*2.4. Human Health Risk Assessment*

The human health risk assessment is the basis for controlling groundwater pollution and ensuring a safe drinking water supply [49,60–62]. Groundwater can affect human health through various exposure pathways, the most common of which are drinking water intake and dermal contact [63]. The model recommended by the Ministry of Ecology and Environment of the P.R. China [64] based on the United States Environmental Protection Agency models [65] was adopted in this study. There are many agricultural and industrial production activities in the study area. Therefore, representative pollutants F−, nitrogen (NO3-N, NO2-N, NH4-N), and PTEs (Fe, Mn, Hg, As, Cd, Cr6+, and Pb) are selected as the parameters of risk assessment. Due to differences in the physiology of males, females, and children, this study separately evaluated the health risks of oral intake and dermal intake.

The non-carcinogenic risk through drinking water intake is calculated as follows [60,63]:

$$\text{Intake}\_{\text{oral}} = \frac{\mathbb{C} \times \text{IR} \times \text{EF} \times \text{ED}}{\text{BW} \times \text{AT}} \tag{5}$$

$$\text{HQ}\_{\text{oral}} = \frac{\text{Intake}\_{\text{oral}}}{\text{RfD}\_{\text{oral}}} \tag{6}$$

The non-carcinogenic risk through dermal contact is expressed as follows [42]:

$$\text{Intake}\_{\text{demand}} = \frac{\text{DA} \times \text{EV} \times \text{SA} \times \text{EF} \times \text{ED}}{\text{BW} \times \text{AT}} \tag{7}$$

$$\mathbf{DA} = \mathbf{K} \times \mathbf{C} \times \mathbf{t} \times \mathbf{CF} \tag{8}$$

$$\text{SA} = \text{239} \times \text{H}^{0.417} \times \text{BW}^{0.517} \tag{9}$$

$$\text{HQ}\_{\text{demand}} = \frac{\text{Intake}\_{\text{demand}}}{\text{RfD}\_{\text{demand}}} \tag{10}$$

$$\text{RfD}\_{\text{demand}} = \text{RfD}\_{\text{oral}} \times \text{ABS}\_{\text{gi}} \tag{11}$$

where Intakeoral, Intakedermal, HQoral, HQdermal, RfDoral, and RfDdermal represent the chronic daily dose via ingestion and dermal contact (mg/(kg day)), the hazard quotient through oral and dermal exposure pathways, reference dose for oral and dermal contact pathways (mg/(kg day)), respectively. C, DA, SA, and ABSgi are the pollutant concentration of groundwater (mg/L), exposure dose (mg/cm<sup>2</sup> ), skin surface area (cm<sup>2</sup> ), and gastrointestinal absorption factor, respectively. The definitions and values of other parameters are shown in Tables 1 and 2.

**Table 1.** Definition and values of key parameters for human health risk assessment.


a refer to [64]; <sup>b</sup> refer to [66]; <sup>c</sup> refer to [67]; <sup>d</sup> refer to [63].

**Table 2.** The values of RfD, ABSgi, and SF for different ions.


The total non-carcinogenic risks are calculated as follows [1,29,45]:

$$\rm{HQ}\_i = \rm{HQ}\_{\rm{oral}} + \rm{HQ}\_{\rm{dermal}} \tag{12}$$

$$\text{HI}\_{\text{total}} = \sum\_{\mathbf{i}=1}^{\text{n}} \text{HQ}\_{\mathbf{i}} \tag{13}$$

where HQ is the non-carcinogenic hazard quotient and HI is the hazard index. i represents the risk assessment parameters. When the value of HQ and HI is less than 1, it is safe for human health. HI > 1 indicates unacceptable risk, and residents are exposed to noncarcinogenic risks [60,64].

In addition to non-carcinogenic risk, As, Cd, and Cr6+ can also create carcinogenic risks for humans [7,41]. The carcinogenic risk through drinking water intake and dermal contact is calculated as follows:

$$\text{CR}\_{\text{oral}} = \text{Intake}\_{\text{oral}} \times \text{SF}\_{\text{oral}} \tag{14}$$

$$\text{CR}\_{\text{demand}} = \text{Intake}\_{\text{demand}} \times \text{SF}\_{\text{demand}} \tag{15}$$

$$\text{SF}\_{\text{demand}} = \frac{\text{SF}\_{\text{oral}}}{\text{ABS}\_{\text{g}^{\text{l}}}} \tag{16}$$

$$\text{CR}\_{\text{total}} = \text{CR}\_{\text{oral}} + \text{CR}\_{\text{demand}} \tag{17}$$

where CR denotes the carcinogenic risk. SF is the slope factor for the carcinogenic contaminants (mg/(kg day))−<sup>1</sup> . The SForal values for As, Cd, and Cr6+ are shown in Table 2. The average time (AT) for carcinogenic risk is set at 27,740 days for both adults and children, as the harm to human health caused by cadmium, chromium, and arsenic will last a lifetime [64]. The acceptable limit for CR is 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> .
