Effects of technetium on marine micro-organisms

Eleven bacterial species have been isolated from the upper layer of intertidal sediments collected along the Belgian coast (Coxyde). Three of them (no. 1, 4 and 11) have been chosen for their halophilous character. One species has been identified as Flavobacterium halmephilum, the other two are being investigated. Effects of technetium (99Tc) have been studied on a mixed bacterial population isolated from sediments, as well as on the three halophilic species.At the concentrations utilized in this work (up to 100 microg ml-1), 99Tc has no evident effects on bacterial growth. Uptake of technetium (99Tc and/or 95mTc) has been investigated in the mixed bacterial population, in the three halophilic bacteria (including Flavobacterium halmephilum) and in the benthic ciliate Uronema marinum. It has been found that technetium is taken up by all these micro-organisms. However, the transfer factor (TF) in bacteria may vary considerably (from 0.5 to 200), but the cause of this variability is not known and deserves further study.The ciliate Uronema marinum, which feeds on living marine bacteria, was found to take up 95mTc added to the culture medium. However, the TF in this ciliate is rather low (from 1.4 to 5.5). Because it feeds on bacteria, Uronema marinum is supposed to take up technetium from water (direct contamination) as well as from contaminated bacteria (indirect contamination). Experiments with 95mTc-labeled bacterial cells might be useful, as they could indicate which form of contamination (direct or indirect) is prevailing

Rejet accidentel d’iode-131 par l’IREsur le site de Fleurus : retour d’expérience de l’autorité de sûreté belge

L’IRE (Institut national des radioéléments) produit des radionucléides pour la médecine nucléaire à partir de cibles irradiées d’uranium hautement enrichi. Le 22/08/2008, lors du transfert de résidus de production frais dans un réservoir de décroissance pratiquement vide, le mélange des liquides a conduit au dégagement d’environ 47 GBq d’iode-131, sous forme moléculaire, dans l’atmosphère. Les premières évaluations conservatives des conséquences radiologiques n’exigeaient pas la mise en place d’actions de protection directe de la population comme la mise à l’abri ou l’ingestion de comprimés d’iode stable. Toutefois, les dépôts estimés d’iode-131 pouvaient localement atteindre et dépasser les niveaux de référence dérivés pour la contamination du lait (4 kBq/m2) et des légumes-feuilles (10 kBq/m2). Pour cette raison, et parce qu’il subsistait une menace de rejet ultérieur, le plan d’urgence fédéral a été activé le 28/08 et la population potentiellement concernée s’est vu recommander d’éviter la consommation de fruits, de légumes et de lait frais produits localement. Les actions de protection sont levées le 7/09 et le plan d’urgence est levé le 12/09. La principale leçon tirée de cet événement est l’importance primordiale de l’échange rapide d’informations, aussi précises et complètes que possible, entre les différents niveaux, de l’exploitant à la population, en passant par les autorités fédérales et locale

Determination of mercury and thallium in the North Sea and in the Scheldt estuary

This article reports the optimization of analytical methods for the determination of mercury and thallium at ultra-low levels (ng.l-1) in sea water. special care was taken to avoid contamination and losses during all stages of the analytical scheme. For this purpose, preliminary experiments were carried out to investigate the stability of the samples and the suitability of the Niskin-samplers for the mercury analyses. The mercury content of the water was determined on the ship hy means of reduction-aeration/amalgamation combined with cold vapour atomic absorption (CVAAS) .The suspended particulate matter and the sediments were analysed in the same way, after acid attack. The mercury concentrations ranged from 0.3 to 1.5 ng.1-1 for Atlantic and North Sea water. Somewhat higher values were found in coastal waters. The significant input from the river Scheldt (appr. 220 kg.y-1) was proven by the analysis of the river water, with values ranging from 10 ng.1-1 in the estuary to 45 ng.1-1 in Antwerpen. 10 to 30% of the mercury was linked to suspended particles in the Scheldt. The mercury concentrations in the sediments were in the North Sea below 100 ng.g-1, but as high as 100 to 500 ng.g-1 in the Scheldt. The measurements indicate that the affinity of the mercury for the suspended particles increases with higher chloride concentration in the river water. The thallium content of the water was determined hy electro-thermal atomic absorption spectrometry (ETAAS) after preconcen- tration on anion exchanger. In the ocean water the concentrations varied from 6 ng.1-1 in the open sea up to 20 ng.1-1 at the mouth of Scheldt and Thames. In the Scheldt much higher concentrations were found (50-150 ng.1-1) of which generally less than 10% was associated with the particulate phase

Etude de l’absorption du technétium 99 par le riz irrigué (Oryza sativa L.)

L’absorption du technétium, radionucléide artificiel essentiellement issu du cycle du combustible nucléaire, a été étudiée chez le riz (Oryza sativa L.) en aquiculture et en sol irrigué par une solution contaminée. Les cinétiques d'absorption en flux continu pour différentes concentrations en 99TC (0,017 à 17 µCi. I-1) révèlent l'existence de deux phases : la première à dominance passive (diffusion dans les espaces libres) et la seconde, linéaire, résultant de la pénétration du technétium dans les cellules et de ses conséquences. L’évolution de la désorption met en évidence la présence de deux compartiments dont le premier correspondrait aux “espaces libres apparents” tandis que le second, comptant plus des 95 % de l'activité de la plante, représenterait la fraction absorbée. La demi-vie biologique dans ce second compartiment est telle (40 à 50 jours) qu’en cas de pollution accidentelle, une décontamination totale des plantes ne peut être attendue. Comme les essais en aquiculture, les essais en sol montrent l’apparition de symptômes de toxicité pour une concentration dans la solution d’irrigation de 17 µCi.I-1. Les facteurs de transfert calculés sont très élevés, de l’ordre de 1000 pour les parties aériennes végétatives. La répartition du technétium entre les différentes parties de la plante varie selon la concentration en 99TC mais plus de 90 % sont localisés dans les parties aériennes; les caryopses (parties comestibles) n’en renferment que 1 %

Use of the true absorption coefficient as a measure of bioavailability of radiocaesium in ruminants

Limitations of existing methods to describe the bioavailability of dietary radionuclides to ruminants (the transfer coefficient and apparent absorption coefficient) have led to the alternative suggestion of using the true absorption coefficient (A t). Various approaches to estimatingA t for radiocaesium, involving the intravenous administration of a second isotope, are presented and discussed with reference to results from studies in which a range of radiocaesium sources were examined in sheep. Although estimates ofA t differed between the sources, they were reasonably consistent between measurement techniques. Those methods which involved the estimation of endogenous faecal excretion of radiocaesium could be used with previously contaminated animals and did not require continuous administrations of radiocaesium isotopes, but gave unreliable results for sources of low bioavailability. Methods based on estimating the turnover rate of dietary radiocaesium through blood plasma were sufficiently sensitive to measureA t for the range of sources studied. However, they require previously uncontaminated animals and continuous administration of both isotopes for approximately 7 days. Bioavailability is more effectively measured asA t than as the transfer or apparent absorption coefficients sinceA t does not incorporate factors relating to the metabolism of radiocaesium in the tissues of the animal. The results of these studies show that differences in transfer coefficients between sheep and cattle and between sheep of differing ages are not due to variation in absorption across the gut. The potential for applying these approaches to other radioactive elements is discussed

The true absorption of 131I, and its transfer to milk in cows given different stable iodine diets

The influence of the stableiodine content in the diet on the absorption of radioiodine and its transfer to cow's milk was investigated for cows at different stages of lactation. Three different rates of stableiodine: a low intake rate of 4 mg d−1, a moderate intake of 35 mg d−1 and a high rate of 75 mg d−1 were fed to two groups of three lactating cows in mid- and late-lactation. The transfer to milk of a single oral administration of radioiodine was measured for the three different intake rates. The lactation phase had no significant effect on iodinetransfer to milk; therefore, the data from the two lactation groups were pooled for further statistical analyses. The mean transfer coefficient values for oral radioiodine to milk increased from 0.020 d l−1 for the low treatment to 0.024 d l−1 for the moderate stableiodine rate. There was a statistically significant decrease in the transfer to milk for the high stable dietary iodine intake rate (mean transfer coefficient=0.018 d l−1) compared with the moderate treatment. These differences were not due to effects on absorption since trueabsorption was complete for all three stableiodine treatments, but rather to differential affinities and saturation levels of the thyroid and milk pathways competing for the available iodine. The same behaviour and comparable values of transfer coefficients (range 0.015–0.020 d l−1) were observed for stableiodine

Development and testing of a revised dynamic model of radiocaesium transfer to sheep tissues

The model of radiocaesium transfer to sheep presented by Galer et al. [1] provides reliable predictions only for sheep of a similar body weight to those used in the development of the model (approximately 30 kg). To extend the applicability of the model, it was necessary to re-parameterise it in terms of activity concentrations in tissues rather than total activities within them (although for gut compartments the use of activity has been retained). The rate coefficients for the new model have been estimated by fitting the model to the data used by Galer et al. [1] which was derived from a single calibration experiment. The new model was found to account for 94% of the observed variation in the data (n=42), a result similar to that obtained by Galer et al. [1]. The model has also been tested against data not used in its development but obtained from four separate experiments undertaken by three different laboratories. Good agreement between the predictions of the new model and observations was found for most circumstances and for several breeds of sheep with different body weights. It is concluded that the new model provides a useful dynamic description of radiocaesium transfers to the tissues of sheep of different breeds and under different contamination scenarios

Long-term availability of Tc deposited on soil after accidental releases.

Considerable uncertainties are associated with the transfer of Tc from soil to plant. Mathematical models built to simulate that transfer generally use a single value derived from short-term experiments. Recent observations have, however, given a clear indication that the soil-to-plant transfer varies with time, depending on the biogeochemical cycling of this element. The long-term behavior of Tc in soils accidentally contaminated has been studied for 4 y in lysimeters exposed to natural climatic conditions. An important fraction of the deposit (70%) is rapidly removed from the 20-cm plow layer with a half-time of 54 +/- 2 d; the remaining fraction tends to persist in the soil for long periods of time (half-time = 30 +/- 16 y). Immediately after the deposit, the plant-to-soil concentration ratios are very high (about 400); they decrease to six 3 y after the contamination. The shape of the evolution of the contamination measured in grass after an accidental deposit is best-fitted to a sum of two exponential functions; the environmental half-times estimated for the two components are about 30 d and 2 to 3 y, respectively

Brachytherapy quality assurance in the PORTEC-4a trial for molecular-integrated risk profile guided adjuvant treatment of endometrial cancer

Biological, physical and clinical aspects of cancer treatment with ionising radiatio