2.4.2. Human Health Risk Assessment

The evaluation of drinking water quality needs to be completed by a health risk assessment as polluted water may cause adverse effects on the human body through water intake and dermal contact [1,38,42]. In this study, the potential risks through dermal contact pathway were neglected for non-carcinogenic risk because it is usually low [27,38,39], and water contamination in the study area was not considerably high as listed in Table 1. The risk assessment parameters selected for this study are NH<sup>4</sup> + , NO3¯, NO2¯, F¯ and Cr6+, using the models recommended by the Ministry of Environmental Protection of the P.R. China [30], which are also based on the model recommended by the United States Environmental Protection Agency [29,39].


**Table 1.** Statistical analysis of physicochemical indices for water samples collected in Tongchuan.

<sup>1</sup> Percentage of samples exceeding the P.R. China national standards, <sup>2</sup> percentage of samples exceeding WHO standards. BDL, below detection limit. All units for all parameter indices are in mg/L, except for pH (non-dimensional) and EC (µS/cm).

> According to the references mentioned above, the non-carcinogenic risk through the oral intake pathway is calculated as follows:

$$Intake\_{oral} = \frac{\mathbb{C} \times IR \times EF \times ED}{BW \times AT} \tag{7}$$

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

where *Intakeoral* denotes the daily average exposure dosage through oral pathway per unit weight (mg/(kg·d)), *C* is the concentration of the parameter in water (mg/L), and *IR* represents the ingestion rate of water through drinking (L/d). *EF* and *ED* represent the exposure frequency (d/a) and exposure duration (a), respectively. *BW* and *AT* are the average body weight (kg) and average time of non-carcinogenic effects (d), respectively.

For this study, the ingestion rate of water used was based on statistical investigation that considers 1.5 L per day for adults and 0.7 L per day for children under 12 years old [38]. For non-carcinogenic risk assessment, *EF* is 365 days per year for both adults and children. *ED* is 30 years for adults and 12 years for children. *BW* is 15.9 kg for children, 56.8 kg for adults [30]. The average time (*AT*) for non-carcinogenic effects on children is 4380 days, whereas it is 10,950 days for female and male adults. *HQoral* and *RfDoral* represent the hazard quotient and the reference dosage for non-carcinogenic pollutants through the oral exposure pathway (mg/(kg.d)), respectively. This study considered the *RfDoral* values for NH<sup>4</sup> + , NO<sup>3</sup> −, NO<sup>2</sup> <sup>−</sup>, F<sup>−</sup> and Cr6+ as 0.97, 1.6, 0.1, 0.04 and 0.003 mg/(kg.d), respectively [1,30,38]. *HQ* with a value exceeding 1 indicates a high potential health risk [21]. In addition, Cr6+ can also cause carcinogenic risks through drinking water intake and dermal contact. The total carcinogenic risk is the sum of calculated cancer risk through drinking pathway and that of dermal contact and is calculated as follows [1,30]:

$$\text{CR}\_{oral} = \text{Intake}\_{oral} \times \text{SF}\_{oral} \tag{9}$$

$$\text{CR}\_{\text{demand}} = \text{Intake}\_{\text{demand}} \times \text{SF}\_{\text{demand}} \tag{10}$$

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

$$
\mathbb{C}\mathbb{R}\_{total} = \mathbb{C}\mathbb{R}\_{oral} + \mathbb{C}\mathbb{R}\_{demand} \tag{12}
$$

where *CRoral* represents the carcinogenic risk through the oral exposure pathway. The *CR* limit is set as 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> . *Intakeoral* denotes daily average exposure dosage through oral pathway per unit weight (mg/(kg·d)), *SForal* is the slope factor for the carcinogenic pollutants (mg/(kg·d)−<sup>1</sup> . The *SForal* value of Cr6+ is set as 0.5 (mg/(kg·d))−<sup>1</sup> by the Ministry of Environmental Protection of the P.R. China [30]. *ABSgi* is the gastrointestinal absorption factor, and its value is 1 for all contaminants except for Cr6+, with *ABSgi* equals 0.025 [1,30,55].

The *Intakedermal* is calculated as [1,30,38] as in Equations (13)–(15):

$$Intake\_{demand} = \frac{DA \times EV \times SA \times EF \times ED}{BW \times AT} \tag{13}$$

$$DA = \mathbb{K} \times \mathbb{C} \times t \times \mathbb{C} \text{F} \tag{14}$$

$$SA = \text{239} \times H^{0.417} \times BW^{0.517} \tag{15}$$

where *DA* and *SA* are the exposure dosage of every single event in mg/cm<sup>2</sup> and the contacting area skin surface (cm<sup>2</sup> ), respectively. *EV* is the daily exposure frequency of dermal contact set at 1 for this study. *ED* is the exposure duration for carcinogenic risk, different from non-carcinogenic risk, and is set as 25,550 days for both adults and children. *K* is the coefficient of skin permeability (0.001 cm/h), *t* is the contact duration, which is set as 0.4 h/day for both adults and children [1,38]. *CF* is a conversion factor that equals 0.001, and *H* denotes the average height of the population estimated at 165.3 cm for males, 153.4 cm for females and 99.4 for children [1].
