Uranium and phosphate behavior in the vadose zone of a fertilized corn field

Phosphate fertilizers contain approximately 200 mg x kg-1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1-50 mg x kg-1) and phosphates (22-33 mg x kg-1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg x l-1 and phosphates between 1 and 0.3 mg x l-1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved. (author)