Monitoring of radionuclides in the natural waters of Novosibirsk, Russia

Results of the investigation of ²³⁸U, ²³²Th, ²²⁶Ra and ²²²Rn content in the natural waters of Novosibirsk city and adjacent territories are presented for the first time. Hydraulic interrelations between the aquifer systems of Quaternary, Neogene and Paleogene sediments, Upper Devonian – Lower Carboniferous sediments and Upper Paleozoic granites predetermined the features of hydrogeological structure. Twenty-five chemical types of water were established, with the domination of HCO₃ Mg–Ca, HCO₃ Na–Mg–Ca and SO₄–HCO₃ Na–Mg–Ca. The amount of total dissolved solids varies from 127 to 1848 mg l⁻¹, pH from neutral to alkaline (6.9–9.5). The values of Eh vary from reductive −157 mV (O₂dᵢₛₛₒₗᵥₑd = 0.3 mg l⁻¹) to oxidative +280 mV (O₂dᵢₛₛₒₗᵥₑd = 19.4 mg l⁻¹). Silicon content varies from 0,14 to 11,77 mg l⁻¹. The ranges within which the concentrations of radioactive elements vary in natural waters are: radon (²²²Rn) 0–1216 Bq.l⁻¹, uranium (²³⁸U) 9.75∙10⁻⁸ – 0.098 mg l⁻¹, thorium (²³²Th) 2.2∙10⁻⁷ – 2.1∙10⁻³ and radium (²²⁶Ra) 1.6∙10⁻¹² – 3,5∙10⁻⁷ mg l⁻¹. The maximal content of these elements in the waters of boundary territories reach ²²²Rn – 43,764 Bq.l⁻¹, ²³⁸U–6.5 mg l⁻¹ and ²²⁶Ra – 3.7∙10⁻⁷ mg l⁻¹. The ²³²Th/²³⁸U ratio is 4.20∙10⁻⁵ – 2.96. The concentrations of uranium and thorium in the geological objects of Novosibirsk vary within the ranges (mg.kg⁻¹): ²³⁸U = 1.6–3.6 and ²³²Th = 5.55–13.6 for sedimentary rocks, and ²³⁸U = 0.2–47.2 and ²³²Th = 0.8–44.1 in intrusive formations. It is established that waters with high radon content relate to the aquiferous zones of Upper Devonian - Lower Carboniferous shale rocks and hornfels, as well as Upper Paleozoic granites. The highest concentrations of radionuclides are characteristic of the aqueous scattering halos of the uranium ore deposit.