Monitorization of uranium and thorium concentration and isotope ratios in groundwater from a semiarid basin in Central Spain by single and multicollector sector field ICP-MS

Abstract

The radionuclides from uranium and thorium decay series can be used to obtain highly valuable information from aquatic systems due to their physical and chemical properties. Thus, 234U/238U and 232Th/230Th activity ratios in groundwater can be used to investigate transport phenomena and flow relationships in hydrological reservoirs, redox conditions or weathering processes in the aquifer. Our hypothesis lays on the potentiality of isotope ratios to act as environmental proxies either by themselves or through their consideration as part of multivariate studies. The aim of this work is to develop a simple, fast and sensitive strategy for the measurement and monitoring of U and Th isotope ratios in groundwater samples and apply it for the control of water samples coming from a highly anthropized river basin. Sample measurement strategy consisted on taking two subsamples, the first one was diluted in 2% HNO3 then U, Th and other trace elements were directly measured by ICP-HR-MS (Thermo Element XR), whereas one-step column resin chemistry was applied to the second one in order to separate U and Th fraction and then isotope ratios were measured by MC-ICP-MS (Thermo Neptune).