Mobility indices and doses from 210Po and 210Pb activity concentrations data in Brazilian spas groundwaters

²¹⁰Po and ²¹⁰Pb activity concentrations in spas groundwaters occurring at São Paulo (SP) and Minas Gerais (MG) states, Brazil, have been reported in this paper with a dual purpose: to compare different indices for evaluating the radionuclides mobility into waters and to evaluate the drinking water quality from dose calculations. The waters (75 sampling points) are extensively used for drinking in public places, bottling and bathing purposes, among other. The samples were taken from springs and wells drilled at different aquifer systems inserted in Paraná and Southeastern Shield hydrogeological provinces. The WHO guideline reference value for ²¹⁰Pb and ²¹⁰Po of 0.1 Bq/L in drinking water was not reached for ²¹⁰Pb but the ²¹⁰Po levels were equal or above it in four spas groundwaters from MG State. The maximum WHO guidance dose level of 0.1 mSv/yr was also reached or surpassed in them. The ²¹⁰Pb “mobility index” taking into account the ratio of the weight of the dissolved ²¹⁰Pb per unit volume of solution to its weight per unit weight of the rock matrix yielded values in the range of 0.01–5.2 kg/m³. Another “mobility index” (Preference Ratio) expressing the ratio of ²¹⁰Pb and ²³⁸U in the waters divided by the ratio of ²¹⁰Pb and ²³⁸U in the rock matrices provided values between 0.004 and 7994. The ²¹⁰Pb/²³⁸U activity ratios of some spas groundwaters suggested preferential ²³⁸U transport relative to ²¹⁰Pb into the liquid phase, whereas the ratio of the ²¹⁰Pb to ²³⁸U mobility indices indicated the opposite. Such finding showed a better usefulness of the mobility indices for evaluating processes affecting the radionuclides release into the liquid phase during the water/rock interactions.