Phosphogypsum (PG) is a residue of the phosphate fertilizer industry that has relatively high concentrations of 226Ra and other radionuclides. Thus, it is interesting to study the effect of PG applied as a Ca amendment on the levels and behavior of radionuclides in agricultural soils. A study involving treatments with 13 and 26 Mg ha(-1) of PG and 30 Mg ha(-1) of manure was performed, measuring 226Ra and U isotopes in drainage water, soil, and plant samples. The PG used in the treatment had 510 +/- 40 Bq kg(-1) of 226Ra. The 226Ra concentrations in drainage waters from PG-amended plots were similar (between 2.6 and 7.2 mBq L(-1)) to that reported for noncontaminated waters. Although no significant effect due to PG was observed, the U concentrations in drainage waters (200 mBq L(-1) for 238U) were one order of magnitude higher than those described in noncontaminated waters. This high content in U can be ascribed to desorption processes mainly related to the natural adsorbed pool in soil (25 Bq kg(-1) of 238U). This is supported by the 234U to 238U isotopic ratio of 1.16 in drainage waters versus secular equilibrium in PG and P fertilizers. The progressive enrichment in 226Ra concentration in soils due to PG treatment cannot be concluded from our present data. This PG treatment does not determine any significant difference in 226Ra concentration in drainage waters or in plant material [cotton (Gossipium hirsutum L.) leaves]. No significant levels of radionuclides except 40K were found in the vegetal tissues.

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Abstract, The experiments on the study of the kinetic transfer coefficients of conservative and non-conservative radionuclides, in aquatic environments, need to determine radionuclide activity in large number of samples. Different radioactivity measurement techniques can be selected for analyses, but the liquid scintillation technique is preferred due to its easy sample treatment and its low time consumption. Samples are initially traced with a known activity of a selected radionuclide ( 239 Pu, MI Am or "Tc). The transference of radionuclides, from the water to the suspended matter, is studied through the determination of the residual activity in aliquots of water sample, which are successively collected with time. In this work, we present the experimental procedures used for the 239 Pu, 241 Am and "Tc activity measurement by liquid scintillation counting, using a Wallac Quantulus 1220 spectrometer. Results of the application of this technique to traced water samples are also shown in this study.

Abstract. The interest on transfer coefficients studies have increased recently, since they are important parameters required understanding and reliably modelling the dispersion of conservative and non-conservative radionuclides in aquatic environments. The approaches, based in the implementation of the uptake kinetics of dissolved radionuclides by solid particles, are more appropriate than those based in the use of the distribution coefficients, k^. In this work, we present a series of tracing experiments to study the uptake of Pu, Am and Tc in natural aqueous suspensions from three aquatic systems (Gergal reservoir, Guadalquivir river, and the estuary of Tinto river) located in the South of Spain. The kinetic transfer coefficient for direct sorption depends on the total available surface of particles and on the concentration of active sites in the surface layer (what depends on the mineral composition, free edges, pores, coatings, etc.). In order to compare results from different environments and to fix the conditions of applicability of the derived coefficients, it is necessary to handle the particle size spectra and the mineral composition of natural occurring suspended loads. The time dependent uptake curves, covering up to a large period, are fitted to the numerical solutions calculated with different models of the uptake kinetics.