Estimation of annual effective dose due to natural and man-made radionuclides in the metropolitan area of the Bay of Cadiz (SW of Spain).

In order to investigate the radiological hazard of naturally occurring radioactive material (NORM) and man-made (137)Cs radionuclide in the Bay of Cádiz, 149 samples of sediments have been analysed. Activity concentration in all the samples was determined using a HPGe detection system. Activity concentrations values of (226)Ra, (232)Th, (40)K and (137)Cs in the samples were 12.6±2.6 (2.5-40.6), 18.5±4.0 (2.8-73.4), 451±45 (105-1342) and 3.2±1.3 (0.2-16.0) Bq kg(-1), respectively. Outdoor external dose rate due to natural and man-made radionuclides was calculated to be 35.79±1.69 (4.71-119.16) nGy h(-1) and annual effective dose was estimated to be 43.89±2.27 (5.78-146.14) µSv y(-1). Results showed low levels of radioactivity due to NORM and man-made (137)Cs radionuclide in marine sediments recovered from the Bay of Cádiz (Spain), discarding any significant radiological risks related to human activities of the area. Furthermore, the obtained data set could be used as background levels for future research.

An alternative radiometric method for calculating the sedimentation rates: application to an intertidal region (SW of Spain).

A new method using the inventory determined for the activity of the radionuclide (137)Cs, coming from global radioactive fallout has been utilised to calculate the sedimentation rates. The method has been applied in a wide intertidal region in the Bay of Cádiz Natural Park (SW Spain). The sedimentation rates estimated by the (137)Cs inventory method ranged from 0.26 cm/year to 1.72 cm/year. The average value of the sedimentation rate obtained is 0.59 cm/year, and this rate has been compared with those resulting from the application of the (210)Pb dating technique. A good agreement between the two procedures has been found. From the study carried out, it has been possible for the first time, to draw a map of sedimentation rates for this zone where numerous physico-chemical, oceanographic and ecological studies converge, since it is situated in a region of great environmental interest. This area, which is representative of common environmental coastal scenarios, is particularly sensitive to perturbations related to climate change, and the results of the study will allow to make short and medium term evaluations of this change.

Incidences of polluting episodes in sedimentary media.

There exist diverse radioactivity sources in the environment coming from anthropogenic activities that alter the natural levels of radiation. The detailed study of the environmental impact of these sources is of great interest, because it provides knowledge for subsequent decontamination works and environmental control. In this work, it is analyzed the radioactive contamination caused by the radionuclide (226)Ra in sedimentary media under a liquid sheet. In this way, the dumping of the radionuclide in sediment columns has been studied in laboratory, determining how its penetration in depth develops along time and for different grain sizes. For this purpose, a migration model based on the numeric resolution of the diffusion equation has been devised.

Sedimentology models from activity concentration measurements: application to the "Bay of Cadiz" Natural Park (SW Spain).

A previous study on seabed sediments of the Bay of Cadiz (SW of Spain) enabled us to identify several relations between sedimentological variables and activity concentrations of environmental radionuclides such as (137)Cs, (226)Ra, (232)Th and (40)K. In this paper the study has been extended to a large neighbouring inter-tidal area in order to establish if the above mentioned models can be generalized. As a result we have determined that the measured activity concentrations are closely to the values predicted by the theoretical models (correlation coefficient range=0.85-0.93). Furthermore, the proposal model for granulometric facies as a function of activity concentrations of the abovementioned radionuclides provides for the sediments distribution a representation which agrees with the values of the tidal energy distribution obtained using numeric models calibrated with experimental data from current meters and water level recorders.

Diffusion of (226)Ra and (40)K radionuclides reproduced in underwater sedimentary columns in laboratory.

The potential radiological impact of the increase of radioactive substances in the environment makes interesting the study of the migration of the contaminant radionuclides in soils and sediments, which are the last receiver system of these substances. By using a battery of sedimentary columns controlled in the laboratory, the diffusion of the (226)Ra and (40)K radionuclides has been studied, assessing their respective effective diffusion coefficients in a similar sedimentary medium. A decreasing temporal evolution is obtained, associated to the progressive 'fixation' of the radionuclides by the clay minerals of the sediment, followed by a constant tendency. A timescale of the 'fixation' by the sediment is determined, being of the order of days for (226)Ra and of the order of months for (40)K, so the progressive 'fixation' of (40)K by the clay minerals of the sediments is slower than in the case of (226)Ra.

Levels of 137Cs in muddy sediments of the seabed of the Bay of Cadiz, Spain. Part I. Vertical and spatial distribution of activities.

This is the first of a two-part paper. This first part describes a detailed study conducted of the spatial and vertical distribution of the concentration of the radionuclide (137)Cs, utilising columns of sediment extracted from the seabed of the Bay of Cadiz (Spain) as specimens. The activity concentrations have been measured by means of gamma spectrometry using a HPGe detector and (137)Cs is used as an indicator of the sedimentation and contamination processes in the zone. At the same time the relationship between the levels of activity found and other hydrodynamic and sedimentological variables characteristic of the zone have been studied. The experimental results obtained will also serve to develop a model of the distribution of (137)Cs, which will be presented in the second part of this paper.

Levels of 137Cs in muddy sediments on the seabed in the Bay of Cadiz (Spain). Part II. Model of vertical migration of (137)Cs.

This second part of the study reports the development of a model to describe the vertical migration of the artificial radioisotope (137)Cs in the sediment column on the seabed of the Bay of Cadiz. The application of the model provides an overall picture of the process of sedimentation in the Inner Bay of Cadiz. The spatial distribution of the rate of sedimentation enables us to study the sources of sediments and the means by which the sediments have been transported. A method has been derived from the rate of sedimentation to perform the dating of the layers of sediment. The model describes the behaviour of (137)Cs in the area under study, taking into account the time of residence in the zones that are the source of accumulation, the origin of the sedimentary material, together with the diffusion of the radionuclide in the sediment of the seabed.

Environmental impact of unleaded gasolines in the bay of Cádiz (Spain).

Given the strategic situation of the José León de Carranza bridge, which spans the Bay of Cádiz (in the SW of Spain) and carries very heavy motor traffic, together with knowledge of the currents and tidal flows in the zone, we have used a technique of radioactive dating of sediments to study the temporal evolution presented by contamination from lead in the sediment column. This has allowed us to observe the environmental impact, in terms of the concentration of Pb in the sea bed sediments, that has been produced in the zone by the introduction of unleaded gasolines as substitutes for traditional automobile fuels that employ organic forms of tetra methyl lead as an antidetonant agent in the fuel.

Dating of marine sediments and time evolution of heavy metal concentrations in the Bay of Cádiz, Spain.

In this paper the time evolution of heavy metal concentration of Pb, Zn, Cd and Hg, in the sediments of the Bay of Cádiz (southwest of Spain) is studied during the past century, as a result of the industrial influence in the zone. The study has been performed using sedimentary profiles that have been extracted from the seabed. The measurement of 210Pb and 137Cs radionuclides has provided the dating of the sediment layers, up to a depth corresponding to the age of 115 years. The relative sedimentation rates obtained are around 0.2 cm/year. The 137Cs activity profile reflects the concentration of this radionuclide in the atmosphere and into aquatic systems during the second half of the twentieth century. This profile has been used to ratify the results provided by the 210Pb dating method.

Relationships between sea-bed radionuclide activities and some sedimentological variables.

Natural radionuclides (232Th, 226Ra, 40K) and 137Cs, coming from atmospheric radioactive fallout, have been measured in sea-bed sediments of the Bay of Cádiz (South Western Spain). In this report, multivariate analysis methods have been employed to study the relationships between the activities of the radionuclides and some sedimentological variables like granulometric facies, organic content and apparent density. The correlation functions found show that it is possible to determine, with a satisfactory degree of approximation, the granulometric facies of the sediments using only radiometric information.