Distribution of natural radionuclides in sequentially extracted fractions of sediments from a marsh area in Southwest Spain: U isotopes

A study of the distribution of U in different fractions of intertidal sediments collected in a marsh area enhanced by the radioactive wastes discharged from a fertilizer complex has been carried out. The study has shown that U isotopes are mainly located in non-residual fractions of the sediments. Coprecipitation with amorphous ferromanganese oxyhydroxides is the main process of incorporation of this element from the water column into the sediment. The residual fractions only contain some 5% of the total U in the sediment. Moreover, all fractions seem to reflect the same pattern of contamination, with in fact a quite good relationship between the U in most extracted fractions. Thus, those sediments located along the Odiel river basin have higher U concentrations in all the sequentially extracted fractions. Concentration ratios for Spartina densiflora have also been studied. In this paper, it has been considered that not all the substrate sediment takes part in the uptake of elements by the plant but only the non-residual fractions. Thus, a study of the dependence of these concentration ratios on the concentration in the non-residual fraction of sediments has been carried out. ( 1999 Elsevier Science Ltd. All rights reserved

Uranium and thorium concentrations in an estuary affected by phosphate fertilizer processing: Experimental results and a modelling study

The Odiel river, in southwest Spain, forms an estuarine system which is affected by waste disposal from a fertilizer complex. Uranium and thorium concentrations in waters and suspended matter, activity ratios and distribution coefficients, kd, have been measured along the river during two different tidal states. The results have shown that a radioactive impact is being delivered to the river, as well as a significant variability depending on the sampling point and the tidal state. Thus, a quantitative study of the distribution of radio-nuclides can be carried out best by means of a mathematical model. The model includes the partition of radio tracers between four phases (water, suspended matter and two sediment fractions) and has been designed for non-equilibrium conditions. Thus, radiotracer transfers are described in terms of kinetic transfer coefficients instead of Kds. The model simultaneously solves the hydrodynamic equations, the suspended matter equation (including depostion and resuspension processes) and the equations which describe the time evolution of radionuclide concentrations in each one of the four phases. The model has yielded good results in predicting U and Th concentrations in water and suspended matter, distribution coefficients and mass ratios

Soil to plant transfer of 226 Ra in a marsh area: Modelling application

¹he Odiel river forms an estuarine system which surrounds a large marsh area. A phosphate fertilizer processing complex releases its wastes into the estuary. ¹he presence of 226Ra in soils and plants (Spartina Densiflora) from the marsh has been investigated. Concentrations up to 700 and 15 mBq g~ 1 have been detected in soil and plant samples, respectively. Soil to plant concentration ratios have been calculated and some activity ratios have also been investigated. A model which is able to simulate the dispersion of radionuclides in the marsh has been applied. ¹he model includes the ex-change of radionuclides between water and the solid phase (suspended matter and bottom sediments) and the transfer of radionuclides to the plants. Model results are, in general, in good agreement with measurements. ( 1998 Elsevier Science ¸td. All rights reserved

Sedimentary speciation of U and Th isotopes in a marsh area at the southwest of Spain

A study of the distribution of U and Th-isotopes in different fractions of intertidal sediments collected in a marsh area has been carried out. This marsh area is affected by the releases of natural radionuclides from fertilizer industries carried out into the Odiel river. The study has shown that uranium is mainly located in non-residual fractions of the sediments and particularly coprecipitated with amorphous ferromanganese oxyhydroxides. In the case of Th isotopes, the contribution of residual fractions is higher than that of non-residual fractions, being the main non residual fraction again the amourphous ferromanganese oxyhydroxides. However, all fractions seems to reflect the same pattern of contamination. Thus, those sediments located along the Odiel river basin have the higher concentration in all sequentially extracted fractions. Some interesting activity and mass ratios have also been investigated

Radioactive impact of phosphate ore processing in a wet marshland in southwestern Spain

In this paper an extensive study of the presence of natural radionuclides in a marshland area located in the vicinity of a phosphoric acid production complex in southwestern Spain is presented. This marsh is a natural reservation where significant biological activity takes place. The marsh is highly affected by the inflow of water from the Odiel river which is enhanced with natural radionuclides from industries which use phosphate rocks as raw material for fertilizer production. Sediment samples, collected from the intertidal zone, showed that wastes from the phosphate industries have resulted in enhanced radioactivities in the marsh.European Union (UE) FI3P-CT92003

A six-phase model to simulate the contamination by non-conservative radionuclides of sediments, soils and plants in a marsh area. Application to the Odiel marsh in southwest Spain

A numerical model to simulate the dispersion of non-conservative radionuclides in an estuarine system that surrounds a marsh area has been developed. The model includes six phases: water, two types of suspended particles (natural particles in the estuary and contaminated particles released from the source of contamination), bottom sediments, soils and plants (Spartina densiflora). Radionuclides in water and suspended matter are transported along the river by advection and diffusion processes, ionic exchanges between water and the solid phases and deposition of suspended particles on bottom sediments also occur. Radionuclides are incorporated in soils in the marsh during the time that they are covered by water. Finally, they are transferred from the soil to the plants. All these processes are represented by a set of partial differential equations. A spatial and temporal discretization is carried out and a finite differences scheme is adopted to solve them. The model must run over long time scales (years) if model results are to be compared with experimental measurements in the estuary and marsh. Thus, residual water circulation is used to solve the advective-diffusive terms in the equations. Ionic exchanges are described by kinetic transfer coefficients and the transfer of radionuclides from soils to plants by concentration ratios, CR. The model is applied to the Odiel marsh. The Odiel river forms an estuarine system (which surrounds a large marsh area) in which a phosphate fertilizer-processing complex releases its waste. The model yields good results in predicting 238U, 210Po and 232Th concentrations in bottom sediments, soils and plants collected from the river and marsh. A predictive study, concerning the process of cleaning of the marsh, has also been carried out.European Union FI3P-CT92-003

U and Th speciation in river sediments

A study of the distribution of some natural radionuclides in different chemical fractions of river bottom sediments has been carried out. The study has shown that the majority of the total U in sediments is located in the non-residual fractions, while Th is more likely to be present in the residual ones. This difference between U and Th reflects largely a much higher mobility of U relative to Th in surface and near-surface environments. Coprecipitation with amorphous ferromanganese oxyhydroxides is the main process of U and Th incorporation from the water column into the soil particles. Moreover, the distribution of the radionuclides and the analysis of the Th/U mass ratios in different chemical fractions of sediments has made an unequivocal connection between the enhanced U content in river sediments and the wastes discharged into the rivers by the operation of fertilizer industries

Enhanced U and Th concentrations in soils from a wet marshland washed by contaminated riverwaters

A study of the presence of U and Th isotopes in soil samples from a saline wet Marshland located close to a phosphoric acid production factory is presented. The samples were collected during low tide in areas washed by water during high tide. The incoming Odiel riverwaters, which directly receive the wastes from this factory, provokes the enhancement of radioactivity in certain zones of the studied area. Comparison of radionuclide concentrations between the fine particle fraction (≤ 63.5 μm) and the total soil fraction has given some hint on the processes by which contamination takes place.European Union (UE) FI3P-CT92003

U/Th dating of impure carbonates: 230Th/232Th activity ratios in detrital material

In environmental age dating the 230Th/232Th activity ratio is widely used as an indicator of detrital contamination. A clear relationship between this activity ratio and the carbonate sample’s age has previously been demonstrated, whereby a detrital correction must be applied when the 230Th/232Th activity ratio of the leach drops to 20. We demonstrate that in some cases carbonate samples with 230Th/232Th well above 20 must be corrected, otherwise an overestimation of the sample’s age is obtained. Evaluation of the relationship between 230Th/234U and 230Th/232Th in the carbonate’s aliquots will enable evalua-tion of the limit at which a carbonate can be considered pure or impure.European Union (UE) EU MEDOC Programme: 2002-02-4.1-U-04

U-series dating applied to speleothems from Los Covachos Cave, South of Spain

U-Series dating method is applied to speleo thems from Los Covachos Cave in the south of Spain. A combination of solvent extraction method with ion exchange resins is used for uranium and thorium isotopes. Uranium concentrations are low and for younger samples correction by detrital contamination is necessary. Ages obtained range from 30 to 135 ky with a hiatus between 50 and 80 ky BP. Changes in uranium isotopes activity ratios indicate a change in climatic conditions