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Journal of Geographical Sciences >

2015 , Vol. 25 >Issue 12: 1439 - 1451

DOI: https://doi.org/10.1007/s11442-015-1244-1

Research Articles

Contamination and health risk assessment of heavy metals in road dust in Bayan Obo Mining Region in Inner Mongolia, North China

  • LI Kexin ,
  • LIANG Tao , * ,
  • YANG Zhiping , * ,
  • YANG Zhiping
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  • Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
*Corresponding author: Liang Tao, Professor, E-mail: ; Wang Lingqing, E-mail:

Received date: 2015-03-04

  Accepted date: 2015-05-10

  Online published: 2015-12-31

Supported by

National Natural Scientific Foundation of China, No.41571473, No.41401591

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

The objective of this study was to investigate the concentration and spatial distribution patterns of 9 potentially toxic heavy metal elements (As, Cd, Co, Cr, Pb, Cu, Zn, Mn, and Ni) in road dust in the Bayan Obo Mining Region in Inner Mongolia, China. Contamination levels were evaluated using the geoaccumulation index and the enrichment factor. Human health risks for each heavy metal element were assessed using a human exposure model. Results showed that the dust contained significantly elevated heavy metal elements concentrations compared with the background soil. The spatial distribution pattern of all tested metals except for As coincided with the locations of industrial areas while the spatial distribution of As was associated with domestic sources. The contamination evaluation indicated that Cd, Pb, and Mn in road dust mainly originated from anthropogenic sources with a rating of “heavily polluted” to “extremely polluted,” whereas the remaining metals originated from both natural and anthropogenic sources with a level of “moderately polluted”. The non-cancer health risk assessment showed that ingestion was the primary exposure route for all metals in the road dust and that Mn, Cr, Pb, and As were the main contributors to non-cancer risks in both children and adults. Higher HI values were calculated for children (HI=1.89), indicating that children will likely experience higher health risks compared with adults (HI=0.23). The cancer risk assessment showed that Cr was the main contributor, with cancer risks which were 2-3 orders of magnitude higher than those for other metals. Taken in concert, the non-cancer risks posed by all studied heavy metal elements and the cancer risks posed by As, Co, Cr, Cd, and Ni to both children and adults in Bayan Obo Mining Region fell within the acceptable range.

Key words： road dust; heavy metal elements; contamination assessment; health risk assessment; Bayan Obo Mining Region

Cite this article

LI Kexin , LIANG Tao , YANG Zhiping , YANG Zhiping . Contamination and health risk assessment of heavy metals in road dust in Bayan Obo Mining Region in Inner Mongolia, North China[J]. Journal of Geographical Sciences, 2015 , 25(12) : 1439 -1451 . DOI: 10.1007/s11442-015-1244-1

1 Introduction

Road dust is comprised of solid particles which accumulate on impervious, hard road surfaces, such as cement and sidewalks in urban areas (Liu et al., 2014). Road dust plays an active role as a “sink and source” of pollutants due to enhanced levels of metals and other pollutants and frequent interactions of dust with the atmosphere and other mediums through resuspension and deposition of dust particles (Moreno et al., 2013). Therefore, road dust can contribute significantly to environmental pollution in urban areas and is considered an indicator of heavy metal contamination from atmospheric deposition (Zheng et al., 2010a). Moreover, heavy metal elements in road dust are known to easily enter the human body through ingestion, inhalation, and dermal contact (Cook et al., 2005). The adverse effects on human health from exposure to heavy metal elements have been well-documented (Valko et al., 2006; Zheng et al., 2006; Sun et al., 2010), necessitating a thorough determination of the health risks of road dust containing to local residents (Shi et al., 2008).
Several prior studies have evaluated the concentration, distribution, pollution potential, and health risks of heavy metals in road dust (Zheng et al., 2010a; Apeagyei et al., 2011). However, most previous research focused on road dust in capital cities or mega-cities which were characterized by dense traffic and overpopulation. Small regions affected mainly by mining activities have received relatively limited attention. Mining activities are notorious for their adverse impacts on the environment (Wang et al., 2008). Large quantities of dust laden with high levels of heavy metals can be released into the air and deposited as road dust as a result of mining operations including crushing, grinding, excavating, smelting, and refining (Csavina et al., 2012). Thus, in comparison with mega-cities or capital cities, the environmental and human health risks associated with road dust metals in mining regions requires further investigation.
Bayan Obo is a mining town in western Inner Mongolia. Mining activities were in operation for 80 years before the discovery of iron minerals in 1927 and rare earth elements (REE) minerals in 1936. Larger-scale mining has led to soil pollution with heavy metals in Bayan Obo (Guo et al., 2011; Si et al., 2015). However, the contamination characteristics of heavy metals in road dust in Bayan Obo, as well as the association between dust-borne metallic elements and their adverse human health impacts, are not well understood.
In an effort to supplement previous research and obtain more information regarding road dust pollution in Bayan Obo, the objectives of this study were to 1) investigate the mass concentration of heavy metal components of road dust collected in Bayan Obo and analyze their spatial variation; 2) evaluate the contamination levels of these metals using the geo-accumulation index (Igeo) and enrichment factor (EF); and 3) develop a quantitative estimation of the non-carcinogenic and carcinogenic risks of heavy metals in road dust to local residents.

2 Materials and methods

2.1 Site description

Bayan Obo Mining Region (hereafter Bayan Obo for short) (41°46′58″N, 109°58′25″E) is considered the largest known (REE)-Fe-Nb deposit. Located in the west of Inner Mongolia, Bayan Obo contains large reserves on iron, niobium, and REE. Containing 1.4 billion tons of iron, 1 million tons of Nb2O5, and more than 40 million tons of REE minerals (70% of global REE storage) (Wu, 2008), Bayan Obo contributes 45% of worldwide REE production (Drew et al., 1990). The main minerals present are bastnasite, monazite, and RE-Nb minerals such as aeschynite, felgusonite, and columbite. The mining region is comprised of 3 ore zones: the Main Orebody, the East Orebody, and the West Orebody. The region is 48 km2 in area, 18 km in length from east to west, and 3 km in width from north to south. The Main Orebody and the East Orebody contain 5.41% and 5.18% rare earth oxides (REOs), respectively, while the West Orebody is still in the exploitation process. Iron and REE minerals are currently extracted at a rate of 15,000 tons per day from the Main and East Orebodies. The raw minerals are transported through railways to Baotou city for reprocessing, while the 8 tons of tailing products produced each year are disposed of freely in open pits (Wang et al., 2014).
Bayan Obo is characterized by a cold semi-arid climate with a mean annual temperature of 7.2°C. Prevailing winds are southeast towards the residential area with an average wind speed of 1.2 m·sec-1. Nearly 30,000 people live in the residential area located in the south of the ore body, most of them work for the mining industry. The dry climate and strong winds allow for extensive dispersal of the dust in mining sites, especially in the downwind direction towards the residential areas. The vast grasslands in the areas cannot effectively block dust dispersion due to intense winds.

2.2 Sample collection

A total of 23 points distributed in the main residential area were selected as road dust sampling sites in Bayan Obo Mining Region (Figure 1), including sites near the mine. There are no commercial activities in the Bayan Obo region. At each sampling site, approximately 200g of composite road dust from 3-5 sub-sampling sites were collected in April 2014 from impervious surfaces (road, pavement and gutter) using a clean polyethylene brush and tray. The exact location of each sampling site was measured by global positioning system (GPS). All road dust samples were stored in self-sealed polyethylene bags, labeled, and transported to the laboratory for analysis.
Figure 1 Map of the study area and sampling sites in Bayan Obo Mining Region (April 2014)

2.3 Sample processing

All samples were air-dried naturally for approximately 15 days, sieved through a 2.0 mm mesh nylon sieve to remove small stones and debris, and then carefully resieved through a 0.1 mm sieve. Prior to determination of heavy metals concentrations, sieved dust samples were ground and then a 0.5g milled dust sample was digested in a mixture of HNO3, HClO4 and HF solution by heating to obtain ca. 0.5 ml of colorless solution. After cooling, the solution was transferred to a test tube and then diluted to 25 mL with deionized water. Concentrations of Cr, Cu, Zn, Pb, and Ni were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES, Optima 5300 DV, Perkin Elmer) and concentrations of Cd and Co were analyzed by inductively coupled plasma mass spectrometry (ICP-MS, ELAN DRC-e, Perkin Elmer SCIEX). Each measurement was conducted in duplicate. National reference samples, replicates, and blanks were used to ensure accuracy of the results. The relative errors of all measurements were less than 5% on average. To prevent potential contamination of the samples, all chemical treatments were performed in an ultra-clean laboratory, and all reagents were at high purity grade.

2.4 Contamination assessment methodology

2.4.1 Geoaccumulation index
The geoaccumulation index (Igeo) developed by Müller (1969) was previously adopted to assess metal pollution (Wei et al., 2009; Lu et al., 2009; Fu et al., 2012). In this study, Igeo was used to identify whether the road dust in Bayan Obo were polluted by heavy metals and quantify the degree of the contamination. Igeo was calculated by:
Igeo = log2 (Cn/1.5Bn) (1)
Table 1 The classification of contamination levels based on the Igeo values
Igeo value Class
Igeo ≤0 Unpolluted
0 < Igeo≤1 Unpolluted/Moderately polluted
1 < Igeo≤2 Moderately polluted
2 < Igeo≤3 Moderately polluted/Strongly polluted
3 < Igeo≤4 Strongly polluted
4 < Igeo≤5 Strongly polluted/Extremely polluted
Igeo > 5 Extremely polluted
where Cn is the concentration of the metal in the road dust, Bn is the background level of metals in soils of Inner Mongolia (Gao et al., 2007; Xu and Tao, 2004), and the factor 1.5 is a constant value to account for possible variations in background values (Wei et al., 2009). Based on Igeo values, the sites were categorized into seven classes (Table 1) (Müller, 1969).
2.4.2 Enrichment factor
Enrichment factor (EF) has been widely used to differentiate anthropogenic and natural sources of trace elements in soils (Lu et al., 2009). EF is defined as:
where Cn and R are concentrations of the metal and reference element, respectively, in the road dust or the background soil. In this study, Al was selected as the reference material. A value of EF close to 1 indicates a crustal origin, whereas those EF values >10 indicates a non-crustal source (Wang et al., 2014).

2.5 Health risk assessment model

2.5.1 Exposed dose
In this study, the risk assessment model developed by the Environmental Protection Agency of the United States (US EPA) was used to evaluate the health risks posed by heavy metals in road dust. Local residents were divided into adults and children and the following exposure categories were used: (1) adults and children through mouth and nose; 2) ingestion of dust particles through mouth; and 3) dermal contact with dust through exposed skin. According to the human health evaluation manual (Part A) and supplemental guidance for dermal risk assessment (Part E) (EPA, 1989; 2004), the daily intake dose (D) of a pollutant through each pathway can be evaluated:
According to the classification list developed by the International Agency for Research on Cancer (IARC), four carcinogenic metals (As, Cd, Cr and Ni), and one possible carcinogen Co (Group 2B) were investigated for their carcinogenic risks (IARC, 2014). The life time average daily dose for these five metals was calculated by:
where C is the upper limit of the 95% confidence interval for the mean (95% UCL), which is considered as a conservative estimate of the “reasonable maximum exposure” (EPA, 1992). Since the concentrations of most metals in the road dust samples followed an approximate log-normal distribution, the 95% UCL in this study was calculated using previously described methods (Zheng et al., 2010a; Zheng et al., 2010b). The other exposure factors for these models are shown in Table 2.
2.5.2 Risk characterization
For non-carcinogenic risks, Hazard quotient (HQ) was used to assess the non-carcinogenic risks posed by metals in road dust.
HQ=D/RfD (7)
where RfD is the corresponding reference dose. An HQ<1 indicates no adverse health effects, while HQ>1 indicates that adverse health effects are likely to occur.
The hazard index (HI) is equal to the sum of HQs and is used to represent the total potential non-carcinogenic risks of different pollutants via three exposure routes described previously. An HI<1 indicates that there is no significant risk of non-carcinogenic effects. If HI>1, then a noncarcinogenic effect is likely to exist (EPA, 1989).
In the case of carcinogenic risks, the life time cancer risk can be estimated by:
R=LADD/SF (8)
where SF is the corresponding slope factor. Any cancer risk in the range of 10-6-10-4 is considered acceptable by the US EPA (1989). The RfD and SF values of all investigated metals (Ferreira-Baptista and De Miguel, 2005; Zheng et al., 2010) are presented in Tables 7 and 8.
Table 2 Exposure factors
Factor Definition Value Unit Reference
Adults Children
BW Average body weight 70 15 kg EPA, 1989
IngR Ingestion rate 100 200 mg·day-1 EPA, 1989
InhR Inhalation rate 20 7.6 m3·day-1 Zheng et al., 2010a
PEF Particle emission factor 1.36×109 m3·kg-1 EPA, 2001
SA Surface areas of the skin that contacts the airborne particulates 5700 2800 cm-2 EPA, 2004
SL Skin adherence factor 0.07 0.2 mg·m-3
EF Exposure frequency 180 180 days·year-1 Zheng et al., 2010a
ED Exposure duration 24 6 years EPA,2001
ET Exposure time 24 hours·day-1
AT (non-cancer risk) Averaging time ED×365 days
AT (cancer risk) Averaging time 70×365 days
ABS Dermal absorption factor 0.03 for As,
0.001 for other metals		 - EPA,2004
CF Conversion factor 1×10-6 kg·mg-1
Table 3 The concentrations of heavy metals in road dust collected in Bayan Obo (April 2014, mg·kg-1)
Concentration Maximum Minimum Mean Geometric mean Median S.D. Inner Mongolia B.
Cd 4.63 1.21 2.20 2.05 1.83 0.90 0.037
Co 41.27 20.65 26.94 26.62 25.74 4.49 9.0
Cr 260.80 85.09 141.24 136.76 139.60 38.46 35.7
Cu 51.09 20.49 36.39 35.75 36.36 6.79 12.7
Pb 526.70 88.04 183.93 167.51 160.50 95.41 13.5
Zn 729.00 192.00 299.37 283.92 261.80 117.51 47.5
As 19.46 8.01 12.02 11.78 11.49 2.57 6.1
Ni 49.82 24.96 31.25 30.85 29.41 5.52 16.6
Mn 7956.00 1575.00 3407.30 3206.43 3172.00 1349.94 434.3

3 Results

3.1 Heavy metals contents in road dust

The descriptive statistics related to heavy metal content of dust in the Bayan Obo region are listed in Table 3. The background values of the metals in soils of Inner Mongolia are also shown in Table 3. The concentrations of 9 metals varied widely in this region and followed the order of Mn>Zn>>Pb>Cr>Cu>Ni>Co>As>Cd. All road dust showed contained elevated concentrations of heavy metals in comparison with those of Inner Mongolia background average concentrations (Xu and Tao, 2004; Gao et al., 2007). This was particularly true for Cd, which exceeded the background value 60-fold.
The mean heavy metal content was compared to the data collected from other cities or regions reported in previous studies (Table 4). These results indicated that the road dust in residential areas of Bayan Obo contains considerably higher concentrations of Cd, Co, and Mn, and lower levels of in Cu, Zn and Ni compared with other cities, except for Ni in Hangzhou (Zhang and Wang, 2009). The concentration of Cr was close to that measured in Shanghai (Shi et al., 2008), Nanjing (Liu et al., 2014), and Baoji (Lu et al., 2009), where urban environments were heavily affected by human activities. Additionally, the Pb content in Bayan Obo, which exceeded that measured in Urumqi (Wei et al., 2009) and Nanjing (Liu et al., 2014), was still detected at a relatively low level compared with other industrial and developed cities.
Table 4 The average concentrations of heavy metals in road dust in different areas (mg·kg-1)
Concentration Cd Co Cr Cu Pb Zn As Ni Mn Reference
Bayan Obo 2.20 26.94 141.24 36.39 183.93 299.37 12.02 31.25 3407.30 This study
Hangzhou 1.59 19.96 51.29 116.04 202.16 321.40 25.88 509.56 Zhang and Wang, 2009
Urumqi 1.17 10.97 54.28 94.54 53.53 294.47 43.28 926.60 Wei et al., 2009
Shanghai 1.23 159.30 196.80 294.90 733.80 83.98 Shi et al., 2008
Baoji 15.90 126.70 123.17 433.20 715.30 19.80 48.80 804.20 Lu et al., 2009
Nanjing 139.0 238.0 113.0 307.0 47.0 786.0 Liu et al., 2014
Inner Mongolia B. 0.037 9.0 35.7 12.7 13.5 47.5 6.1 16.6 434.3 Xu et al., 2004
Gao et al., 2007
China B. 0.07 11.2 53.9 20.0 23.6 67.7 11.2 23.4 482.0 Xu et al., 2004

3.2 Spatial distributions of heavy metals in road dust

The spatial distribution pattern of 9 potentially toxic metals (As, Cd, Co, Cr, Pb, Cu, Zn, Mn and Ni) in road dust in Bayan Obo is presented in Figure 2. Cd, Cr, Co, Pb, Cu, Mn, Ni, and Zn show spatial distribution patterns which coincide with the locations of industrial areas. The concentrations of those eight metals were higher near tailing ponds and ore bodies in the west and north, and in good agreement with the predominated wind direction. These results indicated that heavy metals (except for As) likely originate from industrial sources in the study region. The spatial distribution pattern of As was very different from those of the other tested metals. The hot-spot areas of As were mainly associated with residential areas located in the south of the study region, suggesting that As contamination may be primarily associated with domestic pollution sources. Several restaurants in these areas were used by residents for ceremonies and celebrations which often included the use of large amounts of fireworks. Additionally, residents in Bayan Obo region still cook by the coal-fired style, which can result in significant arsenic emissions (Zhang et al., 2002).
Figure 2 Map of the study area and sampling sites in Bayan Obo Mining Region (April 2014)

3.3 Contamination assessment results

High “absolute” values of metals are not necessarily positively correlated to higher metal contamination levels due to variations in geochemical background levels, land use patterns,and human activities among different cities. Therefore, the geoaccumulation index was used to assess the contamination extent. The average Igeo values of As, Ni, Cu, and Co fell in the range of 0-1 (Figure 3), indicating that the road dust in Bayan Obo residential areas were polluted or moderately polluted by these four metals. The average Igeo value of Cr and Zn were 1.35 and 1.99, respectively, placing those two metals into the class of moderately polluted. The average Igeo value for Mn (2.30) resulted in a moderately to heavily polluted determination, while the average index of Pb (slightly higher than 3), pointed to a heavy contamination. Cd contamination resulted in the highest Igeo value (5.21), suggesting that the road dust was extremely polluted by Cd in Bayan Obo residential areas. Take in concert, the contamination levels of the 9 studied heavy metals were in the order of Cd>Pb>Mn>Zn>Cr>Co>Cu>As>Ni.
Figure 3 The Igeo value of heavy metals in road dust in Bayan Obo (April 2014)
The Igeo values of heavy metals in this study were also compared to results from other cities reported in previous studies. As shown in Table 5, the road dust in residential areas of Bayan Obo was contaminated by Cr, Cd, Pb, Mn, and Co at higher levels, whereas by Cu, As, and Ni was relatively low compared to other cities. Contamination by Zn was higher compared with cities without industry and overpopulation, such as Hangzhou(Zhang and Wang, 2009) and Urumqi (Wei et al., 2009), but lower than that measured in the heavy industrial city of Baoji (Lu et al., 2009) and developed city of Shanghai (Shi et al., 2008). Despite the low absolute Pb concentrations, levels of Pb pollution were still higher than those in other cities and similar with that measured in Baoji (Lu et al., 2009), in which the absolute Pb concentration was 2.36 times higher than that in Bayan Obo.
Figure 4 Non-carcinogenic risk distribution of different exposure ways for children and adults in Bayan Obo (April 2014)
Table 5 The average Igeo values of heavy metals in road dust in different areas
Igeo Cd Co Cr Cu Pb Zn As Ni Mn Reference
Bayan Obo 5.21 0.98 1.35 0.90 3.05 1.99 0.36 0.31 2.30 This study
Hangzhou 3.14 0.10 -1.10 1.70 2.42 1.51 -0.88 -0.98 Zhang and Wang, 2009
Urumqi 0.80 -0.30 -0.10 0.40 0.30 0.50 0.00 0.00 Wei et al., 2009
Shanghai 2.65 0.50 2.19 2.94 2.54 0.84 Shi et al., 2008
Baoji 1.79 3.19 2.58 3.04 0.17 -0.21 Lu et al., 2009
EFs were used to identify whether the heavy metals originated from non-crustal sources or crustal sources. The EF values for nine studied metals in road dust of Bayan Obo are listed in Table 6. The average values of EF for Cd, Pb, and Mn were greater than 10, indicating that enrichment of these three metals, particularly Cd, was caused by anthropogenic sources, whereas the average values of EF for Cr, Cu, Co, As and Ni ranged between 2.6-5.5, implying mixed influence of both crustal and non-crustal sources. Although the EF value for Zn (8.82) was slightly lower than the threshold value (=10), it is reasonable that anthropogenic sources heavily contributed to Zn contamination.
Table 6 The average EFs values of heavy metals in road dust collected in Bayan Obo (April 2014)
Cd Cr Cu Pb Zn Co As Ni Mn
EF 81.37 5.31 3.74 19.51 8.82 3.98 2.57 2.53 11.0

3.4 Health risk assessment results

3.4.1 Non-carcinogenic risk assessment
The HQ and HI for Cr, Ni, Pb, Cd, Cu, Mn, As, Co and Zn in road dust samples of Bayan Obo residential areas were calculated (Table 7). The integrated HI values were 1.89 for children and 0.23 for adults living in Bayan Obo region, indicating children are likely to experience significantly higher non-cancer risks.
Among three different exposure pathways, the HQing values were the highest and contributed the most to HIs for both children and adults, indicating that ingestion of road dust appears to be the most threatening exposure way to human health in Bayan Obo (Figure 4). The inhalation of road dust had the lowest contribution to health risks for children and the HQinh values were 2-4 orders of magnitude lower compared with the other two pathways for children, indicating that the non-cancer risks posed by the inhalation of resuspended road dust might be negligible compared with ingestion and dermal contact. Similar results were obtained by previous studies (Ferreira-Baptista and De Miguel, 2005; Zheng et al., 2010a).
Table 7 HIs for each non-carcinogenic metal in road dust collected in Bayan Obo (April 2014)
C (95%UCL) Oral RfD Inhal RfD Dermal RfD HQ ingestion
Adult Children
Cd 2.59 1.00E-03 1.00E-03 5.00E-05 1.82E-03 1.70E-02
Cr 157.87 3.00E-03 2.86E-05 6.00E-05 3.71E-02 3.46E-01
Cu 39.33 4.00E-02 4.02E-02 1.20E-02 6.93E-04 6.47E-03
Pb 225.19 3.50E-03 3.52E-03 5.25E-04 4.53E-02 4.23E-01
Zn 350.18 3.00E-01 3.00E-01 6.00E-02 8.22E-04 7.68E-03
Ni 33.63 2.00E-02 2.06E-02 5.40E-03 1.18E-03 1.11E-02
Co 28.88 2.00E-02 5.71E-06 1.60E-02 1.02E-03 9.49E-03
As 13.13 3.00E-04 3.01E-04 1.23E-04 3.08E-02 2.88E-01
Mn 3991.06 4.60E-02 1.43E-05 1.84E-03 6.11E-02 5.70E-01
Sum 1.80E-01 1.68E+00
HQ inhalation HQ dermal HI
Adult Children Adult Children Adult Children
Cd 2.81E-07 4.98E-07 1.52E-04 9.98E-04 1.98E-03 1.80E-02
Cr 5.71E-04 1.01E-03 7.39E-03 4.84E-02 4.50E-02 3.95E-01
Cu 1.01E-07 1.80E-07 1.00E-05 6.55E-05 7.03E-04 6.53E-03
Pb 6.98E-06 1.24E-05 1.27E-03 8.32E-03 4.66E-02 4.31E-01
Zn 1.34E-07 2.38E-07 1.82E-05 1.19E-04 8.41E-04 7.79E-03
Ni 1.65E-07 2.93E-07 1.71E-05 1.12E-04 1.20E-03 1.12E-02
Co 5.23E-04 9.27E-04 5.06E-06 3.32E-05 1.55E-03 1.05E-02
As 4.57E-06 8.11E-06 9.00E-03 5.90E-02 3.98E-02 3.47E-01
Mn 2.89E-02 5.13E-02 6.10E-03 3.99E-02 9.61E-02 6.62E-01
Sum 3.00E-02 5.32E-02 2.40E-02 1.57E-01 2.34E-01 1.89E+00
Additionally, children were found to experience higher health risks through ingestion compared with adults. The values of HQing for children were 9.33 times higher than those for adults and accounted for larger proportions (88.9% for children, 76.9% for adults) in integrated HI values. This result may be partially attributed to the special behavior patterns of children, particularly frequent hand-to-mouth contact.
The HIs for all studied metals were ranked in the order: Mn>Pb>Cr>As>Cd>Co> Ni>Zn>Cu for adults, and Mn>Pb>Cr>As>Cd>Ni>Co>Zn>Cu for children (Table 7 and Figure 5). Mn, Cr, Pb, and As were the main contributors to health risks posed by road dust metals exposure for both children and adults, and Cu had the smaller contribution. The HQinh of Mn and the HQderm of Cr and As were 2-5 orders of magnitude higher than those of other metals for both children and adults, suggesting that exposure to Cr and As via dermal contact, and for Mn through inhalation, may produce the most serious health effects.
The HI values for all metals tested in this study were within the safe level (=1), suggesting minimal non-carcinogenic risk to children and adults from exposure to road dust metals. However, the integrated HI for children (HI=1.89) slightly exceeded the safe level (=1), indicating that the potential health risk to children should be addressed and studied in more detail.
Figure 5 The HQs of each heavy metal in road dust in Bayan Obo for adults (a) and children (b) (April 2014)
3.4.2 Carcinogenic risk assessment
The cancer risks according to inhalation exposure to Cd, Cr, Ni, Co, and As are presented in Table 8. Results showed that the overall risk of cancer decreased in the order Cr>Co>As> Ni>Cd. The leading heavy metal was Cr for which cancer risks were 1-3 orders of magnitude higher than those for other metals. Overall, cancer risk values for all heavy metals in this study were within the acceptable range, implying negligible carcinogenic risk.
Table 8 Cancer risks for each carcinogenic metal in road dust collected in Bayan Obo (April 2014)
Cd Cr Ni Co As
Inhal SF 6.30E+00 4.20E+01 8.40E-01 9.80E+00 1.51E+01
R 8.37E-10 3.40E-07 1.45E-09 1.45E-08 1.02E-08

4 Conclusions

A total of 23 road dust samples were collected from Bayan Obo Mining Region in the spring of 2014. The concentration and spatial distribution patterns of 9 potentially toxic heavy metal elements (As, Cd, Co, Cr, Pb, Cu, Zn, Mn, and Ni) in road dust were analyzed. Contamination levels were evaluated using the geoaccumulation index and the enrichment factor. Human health risks for each heavy metal element were assessed using a human exposure model.
Results showed: (1) Concentrations of Cd, Co, Zn, Pb, Ni, As, Cu, Mn, and Cr were significantly higher compared with background values. (2)The spatial distribution of Cd, Co, Zn, Pb, Ni, Cu, Mn, and Cr were all in accordance with the locations of industrial areas and the predominant wind direction, indicating that these eight metals likely originated from industrial sources. The spatial distribution of As showed a different pattern and was instead primarily associated with domestic pollution sources, including firework use and coal combustion. (3) Contamination assessments showed that the road dust in Bayan Obo was contaminated by all investigated metals to varying extents. Cd, with an average Igeo value of 5.21, presented the highest pollution risk. Moreover, the road dust was categorized as heavily polluted by Mn and Pb and moderately polluted by Zn and Cr, whereas Cu, As, Ni and Co in the dust were rated as “moderately polluted” to “polluted” based on average Igeo values. (4) EF values indicated that accumulation of Cd, Pb, and Mn in road dust was caused mainly by human activities, whereas the enrichment of other metals derived from a combination of crustal and anthropogenic sources. The EF value of Zn (8.82) was close to the threshold value 10, implying a greater influence from human activities. (5) The health risks analysis showed that ingestion was the dominant exposure pathway for both children and adults. The sum of HI values for Mn, Cr, Pb, and As accounted for nearly 98% of the integrated HI values, indicating that these four metals were the greatest contributors to non-cancer risks. (6) Among the 5 carcinogenic metals, Cr was the leading contributor to cancer risks, followed by Co, As, Ni, and Cd. (7) Although both non-carcinogenic and carcinogenic risk for each metal fell within acceptable values, children were more susceptible than adults and experienced higher non-carcinogenic risk from exposure to metals in road dust. The risks to children living in the mining region of Bayan Obo from exposure to mining-related activities should receive greater attention.

The authors have declared that no competing interests exist.

References

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Apeagyei E, Bank M S, Spengler J D, 2011. Distribution of heavy metals in road dust along an urban-rural gradient in Massachusetts.Atmospheric Environment, 45(13): 2310-2323.Human exposures to particulate matter emitted from on-road motor vehicles include complex mixtures of metals from tires, brakes, parts wear and resuspended road dust. The aim of this study was to assess road dust for metals associated with motor vehicle traffic, particularly those metals coming from brake and tire wears. We hypothesized that the road dust would show significant difference in both composition and concentration by traffic type, road class and by location. X-ray fluorescence (XRF) analyses of 115 parked car tires showed Zn and Ca were likely associated with tire wear dust. XRF results of three used brake pads indicated high concentrations of Fe, Ti, Cu, Ba, Mo and Zr. To assess heavy metal exposures associated with tires and brake wear adjacent to roads of varying traffic and functional classes, 85 samples of road dust were collected from road surfaces adjacent to the curb and analyzed by XRF. Median concentrations for Fe, Ca and K were greater than Ti (1619ppm), with concentration ratios of Fe: Ca: K: Ti [16:5:3:1]. Cumulative frequency distribution graphs showed distribution of Fe, Ba, Cu, and Mo were similar regardless of road traffic rating. However, Zn, Ti, and Zr varied significantly (<0.05) with traffic ratings of roadways (heavy>moderate>low traffic). Fe, Ba, Cu, and Mo also had similar distributions regardless of road class while composition of Zn, Ti, and Zr varied significantly across road class (<0.05) (Major roads>Minor roads>highway). In comparing urban road dust to rural road dust, we observed Fe, Ca, K, and Ti were significantly greater in urban road dust (<0.05). In urban road dust the Fe: Ca: K: Ti relationship with median Ti of 2216ppm was 12: 6: 3.5: 1. These results indicate that roadway dust may be important sources of metals for runoff water and localized resuspended particulate matter.

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Cheng X, Taylor R N, Li Wet al., 2012. Comparison of fluorite geochemistry from REE deposits in the Panxi region and Bayan Obo, China.Journal of Asian Earth Sciences, 57: 76-89.The fluorites from three deposits in Panxi region show uniform initial Sr and Nd isotopic compositions similar to their associated carbonatites, but differ from ore-veins found intruding wall rocks, e.g. granite in Maoniuping and syenite in Daluxiang. This is not consistent with a model for fluorite formation involving interaction of F-rich, carbonatite-exsoloved fluid with wall rocks. Instead, the fluorite in Panxi region may precipitate from a residual carbonthermal fluid, which was dominated by Ca, CO 2 but also contained F, H 2 O and REE, and derived from the fractioned carbonatitic magma. Fluorite deposition produced a sharp drop in the activity of F 鈭 , which destabilized the REE fluoride complexes and caused deposition of REE minerals. In Bayan Obo, the fluorite typically has higher La/Ho than that in Panxi region and is characterized by a consistent LREE enrichment relative to MREE and negligible to positive Y anomalies. This is consistent with the compositional change of the hydrothermal fluids, which were infiltrated by external F-, LREE-rich fluids. The 87 Sr/ 86 Sr of Bayan Obo fluorite is relatively low radiogenic, and has a large range (0.7038鈥0.7065): similar characteristics to the carbonatite dykes found near the ore bodies. This supports a model for fluorite and REE mineral genesis involving the interaction of a carbonatite-derived fluid and the ore-hosted dolomitic marble.

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Cook A G, Weinstein P, Centeno J A, 2005. Health effects of natural dust.Biological Trace Element Research, 103(1): 1-15.<a name="Abs1"></a>This article reviews the health effects of trace elements carried in natural dusts of geologic or geochemical origin. The sources of these dusts are diverse, including volcanoes, dust storms, long-range transport of desert dust, and displacement through natural processes such as landslides and earthquakes. The primary focus is dust exposures affecting communities rather than occupational groups (which have been comprehensively explored in other publications). The principal elements and compounds reviewed are trace metals (including As, Hg, Cd, and Fe), radioactive elements, fluoride, silicates, natural asbestiform compounds, and alkali salts. The pathways by which such agents affect human populations are explored, including carriage through water, air, soil, and the food chain. The mechanisms of biotoxicity and the acute and chronic consequences on health associated with these elements are described. The discussion explores problems inferring risk and disease causation from natural dust exposures using standard epidemiological indicators, particularly for chronic outcomes, and will argue for the importance of the ecological perspective in assessing pathogenesis. The authors stress the global scale of the problem, which remains underevaluated and underreported in terms of health implications.

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Csavina J, Field J, Taylor M Pet al., 2012. A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations.Science of the Total Environment, 433: 58-73.Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.

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Drew L J, Meng Q, Sun W, 1990. The Bayan Obo iron-rare-earth-niobium deposits, Inner Mongolia.China. Lithos, 26(1): 43-65.

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Ferreira-Baptista L, De Miguel E, 2005. Geochemistry and risk assessment of street dust in Luanda, Angola: A tropical urban environment.Atmospheric Environment, 39(25): 4501-4512.<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">A total of 92 samples of street dust were collected in Luanda, Angola, were sieved below 100&#xA0;μm, and analysed by ICP-MS for 35 elements after an aqua-regia digestion. The concentration and spatial heterogeneity of trace elements in the street dust of Luanda are generally lower than in most industrialized cities in the Northern hemisphere. These observations reveal a predominantly &ldquo;natural&rdquo; origin for the street dust in Luanda, which is also manifested in that some geochemical processes that occur in natural soils are preserved in street dust: the separation of uranium from thorium, and the retention of the former by carbonate materials, or the high correlation between arsenic and vanadium due to their common mode of adsorption on solid particles in the form of oxyanions. The only distinct anthropogenic fingerprint in the composition of Luanda's street dust is the association Pb&ndash;Cd&ndash;Sb&ndash;Cu (and to a lesser extent, Ba&ndash;Cr&ndash;Zn). The use of risk assessment strategies has proved helpful in identifying the routes of exposure to street dust and the trace elements therein of most concern in terms of potential adverse health effects. In Luanda the highest levels of risk seem to be associated (a) with the presence of As and Pb in the street dust and (b) with the route of ingestion of dust particles, for all the elements included in the study except Hg, for which inhalation of vapours presents a slightly higher risk than ingestion. However, given the large uncertainties associated with the estimates of toxicity values and exposure factors, and the absence of site-specific biometric factors, these results should be regarded as preliminary and further research should be undertaken before any definite conclusions regarding potential health effects are drawn.</p>

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Fu K, Su B, He Det al., 2012. Pollution assessment of heavy metals along the Mekong River and dam effects.Journal of Geographical Sciences, 22(5): 874-884.Abstract<br/><p class="a-plus-plus">The resource development and changes of hydrological regime, sediment and water quality in the Mekong River basin have attracted great attentions. This research aimed to enhance the study on transboundary pollution of heavy metals in this international river. In this study, eight sampling sites were selected to collect the bed sand samples along the mainstream of the Mekong River. In addition, the contents of 5 heavy metal elements and their spatial variability along the mainstream of the river were analyzed. The geoaccumulation index (I<sub class="a-plus-plus">geo</sub>) and potential ecological risk analysis were employed to assess heavy metal pollution status in the mainstream of the Mekong River. The results show that the average content of the heavy metal elements Zn is 91.43 mg/kg, Pb is 41.85 mg/kg, and As is 21.84 mg/kg in the bed sands of the Upper Mekong River, which are higher than those (Zn 68.17 mg/kg, Pb 28.22 mg/kg, As 14.97 mg/kg) in the Lower Mekong. The average content of Cr in the Lower Mekong is 418.86 mg/kg, higher than that in the Upper Mekong (42.19 mg/kg). Luang Prabang has a very high Cr concentration with 762.93 mg/kg and Pakse with 422.90 mg/kg. The concentration of Cu in all of the 8 sampling sites is similar, except for in Jiajiu with 11.70 mg/kg and Jiebei with 7.00 mg/kg. The results of the geoaccumulation index reveal that contaminations caused by Zn and Pb while Pb and As are more than those by Zn in Upper Mekong. Cr is the primary pollutant in the Lower Mekong, especially at Luang Prabang and Pakse. Slight pollution with As also occurs in Pakse. The potential ecological risk index indicates that the potential ecological risk of heavy metals in the mainstream of the Mekong River is low. We argue that the pollution of water quality and contamination of heavy metals in bed sediment caused by mining of mineral resources or geochemical background values in the Mekong is not transmitted from the Upper to the Lower Mekong because of the reservoir sedimentation and dilution along the river.</p><br/>

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Gao H, Wang X, Zhang Qet al., 2007. Characteristics of soil background value in Hetao area, Inner Mongolia. Geology and Resources, 16(3): 209-212. (in Chinese)Based on the multi-target regional geochemical survey for surficial soil in Hetao area,Inner Mongolia,the background value of soil is analyzed.The result shows that most of the element contents in the area are lower than those in the rest regions of China as well as in the world.However,some elements are higher in content than other areas,such as CaO,MgO,As and F.Such analysis of the background value of soil will provide basic data for local agriculture,environment and endemic disease study.

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Guo W, Fu R, Zhao Ret al., 2011. Distribution Characteristic and Assessment of Soil Heavy Metal Pollution in the Iron Mining of Baotou in Inner Mongolia.Chinese Journal of Environmental Science, 32(10): 3099-3105. (in Chinese)The pollution status and total concentration of soil heavy metals were analyzed around tailing reservoir of Baotou and iron mining of Bayan Obo located in Inner Mongolia grassland ecosystem. Aim of the study is to control soil heavy metal pollution of grassland mining area and provide the basic information. The results indicated that the soils from different directions of the tailing reservoir were contaminated by Pb, Cu, Zn and Mn. According to the single factor pollution index, the pollution degree was Mn > Zn > Pb > Cu. According to Nemerow integrated pollution index, the indexes of the northeast, southeast, southwest, and northwest of the tailing reservoir, were 2.43, 10.2, 1.88, 1.64. Soils from the southeast had the most serious heavy metal contamination because of the dominant wind of northwest. Within 50 m from the edge of tailing reservoir, heavy metal contamination was most serious except Cu. With regard to Bayan Obo iron mining, the single factor pollution index indicated that the soils from the six surveyed regions were contaminated by Pb, Cu, Zn and Mn. The integrated pollution index indicated that the indexes of the six regions, such as the mining area, the dump, outside the dump, outside the urban area, east region of the railway, and west region of the railway, were 14.3, 4.30, 2.69, 3.41, 2.88, and 2.20, respectively. The soil pollution degree of the mining area was the highest. Additionally, the transport of ore resulted in soil heavy metal pollution along railway. In general, soils of the two studied areas had the similar pollution characteristic, and the elements of heavy metal contamination were corresponding with the concentrations of tailings. The health and stabilization of grassland ecosystem are being threatened by soil heavy metals.

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IARC (International Agency for Research on Cancer), 2014. Agents Classified by the IARC Monographs, Vol. 1-109.

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Liu E, Yan T, Birch Get al., 2014. Pollution and health risk of potentially toxic metals in urban road dust in Nanjing, a mega-city of China.Science of the Total Environment, 476: 522-531.Spatial variations in concentrations of a suite of potentially toxic metals (Ba, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and Ca in road dusts (n02=0299) from urban trunk roads (TR) in Nanjing, a mega-city in China, were established. Metal pollution levels, sources and human health risk (non-carcinogenic) were studied. In contrast to previous studies, we labeled the indicative metals relating to non-exhaust traffic emissions by comparing metal pollution between crossroad and park road dusts, and then anthropogenic sources of metals in TR dusts were assessed combining their spatial pollution patterns, principal component analysis and Pb isotopic compositions. Results showed that the metals were enriched in TR dusts compared to background soil concentrations with mean enrichment factors (EFs) of 2.2–23, indicating considerable anthropogenic influence. The degrees of metal pollution ranged from minimal to extremely high and ranked by Ca02>02Cu02>02Pb02≈02Zn02>02Cr02≈02Fe02>02Ni02≈02Ba02>02Mn on average. Pollution of Cr, Cu, Fe, Mn, Ni, Pb and Zn in TR dusts resulted primarily from industrial emissions (e.g., coal combustion and smelting) and high pollution levels were found close to suburb industrial complexes, whereas pollution of Ba and Ca was mainly related to construction/demolition sources and was generally distributed homogeneously. The relatively minor contribution of non-exhaust traffic emissions to metal pollution in TR dusts was considered to be due to overwhelming industrial and construction/demolition contributions, as well as to the dilution effect of natural soil particles. Ingestion appears to be the major route of exposure for road dust for both adults and children, followed by dermal contact. The non-carcinogenic health risk resulting from exposure to the potentially toxic metals in TR dusts was within the safe level based on the Hazard Index (HI), except in pollution hotspots where exposure to Pb, Cr, and Cu may be hazardous to children.

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Lu X, Li L Y, Wang Let al., 2009. Contamination assessment of mercury and arsenic in roadway dust from Baoji, China. Atmospheric Environment, 43(15): 2489-2496.<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">The physicochemical properties and the contamination levels of mercury and arsenic in roadway dust from Baoji, NW China were investigated using an Atomic Fluorescence Spectrophotometer. Contamination levels were assessed based on the geoaccumulation index and the enrichment factor. The results show that magnetic susceptibilities of roadway dust were higher than Holocene loess&ndash;soil of central Shaanxi Loess Plateau. The mean contents of organic matter, PM10 and PM100 were 8.8%, 21.8% and 98.6%, respectively. Mercury concentration ranged from 0.48 to 2.32&nbsp;μg&nbsp;g<sup>&minus;1</sup> with a mean value of 1.11&nbsp;μg&nbsp;g<sup>&minus;1</sup> 17.1 times the Chinese soil mercury background value and 37 times the Shaanxi soil mercury background value. Arsenic concentration ranged from 9.0 to 42.8&nbsp;μg&nbsp;g<sup>&minus;1</sup> with a mean value of 19.8&nbsp;μg&nbsp;g<sup>&minus;1</sup> 1.8 times the Chinese and Shaanxi soil arsenic background values. The geoaccumlation index and enrichment factor indicate that mercury in the dust mainly originated from anthropogenic sources with ratings of &ldquo;strongly polluted&rdquo; and &ldquo;strongly to extremely polluted&rdquo; whereas arsenic in dust originated from both natural and anthropogenic sources, with a ratings of &ldquo;moderately to strongly polluted&rdquo; and &ldquo;strongly polluted&rdquo;. Industrial activities, such as a coal-fired power station, coke-oven plant, and cement manufacturing plant, augmented by vehicular traffic, are the anthropogenic sources of mercury and arsenic in the roadway dust.</p>

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Lu X, Wang L, Lei Ket al., 2009. Contamination assessment of copper, lead, zinc, manganese and nickel in street dust of Baoji, NW China,Journal of Hazardous Materials, 161: 1058-1062.Abstract Street dusts collected from Baoji, NW China were analyzed for Cu, Pb, Zn, Mn and Ni by using PANalytical PW-2403 wavelength dispersive X-ray fluorescence spectrometry and assessed the contamination level of heavy metals on the basis of geoaccumulation index (I(geo)), enrichment factor (EF), pollution index (PI) and integrated pollution index (IPI). The results indicate that, in comparison with Chinese soil, street dusts in Baoji have elevated metal concentrations as a whole. The concentrations of heavy metals investigated in this paper are compared with the reported data of other cities. The calculated results of I(geo) and EF of heavy metals reveal the order of I(geo) and EF are Pb>Zn>Cu>Ni>Mn. The high I(geo) and EF for Pb, Zn and Cu in street dusts indicate that there is a considerable Pb, Zn and Cu pollution, which mainly originate from traffic and industry activities. The I(geo) and EF of Mn and Ni are low and the assessment results indicate an absence of distinct Mn and Ni pollution in street dusts. The assessment results of PI also support Pb, Zn and Cu in street dusts presented serious pollution, and IPI indicates heavy metals of street dust polluted seriously.

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Moreno T, Karanasiou A, Amato Fet al., 2013. Daily and hourly sourcing of metallic and mineral dust in urban air contaminated by traffic and coal-burning emissions.Atmospheric Environment, 68: 33-44.A multi-analytical approach to chemical analysis of inhalable urban atmospheric particulate matter (PM), integrating particle induced X-ray emission, inductively coupled plasma mass spectrometry/atomic emission spectroscopy, chromatography and thermal-optical transmission methods, allows comparison between hourly (Streaker) and 24-h (High volume sampler) data and consequently improved PM chemical characterization and source identification. In a traffic hot spot monitoring site in Madrid (Spain) the hourly data reveal metallic emissions (Zn, Cu, Cr, Fe) and resuspended mineral dust (Ca, Al, Si) to be closely associated with traffic flow. These pollutants build up during the day, emphasizing evening rush hour peaks, but decrease (especially their coarser fraction PM2.5-10) after nocturnal road washing. Positive matrix factorization (PMF) analysis of a large Streaker database additionally reveals two other mineral dust components (siliceous and sodic), marine aerosol, and minor, transient events which we attribute to biomass burning (K-rich) and industrial (incinerator?) Zn, Pb plumes. Chemical data on 24-h filters allows the measurement of secondary inorganic compounds and carbon concentrations and offers PMF analysis based on a limited number of samples but using fuller range of trace elements which, in the case of Madrid, identifies the continuing minor presence of a coal combustion source traced by As, Se, Ge and Organic Carbon. This coal component is more evident in the city air after the change to the winter heating season in November. Trace element data also allow use of discrimination diagrams such as V/Rb vs. La/Ce and ternary plots to illustrate variations in atmospheric chemistry (such as the effect of Ce-emissions from catalytic converters), with Madrid being an example of a city with little industrial pollution, recently reduced coal emissions, but serious atmospheric contamination by traffic emissions. (C) 2012 Elsevier Ltd. All rights reserved.

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Muller G, 1969. Index of geo-accumulation in sediments of the Rhine River.Geo Journal, 2(3): 108-118

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Risk Assessment Guidance for Superfund .Volume I: Human Health Evaluation Manual, Part E: Supplemental Guidance for Dermal Risk Assessment. EPA/540/R/99/005, OSWER9285.7-02EP PB99-963312, 2004. Office of Superfund Remediation and Technology Innovation, U.S. Environmental Protection Agency Washington, D.C.

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Risk Assessment Guidance for Superfund Volume I Human Health Evaluation Manual (Part A) EPA/540/1-89/002, 1989. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency Washington, D.C.Cleanup Program " for regional implementation. Draft versions of this policy were distributed for

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Shi G, Chen Z, Xu Set al., 2008. Potentially toxic metal contamination of urban soils and roadside dust in Shanghai.China. Environmental Pollution, 156: 251-260.

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Si W, Liu J, Cai Let al., 2015. Health risks of metals in contaminated farmland soils and spring wheat irrigated with Yellow River water in Baotou, China.Bulletin of Environmental Contamination and Toxicology, 94(2): 214-219.The consumption of water and food crops contaminated with metals is a major food chain route for human exposure. We investigated the health risks of metals in Yellow River (YR) water, farmland soil and spring wheat in the Baotou region, northern China. Data indicated that long-term irrigation with polluted YR water led to metal accumulation in local farmland soil and spring wheat. The consumption of YR water and spring wheat in Baotou region can cause adverse health effects to local people, specifically because of Hg, Pb, and Se in YR water and Cu, Zn, Cd, and Mn in spring wheat. The integrative risk of various metals depends mainly on the spring wheat intake. Current results emphasized the need for routine monitoring and management in order to avoid contamination of YR water and spring wheat from the wastewater irrigation system in Baotou region.

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Sun C, Bi C, Chen Zet al., 2010. Assessment on environmental quality of heavy metals in agricultural soils of Chongming Island, Shanghai City.Journal of Geographical Sciences, 20(1): 135-147.<a name="Abs1"></a>The environmental quality of heavy metals (Pb, Cd, Cr, As, Hg) in agricultural surface soil of Chongming Island was assessed by national, local and professional standards based on a large scale investigation, in which 28 samples from vegetable plots, 65 samples from paddy fields and 9 samples from watermelon fields were collected from whole island area. Results showed that the average concentration of Pb, Cd, Cr, As and Hg was 21.6 mg·kg<sup>&#8722;2</sup> 0.176 mg·kg<sup>&#8722;2</sup> 69.4 mg·kg<sup>&#8722;2</sup> 9.209 mg·kg<sup>&#8722;2</sup> and 0.128 mg·kg<sup>&#8722;2</sup> respectively. Compared with the background value of Shanghai City soil, except for Pb and Cr, all the other heavy metals average concentrations in Chongming Island agricultural surface soil exceeded their corresponding natural-background values. The concentrations of Cd, As and Hg were 33.0%, 1.2% and 26.3% higher than the background value of Shanghai City, respectively. In addition, inverse distance interpolation (IDW) tool of GIS was also applied to study the spatial variation of heavy metals. The results indicated that most of agricultural soil quality was good, and the ratio of ecological, good soil, certified soil and disqualified soil were 1.26%, 97.1%, 1.47% and 0.12%, respectively. About 10.1%, 85.7%, 27.0%, 55.4% and 55.2% soil samples exceeded the Pb, Cd, Cr, As and Hg background value of Shanghai City, respectively. Among these three land use type soils, vegetable soil was most seriously polluted by heavy metals, which is probably related to the over-application of pesticides. The annual deposition fluxes of Pb, Cd, As and Hg were 7736 &#956;g·m<sup>&#8722;2</sup>·a<sup>&#8722;2</sup> 208 &#956;g·m<sup>&#8722;2</sup>·a<sup>&#8722;2</sup> 2238 &#956;g·m<sup>&#8722;2</sup>·a<sup>&#8722;2</sup> and 52.8 &#956;g·m<sup>&#8722;2</sup>·a<sup>&#8722;2</sup> respectively. Crop straw burning was the important source of heavy metals of atmospheric deposition, and atmospheric deposition contributed a lot to heavy metals in agricultural soil in Chongming Island.

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Supplemental Guidance for Developing Soil Screening Level for Superfund Sites. OSWER9355.4-24, 2001. Office of Solid Waste and Emergency Response, Environmental Protection Agency Washington, D.C.

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Supplemental Guidance to RAGS: Calculating the Concentration Term. PB92-963373, 1992. Office of Solid Waste and Emergency Response, Environmental Protection Agency Washington, D.C.

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Valko M, Rhodes C J, Moncol Jet al., 2006. Free radicals, metals and antioxidants in oxidative stress-induced cancer.Chemico-biological Interactions, 160(1): 1-40.Oxygen-free radicals, more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS) are well recognised for playing a dual role as both deleterious and beneficial species. The 鈥渢wo-faced鈥 character of ROS is substantiated by growing body of evidence that ROS within cells act as secondary messengers in intracellular signalling cascades, which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. The cumulative production of ROS/RNS through either endogenous or exogenous insults is termed oxidative stress and is common for many types of cancer cell that are linked with altered redox regulation of cellular signalling pathways. Oxidative stress induces a cellular redox imbalance which has been found to be present in various cancer cells compared with normal cells; the redox imbalance thus may be related to oncogenic stimulation. DNA mutation is a critical step in carcinogenesis and elevated levels of oxidative DNA lesions (8-OH-G) have been noted in various tumours, strongly implicating such damage in the etiology of cancer. It appears that the DNA damage is predominantly linked with the initiation process. This review examines the evidence for involvement of the oxidative stress in the carcinogenesis process. Attention is focused on structural, chemical and biochemical aspects of free radicals, the endogenous and exogenous sources of their generation, the metal (iron, copper, chromium, cobalt, vanadium, cadmium, arsenic, nickel)-mediated formation of free radicals (e.g. Fenton chemistry), the DNA damage (both mitochondrial and nuclear), the damage to lipids and proteins by free radicals, the phenomenon of oxidative stress, cancer and the redox environment of a cell, the mechanisms of carcinogenesis and the role of signalling cascades by ROS; in particular, ROS activation of AP-1 (activator protein) and NF-魏B (nuclear factor kappa B) signal transduction pathways, which in turn lead to the transcription of genes involved in cell growth regulatory pathways. The role of enzymatic (superoxide dismutase (Cu, Zn-SOD, Mn-SOD), catalase, glutathione peroxidase) and non-enzymatic antioxidants (Vitamin C, Vitamin E, carotenoids, thiol antioxidants (glutathione, thioredoxin and lipoic acid), flavonoids, selenium and others) in the process of carcinogenesis as well as the antioxidant interactions with various regulatory factors, including Ref-1, NF-魏B, AP-1 are also reviewed.

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Wang L, Guo Z, Xiao Xet al., 2008. Heavy metal pollution of soils and vegetables in the midstream and downstream of the Xiangjiang River, Hunan Province.Journal of Geographical Sciences, 18(3): 353-362.<a name="Abs1"></a>A total of 219 agricultural soil and 48 vegetable samples were collected from the midstream and downstream of the Xiangjiang River (the Hengyang-Changsha section) in Hunan Province. The accumulation characteristics, spatial distribution and potential risk of heavy metals in the agricultural soils and vegetables were depicted. There are higher accumulations of heavy metals such as As, Cd, Cu, Ni, Pb and Zn in agricultural soils, and the contents of Cd (2.44 mg kg<sup>&#8722;1</sup>), Pb (65.00 mg kg<sup>&#8722;1</sup>) and Zn (144.13 mg kg<sup>&#8722;1</sup>) are 7.97, 3.69 and 1.63 times the corresponding background contents in soils of Hunan Province, respectively. 13.2% of As, 68.5% of Cd, 2.7% of Cu, 2.7% of Ni, 8.7% of Pb and 15.1% of Zn in soil samples from the investigated sites exceeded the maximum allowable heavy metal contents in the China Environmental Quality Standard for Soils (GB15618-1995, Grade II). The pollution characteristics of multi-metals in soils are mainly due to Cd. The contents of As, Cd, Cu, Pb and Zn in vegetable soils are significantly higher than the contents in paddy soils. 95.8%, 68.8%, 10.4% and 95.8% of vegetable samples exceeded the Maximum Levels of Contaminants in Foods (GB2762-2005) for As, Cd, Ni and Pb concentrations, respectively. There are significantly positive correlations between the concentrations of Cd, Pb and Zn in vegetables and the concentrations in the corresponding vegetable soils (<i>p</i>&lt;0.01). It is very necessary to focus on the potential risk of heavy metals for food safety and human health in agricultural soils and vegetables in the midstream and downstream of the Xiangjiang River, Hunan Province of China.

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Wang L, Liang T, Zhang Qet al., 2014. Rare earth element components in atmospheric particulates in the Bayan Obo mine region. Environmental Research, 131: 64-70.The Bayan Obo mine, located in Inner Mongolia, China, is the largest light rare earth body ever found in the world. The research for rare earth elements (REEs) enrichment in atmospheric particulates caused by mining and ore processing is fairly limited so far. In this paper, atmospheric particulates including total suspended particulate (TSP) matter and particles with an equivalent aerodynamic diameter less than 10聽渭m (PM) were collected around the Bayan Obo mine region, in August 2012 and March 2013, to analyze the levels and distributions of REEs in particles. The total concentrations of REEs for TSP were 149.8 and 239.6聽ng/m, and those for PMwere 42.8 and 68.9聽ng/m, in August 2012 and March 2013, respectively. Enrichment factor was calculated for all 14 REEs in the TSP and PMand the results indicated that REEs enrichment in atmosphere particulates was caused by anthropogenic sources and influenced by the strong wind in springtime. The spatial distribution of REEs in TSP showed a strong gradient concentration in the prevailing wind direction. REE chondrite normalized patterns of TSP and PMwere similar and the normalized curves inclined to the right side, showing the conspicuous fractionation between the light REEs and heavy REE, which supported by the chondrite normalized concentration ratios calculated for selected elements (La/Yb, La/Sm, Gd/Yb).

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Wei B, Jiang F, Li Wet al., 2009. Spatial distribution and contamination assessment of heavy metals in urban road dusts from Urumqi, NW China.Microchemical Journal, 93: 147-152.lt;h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">This study reports the spatial distribution pattern and degree of heavy metal pollution (Cd, Cr, Cu, Ni, Pb, Mn, Be, Co, Zn and U) in 169 urban road dust samples from urban area of Urumqi city. The spatial distribution pattern shows that Cu, Pb, Cr and Zn have similar patterns of spatial distribution. Their hot-spot areas were mainly associated with main roads where high traffic density was identified. Ni and Mn show similar spatial distributions coinciding with the industrial areas, while the spatial distribution patterns of Co and U show hot-spot areas were mainly located in the sides of the urban area where the road dust was significantly influenced by natural soils. The spatial distributions of Be and Cd were very different from other metals. The geo-accumulation index suggests that road dust in Urumqi city was uncontaminated to moderately contaminated with Cd, Cu, Ni, Pb, Mn, Be, Zn and U. The integrated pollution index shows IPIs of all road dust samples were higher than 1, suggesting that the road dust quality of Urumqi city has clearly been polluted by anthropogenic emission of heavy metals. Moreover, the spatial distribution pattern of IPIs also shows several distribution trends in the studied region.</p>

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Wu C, 2008. Bayan Obo Controversy: Carbonatites versus Iron Oxide‐Cu‐Au‐(REE‐U).Resource Geology, 58(4): 348-354. (in Chinese)ABSTRACT The Bayan Obo Fe-REE-Nb deposit is the world&rsquo;s largest rare earth element (REE) resource and its genesis has been the subject of much debate for many years. The most popular are the carbonatite-related and hydrothermal Fe oxide-Cu-Au-(REE-U) genetic models. Comparisons of geologic setting, lithology, mineral assemblages, metal associations, geochemistry (particularly REE and light REE/heavy REE ratios), fluid chemistry and isotopics indicate that the Bayan Obo deposit shares features of both types, which are classified differently; that is, the carbonatites model is host-rock based, while the Fe oxide-Cu-Au-(REE-U) model is essentially mineral assemblage and metal association based. A speculative classification scheme is tentatively put forward to link the two models, but many questions remain for further studies.

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Xu S, Tao S, 2004. Coregionalization analysis of heavy metals in the surface soil of Inner Mongolia.Science of the Total Environment, 320: 73-87.Due to potential problems associated with their deficiencies or toxicities, heavy metals in soils are of great environmental concern. To evaluate heavy metal contents and their relationships in the surface soil of Inner Mongolia, soil samples were collected from 344 sites and contents of copper, lead, zinc, cadmium, nickel, chromium, mercury, cobalt, vanadium and manganese were determined. In this article, coregionalization of these ten heavy metals is investigated using factorial kriging. Vegetation type, parent material type and soil pH, with respective characteristic ranges of 200, 400 and over 1000 km, are identified as the primary factors that control the spatial distribution of soil heavy metals. At the scale of 200 km, heavy metal relationships mainly reflect the result of biocycling. Their relationships at the intermediate scale (400 km) are thought to be derived from the atomic substitution of metals in the parent materials. Effects of soil pH on the adsorption of heavy metals by soil organic materials could explain their relationships at the large spatial scale (over 1000 km).

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Zhang J, Zheng C, Liu Jet al., 2002. Advance of pollution and retention of arsenic in coal combustion.Coal Conversion, 25(2): 23-28. (in Chinese)An overview of pollution and retention of trace in coal combustion is presented in this paper.The environmental pollution and the harm on human being health of trace arsenic in coal combustion are reviewed.Arsenic transformation and partitioning in coal combustion systems as well as the species of arsenic in flue gas are discussed.And the arsenic emission factors for coal fired utility boilers,for coal fired industrial boilers,and for coal fired commercial/instiutional boiles in USA are displayed.Finally the mechanism of arsenic sorption with different sorbents and the feasibility of decreasing arsenic emission by sorbents in coal combustion are put forward.Research on trace arsenic emission in coal combustion should be taken into account.\;

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Zhang M, Wang H, 2009. Concentrations and chemical forms of potentially toxic metals in road-deposited sediments from different zones of Hangzhou, China.Journal of Environmental Sciences, 21: 625-631.

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Zheng G, Yue L, Li Zet al., 2006. Assessment on heavy metals pollution of agricultural soil in Guanzhong district.Journal of Geographical Sciences, 16(1): 105-113.<a name="Abs1"></a>The monitored soil samples were collected from Heihui irrigated area, Jiaokou irrigated area, Qianhe river valley and Jinghe river valley (hereafter Heihui, Jiaokou, Qianhe and Jinghe for short respectively) of Guanzhong District. According to the Environment Quality Standard for Soil (GB15618-1995II), we evaluated the pollution status of heavy metals (Cd, As, Cr and Pb) that could seriously endanger soil environment and human health by using single-factor index and synthetic pollution index methods. The results indicate that the synthetic pollution indices <i>P</i> <sub> <i>i</i> </sub> of soil heavy metals are less than 0.7 in Heihui, Jiaokou, Qianhe and Jinghe of Guanzhong, the single-factor indices <i>P</i> <sub> <i>i</i> </sub> of soil heavy metals of most soil samples are less than 0.7, so the soil environmental quality is in a good condition in Guanzhong on the whole; the enrichment degree of soil heavy metals is in the order of Heihui, Jinghe, Qianhe and Jiaokou; the contaminated degree of soil heavy metals has the feature of Cd &gt; As &gt; Cr &gt; Pb; heavy metals contents in the cultivated horizon soil are generally higher than those in its underlayer soil, heavy metals contents of soil have the characteristic of enriching towards the cultivated horizon; Cd exceeds standard in the soil samples HS07a, b and HS08a, b at the Yangtao orchard in Heihui and in the soil sample QHS01a at the suburban vegetable plot in Qianhe, which was mainly caused by the long-term irrational use of chemical fertilizer and pesticide.

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Zheng N, Liu J, Wang Qet al., 2010a. Health risk assessment of heavy metal exposure to street dust in the zinc smelting district, northeast of China.Science of the Total Environment, 408(4): 726-733.ABSTRACT Heavy metal contamination in the street dust due to metal smelting in the industrial district of Huludao city was investigated. Spatial distribution of Hg, Pb, Cd, Zn and Cu in the street dust was elucidated. Meanwhile, noncancer effect and cancer effect of children and adults due to exposure to the street dust were estimated. The maximum Hg, Pb, Cd, Zn and Cu contents in the street dust are 5.212, 3903, 726.2, 79,869, and 1532 mg kg(-1), and respectively 141, 181, 6724, 1257 and 77.4 times as high as the background values in soil. The trends for Hg, Pb, Cd, Zn and Cu are similar with higher concentrations trending Huludao zinc plant (HZP). The exponential equation fits quite well for the variations of Pb, Cd, Zn and Cu contents with distance from the pollution sources, but not for Hg. The biggest contribution to street dust is atmospheric deposition due to metal smelting, but traffic density makes slight contribution to heavy metal contamination. According to the calculation on Hazard Index (HI), in the case of noncancer effect, the ingestion of dust particles of children and adults in Huludao city appears to be the route of exposure to street dust that results in a higher risk for heavy metals, followed by dermal contact. The inhalation of resuspended particles through the mouth and nose is almost negligible. The inhalation of Hg vapour as the fourth exposure pathway to street dust is accounting for the main exposure. Children are experiencing the potential health risk due to HI for Pb larger than safe level (1) and Cd close to 1. Besides, cancer risk of Cd due to inhalation exposure is low.

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Zheng N, Liu J, Wang Qet al., 2010b. Heavy metals exposure of children from stairway and sidewalk dust in the smelting district, northeast of China.Atmospheric Environment, 44(27): 3239-3245.<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">The aim of this work was to study metals accumulation in stairway (inside the residential building) and sidewalk (outside the residential building) dust, and health risk of children due to dust exposure. The investigation included the: (a) spatial distributions of Hg, Pb, Cd, Zn and Cu in stairway and sidewalk dust, (b) source analysis of metals in stairway and sidewalk dust, and (c) assessment of the children health risks due to metals exposure from stairway and sidewalk dust. In the smelting district of Huludao, the maximum Hg, Pb, Cd, Zn and Cu contents in stairway dust were 5.324, 4594, 936.8, 48&nbsp;253, 1377&nbsp;mg&nbsp;kg<sup>&minus;1</sup> respectively, and were 144, 213, 8674, 760 and 69.5 times as high, respectively, as the background values in soil. A strong positive relationship was shown between the stairway and sidewalk dust for each metal (<em>p</em>&nbsp;&lt;&nbsp;0.01). The trends for Hg, Pb, Cd, Zn and Cu in the stairway and sidewalk dust were similar and with higher concentrations trending Huludao Zinc Plant (HZP). Atmospheric deposition due to metal smelting from HZP was the common source of heavy metals in the sidewalk and stairway dust. Vehicular traffic affected the metal accumulation in dust, but their contribution was slight comparing with atmospheric emission from HZP. Almost all hazard indexes (HIs) for metals due to stairway dust exposure in this study were lower than 1. The health risk for children was low if they would not play in the stairway. However, children were also experiencing the potential health risk from Cd and Pb exposure from sidewalk dust outside residential building, especially near HZP.</p>

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