**1. Introduction**

Groundwater is an important source for drinking and other various purposes for the majority of the population around the world, especially in arid and semiarid regions where precipitation and runoff are rare [1–6]. In addition to drinking, groundwater is useful for domestic, industrial and agricultural purposes. Due to the increased demand for groundwater, the groundwater table is subject to fluctuations, and aquifers are becoming contaminated in the context of climate change, rapid population growth, industrial development and urban expansions [7–12]. This situation is also aggravated where natural phenomena are controlling the physicochemical parameters of groundwater, such as rock influences, volcanic eruption or marine salt intrusions [13].

There is a critical increase in freshwater demand correlated with the rapid growth of the population all over the world [14] and intensive agriculture activities [15,16]. The increment of the population also leads to the expansion of cities and municipal waste that affect the groundwater quality through organic and inorganic contaminants [17–20]. Furthermore, industrialization is one of the most significant factors affecting groundwater quality through the effluents released into the nature [21–24]. Papazotos et al. [25]

**Citation:** Nsabimana, A.; Li, P.; He, S.; He, X.; Alam, S.M.K.; Fida, M. Health Risk of the Shallow Groundwater and Its Suitability for Drinking Purpose in Tongchuan, China. *Water* **2021**, *13*, 3256. https:// doi.org/10.3390/w13223256

Academic Editor: Dimitrios E. Alexakis

Received: 16 October 2021 Accepted: 15 November 2021 Published: 17 November 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

investigated the impact of water–rock and agricultural activities in the Psachna Basin (Greece) on groundwater quality and found that groundwater was strongly affected by the ultramafic geological environment with anthropogenic activities as revealed by high concentrations of Cr, Cr6+, and NO<sup>3</sup> −. Water-ultramafic rock processes can also increase the concentration of Cr in groundwater as investigated by Vasileiou et al. [26] in their study on hydrogeochemical processes and natural background levels of chromium in an ultramafic environment in Macedonia (Greece), and they found a high concentration of Cr6+ ranging from 0.5 to 131 µg/L in groundwater of western Vermino Mountain. In addition, Chen et al. [27] found rock dissolution and precipitation of Ca-As and CaF2, which controlled a high concentration of As and CaF<sup>2</sup> in northwest China. In terms of groundwater pollution by marine intrusion, Zissimos et al. [28] tested the occurrence and distribution of Cr in groundwater and surface water in Cyprus and found that the highest Cr6+ concentration observed in the Troodos area was 26 µg/L. However, the abnormal concentrations of Cr6+ (460 µg/L) and As (15 µg/L) were detected in groundwater along the coastline in the Schinos area (Greece) due to seawater intrusion [29].

Given the importance of groundwater for humanity and considering its vulnerability facing pollution issues as aforementioned, numerous studies have been conducted to evaluate groundwater quality to ensure the health of consumers. As a result, governments and states implemented controlling structures for water quality in order to preserve the population health [14]. In this regard, many groundwater quality investigations have been conducted based on the guidelines set by governments and organizations such as the World Health Organization (WHO) and the Ministry of Environmental Protection of the P.R. China [30]. Based on the aforementioned guidelines, serious drinking groundwater contamination was reported by many scholars all over the world [15,16,18,31–36]. However, few of them were associated with groundwater pollution and health risk assessment. To obtain the results, many approaches were used by the researchers. Ni et al. [37] used the geostatistical spatial analysis function of ArcGIS to map the evaluated carcinogenic and non-carcinogenic risks in the Sichuan Basin, China. Their study showed that total cancerous and non-cancerous risks were found in 5% and 8% of samples, respectively. Using a comprehensive water quality index assessment, Wu and Sun [38] found that 60% of sampled water was unsuitable for drinking in the alluvial plain located in mid-west China. Chen and her colleagues [27] used a triangular fuzzy numbers approach to assess health risk by As and CaF<sup>2</sup> in groundwater and found that their concentrations were higher in the shallow groundwater, which exceeded the acceptable limit (1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> ) set by the Ministry of Environmental Protection of the P.R. China for Cr6+ and As [30].

Studies performed in the northwest of China reported high nitrate concentrations representing health risk concerns for the population [38] due to anthropogenic activities, especially fertilizers used in agriculture [39]. N-bearing and P-bearing fertilizers can cause the oxidation of geogenic Cr, which results in elevated Cr6+ [19]. Wei et al. [34] also reported that nitrate pollution was a major environmental geological problem in the groundwater in part of China. In addition, Li et al. [21] reported a severe water stress in the Chinese Loess Plateau aggravated by the high fluoride concentration in drinking water.

The Tongchuan region is situated in the middle edges of the Loess Plateau and is adjacent to the Weihe River Valley and Guanzhong Basin, and the main water supply aquifer in this area is a phreatic aquifer with thickness ranging from 25 to 60 m [34,39]. The main objective of the present study is to enhance the understanding of the association between water quality and health risk assessment. Specifically, this study aims to characterize the major pollutants in shallow groundwater, to check their concentration based on the depth of wells, to determine the water quality index and make its distribution map, and to assess the water's potential risks to human health. To understand the status of groundwater quality, the water quality index (WQI), hydrochemical correlation analysis, and graphical approaches were used. The health risk assessment was performed considering daily average exposure dosage through oral pathway per unit weight (mg/(kg.d)) for drinking water intake; and for dermal contact, the exposure dosage of every single event in mg/cm<sup>2</sup> and

the skin surface (cm<sup>2</sup> ) were taken into consideration. Geographical information system approaches helped to better understand the results of this study. event in mg/cm2 and the skin surface (cm2) were taken into consideration. Geographical information system approaches helped to better understand the results of this study.

and graphical approaches were used. The health risk assessment was performed considering daily average exposure dosage through oral pathway per unit weight (mg/(kg.d)) for drinking water intake; and for dermal contact, the exposure dosage of every single

*Water* **2021**, *13*, x FOR PEER REVIEW 3 of 21

### **2. Materials and Methods 2. Materials and Methods**

### *2.1. Study Area 2.1. Study Area*

Tongchuan City is 70 km away from Xi'an City, the capital city of Shaanxi Province (Figure 1). It belongs to the Chinese Loess Plateau, with longitude between 108◦35044" E and 109◦29022" E and latitude between 34◦48027" N and 35◦35023" N. The altitude of Tongchuan City ranges from 900 to 1350 m above mean sea level [39]. The study area is situated in the middle edges of Loess Plateau and adjacent to the Weihe River Valley and Guanzhong Basin [34,40]. Tongchuan lies in the transition zone of semi-humid and semi-arid climate with annual mean rainfall and evaporation of around 540 and 1964 mm, respectively. The annual temperature of Tongchuan City is 8.9–12 ◦C [34,39]. Precipitation, reservoir leakage and irrigation are the main recharges of groundwater, whereas discharge to some rivers such as the Beiluo River and Juhe River, evaporation and artificial extraction [34] are the main discharge pathways of groundwater. Li et al. [39] estimated the groundwater recharge at 52.8% from precipitation and 40.1% from irrigation infiltration, whereas 37.4% and 44.9% of groundwater were discharged by artificial extraction and the lateral outflow, respectively. Geologically, the study area is dominated by Quaternary loess divided into three landforms, including loess tableland, loess gully and alluvial terrace. Furthermore, this area has several layers from top down [39]: Holocene loess layer and upper Pleistocene loess layer, which are unsaturated. The middle Pleistocene layer is composed of silty clay, which separates the phreatic aquifer and the confined aquifer partially formed by the lower Pleistocene loess layer, alluvial, sand and gravel layers. The phreatic aquifer with a thickness of 25 to 60 m is the main water supply aquifer in this area. Tongchuan City is 70 km away from Xi'an City, the capital city of Shaanxi Province (Figure 1). It belongs to the Chinese Loess Plateau, with longitude between 108°35′44″ and 109°29′22″ E and latitude between 34°48′27″ and 35°35′23″ N. The altitude of Tongchuan City ranges from 900 to 1350 m above mean sea level [39]. The study area is situated in the middle edges of Loess Plateau and adjacent to the Weihe River Valley and Guanzhong Basin [34,40]. Tongchuan lies in the transition zone of semi-humid and semi-arid climate with annual mean rainfall and evaporation of around 540 and 1964 mm, respectively. The annual temperature of Tongchuan City is 8.9–12 °C [34,39]. Precipitation, reservoir leakage and irrigation are the main recharges of groundwater, whereas discharge to some rivers such as the Beiluo River and Juhe River, evaporation and artificial extraction [34] are the main discharge pathways of groundwater. Li et al. [39] estimated the groundwater recharge at 52.8% from precipitation and 40.1% from irrigation infiltration, whereas 37.4% and 44.9% of groundwater were discharged by artificial extraction and the lateral outflow, respectively. Geologically, the study area is dominated by Quaternary loess divided into three landforms, including loess tableland, loess gully and alluvial terrace. Furthermore, this area has several layers from top down [39]: Holocene loess layer and upper Pleistocene loess layer, which are unsaturated. The middle Pleistocene layer is composed of silty clay, which separates the phreatic aquifer and the confined aquifer partially formed by the lower Pleistocene loess layer, alluvial, sand and gravel layers. The phreatic aquifer with a thickness of 25 to 60 m is the main water supply aquifer in this area.

**Figure 1.** Study area and samples distribution. **Figure 1.** Study area and samples distribution.

### *2.2. Groundwater Samples 2.2. Groundwater Samples*

For this study, 48 groundwater samples were collected from the wells and boreholes distributed in the study area. The criteria for the selection of water samples were based on the depth of wells, water purposes and the zone of collection. The sampling locations were recorded by coordinates using a portable GPS device and are shown as Figure 1. Samples were collected in pre-cleaned plastic polyethylene bottles for physicochemical analysis after the wells were pumped for 10 min. Before sampling, all the containers were washed and rinsed thoroughly with the groundwater to be sampled. Water was filtered through 0.45 µm filter during sampling. Sample collection, handling, and preservation complied with the standard procedures recommended by Standard Examination Methods for Drinking Water [30] to ensure data quality and consistency. The water samples were analyzed in the Soil and Water Testing Center of Shaanxi Institute of Engineering Investigation, China.
