Relationship of thorium, uranium isotopes and uranium isotopic ratios with physicochemical parameters in cenote water from the Yucatán Peninsula.

Uranium (U) and Thorium (Th) concentrations are normally low in the water (<30 and 5 ng mL, respectively). However, we performed a direct analysis of Th, U, U and U in cenote water from the Yucatán Peninsula using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) as a rapid response technique to perform environmental radioactivity monitoring. Water samples were collected in 2021 from the cenotes and these were certificated by zones (PYNO, PYNE and PYSE) and monitoring depth [surface water (n = 52) and depth water (n = 48)]. Moreover, physicochemical parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), and temperature were measured in situ. Results obtained were total U and Th levels below permissible for human consumption. However, physicochemical parameters must be considered before use because it is outside the permissible limits in most cenotes. The median concentration value for U, U, U and Th in surface + depth water were 0.0001 ng mL, 0.0130 ng mL, 1.76 ng mL, and 0.062 ng mL, respectively. In addition, isotopic ratio of U/U in surface + depth water was 0.00730. In addition, the PYNO zone showed a correlation between Th with EC and TDS. The PYSE zone showed a correlation between Th and temperature, and U/U with pH, while PYEN did not show correlations. In conclusion, the first time evaluated U isotope concentrations and isotopic ratios of U and Th in cenote water from the Yucatán Peninsula, where U and Th concentrations were found below the permissible limits mentioned by guidelines for drinking-water quality. The average of U/U is similar to isotopic ratios in "natural" water.