## 2 Material and Methods
### Health Risk Assessment of Metals in Settled House Dust  
The present study aims to calculate the exposure of children and their parents to metals in house dust based on the assessment method of human exposure risk developed by US Environmental Protection Agency [24]. Residents are exposed to dust through three main pathways: ingestion, inhalation, and dermal contact. The dose received through each of the pathways was calculated by the following equations:  
\[D_{ingestion}=\text{ C }\times\frac{\text{IngR }\times\text{ EF }\times\text{ ED}}{\text{BW }\times\text{ AT}}\times 10^{-6} \tag{3}\]  
\[D_{dermal}=\text{ C }\times\frac{\text{SA }\times\text{ SL }\times\text{ ABS }\times\text{ EF }\times\text{ ED}}{\text{BW }\times\text{ AT}}\times 10^{-6} \tag{4}\]  
\[D_{inhalation}=\text{ C }\times\frac{\text{InhR }\times\text{ EF }\times\text{ ED}}{\text{PEF }\times\text{ BW }\times\text{ AT}} \tag{5}\]  
The available studies on the carcinogenic risk parameters in the current assessment standards have been conducted, taking into account only the pathway of inhalation [25]. Therefore, the daily average exposure for life through inhalation of a carcinogenic metal (\(LD_{inhalation}\) ) was calculated by:  
\[LD_{inhalation}=\frac{\text{C }\times\text{ EF }}{\text{PEF }\times\text{ AT}}\times\left(\frac{\text{InhR}_{\text{child }}\times\text{ ED}_{\text{child}}}{\text{BW}_{\text{child}}}+\frac{\text{ InhR}_{\text{adult }}\times\text{ ED}_{\text{adult}}}{\text{BW}_{\text{adult}}}\right) \tag{6}\]  
where C is the concentration (mg/kg) of the metal in the dust. IngR is the ingestion rate, estimated in the present study to be equal to 200 (mg/day) for children and 100 (mg/day) for their parents [26]. InhR is the inhalation rate and was considered as 5.71 for children and 19.02 for adults (m\({}^{3}\)/day) [27]. Exposure frequency (EF), taking into account holidays, was assumed as 335 days per year. Exposure duration (ED) was taken as 5 years for children and 25 years for adults. AT is the averaging time (ED \(\times\) 365 days for noncarcinogens and 70 \(\times\) 365 days for carcinogenesis). BW is the average body weight (13 Kg for children and 70 Kg for adults). The surface area of skin exposure (SA) was considered to be 1150 cm\({}^{2}\) for children and 2145 cm\({}^{2}\) for their parents. The skin adhesive capacity (SL) was taken as 0.2 for children and 0.07 for adults. The skin absorption factor (ABS) was considered as 0.001 [15]. PEF is the particulate emission factor, in this study, 1.36 \(\times\) 10\({}^{9}\) m\({}^{3}\)/kg.  
The doses that were calculated for each element and exposure pathway were subsequently divided by the corresponding reference dose (RfD) (mg/kg \(\times\) day) to obtain the noncancer risk (HQ), while the dose was multiplied by the corresponding slope factor (SF) to calculate the level of cancer risk [15]. The hazard index (HI) is the sum of HQ. It is supported that if HQ or HI \(<\) 1, the risk is small, whereas in case HQ or HI \(>\)1, there is a noncarcinogenic risk. Risk refers to the risk of cancer, indicating the probability of cancer, which is usually expressed as the proportion of cancer population in unit population. The acceptable risk is within the range of 10\({}^{-6}\) to 10\({}^{-4}\)[15; 27].