Spatial Distribution of Potentially Toxic Trace Elements in Soils

Downstream of a Lead–Zinc Mine in Southern China

Pengwei Qiao

, Sucai Yang

, Nan Dong

, Mei Lei

and Yanjun Cheng

Beijing key Laboratory of Remediation of industrial Pollution Sites, Environmental Protection Research Institute of Light

Industry, Beijing 100089, China.

Comprehensive Institute of Geotechnical Investigation and Surveying, Ltd., Beijing 100007, China.

Institute of Geographic Sciences and Natural Resources Research, Chinese, Beijing 100101, China.

Keywords: Soil contamination, Potentially toxic trace elements (PTEs), Risk evaluation, Spatial variability

Abstract: Spatial distribution of potentially toxic trace elements (PTEs) concentrations in soils is essential for pollution

and risk evaluation. In this study, 33 samples were collected downstream of a lead–zinc mine in Southern

China. Contamination factors (CFs) of As, Pb, Zn, Cu, Cr, and Ni were all near 1 (low contamination), while

12% of the sample sites showed high contamination of Cd (CF>6). The highest concentration of Cd was about

40× natural background value of study area. Variogram analysis allowed detecting the principal direction of

variation. High soil pH value and rocks could prevent PTEs vertical migrating in the mountain. The spatial

distribution of Zn and Cu may be resulted from lateral transportation with soil erosion.

1 INTRODUCTION

Potentially toxic trace elements (PTEs) in soils have

negative effects on environment and food quality

(Song et al., 2009; Liu et al., 2015), and may threaten

human health (Chen et al., 2005; Salehipour et al.,

2015; Praveena et al., 2015). Spatial distribution of

PTEs is important for evaluation of contamination

level.

There are many occurrence elements in Pb-Zn

mine, such as Cd (Hosseini-Dinani et al., 2015; Ye et

al., 2016). These elements have potential hazards for

environment. Therefore, assessment contamination

level of PTEs in Pb-Zn mine is necessary.

In addition, the study area is located in the

downstream of Pb-Zn mine in southern China, which

is near residence community. Therefore, assessment

contamination level in this region is important.

However, the exist researches mainly been conducted

in upstream regions that are heavily polluted (Zhang

et al., 2013), while few studies about downstream

areas have been conducted.

The objectives of this paper were to: (1) assess

contamination degree of PTEs, (2) analyse spatial

distribution of PETs downstream a Pb-Zn mine.

2 MATERIALS AND METHODS

2.1 Study Area

The study area lies in Huanjiang County in southern

China. Study area is located downstream of a lead–

zinc mine with an area about 300 km2, where was

polluted by a tailing dam break in 2001. This region

was contaminated by PTEs, such as As, Pb, Cd, Cu,

Cr, Ni, Zn. Mountains with calcareous soil are located

in the east of the study area, while the west is

relatively flat with red soil. The land use types include

farmland, forests, orchards and grasslands. Forests

are mainly distributed in the eastern mountains

(Figure 1). After the tailing dam broke, the flood level

reached about 123 m above the Huanjiang River

surface, while low-lying areas in the west were

submerged.

260

Qiao, P., Yang, S., Dong, N., Lei, M. and Cheng, Y.

Spatial Distribution of Potentially Toxic Trace Elements in Soils Downstream of a Lead–Zinc Mine in Southern China.

DOI: 10.5220/0008188502600263

In The Second International Conference on Materials Chemistry and Environmental Protection (MEEP 2018), pages 260-263

ISBN: 978-989-758-360-5

Figure 1: Soil sample locations.

2.2 Sampling and Chemical Analysis

Approximately 33 topsoil samples (0–20 cm) were

collected from the study area (Figure 1). Of these, 11

samples were from forest areas with calcareous soil,

while 19 samples were from orchard areas with red

soil, and 3 samples were from orchard areas, where

were underlain by paddy soil.

Soil samples were air-dried and ground to be able

to pass through a 100-mesh sieve. And then they were

digested with HNO3 and H2O2, and added HCl

adapting to the follow-up instrument according to

USEPA (United States Environmental Protection

Agency) Method 3050B (1996). The concentrations

of As were determined by atomic fluorescence

spectroscopy (HG-AFS, AFS-9800, Haiguang

Instrumental CO., China), whereas Pb, Cd, Cu, Zn,

Ni, and Cr were determined by inductively coupled

plasma optical emission spectrometry (ICP-OES,

Optima 5300DV, PerkinElmer, USA). Samples of

certified standard reference materials for soil (GSS-

2) were obtained from the Chinese National Standard

Material Centre, which was used for quality control.

Soil pH values were determined in solution using a

portable pH meter (Orion Model 868 pH).

2.3 Data Processing Methods

Theoretical variogram models were fitted by GS+

(version 9). Spatial distribution maps of PETs were

produced by ArcMap (version 9.3) and ArcScene

(version 9.3). Contamination level graphic of PTEs

was produced by Origin (version 8).

In addition, the contamination level of PTEs is

expressed in terms of contamination factor (CF),

which is the common evaluation method in many

existing literatures (Hakanson, 1980; Liu et al., 2005).

The assessment results of CF are trustworthy. The

greater the CF value, the more serious pollution of

PTEs in soils.

CF=C

Sample/ C

Standard (1)

CmSample is the PTEs concentration (mg/kg) of

sample, and CmStandard is the Environmental Class

2 Standard (mg/kg). CF<1 refers to low

contamination; 1≤CF<3 indicates moderate

contamination; 3≤CF≤6 indicates considerable

contamination; and CF>6 indicates very high

contamination (Mmolawa et al., 2011).

3 RESULTS AND DISCUSSION

3.1 Degree of PTEs Contamination in

Soils

The concentrations of Cd ranged from 0.28 mg/kg to

3.22 mg/kg, with a geometric mean of 0.80 mg/kg.

CVs of all PTEs were all less than 13%, indicating

weak variability. For all samples, the exceeding

standard rate of As, Pb, Cd, Zn and Ni was 3%, 45%,

97%, 15% and 24% respectively. The standard value

refer to Class 2, environmental quality standard for

soils (GB15618-1995), which is a national standard

of People's Republic of China.

Table 1: Standard concentration (mg/kg) of PTEs.

Metals

Class 2

300

0.3

200

100

250

Natural

background

15.7

18.9

0.08

67.5

17.3

42.6

9.81

Based on CF, only Cd reached high contamination

level, 12% of sample sites showing very high

contamination, 24% with considerable contamination

and 60% with moderate contamination. Low

contamination levels of As, Pb, Zn, Cr, Cu and Ni

were observed (Figure 2). This reflected that, Cd was

the most important contaminant downstream of a Pb–

Zn mining facility. These results were accordance

with previous study (Wang et al., 2009). This

phenomenon could be interpreted that, Cd was the

occurrence trace element and was enriched

surrounding Pb-Zn mine (Ye et al., 2016).

Spatial Distribution of Potentially Toxic Trace Elements in Soils Downstream of a Lead–Zinc Mine in Southern China

261

Figure 2: Contamination factors of As, Cd, Ni, Pb and Zn

concentration for the 33 sites studied.

According to the natural background value of

Huanjiang County (Ban and Ding, 1991) (Table 1),

all the PTEs had accumulated in topsoils. These PTEs

may result from the tailing dam broke, but also may

result from irrigation with the water from Huanjiang

River. Concentrations of PTEs in the branches of

Huanjiang river were as follows: As (0.015 mg/L), Cd

(0.002 mg/L), Cr (0.058 mg/L), Cu (0.024 mg/L), Ni

(0.037 mg/L), Pb (0.040 mg/L), Zn (0.606 mg/L).

These values were all near the standard for domestic

drinking water quality (GB5749-85). But use of water

containing PTEs at this levels could result in their

accumulation in soils.

3.2 Spatial Distribution of PTEs

Spatial distribution characteristic was expressed by

variogram models fitted by GS+ software. The best-

fit theoretical models were selected based on the

highest decision coefficient value (r2), while the ratio

of nugget to sill (RNS) reflected the degree of spatial

dependence. Principal direction was the spatial

distribution trend of PTEs (Table 2).

Table 2: Theoretical variogram models and their fitting

effect for PTEs.

Metals

Model

RNS

Principal

Direction

Gaussian

0.05

0.96

E-W

Gaussian

2.95

0.82

E-W

Exponential

24.0

0.97

E-W

Spherical

21.3

0.91

E-W

Exponential

6.12

0.90

E-W

Gaussian

0.50

0.98

NW-SE

Gaussian

25.7

0.85

E-W

Semivariances of Cd and Cu were best fit with

exponential model, while As, Pb, Ni, and Zn were

best fit with Gaussian model and Cr with Spherical

model. RNS for Ni was between 25% and 75%,

reflecting moderate spatial dependence, while for As,

Pb, Cd, Cr, Cu and Zn were all less than 25%,

showing strong spatial dependence. The principal

direction of variation of Zn was NW–SE, while that

of the other PTEs were E–W. The principal direction

of pH value was E–W, with high pH value on the west

(Figure 3).

The regions with higher concentrations of As, Pb,

Cd, Cr, Ni were mainly in higher terrain area, where

with calcareous soil, and higher pH value. These

areas were not flooded (Figure 3). This might because

that, higher pH value decreased the vertical migration

ability of PTEs, while rocks on the mountain also

could prevent the transportation of PTEs.

Additionally, lower pH value in relatively flat regions

in the west likely increased PTEs bioavailability,

enabling plants to absorb the PTEs, reducing

concentrations of PTEs in soils. Furthermore,

calcareous soil on the mountain has a high

background value. this phenomenon was accordance

with the conclusion of (Ban and Ding, 1991) and

(Wang et al., 2005), the difference between

concentrations of PTEs in soil parents is significant.

Higher concentrations of Zn were observed in the

north and northwest, that was parallel to the direction

of the Huanjiang River flow. Overall, concentrations

of PTEs were relatively high in the downstream

region, which could be explained by lateral migration

and accumulation downstream (Qiao et al., 2014).

Figure 3: Spatial distribution of seven PTEs.

MEEP 2018 - The Second International Conference on Materials Chemistry and Environmental Protection

262

4 CONCLUSIONS

Overall, low contamination levels of As, Cu, Cr, Zn,

Ni were observed in the study area, while Pb and Cd

were present at considerable contamination levels.

However, based on natural background values of

study area, all PTEs had an accumulation trend in

soils. Spatial anisotropy of the seven PTEs was

significant, with the principal direction of variation of

As, Pb, Cd, Cr, and Ni being E–W and that of Zn and

Cu being NW–SE. Spatial anisotropy of As, Pb, Cd,

Cr and Ni were in accordance with the spatial

distribution of soil type and pH value. Higher pH

values and rocks on the mountain could prevent

vertical migration of PTEs. Lower pH value in the flat

regions could increase transportation of PTEs. Spatial

distribution of Zn and Cu may result from lateral

transportation by soil erosion.

ACKNOWLEDGEMENTS

This work was supported by Beijing Postdoctoral

Research Foundation, and the postdoctoral program

set up by Beijing Key Laboratory of Remediation of

Industrial Pollution Sites, Environmental Protection

Research Institute of Light Industry, Beijing, China,

Uncertainty Analysis and Cause Analysis of Spatial

Distribution of Soil Pollution.

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