*3.6. Health Risk Assessment*

Table 6 presents the calculated health risk to adults and children when they are exposed to the contaminants in groundwater through drinking water intake. The total health risk due to contaminated drinking water intake ranges from 0.21 to 4.71, with a mean of 0.89 for adults. For children, the health risk is evaluated through the hazard quotient ranged from 0.35 to 7.85 with a mean of 1.52. Considering that HQ > 1 for non-carcinogenic risk indicates high potential health risk [1], water from wells represented by samples TW1- 008, TW1-009, TW1-037, TW1-041, TW1-047, TW1-049 to TW1-054, TW1-059 to TW1-061, TW2-014 to TW2-067 was not safe, especially for children.

activities.


**Table 5.** Water quality index values and water types of the samples. TW1-032 16.13 Excellent TW1-055 25.67 Excellent TW2-066 54.70 Good

TW1-012 30.86 Excellent TW1-050 16.25 Excellent TW2-043 13.98 Excellent TW1-013 12.02 Excellent TW1-051 14.03 Excellent TW2-044 33.59 Excellent TW1-014 18.41 Excellent TW1-052 166.56 Poor TW2-045 39.97 Excellent TW1-023 13.20 Excellent TW1-053 39.17 Excellent TW2-057 23.71 Excellent TW1-025 14.05 Excellent TW1-054 59.63 Good TW2-058 19.68 Excellent

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

**Figure 5.** Water quality distribution in Tongchuan City. **Figure 5.** Water quality distribution in Tongchuan City.

*3.6. Health Risk Assessment*  Table 6 presents the calculated health risk to adults and children when they are ex-As shown in Figure 6, NO<sup>3</sup> − contributes a considerable amount to non-carcinogenic risk for both adults and children and is followed by F−, Cr6+, and lastly, by NO<sup>2</sup> −.

posed to the contaminants in groundwater through drinking water intake. The total health The respective HQ mean values for adults are 0.54, 0.31, 0.02, 0.02, and 0.90, 0.52, 0.07, and 0.03 for children. HN<sup>4</sup> <sup>+</sup> has zero contribution to health risk in this study area for both adults and children. High nitrate health risk is probably due to the anthropogenic activities, especially fertilizers in agriculture [21]. In addition, Wei et al. [34] reported that NO<sup>3</sup> − pollution was a major environmental geological problem in the groundwater for this region. Overall, 27.1% and 54.2% of the samples present a health risk through drinking water intake for adults and children, respectively.


**Table 6.** Calculated hazard quotient (HQ) of non-carcinogenic risk for adults and children.

In this study, Cr6+ was also considered as a carcinogenic risk pollutant. Considering the acceptable *CRtotal* limit set as 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> by the Ministry of Environmental Protection of the P.R. China [30], the results shown in Table 7 revealed a critical carcinogenic risk by drinking and daily contact of water from six (12.5%) wells in the study area.

As shown in Figure 6, NO<sup>3</sup>

Mean 0.00 0.54 0.02 0.31 0.02 0.89 0.00 0.90 0.03 0.52 0.07 1.52

risk for both adults and children and is followed by F<sup>−</sup>

**Figure 6.** Representation of the mean HQ for non-carcinogenic (NH<sup>4</sup> + , NO<sup>3</sup> − , NO<sup>2</sup> − , F<sup>−</sup> , Cr6+) contaminants. **Figure 6.** Representation of the mean HQ for non-carcinogenic (NH<sup>4</sup> <sup>+</sup>, NO<sup>3</sup> −, NO<sup>2</sup> −, F−, Cr6+) contaminants.

<sup>−</sup> contributes a considerable amount to non-carcinogenic

, Cr6+, and lastly, by NO<sup>2</sup>

− .

The respective HQ mean values for adults are 0.54, 0.31, 0.02, 0.02, and 0.90, 0.52, 0.07, and 0.03 for children. HN<sup>4</sup> <sup>+</sup> has zero contribution to health risk in this study area for both **Table 7.** Calculated carcinogenic risk due to Cr6+ in water intake and dermal contact.


TW1-005 0 0 TW1-043 0 0 TW2-018 4.25 × 10‒4 7.01 × 10‒4

TW1-007 0 0 TW1-046 0 0 TW2-021 0 0 TW1-008 0 0 TW1-047 0 0 TW2-022 0 0 TW1-009 0 0 TW1-048 0 0 TW2-037 0 0 TW1-010 0 0 TW1-049 0 0 TW2-042 0 0 TW1-012 0 0 TW1-050 0 0 TW2-043 0 0 TW1-013 0 0 TW1-051 0 0 TW2-044 4.18 × 10‒5 6.89 × 10‒5 TW1-014 0 0 TW1-052 0 0 TW2-045 0 0 TW1-023 0 0 TW1-053 0 0 TW2-057 0 0 TW1-025 0 0 TW1-054 0 0 TW2-058 4.18 × 10‒5 6.89 × 10‒5 *CRtotal* ranges from 4.18 <sup>×</sup> <sup>10</sup>−<sup>5</sup> to 4 <sup>×</sup> <sup>10</sup>−<sup>4</sup> for adults and from 6.89 <sup>×</sup> <sup>10</sup>−<sup>5</sup> to 8 <sup>×</sup> <sup>10</sup>−<sup>4</sup> for children. Similar results have also been found by He and Wu [74], Li et al. [75], Wu and Sun [38], Liu et al. [76], Ji et al. [77], and He et al. [78] in their study on groundwater quality and health risk assessment, which confirmed the health threats faced by the population, especially for children in the loess area of northwest China. According to WHO [42], the excessive Cr6+ concentration in drinking water can cause lung cancer via inhalation route. Groundwater from wells represented by samples TW1-004, TW2-014, TW2-018, TW2-044, TW2-058, and TW2-067 with *CRtotal* values of more than 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> must be used with precaution for drinking purposes.

### TW1-032 0 0 TW1-055 0 0 TW2-066 0 0 **4. Conclusions**

TW1-036 0 0 TW1-058 0 0 TW2-067 4.60 × 10‒4 7.58 × 10‒4 TW1-037 0 0 TW1-059 0 0 TW2-069 0 0 In the present study, water quality index (WQI), statistical analysis and graphical approaches were implemented to understand the status of groundwater quality in the Tongchuan area on the Loess Plateau, northwest China. In addition, GIS approaches helped to map the WQI results of this study. Daily average exposure dosage through oral pathway was taken into consideration to calculate health risks to the human body through drinking water intake. 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 considered. The following conclusions can be achieved:


This study will be helpful to local decision makers for implementing measures, policy and strategies to protect groundwater resources and reduce the health risks of residents by groundwater consumption through oral and dermal pathways. It is also useful for international scholars who may find information for similar studies or its improvement.

**Author Contributions:** Research conceptualization, A.N. and P.L.; data curation, S.H., X.H., and A.N.; methodology, A.N.; writing—original draft, A.N.; writing—review and editing, P.L., S.H., X.H., S.M.K.A., and M.F., supervision, P.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Natural Science Foundation of China (42072286 and 41761144059), the Fundamental Research Funds for the Central Universities of CHD (300102299301 and 300102291507), the Fok Ying Tong Education Foundation (161098), and the Ten Thousand Talents Program (W03070125).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All processed data generated or used during the study appear in the submitted article. Raw data may be provided on reasonable request from the corresponding author.

**Acknowledgments:** We acknowledge the members of the Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region of the Ministry of Education, Chang'an University, Shaanxi, China for the groundwater samples processing. The useful and constructive comments from the editors and reviewers are sincerely acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.
