Barra de Valizas – Aguas Dulces area is placed in the strip coast of the 290 Ramsar site, located in the eastern region of Uruguay, on its Atlantic coast. The studied area included two coastal towns and a freshwater lagoon.
The activity concentration of 238-U, 226-Ra, 210-Pb, 232-Th, 40-K and 137-Cs radionuclides in sand, soil and Baccharis articulata were evaluated. For the quantification of those radionuclides, 2 kg sand and soil of 20 cm from the top surface layer, and the hole plant of Baccharis articulata placed in the same soil were collected. Each sample was dried at 60ºC, vegetation sample was milled and all samples were sealed into 100 mL flasks. After approximately four weeks in order to reach secular equilibrium of the 238-U and 232-Th series, samples were measured by gamma-spectrometry with a High Pure Germanium Detector GMX35P4-76-RB, 35 % efficiency and 1,75 % energy resolution for the 60-Co photopeak. IAEA reference materials were used for efficiency calibration, and self-absorption correction was applied for 238-U and 210-Pb determinations. 238-U was studied by the 234-Th photopeak (63.3 keV), 226-Ra by the 214-Bi photopeak (609.3 keV) and 232-Th by the 228-Ac photopeak (911.1 keV). 40-K (1460.0 keV) and 210-Pb (46.5 keV) were evaluated by their own photopeaks, and 137-Cs radionuclide by the 137m-Ba (661.7 keV) photopeak.
The activity concentration for 238-U, 226-Ra and 210-Pb in soil were found to be 14.3 – 19.5, 8.69 – 13.21, 16.60 - 32.3 Bq/kg, respectively, whereas the activity concentration for 238-U, 226-Ra and 210-Pb in sand were 10.9 – 35.8, 7.53 – 26.19, 11.1 – 23.9 32.3 Bq/kg, respectively. Sand and soil samples show high concentration of 238-U than 226-Ra, the 226-Ra/238-U activity ratio was in the range 0.51 – 0.83, therefore there is a low radioactive equilibrium disturbance, because of selective leaching of radium. The 210-Pb/226-Ra activity ratio was found to be in the range 0.91 – 3.70, the equilibrium disturbance is higher in soils than in sands samples, showing an amount of unsupported 210-Pb, which increased with organic matter.
The activity concentrations for 232-Th, 40-K and 137-Cs in soil were 21.4 – 45.6, 186.6 – 307.6, 0.12 – 1.00 Bq/kg, respectively. The activity concentration for 232Th in sand is higher than in soil, 39.8- 749 Bq/kg, whereas the activity concentration of 40-K is lower: 120.0- 160.3 Bq/kg. The activity concentration of 137-Cs in sand samples is below the minimum detectable activity (MDA).
The mean activity concentrations for 210-Pb, 40-K and 137-Cs in Baccharis articulata were 58.7 + 6.1, 238 + 11, 1.82 + 0.65 Bq/kg, respectively. 238-U, 226-Ra, and 232-Th were below the MDA.
The transfer factors for 210-Pb, 40-K and 137-Cs were, 2.33 + 0.47, 1.209 + 0.086 and 1.57 + 0.73 respectiely.
The area shows higher 232-Th activity concentration than worldwide mean for both soil and sand, whereas 226-Ra activity concentration is only higher than worldwide mean for Aguas Dulces´ sands. The 238U series shows disequilibrium for both sand and soil, with high concentration of 238-U and 210-Pb.
210-Pb, 40-K and 137-Cs transfer from soil to vegetation, although more determinations must be made in order to know the 210-Pb fallout intake.