Distributions of arsenic and other heavy metals, and health risk assessments for groundwater in the Guanzhong Plain region of China

Journal Pre-proof Distributions of arsenic and other heavy metals, and health risk assessments for groundwater in the Guanzhong Plain region of China Jiangbo Qiao, Yuanjun Zhu, Xiaoxu Jia, Ming'an Shao, Xiaoqian Niu, Jinyue Liu PII:

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DOI:

https://doi.org/10.1016/j.envres.2019.108957

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YENRS 108957

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Environmental Research

Received Date: 25 September 2019 Revised Date:

13 November 2019

Accepted Date: 22 November 2019

Please cite this article as: Qiao, J., Zhu, Y., Jia, X., Shao, Ming'., Niu, X., Liu, J., Distributions of arsenic and other heavy metals, and health risk assessments for groundwater in the Guanzhong Plain region of China, Environmental Research (2019), doi: https://doi.org/10.1016/j.envres.2019.108957. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.

1

Distributions of arsenic and other heavy metals, and health risk assessments for

2

groundwater in the Guanzhong Plain region of China

3

Jiangbo Qiaoa,c,*, Yuanjun Zhua,c, Xiaoxu Jiab, Ming’an Shaoa,b, Xiaoqian Niub,

4

Jinyue Liu c

5

a

6

Northwest A&F University, Yangling 712100, China

｜

b

8

Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,

9

Beijing 100101, China

State Key Laboratory of Soil Erosion and Dryland Agriculture on the Loess Plateau,

Key Laboratory of Ecosystem Network Observation and Modeling, Institute of

10

c

11

Water Resources, Yangling 712100, China

Institute of Soil and Water Conservation, Chinese Academy of Sciences & Ministry of

12 13

Abstract: The aim of this study was to evaluate the quality of shallow groundwater

14

and deep groundwater in the Guanzhong Plain region of China, as well as the related

15

health risk to humans. In total, 130 groundwater samples were collected comprising

16

116 from shallow groundwater (dug wells) and 14 from deep groundwater (drilled

1｜

wells). The water samples were analyzed to determine the levels of As and 12 other

18

heavy metals (Al, Cd, Mn, Cr, V, Fe, Ni, Cu, Zn, Co, Pb, and Mo). The results

19

showed that the concentrations of As and other heavy metals in the deep groundwater

20

samples were lower than the safe limits, but the Cr concentrations in some shallow

21

groundwater samples exceeded the safe limits. The heavy metal pollution index and

22

heavy metal evaluation index both showed that As and other heavy metals were

23

pollutants at low levels in all of the shallow and deep groundwater sample. Health risk

24

assessments showed that the deep groundwater samples had no associated

25

non-carcinogenic health risks, whereas the shallow groundwater samples had

26

non-carcinogenic health risks due to contamination with Cr and As. Some shallow

2｜

groundwater samples had associated carcinogenic health risks due to contamination

28

with Cr and As, whereas the deep groundwater samples only had carcinogenic health

29

risks because of contamination with Cr. These results suggest that local residents and

30

government departments should be made aware of Cr and As pollution in shallow

31

groundwater.

32

Capsule: we assessed the quality of groundwater in the Guanzhong Plain region of

33

China, where we evaluated the levels of As and 12 other heavy metals.

34

Key words: groundwater, health risk assessment, heavy metal

35 36

1. Introduction

3｜

Groundwater is an important and indispensable source of drinking water, and

38

one-third of all humans rely on this water source (Xing et al., 2013). Due to the rapid

39

development of society, many anthropogenic activities such as mining, industry, and

40

urbanization have affected the quality of groundwater (Griebler and Avramov, 2015;

41

Zahedi et al., 2017) by allowing its contamination with hazardous materials that are

42

harmful to human health, such as As (Ravindra and Mor, 2019), other heavy metals

43

(Singh et al. 2018), fluoride (Xu et al. 2019), nitrates (Li et al. 2018), and

44

polyaromatic hydrocarbons (Rajasekhar et al. 2018).

45

As and other heavy metal pollutants in groundwater can accumulate in the human

46

body over time and cause many diseases (Avigliano and Schenone, 2015), such as by

4｜

damaging kidney functioning, the neurological system, and ossification process

48

(Lohani et al., 2008).

49

Therefore, it is very important to assess the quality of groundwater with respect to

50

As and other heavy metals in order to maintain the provision of safe drinking water

51

for people. Thus, many studies have assessed the quality of groundwater throughout

52

different areas of the world (Arslan and Turan, 2015; Wu et al., 2019; Bhattacharjee

53

et al., 2005; Phan et al., 2010). For example, Li et al. (2016) assessed the groundwater

54

quality and health risk due to contamination in a semiarid region of Northwest China.

55

Ravindra and Mor (2019) evaluated the health risk due to arsenic and other heavy

56

metals in groundwater samples from Chandigarh, India. Bhuiyan et al. (2010)

5｜

evaluated heavy metal pollution in irrigation and drinking water systems in the

58

vicinity of a coal mining area in northwestern Bangladesh. Lu et al. (2015) conducted

59

a human health risk assessment with respect to contamination by trace elements in

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drinking water in Shenzhen, China. Singh and Subramanian (2018) investigated the

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groundwater chemistry and human health risk in a mining region in East Singhbhum,

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Jharkhand, India.

63

The Guanzhong plain is located in the middle of Shaanxi Province (with a total

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area of ~1.9 × 104 km2), which is an important grain production base in China (Lei et

65

al., 2014). Groundwater resources are important as sources of drinking and irrigation

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water for local residents in the Guanzhong Plain area. Therefore, assessing the

6｜

groundwater quality is very important for local and national economic development.

68

In addition, the Guanzhong Plain region is characterized by arid and semiarid areas

69

where water resources are lacking and the groundwater level is deep. Thus, water

｜0

quality assessments are necessary for the development of the Guanzhong Plain region.

｜1

The objectives of this study were: (1) to estimate the spatial distributions of heavy

｜2

metals in groundwater in the Guanzhong Plain region; (2) to compare the differences

｜3

in the distributions of heavy metals in shallow groundwater and deep groundwater

｜4

samples; (3) to assess the water quality and pollution status of groundwater; and (4) to

｜5

assess the non-carcinogenic and carcinogenic risks for populations exposed to arsenic

｜6

and other heavy metals.

｜｜ ｜8

2. Materials and methods

｜9 80

2.1. Study area description

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The Guanzhong Plain is located in the central part of Shaanxi Province

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(34°00′–35°40′N, 107°30′–110°30′E) (Figure 1a). This region has an area of about

83

1.9 × 104 km2 and it measures about 360 km from east to west. The area has a

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temperate semiarid and semi-humid monsoon climate. The average annual

85

temperature is 12–13.6°C and the mean annual precipitation is 530–700 mm, where

86

about 45% of the precipitation falls from July to September. The annual evaporation

8｜

is 1000–1200 mm.

88 89

2.2. Hydrogeology of the study area

90

The Guanzhong Plain located in the west of Fenwei Graben Basin is a Cenozoic

91

fault basin formed by Himalayan movement. The basin began to sag in the late

92

Eocene and continued to subside in the Miocene and Pliocene, thereby accumulating

93

very thick tertiary river lake facies in a clastic rock formation. After entering the

94

Quaternary period, it continued to settle and a thick layer of soft soil accumulated in

95

the rivers and lakes. The local area around the basin was uplifted due to the influence

96

of the secondary fault block. The Tertiary rock formation was denuded and flattened

9｜

into plain terrain, and loess then accumulated to form the loess platform.

98

The Guanzhong Basin River mainly comprises the Weihe River system, which is

99

the largest tributary of the Yellow River originating from Wuyuan County, Gansu

100

Province, and entering the basin via Baoji Gorge. From the west to the east,

101

Guanzhong Basin River traverses the middle of the basin and flows into the Yellow

102

River at Tongguan city. Guanzhong Plain covers the middle and lower reaches of the

103

Weihe River. The river valley is open and the water flow is slow.

104 105

2.3. Collection of water samples and laboratory analysis

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In total, during November 2018, 130 groundwater samples were collected from

10｜

the sampling sites shown in Figure 1b, with 116 from dug wells (shallow groundwater

108

samples) and 14 from drilled wells (deep groundwater samples). The sampling sites

109

were mainly located in Xianyang, Baoji, Tongchuan, Xi’an, and Weinan, where the

110

groundwater levels were low and it was easy to find dug wells. The dug wells were

111

located in rural areas whereas most of the wells in towns were buried. The drilled

112

wells were constructed by the public water supply department. We collected

113

groundwater samples from dug wells at intervals of 10–20 km. The towns had a

114

centralized water supply, so we collected groundwater samples from drilled wells in

115

towns. At each site, we collected 500 mL of groundwater in a plastic bottle, Each

116

sample was sealed with plastic film after its collection and then placed in a freezer. In

11｜

the laboratory, given their low concentrations in groundwater, As and other heavy

118

metals (Al, Cd, Mn, Cr, V, Fe, Ni, Cu, Zn, Co, Pb, and Mo) were determined using

119

inductively coupled plasma-mass spectrometry. The groundwater samples were

120

filtered through a Luer syringe filter (pore size: 0.22 µm) before their analysis. In

121

addition, distilled water was used for blank analyses in order to ensure the reliability

122

of the results.

123 124

2.4. Evaluation indices

125

2.4.1. Heavy metal pollution index (HPI)

126 12｜

HPI was employed to evaluate the total groundwater pollution with heavy metals and it was calculated using equation (1):

128

HPI=

∑    

,

(1)

129

where Wi is the unit weight of the ith parameter, Qi is the sub-index of the ith

130

parameter, and n is the number of heavy metals measured. Qi was determined with

131

equation (2):

132

Qi=∑ 

 

*100,

 

(2)

133

where Mi is the value measured for the ith heavy metal and Ii is the ideal permissible

134

limit for the ith heavy metal. Ii was treated as 0 because the water quality standard in

135

China (2006) does not state ideal values. Si is the maximum allowable concentration

136

of the ith heavy metal according to the water quality standard in China (2006). Wi was

13｜

computed as: 1/Si (Prasad and Bose, 2001; Hoaghia et al., 2016).

138 139 140 141 142

2.4.2. Heavy metal evaluation index (HEI) HEI was used to evaluate the overall quality of water in terms of heavy metals. HEI was calculated with equation (3): 

HEI=∑   ,

(3)



143

where Ci is the measured concentration of the ith heavy metal and Si is the maximum

144

allowable concentration of the ith heavy metal.

145 146 14｜ 148

2.4.3. Human health risk assessment Health risk assessments are conducted to evaluate the risk to an individual's health caused by exposure to a factor by estimating the probability of adverse effects on the

149

human body. The risk types for the metal elements in groundwater that can harm

150

human health are classified according to the risk caused by exposure to carcinogenic

151

metals and non-carcinogenic metals. The health risk assessment models differ for

152

carcinogenic and non-carcinogenic metal elements. In this study, as defined by the

153

International Agency for Research on Cancer (IARC) (2011), As, Cd, and Cr were

154

treated as carcinogens, whereas the other heavy metals were considered

155

non-carcinogens. The two health risk assessment models were evaluated for the heavy

156

metals comprising As, Cd, and Cr by treating them as both carcinogens and

15｜

non-carcinogens.

158 159 160

2.4.3.1. Non-carcinogenic health risk assessment The non-carcinogenic health risk assessments were conducted by evaluating the

161

chronic daily intake (CDI) and the hazard quotient (HQ). CDI was calculated with

162

equation (4): CDI = (C × IR × EF × ED)/(BW × AT),

163

(4)

164

where C is the contaminant concentration (mg/L), IR is the ingestion rate per day (2

165

L/day for adults), ED is the exposure duration (30 years), EF is the exposure

166

frequency (365 days/year), AT represent the average exposure time (ED × 365), and

16｜

BW is the body weight (70 kg) (US Environmental Protection Agency, 1989). HQ was

168

calculated with the following equation:

169 1｜0

HQ =





,

(5)

where RfD is the reference dose as the oral exposure level for a pollutant.

1｜1 1｜2 1｜3 1｜4 1｜5 1｜6 1｜｜

2.4.3.2. Carcinogenic health risk assessment The carcinogenic potential of contaminated groundwater (C) was evaluated using equations (6) and (7): C = CDI × SF C = 1 – exp(–E × SF)

(6) (C ≥ 0.01),

(7)

where CDI was calculated using equation (5) and SF is the slope coefficient. Table 1

1｜8

showed the detailed RfD and SF values for heavy metals (US Environmental

1｜9

Protection Agency, 2002).

180 181 182

2.5. Statistical analysis Descriptive statistics (maximum, minimum, average, and coefficient of variation

183

(CV)) were calculated with SPSS (version 16.0). Spatial interpolation of the

184

distributions of heavy metals was conducted using ArcGIS 10.2.

185 186

3. Results and discussion

18｜ 188

3.1. Spatial distributions of heavy metals in groundwater

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The inverse distance weighted method for spatial interpolation in ArcGIS was

190

employed to determine the spatial distributions of heavy metals (Figure 2) because

191

this approach obtains better results compared with the kriging method. The spatial

192

distributions of the heavy metals varied among the different sites (Figure 2).

193

Groundwater is influenced by natural factors and anthropogenic activities, and the

194

environmental conditions also varied among the different sites, thereby leading to the

195

diverse distributions of the heavy metals.

196

Table 2 shows descriptive statistics for heavy metals in the groundwater samples.

19｜

In the shallow groundwater samples, the mean concentrations of the heavy metals

198

were in the following order: Fe > Cr > Mo > Zn > V > Al > Mn > As > Pb > Cu > Co >

199

Ni > Cd. In the deep groundwater samples, the mean concentrations of the heavy

200

metals were in the following order: Zn > Fe > Mo > Cr > Mn > V > As > Al > Cu >

201

Ni > Pb > Co > Cd. Clearly, the concentrations of heavy metals varied among the

202

samples from different depths. In addition, in the shallow groundwater samples, the

203

variations in V, Fe, Zn, and Cd were moderate, but high for the remaining heavy

204

metals. In the deep groundwater samples, the variations in V, Fe, As, and Cr were

205

high but moderate for the remaining heavy metals. Thus, the spatial distributions of

206

the heavy metals were heterogeneous in the shallow and deep groundwater samples.

20｜

According to the safe water standards defined by the World Health Organization

208

(WHO) (2017), which are similar to the China water quality standard (2006) (Table 3),

209

the concentrations of the heavy metals in the deep groundwater samples were all

210

below the WHO limits (2017), but the concentrations of some heavy metals in the

211

shallow groundwater samples exceeded the safe limits, such as those of Cr and Mo

212

(Figure 2). Thus, the shallow groundwater was polluted in some areas whereas the

213

deep groundwater was always safe to drink. In the shallow groundwater samples, the

214

concentration of Cr exceeded the safe limit in 14 groundwater samples, which were

215

mainly collected in Weinan city (Figure 2). Wang et al. (2012) assessed the Cr

216

concentration distributions in Weinan city and also found that the Cr concentrations

21｜

exceeded the safe limits. The Cr pollution mainly came from industrial sources. In

218

addition, the concentration of Mo exceeded the safe standard in one groundwater

219

sample.

220

In addition, the concentrations of Pb and As were below the WHO limit in the

221

shallow groundwater samples but some were close to the WHO limit, e.g., 9.53 µg/L

222

for Pb (10 µg/L) and 8.12 (10 µg/L) for As (Figure 2). As, Cd, and Cr are carcinogens

223

according to the IARC (2011). Therefore, the concentrations of heavy metals in the

224

groundwater in some areas exceeded or were close to the WHO standard limit (2011),

225

and thus they were not suitable for drinking.

226 22｜ 228

3.2. Differences in heavy metal concentrations in shallow and deep groundwater

229

samples

230

In order to assess the groundwater quality in the Guanzhong Plain region, we

231

compared the heavy metal concentrations in 14 deep groundwater samples and 14

232

shallow groundwater samples from the same sites as the deep groundwater samples.

233

Table 4 shows descriptive statistics for the heavy metals in the shallow and deep

234

groundwater samples. There were no significant differences in the concentrations of V,

235

Mn, Fe, Ni, As, and Cd in the shallow and deep groundwater samples (P > 0.05). The

236

mean concentrations of Al, Cr, Pb, and Co were higher in the shallow groundwater

23｜

samples than the deep groundwater samples, whereas the opposite results were

238

obtained for Cu, Zn, and Mo (P < 0.05). Clearly, there were no consistent trends in

239

the heavy metal concentrations at different depths. The heavy metal concentrations in

240

groundwater are influenced by the leaching of metals from the surface by rainwater,

241

and the geochemistry of aquifers also affects the availability of heavy metals in

242

groundwater (Khodapanah et al., 2009; Ravindra and Garg, 2007). Thus, these factors

243

affected the variable heavy metal concentrations found at different depths.

244

In addition, the variations in the concentrations of most heavy metals were lower

245

in the deep groundwater samples than the shallow groundwater samples (Table 4),

246

possibly because the shallow groundwater was more likely to be influenced by human

24｜

activities compared with the deep groundwater.

248 249 250

3.3. HPI and HEI results HPI and HEI have been employed to evaluate the total heavy metal pollution in

251

groundwater samples in many previous studies (Yari and Sobhanardakani, 2016;

252

Sobhanardakani, 2017). Bhuiyan et al. (2010) assigned the HPI results to three

253

pollution categories comprising: low HPI < 50, medium HPI = 50–100, and high HPI >

254

100 (Siegel, 2002). Bhuiyan et al. (2010) also classified the HEI results into three

255

pollution categories comprising: HEI < 40 indicating a low degree of pollution, HEI =

256

40–80 indicating a medium degree of pollution, and HEI > 80 indicating a high

25｜

degree of pollution. As shown in Figure 3, the HPI and HEI values determined for the

258

shallow and deep groundwater samples collected in the Guanzhong Plain region all

259

indicated a low degree of pollution. The low heavy metal concentrations in the

260

shallow and deep groundwater samples resulted in low HPI and HEI values. The Cr

261

concentrations exceeded the safe limit in some areas but the HPI and HEI evaluate the

262

total pollution degree, which was low in all areas.

263 264 265

3.4. Human health risk assessment Tables 5 and 6 show the health risk assessment results in terms of the

266

non-carcinogenic and carcinogenic health risks associated with heavy metals in the

26｜

groundwater samples. In terms of the non-carcinogenic health risks, the HQ values for

268

heavy metals in the deep groundwater samples were all < 1, whereas the HQ values

269

for the shallow groundwater samples from some areas were >1 for Cr and As (Table

2｜0

5). If HQ ≥ 1, heavy metals may be associated with a potential non-carcinogenic risk

2｜1

(Giri and Singh, 2015). Thus, the deep groundwater samples did not have associated

2｜2

non-carcinogenic health risks, whereas the shallow groundwater sample from some

2｜3

areas had associated non-carcinogenic health risks. In terms of the carcinogenic health

2｜4

risks, the ranges of Cr, As, and Pb in the deep groundwater samples were 0 to 1.09 ×

2｜5

10–2, 9.85 × 10–7 to 4.77 × 10–5, and 5.93 × 10–7 to 2.71 × 10–6, respectively. Thus, the

2｜6

carcinogenic health risks for As and Cd were lower than the maximum acceptable

2｜｜

level of 5 × 10–5 a–1 recommended by ICRP, but the Cr concentrations in some areas

2｜8

exceeded the acceptable level (Table 6). Similarly, Cd had no associated carcinogenic

2｜9

health risks in the shallow groundwater samples, whereas Cr and As had associated

280

carcinogenic health risks in some areas (Table 6). Therefore, pollution with Cr and As

281

should be addressed by the local government to ensure the safety of groundwater

282

supplies in the affected areas.

283 284 285 286 28｜

4. Conclusion

288

In this study, we collected 130 groundwater samples and assessed the groundwater

289

quality in the Guanzhong Plain region in terms of As and 12 other heavy metals based

290

on various evaluation indices in order to evaluate the potential health risks for humans.

291

The main conclusions are as follows.

292

(1) Cr concentrations in the shallow groundwater of some areas exceeded the safe

293

limit, whereas the concentrations of all heavy metals were safe in deep groundwater.

294

Thus, Cr pollution in shallow groundwater should be investigated.

295 296 29｜

(2) The HPI and HEI values indicated that the shallow and deep groundwater samples all had low levels of pollution with heavy metals. (3) Some shallow groundwater samples had non-carcinogenic health risks and

298

carcinogenic health risks associated with Cr and As. Some deep groundwater samples

299

only had carcinogenic health risks due to Cr. Our results may provide an important

300

reference for the management of local groundwater drinking supplies in the

301

Guanzhong Plain region.

302 303 304

Acknowledgments This study was supported by the National Natural Science Foundation of China

305

for a major international cooperation program between China and England

306

(415711300781), the National Natural Science Foundation of China (41371242 and

30｜

41530854), and the Key Deployment Project of the Chinese Academy

308

(KFZD-SW-306). The authors thank the editor and reviewers for their valuable

309

comments and suggestions.

310 311 312 313 314 315 316 31｜ 318 319 320 321 322 323 324 325 326 32｜

328 329 330 331 332 333 334 335 336 33｜ 338 339 340 341 342 343 344 345 346 34｜ 348 349 350 351 352 353 354 355 356 35｜ 358 359 360 361 362 363 364 365 366 36｜ 368 369 3｜0 3｜1

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Table 1 RfD and SF values for As and other heavy metals. Non-Carcinogen Cr Ni Cd Pb As Cu Zn Fe Mn V Mo Al Co Unit: mg (kg*d)–1

RfD 0.003 2 × 10–2 0.0005 1.4 × 10–3 0.0003 5 × 10–3 3 × 10–1 3 × 10–1 1.4 × 10–1 0.007 0.005 0.14 0.0003

Carcinogen Cr Cd As

SF 41 6.1 1.5

Table 2 Descriptive statistics for heavy metals in groundwater samples. Shallow groundwater samples Deep groundwater samples Heavy metal No. Min Max Mean CV No. Min Max Mean CV Al (µg/L) 116 0 66.47 2.46 2.68 14 0 6.55 0.79 0.46 V (µg/L) 116 0.035 15.68 2.93 0.94 14 0.054 5.21 1.98 1.12 Cr (µg/L) 116 0 174.76 21.27 1.6 14 0.000 21.80 5.54 0.68 Mn (µg/L) 116 0.001 43.37 1.21 4.39 14 0.320 19.43 3.30 0.63 Fe (µg/L) 116 2.156 116.61 27.38 0.84 14 2.804 28.63 16.10 2.07 Ni (µg/L) 116 0 1.79 0.07 3.2 14 0 1.82 0.29 0.56 Cu (µg/L) 116 0.003 1.13 0.15 1.24 14 0 3.61 0.56 0.57 Zn (µg/L) 116 0.374 21.11 3.6 0.85 14 2.953 424.22 92.05 0.79 Co (µg/L) 116 0.004 0.62 0.09 1.22 14 0.006 0.24 0.03 0.57 Pb (µg/L) 116 0 9.53 0.3 3.03 14 0 0.38 0.09 0.69 As (µg/L) 116 0.027 8.12 1.2 1.07 14 0.054 2.60 0.99 1.25 Mo (µg/L) 116 0.075 74.08 5.26 1.9 14 0.576 26.09 7.30 0.85 Cd (µg/L) 116 0.006 0.16 0.04 0.72 14 0.008 0.04 0.02 2.03 No., number; Min, minimum; Max, maximum; CV, coefficient of variation

Table 3 Heavy metal concentration limits specified by the WHO and in China. Heavy metals

Al

V

Cr Mn

Fe

Ni

Cu

Zn

Co Pb As Mo

Cd

WHO (µg/L)

200

10 10

70

5

China (µg/L)

200 50 50 100 300 20 1000 1000 50

10 10

70

5

50 500 300 20 1000 5000

Table 4 Descriptive statistics for heavy metals in 14 shallow and 14 deep groundwater samples. Shallow groundwater samples

Deep groundwater samples

Heavy metal

No.

Min

Max

Mean

CV

Min

Max

Mean

CV

Al (µg/L)

14

0

4.95

1.59

0.85

0

6.55

0.79

0.46

V (µg/L)

14

0.255

7.74

2.19

0.89

0.054

5.21

1.98

1.12

Cr (µg/L)

14

0

38.11

10.92

1.27

0.000

21.80

5.54

0.68

Mn (µg/L)

14

0.011

25.83

2.68

2.64

0.320

19.43

3.30

0.63

Fe (µg/L)

14

3.159

47.86

19.81

0.73

2.804

28.63

16.10 2.07

Ni (µg/L)

14

0

0.84

0.14

1.99

0

1.82

0.29

0.56

Cu (µg/L)

14

0.006

0.76

0.19

1.18

0

3.61

0.56

0.57

Zn (µg/L)

14

0.374

12.13

3.95

0.76

2.953 424.22 92.05 0.79

Co (µg/L)

14

0.007

0.33

0.11

0.80

0.006

0.24

0.03

0.57

Pb (µg/L)

14

0

0.74

0.18

1.15

0

0.38

0.09

0.69

As (µg/L)

14

0.027

3.29

0.96

0.82

0.054

2.60

0.99

1.25

Mo (µg/L)

14

0.267

6.18

2.24

0.91

0.576

26.09

7.30

0.85

Cd (µg/L)

14

0.018

0.08

0.04

0.60

0.008

0.04

0.02

2.03

No., number; Min, minimum; Max, maximum; CV, coefficient of variation

Table 5 HQ values obtained from the health risk assessments for non-carcinogenic metals. Heavy metal No.

Min

Max

Mean

No.

Min

Max

Mean

Al (µg/L)

116

0

0.013

0.0005

14

0

0.0013 0.0002

V (µg/L)

116

0.0001

0.0640

0.0120

14

0.0002

0.0213 0.0081

Mn (µg/L)

116 2.490E-07

0.009

0.0002

14

Fe (µg/L)

116

0.0002

0.011

0.0026

14

0.0003

0.0027 0.0015

Ni (µg/L)

116

0

0.003

9.72E-05

14

0

0.0026 0.0004

Cu (µg/L)

116 1.486E-05

0.006

0.0009

14

0

0.0207 0.0032

Zn (µg/L)

116 3.563E-05

0.002

0.0003

14

0.0003

0.0404 0.0088

Co (µg/L)

116

0.0004

0.059

0.0082

14

0.0006

0.0232 0.0033

Pb (µg/L)

116

0

0.195

0.0061

14

0

0.0077 0.0018

Mo (µg/L)

116

0.0004

0.423

0.0301

14

0.0033

0.1491 0.0417

Cr (µg/L)

116

0

1.664

0.2026

14

0.0000

0.2076 0.0527

As (µg/L)

116

0.0038

1.161

0.1718

14

0.0077

0.3710 0.1412

Cd (µg/L)

116

0.0003

0.009

0.0022

14

0.0005

0.0021 0.0010

No., number; Min, minimum; Max, maximum

6.53E-05 0.0040 0.0007

Table 6 Carcinogenic potential of groundwater in the Guanzhong Plain region. Heavy metals

No.

Min

Max

Mean

No.

Min

Max

Mean

Cr (µg/L)

116

0

0.0845

0.0105

14

0

0.0109

0.0028

As (µg/L)

116

4.91E-07

0.0001

2.21E-05

14

9.85E-07

4.77E-05

1.81E-05

Cd (µg/L)

116

4.23E-07

1.22E-05

2.94E-06

14

5.93E-07

2.71E-06

1.32E-06

No., number; Min, minimum; Max, maximum

Figure 1. Location of the Guanzhong Plain in China (a) and the sampling sites (b).

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(a)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

(b)

Figure 2. Spatial distributions of heavy metals in the shallow groundwater (a) and deep groundwater samples (b).

(a)

(b)

(a)

(b)

Figure 3. HPI and HEI values for shallow groundwater (a) and deep groundwater (b) samples in the Guanzhong Plain region.

1. Spatial distributions of heavy metals in groundwater in Guanzhong Plain, China. 2. Differences in heavy metals compared in shallow and deep groundwater samples. 3. Groundwater quality evaluated using two water quality indices. 4. Non-carcinogenic and carcinogenic health risks due to heavy metals assessed.

Declaration of Interest Statement No conflicts of interest exist regarding the submission of this manuscript and manuscript has been approved for publication by all of the authors. On behalf of my co-authors, I declare that the work described is original research that has not been published previously and it is not under consideration for publication elsewhere, in whole or in part. All the authors have approved the submitted manuscript.