A sequential method for the determination of 210Pb, 226Ra, and uranium and thorium radioisotopes by LSC and alpha-spectrometry.

A procedure for the determination of (210)Pb, and alpha-emitting radioisotopes of uranium, thorium, and radium from the same aliquot of a sample has been proposed. The key step consisted in the recovery of Pb(II) and Ra by precipitation of insoluble Pb(NO(3))(2), the uranium and thorium radioisotopes remaining in solution. Afterwards, the fractions were handled by specific, well consolidated procedures. Lead-210 was determined by the LSC technique while the uranium, thorium, and radium radioisotopes were measured with silicon alpha-spectrometers. The procedure was applied to a reference sample and several environmental samples obtaining satisfactory results.

Elimination of natural uranium and (226)Ra from contaminated waters by rhizofiltration using Helianthus annuus L.

The elimination of natural uranium and (226)Ra from contaminated waters by rhizofiltration was tested using Helianthus annuus L. (sunflower) seedlings growing in a hydroponic medium. Different experiments were designed to determine the optimum age of the seedlings for the remediation process, and also to study the principal way in which the radionuclides are removed from the solution by the sunflower roots. In every trial a precipitate appeared which contained a major fraction of the natural uranium and (226)Ra. The results indicated that the seedlings themselves induced the formation of this precipitate. When four-week-old seedlings were exposed to contaminated water, a period of only 2 days was sufficient to remove the natural uranium and (226)Ra from the solution: about 50% of the natural uranium and 70% of the (226)Ra were fixed in the roots, and essentially the rest was found in the precipitate, with only very small percentages fixed in the shoots and left in solution.

Linearity assumption in soil-to-plant transfer factors of natural uranium and radium in Helianthus annuus L.

The linearity assumption of the validation of soil-to-plant transfer factors of natural uranium and (226)Ra was tested using Helianthus annuus L. (sunflower) grown in a hydroponic medium. Transfer of natural uranium and (226)Ra was tested in both the aerial fraction of plants and in the overall seedlings (roots and shoots). The results show that the linearity assumption can be considered valid in the hydroponic growth of sunflowers for the radionuclides studied. The ability of sunflowers to translocate uranium and (226)Ra was also investigated, as well as the feasibility of using sunflower plants to remove uranium and radium from contaminated water, and by extension, their potential for phytoextraction. In this sense, the removal percentages obtained for natural uranium and (226)Ra were 24% and 42%, respectively. Practically all the uranium is accumulated in the roots. However, 86% of the (226)Ra activity concentration in roots was translocated to the aerial part.

Distribution and mobilization of U, Th and 226Ra in the plant-soil compartments of a mineralized uranium area in south-west Spain.

The activity concentrations of natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 225Th) and 226Ra were studied in soil and vegetation samples from a disused uranium mine located in the Extremadura region in the south-west of Spain. The results allowed us to characterize radiologically the area close to the installation and one affected zone was clearly manifest as being dependent on the direction of the surface water flow from the mine. The activity concentration mean values (Bq/kg) in this zone were: 10,924, 10,900, 10,075 and 5,289 for 238U, 234U, 230Th and 226Ra, respectively, in soil samples and 1,050, 1,060, 768 and 1,141 for the same radionuclides in plant samples. In an unaffected zone, the activity concentration mean values (Bq/kg) were: 184, 190, 234 and 7251 for 235U, 234U, 230Th and 226Ra, respectively, in soil samples and 28. 29, 31 and 80 in plant samples. The activity concentrations obtained for 232Th and 228Th showed that the influence of the mine was only important for the uranium series radionuclides. The relative radionuclide mobilities were determined from the activity ratios. Correlations between radionuclide activity concentrations and stable element concentrations in the soil samples helped to understand the possible distribution paths for the natural radionuclides.