## 3 Results and Discussions
### XRF Soil Analysis
#### 3.2.6 Potential Health Risk Assessment
The mean values for the hazard index, presented in Table 12, are also below the health risk threshold, with the following order: As (24.08 \(\times\) 10\({}^{-2}\)) \(>\) Hg (4.41 \(\times\) 10\({}^{-2}\)) \(>\) Ni (2.43 \(\times\) 10\({}^{-2}\)) \(>\) Cu (1.22 \(\times\) 10\({}^{-2}\)) \(>\) Zn (0.65 \(\times\) 10\({}^{-2}\)) \(>\) Cd (0.18 \(\times\) 10\({}^{-2}\)). These results indicate that the highest non-carcinogenic risk to children's health due to exposure to heavy metals in the studied parks is associated with As and Hg. As a conclusion, all the HQ and HI values were lower than one, suggesting that the exposure of children to the heavy metals found in the soil would not affect their health, but all other sources of heavy metals such as food intake or exposure to dust and aerosol from other urban places were not included in this study. All the sources of heavy metals should be connected due to the cumulative character of pollutants and their serious adverse effects on the body; thus, the non-carcinogenic risk associated with exposure to the playground soil cannot be neglected [27]. The cancer risk was calculated using Equations (13)-(17) presented in Table 1. Pathway-specific risks for ingestion and inhalation exposures were assessed. These calculations were performed only for arsenic, as it was the only element with an available cancer slope factor oral pathway, and an inhalation unit risk (IUR) for the inhalation pathway. Only for nickel and cadmium were the inhalation unit risk (IUR) constant values available. The cancer risk (CR) for the oral pathway, calculated for arsenic, showed a maximum value of 1.61 \(\times\) 10\({}^{-4}\) (location 2 ES) and a minimum value of 0.77 \(\times\) 10\({}^{-4}\) (location 4 PS), with an average of 1.08 \(\times\) 10\({}^{-4}\). For the inhalation pathway, the maximum value was observed at location 5 ES (12.19 \(\times\) 10\({}^{-12}\)), with an average of 8.34 \(\times\) 10\({}^{-12}\). The average cancer risk for arsenic was similar between the playground samples and the edge of the park samples, with values of 1.05 \(\times\) 10\({}^{-3}\) and 1.12 \(\times\) 10\({}^{-3}\), respectively. For nickel, the average cancer risk for inhalation (CR\({}_{\rm{inh}}\)) was 35.16 \(\times\) 10\({}^{-10}\), with a maximum of 52.94 \(\times\) 10\({}^{-10}\) at 5 ES and a minimum of 20.44 \(\times\) 10\({}^{-10}\) at 2 ES. For cadmium, the average CR\({}_{\rm{inh}}\) was 0.09 \(\times\) 10\({}^{-9}\), with values ranging from 0.16 \(\times\) 10\({}^{-9}\) at 10 PS to 0.05 \(\times\) 10\({}^{-9}\) at 2 PS. The total cancer risk (TCR), calculated as the sum of the cancer risks for all the elements across the studied locations, had an average of 9.78 \(\times\) 10\({}^{-5}\). The minimum TCR was 8.20 \(\times\) 10\({}^{-5}\)at the fourth location, and the maximum was 1.57 \(\times\) 10\({}^{-3}\) at the sixth location. Based on the obtained TCR values, the locations were ranked as follows: 6 (1.57 \(\times\) 10\({}^{-3}\)) \(>\) 5 (1.27 \(\times\) 10\({}^{-3}\)) \(>\) 3 (1.23 \(\times\) 10\({}^{-3}\)) \(>\) 1 (1.09 \(\times\) 10\({}^{-3}\)) \(>\) 8 (1.08 \(\times\) 10\({}^{-3}\)) \(>\) 2 (1.06 \(\times\) 10\({}^{-3}\)) \(>\) 7 (9.93 \(\times\) 10\({}^{-5}\)) \(>\) 9 (8.95 \(\times\) 10\({}^{-5}\)) \(>\) 10 (8.50 \(\times\) 10\({}^{-5}\)) \(>\) 4 (8.20 \(\times\) 10\({}^{-5}\)). The obtained values were compared to the acceptable cancer risk (CR) thresholds. The generally accepted CR value is 10 \(\times\) 10\({}^{-5}\), while the maximum acceptable limit is 10 \(\times\) 10\({}^{-1}\)[42].