The predictions of a sequential extraction scheme with respect to the mobility of some radionuclides (85Sr,134Cs and110mAg) in two Mediterranean sandy and sandy-loam soils, are compared to short-term soil-to-plant transfer factors and soil migration. Total soil-to-plant transfer is higher in sandy soil than in sandy-loam soil, as expected and predicted by the scheme. The relative transfer to plants of134Cs and85Sr follows the scheme predictions about exchangeable radionuclide fraction, radiosilver being less mobile than expected. Migration in soil of radiocesium and radiostrontium is also higher in sandy soil, especially for the latter radionuclide, the relative behavior of these two radionuclides being nearer to the bioavailable radionuclide fraction defined by the scheme. However, the scheme fails in predicting radiosilver migration, which is lower than deduced by the scheme.
A sequential extraction scheme which indicates the role of organic matter in radionuclide retention was applied to two types of Mediterranean soil (sandy-loam and sandy), with low percentages of organic matter and with different contents of clay mineral, which had been previously contaminated with a radioactive aerosol, containing85Sr,134Cs and110mAg. Different distributions were obtained for the three radionuclides, depending on the type of soil.85Sr was the most available radionuclide for both types of soil, showing significant binding to organic matter in sandy-loam soil.134Cs was the most retained radionuclide: for low-organic-matter soils, its availability seemed to depend on clay mineral content.110mAg associated with available organic sites showed a positive correlation with organic matter content.
The knowledge of the chemical forms of metals is used to assess their availability and uptake by plants, and in sediments the forms of metals determine their transport and mobility in the aquatic media. This information may be obtained by determining chemical forms of metals (speciation) or different phases in which the metals are bound, obtained by applying extraction schemes. The analytical methods used include different steps and all of them must be validated. We report here the recommendations to minimize the errors in this kind of analysis. For validation the use of Certified Reference Materials (CRMs) and the participation in interlaboratory exercises are highly recommended.
A sequential extraction scheme, using distilled water and chloroform: hexane (12), was applied in a study of radionuclide retention by holm oak leaves. To perform this study, holm oak leaves were contaminated by dry deposition using a thermogenerated radioactive aerosol containing134Cs,85Sr and110mAg. The experimental parameters tested were: type and time of shaking, number of successive extractions in each step, and the volume of extractans. From the results obtained, two schemes which give complementary information about radionuclide retention are proposed. The first scheme, using a single water extraction with mechanical shaking, allows us to define two fractions: the fraction removed by water, which is related to total radionuclide retention on leaf surfaces, and the residual fraction, which is associated with radionuclides incorporated into the leaves. The second scheme is based on a two-step extraction with manual shaking using water and chloroform: hexane, and permits us to distinguish among three fractions: the fraction removed by water (which is related to the radionuclide fraction easily leached by rain), the fraction removed by organic solvent (which is associated with the radionuclide fraction strongly retained on leaf surface), and the residual fraction, which may represent the absorbed radionuclide content. Since our objective was to study the retention of134Cs,85Sr and110mAg, simultaneously, the experimental conditions chosen were a compromise of individual suitable conditions for each radionuclide.
Two alternative approaches, a sequential extraction scheme and the calculation of the variation of the distribution coefficient of radiocaesum in different K–Ca–NH4 scenarios, were used to study the behaviour and fractionation of this radionuclide in a forest soil profile. The first approach was applied to samples originating from an experiment in which the original L (litter) layer was replaced by an L layer contaminated with a radioactive aerosol, allowing a downward migration of radiocaesium. The samples belonged to different stages after the contamination. The second approach was applied to samples contaminated with soluble radiocaseium. The results indicate that radiocaesium behaviour is quite similar in the Hand A layers, and that the mineral matter seems to govern the behaviour of radiocaesium in case of direct condensed deposition or when radiocaesium is released from structural components of the organic matter phase.
Humic acids and associated radionuclides were extracted from several soil samples with a significant organic matter content, such as peaty soils and forest soil layers. Extractions were made using two alkaline solutions (Na4P2O7 0.1 mol·1–1 and NaOH 0.1 mol·1–1 under N2). The humic acid content in the extract was determined by the capillary zone electrophoresis technique (CZE) and associated radiocaseium was determined by gamma spectrometry. After analizing a large number of samples and studying the relationship between humic acid and organic matter content it was possible to conclude that the CZE technique may be a good alternative to classical techniques in humic acid determinations, with NaOH extractions leading to higher results than Na4P2O7. Furthermore, the quantification of the radiocaseium desorbed by applying different extractant reagents (NaOH, Na4P2O7, NH4AcO and CaCl2) showed that there may be some organic matter-radionuclide interations, other than those originated by humic acids. which may govern radionuclide retention in soils with a high content of organic matter.
In order to reduce the sample pretreatment in the measurements of - and -emitter radionuclides in environmental analysis, we present the application of the microwave oven to dry different environmental macrosamples such as vegetables, milk, meat, fish, soil and sediment. We have also studied this technique to evaporate water (rain water and seawater) and to optimize acid digestion of sediments. The results show that the microwave oven gives good results for drying environmental macrosamples, for evaporating water samples when applied in acid atack. With the porposed procedures, time of analysis shortened dramatically.
Authors:M. Toribio, J. García, A. Izquierdo-Ridorsa, G. Rauret, A. Coll, I. Vallés, and X. Ortega
The activity of -emitting radionuclides is usually measured by semiconductor detectors (surface barrier or ion implanted). Overlapping and composite bands are quite common problems depending on energy differences of the radionuclides and counting source preparation. The classical approach to activity quantification is based on peak integration and, when it is used, overlapping may be overcome by a detailed study of each case, whereas composite bands can not be completely resolved. Here, spectra of the -emitting plutonium isotopes, obtained by ion implanted semiconductor detectors, have been used to compare the classical approach with a multivariate calibration method (MVC-PLS). The study is performed at environmental activity levels (0–52 dpm). The relative errors obtained for239+240Pu activity determination, using either the classical or the MVC-PLS approach with replicates, are good enough to quantify isotopes at low level activities. The distribution of relative errors is asymmetric, with a positive component for 0–10.5 dpm subset, in the classical approach whereas it is more symmetric in the MVC-PLS method. The results show that the classical approach depends on peak overlap, whereas the MVC does not. As a whole, MVC is a more robust method than the classical approach. Composite bands were studied using the239Pu–240Pu mixture; the MVC approach did not allow individual quantification due to the lack of signal reproducibility. This instability does not affect the regular integration procedures but it is important in the deconvolution processes. The lack of reproducibility is related to the source preparation process.
Authors:J. Tent, M. Vidal, M. Llauradó, G. Rauret, J. Real, and P. Mischler
In order to study the foliar uptake of radionuclides deposited from an aerosol released in an accidental situation, lettuce plants were contaminated with an aerosol containing85Sr,134Cs and110mAg isotopes. The methodology chosen to carry out this study is based on a sequential extraction scheme using water, to evaluate the fraction possibly removed by rain or by washing, and an organic solvent, to distinguish between the fraction adhering to the cuticle and the one incorporated in the leaves. Two procedures are compared. Moreover, the different behavior of the radionuclides in their incorporation into the leaves is deduced from the results obtained.