Enhanced U and Th concentrations in soils from a wet Marshland washed by contaminated riverwaters

A study of the presence of U and Th isotopes in soil samples from a saline wet Marshland located close to a phosphoric acid production factory is presented. The samples were collected during low tide in areas washed by water during high tide. The incoming Odiel riverwaters, which directly receive the wastes from this factory, provokes the enhancement of radioactivity in certain zones of the studied area. Comparison of radionuclide concentrations between the fine particle fraction (≤ 63.5 μm) and the total soil fraction has given some hint on the processes by which contamination takes place.