A. Martínez-Aguirre

The distribution of U, Th and 226Ra derived from the phosphate fertilizer industries on an estuarine system in Southwest Spain

This paper reports an extensive study of the presence of natural radioactivity around a phosphate fertilizer factory complex situated in an estuarine area of southwest Spain. The study has concluded that the wastes from such industries are the cause of the enhancement of natural radioactivity in the immediate environment. Thus, significantly high levels of U- and Th-isotopes and 226 Ra are detected in water and sediment samples collected in this area. These conclusions based on the enhanced isotopic concentrations are further supported by the measured U, Th and Ra isotopic activity ratios being quite different from any observed elsewhere in undisturbed estuaries. These isotope activity ratios appear to be very sensitive indicators of waste disposal practices in such environments

Transfer of natural radionuclides from soils to plants in a marsh enhanced by the operation of non-nuclear industries

Two sampling campaigns were performed in 1993 at the marsh area (Odiel marsh) located in southwestern Spain, in the city of Huelva. Spartina densiflora and substrate soil (5 cm deep) samples were collected in several locations across the area in each campaign. Activity concentrations of 210Po, U-and Th-isotopes were determined in the plant and the substrate samples. The production of phosphoric acid from phosphate mineral in the vicinity clearly enhances the concentrations of these radionuclides in certain areas of the marsh. Moreover, concentrations in plants are affected by the concentration of the same element in its substrate. Indeed, high concentration levels in plants are coincident with high concentration in soils. However, concentration ratios (CR), defined as the ratio between the concentration of an element in the plant and of that in its substrate, are higher when substrate concentrations are low, whereas low CR values are found in areas where substrate concentrations are high. Moreover, both variables (CR and soil concentration) seem to be non-linearly related, at least, in the case of radionuclides from the 238U decay chain.

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.

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.

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

Abstract 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 Th U mass ratios.

Natural radioactivity enhancement by human activities in rivers of the southwest of Spain

The occurrence of anomalous enhancements of U-isotope activities in the surrounding environment of a phosphate fertilizer factory complex at the southwest of Spain has been established. It seems that significant amounts of U, released by such industries, are being accumulated in the environment, which may substantially contribute to the collective radiation dose received by the local population.

U and Th distribution in solution and suspended matter from rivers affected by the phosphate rock processing in southwestern Spain

Abstract A study is presented on the distribution of U and Th isotopes in the solid and liquid fractions of waters collected along the Odiel and Tinto rivers (southwest Spain). Such rivers are affected by the operation of phosphate fertilizer factories. The analysis of activity concentrations and activity ratios in both fractions provides interesting information on the way in which the factories disturb their close environment.

Measurements of U- and Ra-isotopes in rainwater samples

Concentrations of U- and Ra-isotopes in rainwater samples taken in the South Spanish atmospheric environment during the years 1986, 1987 and 1988 are presented. Such data have been obtained by applying a simple method for the simultaneous determination of such radionuclides from the same rainwater sample. Ra is firstly coprecipitated as Ba−Ra sulfate. Then two alternatives can be used for U analysis: a coprecipitation of U with Fe, followed by a selective redissolution of the precipitate with ammonium carbonate, or a solvent extraction technique by using tributyl phosphate. Levels of 0.99 to 1.81 μg/l, 3.4 to 17.9 mBq/l and 0.5 to 5.5 mBq/l, respectively for U,226Ra and224Ra are found during the studied time period. The dependence of such concentration variability on meteorological parameters is discussed.

Anthropogenic emissions of210Po,210Pb and226Ra in an estuarine environment

An extensive study on the distribution of natural radionuclides in an estuarine ecosystem located in Southwestern Spain is presented. This environment is highly affected by the wastes released by a phosphoric acid industry which uses phosphate rocks as raw material for fertilizer production. This rock has generally high concentrations of U and its daughters. The estuary is formed by two rivers, Odiel and Tinto, which have a common mouth into the Atlanic Ocean and a salt marsh (Odiel marsh) affected by the income of Odiel riverwaters. This river receives directly the liquid and part of the solid (gypsum) wastes released from the industries. Besides that, most of the phosphogypsum wastes are stored in uncovered piles at the right margin of the Tinto river. The study has concluded that the wastes from such industries are the cause of the enhanced concentrations found at the bed of both river channels as well as the enhancement found in surface soils in certain zones of the Odiel wet marshland. Indeed, the Northern marsh and the Mojarrera channel at the Odiel marsh seem to be the main sinks of the contaminant released by the phosphoric acid industry.

Natural radioactivity in groundwaters around a fertilizer factory complex in South of Spain.

A study of the concentration of the U isotopes, 226Ra and 230Th in a groundwater system has been carried out. This aquifer, located in the provinces of Sevilla and Huelva, is the most important in the south of Spain having a surface area of 2500 km2. The proximity of a fertilizer factory complex to this aquifer system is of particular concern given that it releases a significant part of its waste directly into the estuary of the Odiel and Tinto rivers, also storing a further part on the right bank of the Tinto river. Investigation has been made of the environmental impact of the fertilizer factory, either as a result of leaching of radionuclides from the phosphogypsum piles or otherwise as a result of intrusion of the Odiel and Tinto waters, both of which are in close contact with the aquifer. Results show U concentration in waters of this system around the phosphogypsum piles to be significantly higher than those in other areas of the same aquifer. The low 226Ra concentrations found in the same locations add support to the origin of part of the U in these samples.