*3.2. Health Risk Assessment*

The study flowchart is shown below (Figure 2), which shows the overall idea of the study, from background investigation, data collection, to health risk assessment, using the Monte Carlo model and Visual Minteq, finally deriving the main ion morphology of carcinogenic factors. The main pathways through which heavy metals pose human health risks are dermal contact and food chain. Human health risks resulting from direct or indirect exposure to groundwater can be assessed by the models recommended by the Ministry of Environmental Protection of Environmental Protection of China, based on models of the United States Environmental Protection Agency (USEPA). Data were analyzed according to the concentration period of precipitation (dry or rainy season) and human physiology (i.e.,

adults and children) [32,33]. Based on the actual situation in China, the Chinese model adopts specific parameters, which are presented in Table 2.

*Water* **2022**, *14*, x FOR PEER REVIEW 7 of 23

**Figure 2.** Research idea flowchart. **Figure 2.** Research idea flowchart.

Cr6+ Inductively coupled plasma atomic emission

spectrometry

**Table 2.** Limit values of several parameters for oral intake and skin contact by type of sensitive group.


EC Conductivity analyzer analysis method Conductivity Analyzer DDS‐11A 0**–**1.999 × 105 μS/cm

TDS Conductivity analyzer analysis method Conductivity Analyzer DDS‐11A 0**–**1.999 × 105μS/cm The average daily dose for oral intake and dermal contact was calculated as follows:

$$Intake\_{\text{oral}} = \frac{\text{C} \times IR \times EF \times ED}{BW \times AT} \tag{2}$$

ICP‐MS ICAPQc 0.0006 mg/L

$$Intake\_{demand} = \frac{DA \times EV \times SA \times EF \times ED}{\mathcal{BW} \times AT} \tag{3}$$

As Atomic fluorescence spectrometry AFS‐920 AFS‐920 0.000046 mg/L

$$DA = \mathbb{K} \times \mathbb{C} \times t \times \mathbb{C} \mathbb{F} \tag{4}$$

$$SA = \text{239} \times H^{0.417} \times BW^{0.517} \tag{5}$$

where *Intakeoral* is the average daily dose of oral intake (mg (kg/d)−<sup>1</sup> ); *DA* and *SA* are defined as the exposure dose (mg/cm<sup>2</sup> ) and skin contact area (cm<sup>2</sup> ) of each event, respectively; and *C* indicates the concentration of pollutants in groundwater (mg/L−<sup>1</sup> ) obtained by laboratory tests. The limit values of oral intake and skin contact of several parameters for the two sensitive groups investigated are illustrated in Table 2.

The non-carcinogenic risk of oral intake and skin contact was calculated as follows:

$$RfD = RfD \times BAS\_{\mathcal{S}^l} \tag{6}$$

$$HQ\_{oral} = \frac{Intake\_{oral}}{RfD\_{oral}}\tag{7}$$

$$HQ\_{drmal} = \frac{Intake\_{drmal}}{RfD\_{drmal}}\tag{8}$$

where *HQ* and *RfD* indicate the non-carcinogenic hazard quotients and the reference doses, respectively [34]. In this study, the *RfD* values of Mn, NO<sup>2</sup> <sup>−</sup>, Fe, F, Pb, Cr6+, Cd, As, and ammonia nitrogen (in terms of N), were found to be 0.14, 0.1, 0.3, 0.04, 0.0014, 0.0003, 0.003, 0.0003, and 0.97 mg (kg d) 1, respectively [35]. *RfDdermal* indicates a gastrointestinal absorption factor that can be calculated by *RfDoral*. Apart from the value of *BASgi* for Cr6 + which was 0.025, the other values *BASgi* were all equal to 1.

The non-carcinogenic risk of oral intake and skin contact absorption was calculated as the total risk, as follows:

$$HI\_i = HQ\_{oral} + HQ\_{dormal} \tag{9}$$

$$HI\_{total} = \sum\_{i=1}^{n} HI\_i \tag{10}$$

where *HI* is a health risk assessment index, which refers to the sum of multiple *HQs* of multiple substances through the two exposure pathways considered. *HQ* and *HI* values lower than 1 are considered safe for human health [36,37]. By contrast, residents may face non-carcinogenic risks when these values exceed 1. The standard value of HI was proposed by the Ministry of Environmental Protection of the China in 2014.

In this study, As and Cr6+ were considered the main carcinogenic factors; their carcinogenic health risk values were calculated as follows:

$$SF\_{demand} = \frac{SF\_{oral}}{ABS\_{gi}}\tag{11}$$

$$\text{CR}\_{oral} = \text{Intake}\_{oral} \times \text{SF}\_{oral} \tag{12}$$

$$\text{CR}\_{demand} = Intake\_{demand} \times SF\_{demand} \tag{13}$$

$$
\mathbb{C}\mathbb{R}\_{\text{total}} = \mathbb{C}\mathbb{R}\_{\text{oral}} + \mathbb{C}\mathbb{R}\_{\text{demand}}\tag{14}
$$

where the *SForal* values of As and Cr6+ were set at 1.5 and 0.5 mg (kg/day)−<sup>1</sup> , respectively; and CR indicates the risk of cancer. According to the regulations of the Ministry of Environmental Protection of China, the acceptable limit value for both parameters is 0.6 [38]. When the calculated value exceeds the limit value, this indicates that there is a risk of cancer in the region, and that it is necessary to take corresponding environmental control measures in time [39].
