Determination of uranium and plutonium isotopes in water and sediment samples of the Cutzamala system dams

Uranium and plutonium isotopes were determined in water and sediment samples from the main dams that feeds the Cutzamala system, Villa Victoria and Valle de Bravo in the State of Mexico, Mexico. Actinides were extract and purify from the samples using chemical and radiochemical techniques, deposited in fine sources and measured by alpha spectrometry. Uranium isotopes in the water and sediment samples were found within the levels of natural uranium. The presence of plutonium isotopes were also detected at very low level and, in some cases, they were undetectable. The uranium activity concentration for water and sediment samples varied from 0.48 to 7.00 mBq/L and from 68 to 1,523 mBq/kg, respectively. The estimated levels for 239+240 Pu in water and sediment samples were found between 0.12 and 0.4 mBq/L and between 1.2 and 17 mBq/kg, respectively. Furthermore, the 234 U/ 238 U isotopic ratios revealed important differences between the studied dams. The samples collected from Valle de Bravo dam exhibit a 234 U/ 238 U isotopic ratios >1. In contrast, samples from Villa Victoria dam present ratios <1. These differences could be associated to the type of discharges, e.g. due to the use of phosphate fertilizers, the rock leaching, among others. The levels of uranium and plutonium isotopes in the water and sediments samples analyzed are very low, and no health effects are expected.