accounted for 64,
17, and 16% of the total Cu content, respectively. The
residual fraction was mainly composed of primary
and secondary minerals containing metals in the
crystalline lattice (Gleyzes et al. 2002). This fraction
is considered relatively inactive, therefore, could
reflect the native metal concentration in soil (Burt et
al. 2003; Kaasalainen and Yli-Halla 2003). On the
other hand, the distribution patterns of both As and
Cu in the subsurface soil were quite similar to those
of the surface soil (Figs. 3 and 4). These results
indicated that large parts of As and Cu in the forest
soil were strongly bound by Fe oxides and clay
minerals, which suggested that the high contents of
As and Cu originated from the weathered metal ores.
In the paddy fields (P1−P3), the contents of As
and Cu exceeded the maximum allowable limit values
considerably (12 and 50 mg kg−1 for As and Cu,
respectively) provided by the “Vietnamese Soil
Quality—Maximum allowable limits of heavy metals
in the soil” for agricultural soils (TCVN 7209–2002;
Table 4). Various studies have been reported As and


84

Water Air Soil Pollut (2009) 197:75–89

Fig. 2 Distribution of As
(a) and Cu (b) in soils
close to tin and tungsten
mines (Dai Tu district, N.
Vietnam)

(mg kg-1)
1000
800
600

(a)

400
140

Surface
200
Subsurface soil

T2
T5 T4
T6
T7

0
T1

(Tungsten) P4

T3

160
120

P5

P6

100

P1
80

P2
P3
160

F
ng
Co

(Tin)

180

200

er
riv

200 m

(b)
(mg kg-1)
400

140

Surface
Subsurface soil
S

T2
T3
T5 T4
T6
120
T7

T1

160

300

(Tungsten) P4
P6

P5

200

100

P1
80

P2

100

P3
160

0
ng
Co

F
(Tin)

180

er
riv

200 m

200


Water Air Soil Pollut (2009) 197:75–89
1,20
1,200

100

1,200
1,20

100

80

1,000
1,00

80

1,000
1,00

As mg kg-1

85

800

800

60

60

600

600
40

400

20

200
Fu

Fl

Forest soil

20

200

0

0

40

400

0

0
T1u T1l T2u T2l T3u T3l

P1u P1l P2u P2l P3u P3l

Paddy soil

T4u T4l T5u T5l T6u T6l T7u T7l P4u P4l P5u P5l P6u P6l
Tea field soil

Paddy soil

Soils from the tungsten mine area

Soils from the tin mine area
Ws-

MggM

P-

HCl-

ResR
s-

Fig. 3 Fractionation of As in soils close to tin and tungsten mines (Dai Tu district, N. Vietnam). Number: sampling locations, u:
surface soil (0–5 cm), l: subsurface soil (20–25 cm)

heavy metal contamination of paddy soils associated
with mining and smelting activities. Tsutsumi (1981)
reported the high As contents (7.6–138 mg kg−1) in
the surface layer of paddy soils in the vicinity of one
Cu mine in Japan. Elevated levels of Cd, Cu, Pb and
Zn were also found in paddy soils taken from the
Daduk Au–Ag–Pb–Zn mine in Korea (Lee et al.
2001). On the other hand, Lu and Zhang (2005) have
reported that the As contamination of paddy soils
(78.5–264 mg kg−1) resulting from mining activities
in the Huayuan Pb–Zn deposits area of Western
Hunan, China was caused by polluted stream water
(0.6–12.6 mg l−1). Kitagishi and Yamane (1981) have
reviewed several studies on As and Cu behavior in
contaminated paddy soils and have shown that
accumulations of these elements were especially

400

100
80

300

Cu mg kg-1

marked in the surface layer. This held true also in
paddy soils (P1−P3) from the tin mining area in our
study. In the case of Cu, the average content in the
surface soils of the paddy fields around the tin mining
area was significantly higher than that of the tea fields
(p<0.05). Moreover, the content in the surface soil
was higher at the site located at the upper reaches of
the stream (P1>P2>P3), although such differences
among the sampling sites were not so conspicuous for
the As content (Fig. 2). In addition, the stream water
running through the tin mining area and the standing
water taken at the P1 site contained high concentrations of As and Cu (Table 5).
Based on the results of the sequential extraction, in
the surface soils of P1−P3, the highest amount of As
was found in the Res-fraction. However, about 34%

60
200
40
100

20

0

0
Fu Fl P1u P1l P2u P2l P3u P3l
Forest soil

T1u T1l T2u T2l T3u T3l T4u T4l T5u T5l T6u T6l T7u T7l P4u P4l P5u P5l P6u P6l

Paddy soil

Tea field soil
Soils from the tungsten mine area

Soils from the tin mine area
Ws-

Paddy soil

Ex-

Aci-

MnO-

OM-

FeO-

Reses-

Fig. 4 Fractionation of Cu in soils close to tin and tungsten mines (Dai Tu district, N. Vietnam). Number: sampling locations, u:
surface soil (0–5 cm), l: subsurface soil (20–25 cm)


86

and 12% of the total As was extracted in the P- and
HCl-fractions and these values were significantly
higher than those in the tea field soils around the
tungsten mining area (p<0.05). At the P2 and P3
sites, in particular, the differences in As content
between the surface and subsurface soils were found
to be almost equivalent to the increased amounts of
As in the P-fraction in the surface soils (Fig. 3). In
contrast, in the surface layers of P1−P3, the highest
amounts of soil Cu were extracted in the MnOfraction, followed by Aci-, Ex-, and FeO- fractions.
The amounts of Cu in these four fractions comprised
about 70% of the total Cu, and the percentage
distributions of Cu in these fractions were significantly higher than those in the soils around the tungsten
mining area (p<0.05). The differences in the total
contents of Cu between the surface and subsurface
soils can be plausibly explained by the increased
amounts of Cu in the Ws-, Ex-, Aci-, MnO-, OM-,
and FeO-fractions of the surface soils (Fig. 4).
Moreover, in the Ws-fraction of the surface soils,
about 0.7–1.6 mg kg−1 of As and 1.22–2.16 mg kg−1
of Cu were detected. Although these amounts
represented only small percentage components of the
total contents of As and Cu, they could be easily
taken up by plants, to cause a potential risk. It has
been reported for As spiked soil that the majority of
As was extracted in the ligand exchangeable fraction
(Lim and Goh 2005; Van et al. 2006). Besides, the
distributions of Cu in paddy soils contaminated with
the river water from the mines were investigated in

Fuchu, Japan (Iimura 1993). These authors have
shown that the Cu in the non-contaminated paddy
soil was mainly found in the residual fraction while in
the contaminated paddy soil, the accumulation of Cu
was observed in the labile fractions, that is, exchangeable, inorganically, and organically bound fractions.
Liang et al. (1991) also studied the fate of added Cu
in seven Saskatchewan soils and showed that sesquioxides and organic matter were the major components
responsible for adsorption of added Cu. Consistent
with these reports, our results suggest that the
accumulations of As and Cu in the surface soils of
these paddy fields were caused by continuous
utilization of the contaminated stream water. They
also indicated that the introduced Cu was mainly
retained by the Fe and Mn oxides during the
oxidation/reduction cycles under rice cultivation,
occluded by organic matter, or adsorbed by clay

Water Air Soil Pollut (2009) 197:75–89

minerals, while the major part of As was held by
these soil constituents as ligand-exchangeable form.
Besides As and Cu, the concentrations of Cd, Pb, Mn,
and Zn in the stream water also exceeded the values
specified by the “Vietnamese standard limitation for
surface water” (TCVN 5942-1995; Table 5). These
results suggested that these elements had been gradually accumulated in the paddy fields although the extent
was less pronounced than in the case of Cu and As, at
present.
3.2.2 Soils Around the Tungsten Mining Area
In general, the total content of As in tea fields

substantially exceeded the permissible values for
agricultural soils in Vietnam (TCVN 7209-2002;
Table 4) and the world-wide As levels for uncontaminated soils reported by Bowen (1979). However, no
significant differences in the total As content were
observed between the tea field soils and the paddy
soils due to large variation of the values in the tea
field soils. In particular, extremely high contents
(312–1,010 mg As kg−1) were detected in the soils
taken from the sites located at higher positions on the
slope (T1−T3), while the lower As level was found in
the tea fields at lower positions (T4−T7). There
appears to be a distinct tendency for the total As to be
higher in the subsurface layer than in the surface layer
of the tea fields at the higher positions (T1−T3),
whereas the reverse was true for the tea fields at the
lower position (T4−T7; Table 4, Fig. 2). In most of
the tea field soils, the total contents of Cu and Pb
were also higher than, or comparable to, the above
mentioned permissible values (70 mg Pb kg−1, TCVN
7209-2002). Similarly to the case of total As,
however, the total contents of Cu and Pb were not
significantly higher than those in the paddy soils. In
addition, except for the T1 site, where the Cu and Pb
contents in the subsurface soil were higher than those
in the surface soil, the differences in Cu and Pb levels
between surface and subsurface soils were not
remarkable compared with the case of As content.
In the surface and subsurface soils of the tea fields,
more than 90% of the total As was found in the Res-,
HCl- and P-fractions. These As chemical forms could

be assumed to be related to poorly crystalline Fe
oxides, sulfide and clay minerals (Norra et al. 2005).
Noticeably, at the sites located at lower positions on
the slope (e.g. T4, T6 and T7), the difference in total


Water Air Soil Pollut (2009) 197:75–89

As content between surface and subsurface layers
corresponded approximately to the increased amounts
of As in the Res-fraction in the surface soil (Fig. 3).
Furthermore, the percentage distribution of As in the
Res-fraction in the surface soils of the tea fields was
significantly higher than that in the paddy soils. These
observations suggested that As was added to the surface
soils by the erosion of the slope of the tungsten mining
area, especially in the fields at lower position. In
addition, a negligible amount of As, ranging from nondetected level to 1.4 mg kg−1, was extracted by water
even when the soils contained high total As. On the
other hand, regardless of the total content and the
sampling position on the slope, the major Cu fractions
in the soils of the tea fields were Res- and FeOfractions. The percentage distributions of Cu in these
two fractions comprised more than 78% of the total Cu
contents (Fig. 4) and they were significantly higher
than those in the paddy soils (p<0.05).
In the valley in which the tungsten mining area is
located, the surface soils of the paddy fields (P4, P5
and P6) showed relatively high As contents while
other elements were generally within the permissible
values (TCVN 7209-2002; Table 4). Similarly to the

Cu contents in the surface soils of the paddy fields
around the tin mining area, the As content in the
surface soil was higher at the site located in the upper
reaches of the stream (P4>P5>P6; Table 4, Fig. 2).
The results of the sequential extraction showed
that, in the surface soils of P4, P5 and P6, about 54
and 30% of the total As were extracted in the Resand P-fractions, and the percentage distribution of As
in the Res-fraction was significantly lower than that in
the tea field soils while the opposite tendency was
observed in the P-fraction (p<0.05). However, when
the distribution of As in the surface layers was
compared to the P4, P5, and P6 sites, it was observed
that the differences in the amounts of As in each
fraction including Res-fraction contributed to the
variation of the total As content (Fig. 3). On the
other hand, the standing water of these paddy fields
(P4, P5 and P6) showed relatively high As concentrations and the values exceeded the “Vietnamese
standard limitation for surface water” (TCVN 59421995; Table 5). Based on the above results, one of the
reasons for the As accumulation in P4, P5 and P6
sites could be ascribed to the utilization of the
contaminated irrigation water, in addition to the
sedimentation of transported materials from the sur-

87

rounding slope of the tungsten mining area due to soil
erosion. In the case of Cu, the major part of soil Cu
was extracted in the non-Res-fractions. Especially, in
the MnO-fraction, the percentage distribution of Cu
was significantly higher than that in the tea field soils

(p<0.05). Further, the amounts of Cu in the nonresidual fractions in the surface soils were higher than
those in the subsurface soils although it was not
statistically significant (Fig. 4). These results imply
the gradual accumulation of Cu at these sites resulting
from the irrigation water containing Cu, although the
values of total Cu were within the permissible value
(TCVN 7209-2002; Table 4).

4 Conclusions
In this study, the As and heavy metal contaminations
of agricultural soils around the tin and tungsten
mining areas in Dai Tu district, Vietnam were
determined. In spite of the relatively close proximity
of these different mines, different pathways of As and
Cu contaminations into farmlands from the mining
areas were indicated. In the paddy fields around the
tin mining area, the main pathway of the As and Cu
contaminations were through the irrigation by the
stream water. On the other hand, in the tea fields
located at lower positions of the slope in the tungsten
mining area, the As accumulation in the surface soils
could be ascribed to the materials transported from
the slope due to erosion. Although the large part of
the accumulated As and Cu were bound by various
soil constituents such as Fe and Mn oxides, organic
matter, and clay minerals, increases in water soluble
As and Cu were also observed, especially for the
paddy fields, which would pose direct risks to the
staple crops and consequently to human health. In
the studied area, large-scale exploitations of ore

deposits by advanced countries have been in progress,
while farmers living in the vicinity of the mine still
continue to use the traditional mining operations.
Regardless of the scale of mining, it is essential to take
measures against the incorporation of toxic elements
into the agricultural soils around the mining areas in this
district. Furthermore, monitoring of the changes in
chemical forms of the contaminants in the agricultural
soils as well as their concentrations in the crops should
be carried out regularly.


88
Acknowledgements The authors would like to thank the
Hung Son commune officers for their valuable help and support
during sample collection. This research was financially supported by a Grant-in-Aid for Scientific Research (grant no.
15380223 and 18380195) from the Japan Society for the
Promotion of Science to KI.

References
Adriano, D. C. (2001). Chapter 1 Introduction. In D. C.
Adriano (Ed.), Trace elements in terrestrial environment:
biogeochemistry, bioavailability, and risks of metals (pp.
22–23). New York: Springer-Verlag.
Anawar, H. M., Garcia-Sanchez, A., & Santa Regina, I. (2008).
Evaluation of various chemical extraction methods to
estimate plant-available arsenic in mine soils. Chemosphere,
70, 1459–1467. doi:10.1016/j.chemosphere.2007.08.058.
Bowen, H. J. M. (1979). Chapter 13 Elements in the geosphere and
the biosphere. In H. J. M. Bowen (Ed.), Environmental

chemistry of the elements (pp. 237–273). London: Academic.
Burt, R., Wilson, M. A., Keck, T. J., Dougherty, B. D., Strom,
D. E., & Lindahl, J. A. (2003). Trace element speciation in
selected smelter-contaminated soils in Anaconda and Deer
Lodge Valley, Montana, USA. Advances in Environmental
Research, 8, 51–67. doi:10.1016/S1093-0191(02)00140-5.
Chen, Z., He, M., Sakurai, K., Kang, Y., & Iwasaki, K. (2007).
Concentrations and chemical forms of heavy metals in urban
soils of Shanghai, China. Soil Science and Plant Nutrition,
53, 517–529. doi:10.1111/j.1747-0765.2007.00173.x.
Chopin, E. I. B., & Alloway, B. J. (2007). Distribution and
Mobility of Trace Elements in Soils and Vegetation
Around the Mining and Smelting Areas of Tharsis,
Ríotinto and Huelva, Iberian Pyrite Belt, SW Spain. Water,
Air, and Soil Pollution, 182, 245–261. doi:10.1007/
s11270-007-9336-x.
Gee, G. W., & Bauder, J. W. (1986). Particle-size analysis. In
A. Klute (Ed.), Methods of soil analysis: Part 1 —
physical and mineralogical methods (pp. 383–411, 2nd
ed.). Madison: American Society of Agronomy, Soil
Science Society of America.
Gleyzes, C., Tellier, S., & Astruc, M. (2002). Fractionation
studies of trace elements in contaminated soils and
sediments: a review of sequential extraction procedures.
Trends in Analytical Chemistry, 21, 451–467. doi:10.1016/
S0165-9936(02)00603-9.
Iimura, K. (1993). Chemical forms and behavior of heavy metals
in the soil. Soil Physical Conditions and Plant Growth. Jpn,
67, 19–27 in Japanese with English summary.
Iwasaki, K., Tsuji, M., & Sakurai, K. (1997). Fractionation of

copper and manganese in agricultural soils near an
abandoned copper mine. Soil Science and Plant Nutrition,
43, 157–169.
Jung, M. C. (2001). Heavy metal contamination of soils and
waters in and around the Imcheon Au–Ag mine, Korea.
Applied Geochemistry, 16, 1369–1375. doi:10.1016/
S0883-2927(01)00040-3.

Water Air Soil Pollut (2009) 197:75–89
Jung, M. C., Thornton, I., & Chon, H.-T. (2002). Arsenic, Sb
and Bi contamination of soils, plants, waters and sediments in the vicinity of the Dalsung Cu–W mine in Korea.
The Science of the Total Environment, 295, 81–89.
doi:10.1016/S0048-9697(02)00042-6.
Kaasalainen, M., & Yli-Halla, M. (2003). Use of sequential
extraction to assess metal partitioning in soils. Environmental Pollution, 126, 225–233. doi:10.1016/S0269-7491
(03)00191-X.
Kabata-Pendias, A., & Pendias, H. (1992). Chapter 5 Trace
elements in plants. In A. Kabata-Pendias, & H. Pendias
(Eds.), Trace elements in soils and plants (pp. 67–87).
Boca Raton: CRC Press.
Keon, N. E., Swartz, C. H., Brabander, D. J., Harvey, C., &
Hemond, H. F. (2001). Validation of an Arsenic sequential
extraction method for evaluating mobility in sediments.
Environmental Science & Technology, 35, 2778–2784.
doi:10.1021/es001511o.
Kitagishi, K., & Yamane, I. (1981). Heavy metal pollution in
soils of Japan. Tokyo: Japan Scientific Societies Press.
Lee, C. G., Chon, H.-T., & Jung, M. C. (2001). Heavy metal
contamination in the vicinity of the Daduk Au–Ag–Pb–Zn
mine in Korea. Applied Geochemistry, 16, 1377–1386.

doi:10.1016/S0883-2927(01)00038-5.
Lee, S. (2006). Geochemistry and partitioning of trace metals in
paddy soils affected by metal mine tailings in Korea. Geoderma, 135, 26–37. doi:10.1016/j.geoderma.2005.11.004.
Liang, J., Stewart, J. W. B., & Karamanos, R. E. (1991).
Distribution and plant availability of soil copper fractions
in Saskatchewan. Canadian Journal of Soil Science, 71,
89–99.
Lim, T. T., & Goh, K. H. (2005). Arsenic fractionation in a fine
soil fraction and influence of various anions on its mobility in
the subsurface environment. Applied Geochemistry, 20,
229–239. doi:10.1016/j.apgeochem.2004.08.004.
Lu, X., & Zhang, X. (2005). Environmental geochemistry study
of arsenic in Western Hunan mining area, P.R. China.
Environmental Geochemistry and Health, 27, 313–320.
doi:10.1007/s10653-004-5735-8.
McGowen, S. L., & Basta, N. T. (2001). Chapter 4 Heavy metal
solubility and transport in soil contaminated by mining and
smelting. In H. M. Selim, & D. L. Sparks (Eds.), Heavy
metals release in soils (pp. 89–107). Boca Raton: Lewis.
Merrington, G., & Alloway, B. J. (1994). The transfer and fate
of Cd, Cu, Pb and Zn from two historic metalliferous mine
sites in the UK. Applied Geochemistry, 9, 67–77.
doi:10.1016/0883-2927(94)90027-2.
Nelson, D. W., & Sommers, L. E. (1982). Total carbon, organic
carbon, and organic matter. In A. L. Pace, R. H. Miller, &
D. R. Keeney (Eds.), Methods of soil analysis: Part 2—
Chemical and Microbiological Properties (pp. 539–579,
2nd ed.). Madison: American Society of Agronomy, Soil
Science Society of America.
Norra, S., Berner, Z. A., Agarwala, P., Wagner, F., Chandrasekharam, D., & Stuben, D. (2005). Impact of irrigation with

As rich groundwater on soils and crops: A geochemical
case study in West Bengal Delta Plain, India. Applied


Water Air Soil Pollut (2009) 197:75–89
Geochemistry, 20, 1890–1906. doi:10.1016/j.apgeochem.
2005.04.019.
O’Neill, P. (1990). Chapter 5 Arsenic. In B. J. Alloway
(Ed.), Heavy metals in soils (pp. 83–99). New York:
Wiley.
Razo, I., Carrizales, L., Castro, J., Díaz-Barriga, F., & Monroy,
M. (2004). Arsenic and heavy metal pollution of soil,
water and sediemnts in a semi-arid climate mining area in
Mexico. Water, Air, and Soil Pollution, 152, 129–152.
doi:10.1023/B:WATE.0000015350.14520.c1.
Rhoades, J. D. (1982). Cation exchange capacity. In A. L. Pace,
R. H. Miller, & D. R. Keeney (Eds.), Methods of soil
analysis: Part 2—chemical and microbiological properties
(pp. 149–165, 2nd ed.). Madison: American Society of
Agronomy, Soil Science Society of America.

89
Soil Survey Staff (2006). Keys to soil taxonomy. Philadelphia,
PA: The 18th World Congress of Soil Science.
Thai Nguyen Department of Planning and Investment (2005).
Brief information on Thai Nguyen Province. http://
thainguyen.gov.vn/eg/index.asp?c=6&KT=2. Accessed 28
February 2008.
Tsutsumi, H. (1981). Arsenic pollution in arable land. In K.
Kitagishi, & I. Yamane (Eds.), Heavy metal pollution in

soils of Japan (pp. 181–192). Tokyo: Japan Scientific
Societies Press.
Van, T. K., Kang, Y., Fukui, T., Sakurai, K., Iwasaki, K.,
Aikawa, Y., & Phuong, N. M. (2006). Arsenic and heavy
metal accumulation by Athyrium yokoscense from contaminated soils. Soil Science and Plant Nutrition, 52, 701–
710. doi:10.1111/j.1747-0765.2006.00090.x.