Assessment of metal contamination and natural radiation hazards in different soil types near iron ore mines, Bahariya Oasis, Egypt

Nine metals (Al, Ba, Cr, Cu, Fe, Mn, Pb, V, and Zn) and three natural radionuclides (⁴⁰K, ²³⁸U, and ²³²Th) were quantitatively determined in the cultivated and uncultivated soils of the Bahariya Oasis where the main mines of the Egyptian iron ore are located. The mean concentrations of Ba, Cr, Cu, Fe, V in the cultivated soils and Al, Cr, Cu, V in the uncultivated soils exceed maximum allowable concentration (MAC). The evaporites-rich uncultivated soils contain high concentrations of Zn. The contamination degrees (C_d) of the cultivated and evaporites-rich uncultivated soils were represented by moderate to extremely high values. All metals are spatially varied and their highest values are recorded in the northern parts of the oasis close to the iron mines. The highest values of the activity concentrations of ⁴⁰K were recorded in the evaporites-rich uncultivated soils. On the other side, the highest values of ²³⁸U, ²³²Th were recorded in the cultivated soils. The cultivated soils samples show higher values of the total absorbed external gamma dose rate (D) and annual effective dose (AED) than the international recommended values (54 nGy/h and 0.07 mSv/y; respectively). The external hazard index (H_ex) for all studied soils are mainly lower than unity. The origin of Bahariya soils is lithogenic and anthropogenic, whereas the role played by groundwater flow, evaporation of near-surface saline groundwater, and phosphatic fertilizers in the soil contamination is more effective than those of iron ore erosion.