The VATO project: An original methodology to study the transfer of tritium as HT and HTO in grassland ecosystem

Tritium (³H) is mainly released into the environment by nuclear power plants, military nuclear facilities and nuclear reprocessing plants. The construction of new nuclear facilities in the world as well as the evolution of nuclear fuel management might lead to an increase of ³H discharges from the nuclear industry. The VATO project was set up by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and EDF (Electricité de France) to reduce the uncertainties in the knowledge about transfers of ³H from an atmospheric source (currently releasing HT and HTO) to a grassland ecosystem. A fully instrumented technical platform with specifically designed materials was set up downwind of the AREVA NC La Hague reprocessing plant (Northwest of the France). This study, started in 2013, was conducted in four main steps to provide an hourly data set of ³H concentrations in the environment, adequate to develop and/or validate transfer models. It consisted first in characterizing the physico-chemical forms of ³H present in the air around the plant. Then, ³H transfer kinetics to grass were quantified regarding contributions from various compartments of the environment. For this purpose, an original experimental procedure was provided to take account for biases due to rehydration of freeze-dried samples for the determination of OBT activity concentrations in biological samples. In a third step, the ³H concentrations measured in the air and in rainwater were reconstructed at hourly intervals. Finally, a data processing technique was used to determine the biological half-lives of OBT in grass.

Inter-comparison of dynamic models for radionuclide transfer to marine biota in a Fukushima accident scenario

We report an inter-comparison of eight models designed to predict the radiological exposure of radionuclides in marine biota. The models were required to simulate dynamically the uptake and turnover of radionuclides by marine organisms. Model predictions of radionuclide uptake and turnover using kinetic calculations based on biological half-life (TB1/2) and/or more complex metabolic modelling approaches were used to predict activity concentrations and, consequently, dose rates of (90)Sr, (131)I and (137)Cs to fish, crustaceans, macroalgae and molluscs under circumstances where the water concentrations are changing with time. For comparison, the ERICA Tool, a model commonly used in environmental assessment, and which uses equilibrium concentration ratios, was also used. As input to the models we used hydrodynamic forecasts of water and sediment activity concentrations using a simulated scenario reflecting the Fukushima accident releases. Although model variability is important, the intercomparison gives logical results, in that the dynamic models predict consistently a pattern of delayed rise of activity concentration in biota and slow decline instead of the instantaneous equilibrium with the activity concentration in seawater predicted by the ERICA Tool. The differences between ERICA and the dynamic models increase the shorter the TB1/2 becomes; however, there is significant variability between models, underpinned by parameter and methodological differences between them. The need to validate the dynamic models used in this intercomparison has been highlighted, particularly in regards to optimisation of the model biokinetic parameters.

Estimation of marine source-term following Fukushima Dai-ichi accident

Contamination of the marine environment following the accident in the Fukushima Dai-ichi nuclear power plant represented the most important artificial radioactive release flux into the sea ever known. The radioactive marine pollution came from atmospheric fallout onto the ocean, direct release of contaminated water from the plant and transport of radioactive pollution from leaching through contaminated soil. In the immediate vicinity of the plant (less than 500 m), the seawater concentrations reached 68,000 Bq.L(-1) for (134)Cs and (137)Cs, and exceeded 100,000 Bq.L(-1) for (131)I in early April. Due to the accidental context of the releases, it is difficult to estimate the total amount of radionuclides introduced into seawater from data obtained in the plant. An evaluation is proposed here, based on measurements performed in seawater for monitoring purposes. Quantities of (137)Cs in seawater in a 50-km area around the plant were calculated from interpolation of seawater measurements. The environmental halftime of seawater in this area is deduced from the time-evolution of these quantities. This halftime appeared constant at about 7 days for (137)Cs. These data allowed estimation of the amount of principal marine inputs and their evolution in time: a total of 27 PBq (12 PBq-41 PBq) of (137)Cs was estimated up to July 18. Even though this main release may be followed by residual inputs from the plant, river runoff and leakage from deposited sediments, it represents the principal source-term that must be accounted for future studies of the consequences of the accident on marine systems. The (137)Cs from Fukushima will remain detectable for several years throughout the North Pacific, and (137)Cs/(134)Cs ratio will be a tracer for future studies.

Molecular cloning of a new member of the p53 family from the Pacific oyster Crassostrea gigas and seasonal pattern of its transcriptional expression level

Like other sessile filter-feeding molluscs, oysters may be exposed in the natural environment to a variety of contaminants. Long-term exposure to pollutants may be one factor affecting prevalence of cancerous-like disorders, such as neoplasia. Environmentally induced alterations in p53 protein expression, in relation to leukemia, have been reported in various mollusc species inhabiting polluted water, suggesting that p53 proteins can also be used as a marker for environmental research. This work reports the cloning and sequencing of a p53-like cDNA in the mollusc bivalve Crassostreagigas. The deduced amino acid sequences of p53 shared a high degree of homology with the homologues from other mollusc species, including typical eukaryotic p53 signature sequences. We examined the p53 transcription expression pattern during the annual cycle in oyster gills and whole soft tissues in four locations along the French coasts. Real-time PCR analysis suggested that strong variations at p53 mRNA level are probably synchronized with the seasonal cycle at the four locations investigated.

Transport of uncharged organic solutes in Xenopus oocytes expressing red cell anion exchangers (AE1s)

When expressed in Xenopus oocytes, the trout red cell anion exchanger tAE1, but not the mouse exchanger mAE1, elicited a transport of electroneutral solutes (sorbitol, urea) in addition to the expected anion exchange activity. Chimeras constructed from mAE1 and tAE1 allowed us to identify the tAE1 domains involved in the induction of these transports. Expression of tAE1 (but not mAE1) is known to generate an anion conductance associated with a taurine transport. The present data provide evidence that (i) the capacity of tAE1 and tAE1 chimeras to generate urea and sorbitol permeability also was associated with an anion conductance; (ii) the same inhibitors affected both the permeability of solutes and anion conductance; and (iii) no measurable water transport was associated with the tAE1-dependent conductance. These results support the view that fish red blood cells, to achieve cell volume regulation in response to hypotonic swelling, activate a tAE1-associated anion channel that can mediate the passive transport of taurine and electroneutral solutes.

Association of the band 3 protein with a volume-activated, anion and amino acid channel: a molecular approach

In response to swelling, cells recover their initial volume by releasing intracellular solutes via volume-sensitive pathways. There is increasing evidence that structurally dissimilar organic osmolytes (amino acids, polyols, methyl amines), which are lost from cells in response to swelling, share a single pathway having the characteristics of an anion channel. However, the molecular identity of this pathway remains to be established. It has been suggested that the erythrocyte anion exchanger (AE1) or some AE1-related proteins could be involved. A direct evaluation of this possibility has been made by comparing the functional properties of two AE1s when expressed in Xenopus laevis oocytes: tAE1 is from a fish erythrocyte which releases taurine when swollen, and mAE1 is from a mammalian erythrocyte which does not regulate its volume when swollen. While mAE1 performs exclusively Cl-/Cl- exchange, tAE1 behaves as a bifunctional protein with both anion exchange and Cl-/taurine channel functions. Construction of diverse tAE1/mAE1 chimaeras allows the identification of protein domains associated with this channel activity. Thus, some AE1 isoforms could act as a swelling-activated osmolyte channel, a result having a potentially important implication in malaria. This review also discusses the possibility that several different proteins might function as swelling-activated osmolyte channels.

A role for the anion exchanger AE1 (band 3 protein) in cell volume regulation

In response to swelling cells recover their volume by releasing ions (mainly K+, Cl-) and different organic solutes (e.g. taurine) via volume-sensitive pathways. Depending on the cause of swelling (net uptake of electrolytes or decrease in external osmolality) cells use specifically some of these pathways. Previous data indicate that the anion exchanger (AE1) is involved in the choice of the regulatory pattern the cells adopt. Molecular cloning and functional expression of AE1 from the trout erythrocyte shows that this anion exchanger can function as a channel mediating taurine fluxes. In the erythrocyte, the channel activation depends on the conditions as the cell is swollen: when swelling is caused by an accumulation of electrolytes (resulting in an increase of the intracellular ionic strength) the channel is not activated and the regulatory volume decrease occurs exclusively by a release of K and Cl via a KCl cotransporter. When swelling is caused by hypotonic shock (resulting in a decrease in intracellular ionic strength) the KCl cotransporter is then mainly inactivated or even silent; conversely the channel is activated and allows volume recovery by mediating the release of both taurine and probably K and Cl. The possibility that AEs function as volume-activated taurine channels in other cell types and as a malaria-induced channel in malaria-infected human red cells is considered.

Trout red blood cell arrestin (TRCarr), a novel member of the arrestin family: cloning, immunoprecipitation and expression of recombinant TRCarr

Arrestins are cytosolic proteins involved in the desensitization of G-protein-coupled receptors. We report the cloning of trout red blood cell arrestin which shows 76, 82 and 52% identity with bovine beta-arrestin1, beta-arrestin2 and retinal arrestin respectively. Antibodies were generated against the C-terminus of trout red blood cell arrestin. These antibodies detected arrestin in erythrocyte cytosol and were able to precipitate the native protein. The Na+/H+ antiporter of trout red blood cell is activated by beta-adrenergic stimulation and is then desensitized whereas the transmembrane signalling pathway is not. To investigate the subcellular distribution of arrestin on beta-adrenergic activation and desensitization of the antiporter, precipitation experiments were carried out on trout erythrocytes. A desensitization-dependent shift in cytosolic arrestin to the membranes could not be detected using the immunoprecipitation technique but we cannot exclude the possibility that a small number of cytosolic arrestins might be involved in the regulation of membrane proteins in trout erythrocyte. Recombinant trout arrestin was produced in a protease-deficient Escherichia coli strain and its functionality was tested in a reconstituted rhodopsin assay. The recombinant protein provides a suitable tool for investigating the target for arrestin in trout red blood cell, which still remains to be identified.

Expression of band 3 anion exchanger induces chloride current and taurine transport: structure-function analysis

Most, but not all, cell types release intracellular organic solutes (e.g. taurine) in response to cell swelling to achieve cell volume regulation. Although this efflux is blocked by classical inhibitors of the electroneutral anion exchanger band 3 (AE1), it is thought to involve an anion channel. The role of band 3 in volume-dependent taurine transport was determined by expressing, in Xenopus oocytes, band 3 from erythrocytes which do (trout) or do not (mouse) release taurine when swollen. AE1 of both species elicited anion exchange activity, but only trout band 3 showed chloride channel activity and taurine transport. Chimeras constructed from trout and mouse band 3 allowed the identification of some protein domains critically associated with channel activity and taurine transport. The data provide evidence that swelling-induced taurine movements occur via an anion channel which is dependent on, or controlled by, band 3. They suggest the involvement of proteins of the band 3 (AE) family in cell volume regulation.

Catecholamine release controlled by blood oxygen tension during deep hypoxia in trout: effect on red blood cell Na/H exchanger activity

Changes in plasma catecholamine levels were measured in trout exposed to acute hypoxia, in order to correlate with acid-base disturbances due to activation of the cAMP-dependent Na+/H+ antiporters of red blood cells, as previously described (Fiévet B., Respir. Physiol. 74, 99-114, 1988). The extracellular acidosis corresponding with the stimulation of the exchangers, occurred when arterial oxygen partial pressure (PaO2) reached around 15 Torr (Thomas S., Respir. Physiol. 74, 77-90, 1988). This blood pH drop coincided with a marked increase in plasma catecholamine levels. The catecholamine secretion was transient and the hormones were cleared provided PaO2 remained above 10 Torr. On the other hand, when PaO2 remained below 10 Torr, there was a persistent secretion of catecholamines. This is in agreement with the fact that the exchangers are 'turned off' or sustained when PaO2 remains above or below 10 Torr respectively, as previously described. Following the transient hormone peak when PaO2 stabilized above 10 Torr, it was possible to trigger the second pattern of continuous catecholamine secretion by controlling water PO2 so that PaO2 declined below 10 Torr. We conclude that the blood oxygen level controls catecholamine secretion during deep hypoxia.