2.6. Health Risk Assessment

Risk assessment is a method for evaluating the probability of occurrence of some contaminants to produce harmful health effects over a period of time. To estimate the potential carcinogenic or non-carcinogenic effects of these contaminants, a health risk evaluation is required [3].

As the main route of exposure to metals in bottled water is through ingestion, the non-carcinogenic human health risk was measured in this study through ingestion. To assess the risk caused by chronic exposure to metals, the exposure dose (D) was calculated according to Equation (2) [13]. Moreover, Hazard Quotients (HQ), hazard index (HI), and carcinogenetic risk (CR) were calculated according to the model used by Mohammadi et al., 2019 [3]. These parameters were established for an adult with an average weight of 70 kg and a water intake rate of 2 L/day.

where D is the exposure dose (mg/kg/day), C is the contaminant concentration (mg/L), IR is the intake rate of contaminated water (L/day), EF is the exposure factor (unitless), BW is the body weight (kg).

The HQ for each metal was calculated by reporting the exposure dose (D) to the oral reference dose (RfD) for the same heavy metal. This parameter was calculated using Equation (3).

The values of RfD for oral ingestion for Pb, Cd, Cr, Co, Ni, Zn, and Cu are 3.6 × 10⁻³ mg/kg/day, 5 × 10⁻⁴ mg/kg/day, 3 × 10⁻³ mg/kg/day, 2 × 10⁻² mg/kg/day, 2 × 10⁻² mg/kg/day, 3 × 10⁻¹ mg/kg/day, and 3.7 × 10⁻² mg/kg/day, respectively [14]. For Ba, Fe, Mn, and Sb, the values of reference dose are 7 × 10⁻² mg/kg/day [3], 7 × 10⁻³ mg/kg/day [15], 4.7 × 10⁻² mg/kg/day [16], 2.8 × 10⁻² mg/kg/day [17] and 3.5 × 10⁻⁴ mg/kg/day, respectively [18].

where HQ is the hazard quotient (unitless); D is the exposure dose (mg/kg/day); and RfD is the reference dose (mg/kg/day), which represents the tolerable daily intake of the metal via oral exposure.

By summing the HQ values for all tested metals, hazard index (HI) is obtained, according to Equation (4). The HI represents the total potential non-carcinogenic health risk caused by the metals present in tested waters [19].

where HI is the hazard index (unitless), and HQ is the hazard quotient (unitless) of all potentially toxic elements tested.

Carcinogenic risk (CR) represents the probability of a person developing any form of cancer throughout life, by exposure to a contaminant 24 h a day, for 70 years (in the case of an adult) [20]. This parameter was evaluated for Pb, Cd, Cr, and Ni, via ingestion pathway, using Equation (5).

where CR is the cancer risk (unitless); D is the exposure dose in mg/kg/day; and CSF is the Cancer Slope Factor, in mg/kg/day. The values of CSF for oral ingestion are 8.4 × 10⁻¹ (Ni), 8.5 (Pb), 6.1 (Cd), and 41 (Cr) [3].