## 2 Materials and Methods
### Risk Assessment
#### 2.5.2 Human Health Risk Assessment (HHRA)  
To assess the human health risk arising from the contacts with roof runoff containing pollutants, the methodology developed by the United States Environmental Protection Agency (US EPA) was applied [64,65]. In the resident scenario, we analyzed ingestion and dermal contact with the investigated elements in roof runoff, in adults (\(\geq 7\)) and children (0-6 years). The inhalational pathway was not investigated due to the fact that the volatile compounds in roof runoff were not analyzed in the present study. The contents of contaminants were taken as the mean values of elements, determined after acid digestion; observing the conservative risk assessment principle, we wanted to achieve the highest risk values for the populations analyzed.  
To estimate the daily intake of contaminants via the ingestion route, the average daily dose (ADD) values were calculated according to Equation (4) [66]:  
\[\text{ADD}=(\text{C}\times\text{IR}\times\text{EF}\times\text{ED})/(\text{BW} \times\text{AT}), \tag{4}\]  
To estimate the daily intake of pollutants via the dermal contact route, the dermal absorbed dose (DAD) values were calculated according to Equation (5) [66]:  
\[\text{DAD}=(\text{C}\times\text{PC}\times\text{SA}\times\text{ET}\times\text{ EV}\times\text{EF}\times\text{ED})/(\text{BW}\times\text{AT}), \tag{5}\]  
where: ADD--ingested average daily dose (mg/kg-day); DAD--dermal absorbed dose (mg/kg-day); C--mean concentration of each element in the roof runoff samples after acid digestion (mg/L);IR--intake rate (L/day); PC--dermal permeability coefficient (cm/h); SA--skin surface area available for contact (cm\({}^{2}\)); ET--event duration (h/event); EV--event frequency (events/day); EF--exposure frequency (days/year); ED--exposure duration (years); BW--body weight (kg); and AT--averaging time (ED in years x 365 days/year, in days; for non-carcinogens ED = 24 years, for carcinogens ED = 70 years, [66]). The exposure parameters, used for the risk assessment calculations under the resident scenario, are given in Table S3.  
To determine the non-carcinogenic and carcinogenic risks for the residents of Krakow, arising from their contacts with roof runoff, the HQ and CR values were calculated, respectively. The values of hazard indices (HQ) were calculated, using Equation (6) [64], and the values of carcinogenic risk (CR) were calculated, using Equation (7) [64].  
\[\text{HQ}=\text{ADD/RfD}, \tag{6}\]  
\[\text{CR}=\text{ADD}\times\text{SF}, \tag{7}\]  
where: HQ--hazard quotient (unitless); CR--carcinogenic risk (unitless); ADD--average daily dose (mg/kg-day), RfD--reference dose (mg/kg-day); and SF--slope factor ((mg/kg-day)-1). For dermal contact, the reference doses (RfD\({}_{\text{d}}\)) and slope factor values (SF\({}_{\text{d}}\)) were calculated according to Equations (8) and (9), respectively [67]:  
\[\text{RfD}_{\text{d}}=\text{RfD}_{\text{o}}/\text{ABS}_{\text{GI}}, \tag{8}\]  
\[\text{SF}_{\text{d}}=\text{SF}_{\text{o}}\times\text{ABS}_{\text{GI}}, \tag{9}\]  
where \(\text{ABS}_{\text{GI}}\) is a fraction of contaminant, absorbed in the gastrointestinal tract (unitless). The values of toxicological parameters, used for the calculations of the resident scenario risk assessment, are given in Table S4.  
The target risk value was set to be equal to 1 (HQ = 1) for non-carcinogenic risk, with respect to both particular the element being investigated (individual HQ values) and total non-carcinogenic risk, defined as the sum of all HQ values calculated. As for carcinogenic risk, the acceptable risk level was set to be equal to \(1\times 10^{-6}\) for a particular contaminant [64,68].