## 4 Results and Discussion  
Ra, \({}^{232}\)Th and \({}^{40}\)K Activity Concentration in the River Sediments, Spatial Distribution and Classification of Hazard Regions  
The activity concentrations of the three naturally occurring \({}^{226}\)Ra, \({}^{232}\)Th and \({}^{40}\)K radionuclides in river sediments across the study area were determined for the sampling points reported in Table 1.  
The obtained results are reported in Table 2. As shown in the Table, the highest average concentration, (31.3 \(\pm\) 8.3) Bq kg\({}^{-1}\), of \({}^{226}\)Ra was obtained for samples from the site ID8 (Siderno-Novito river), whereas the lowest mean value, (14.5 \(\pm\) 4.9) Bq kg\({}^{-1}\), was detected for sediments from the site ID1 (Gioia Tauro-Budello river). Concerning \({}^{232}\)Th, samples from the site ID8 are characterized by the highest average concentration, (43.5 \(\pm\) 4.9) Bq kg\({}^{-1}\), while those from the site ID2 (Gioia Tauro-Petrace river) have the lowest mean value, (20.3 \(\pm\) 2.9) Bq kg\({}^{-1}\). Sediments from the site ID1 show the highest average concentration of \({}^{40}\)K, with (1088 \(\pm\) 98) Bq kg\({}^{-1}\), while the lowest mean concentration of (643 \(\pm\) 53) Bq kg\({}^{-1}\) was obtained for samples from the site ID 6 (Africo-Laverde river). Across all sampling locations, the activity concentration values of \({}^{226}\)Ra ranged between 10.2 and 33.9 Bq kg\({}^{-1}\), with overall mean value of 21.3 \(\pm\) 6.3 Bq kg\({}^{-1}\), that of \({}^{232}\)Th varied from 16.5 to 48.6 Bq kg\({}^{-1}\) and the overall average value is (30.3 \(\pm\) 4.5) Bq kg\({}^{-1}\). The \({}^{40}\)K ranged between 528 and 1450 Bq kg\({}^{-1}\), with an overall average value of (849 \(\pm\) 79) Bq kg\({}^{-1}\). The average values of \({}^{226}\)Ra, \({}^{232}\)Th and \({}^{40}\)K obtained in this study, for each sampling site, were compared with the world average value reported in Reference [1]. All the average values of \({}^{226}\)Ra are lower than that of the world average (35 Bq kg\({}^{-1}\)). For \({}^{232}\)Th, the mean values are lower than that of the world average (30 Bq kg\({}^{-1}\)) except for samples from the sites ID3 (39.5 \(\pm\) 4.8 Bq kg\({}^{-1}\)), ID6 (32.5 \(\pm\) 9.2 Bq kg\({}^{-1}\)), ID7 (34.5 \(\pm\) 5.6 Bq kg\({}^{-1}\)) and ID8 (43.5 \(\pm\) 4.9 Bq kg\({}^{-1}\)). The average concentration of \({}^{40}\)K is higher than the 420 Bq/kg average concentration reported in Reference [1] for all the analyzed samples. Contour maps, showing the spatial distributions of \({}^{226}\)Ra, \({}^{232}\)Th and \({}^{40}\)K, are presented in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Scheme 226. **} & \multirow{2}{*}{ \begin{tabular}{c} **No. of** \\ **Samples** \\ \end{tabular}  } & \multicolumn{2}{c}{\({}^{226}\)Ra} & \multicolumn{2}{c}{\({}^{232}\)Th} & \multicolumn{2}{c}{\({}^{40}\)K} \\  & & \multicolumn{2}{c}{**(Bq kg\({}^{-1}\))**} & \multicolumn{2}{c}{**(Bq kg\({}^{-1}\))**} & \multicolumn{2}{c}{**(Bq kg\({}^{-1}\))**} \\ \cline{3-8}  & & **Range** & **Mean** & **Range** & **Mean** & **Range** & **Mean** \\ \hline
1 & 10 & 10.2–23.6 & 14.5 \(\pm\) 4.9 & 16.5–48.6 & 22.7 \(\pm\) 3.2 & 961–1450 & 1088 \(\pm\) 98 \\ \hline
2 & 10 & 13.6–22.9 & 18.2 \(\pm\) 4.4 & 17.5–23.8 & 20.3 \(\pm\) 2.9 & 949–1028 & 1009 \(\pm\) 88 \\ \hline
3 & 10 & 1  
Figure 2: Contour maps showing the spatial distributions of (**a**) \({}^{226}\)Ra, (**b**) \({}^{232}\)Th and (**c**) \({}^{40}\)K in the investigated region. As can be seen in the \({}^{226}\)Ra map (Figure 2a), there are four distinct regions. The activity concentration of \({}^{226}\)Ra in these regions was classified as low (C\({}_{\text{Ra}}\) < 15 Bq kg\({}^{-1}\)), moderate (15 Bq kg\({}^{-1}\) < C\({}_{\text{Ra}}\) < 20 Bq kg\({}^{-1}\)), high (20 Bq kg\({}^{-1}\) < C\({}_{\text{Ra}}\) < 25 Bq kg\({}^{-1}\)) and very high (C\({}_{\text{Ra}}\) > 25 Bq kg\({}^{-1}\)), which are deep blue, light blue, green and yellow (and red) areas on the map.