Transfer of natural radionuclides from soils to plants in a marsh enhanced by the operation of non-nuclear industries

Two sampling campaigns were performed in 1993 at the marsh area (Odiel marsh) located in southwestern Spain, in the city of Huelva. Spartina densiflora and substrate soil (5 cm deep) samples were collected in several locations across the area in each campaign. Activity concentrations of 210Po, U-and Th-isotopes were determined in the plant and the substrate samples. The production of phosphoric acid from phosphate mineral in the vicinity clearly enhances the concentrations of these radionuclides in certain areas of the marsh. Moreover, concentrations in plants are affected by the concentration of the same element in its substrate. Indeed, high concentration levels in plants are coincident with high concentration in soils. However, concentration ratios (CR), defined as the ratio between the concentration of an element in the plant and of that in its substrate, are higher when substrate concentrations are low, whereas low CR values are found in areas where substrate concentrations are high. Moreover, both variables (CR and soil concentration) seem to be non-linearly related, at least, in the case of radionuclides from the 238U decay chain.