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An atmospheric tracer dispersion study was conducted in a heterogeneous district of the city of Nantes, France, in May 2010 and June 2012 during the measurement campaigns FluxSAP. Vertical (0–100 m) and horizontal (≈ 300 m) profiles were measured at distances of 20 to 1200 m from the tracer gas release location. The vertical profiles show vertical mixing occurring progressively with distance: the 0–100 m air column is homogenous beyond 600 m, whereas at shorter distances a maximum of concentration is observed, either at ground level for distances less than 200 m, or at altitude for intermediate distances. Our measurements are compared with the Briggs-urban model which may be used in emergency situations: the model gives coherent results with our measurements in terms of vertical and horizontal dispersion parameters but we observe concentration differences up to an order of magnitude between model and measurements. Based on our results we propose new relationships for the horizontal and vertical dispersion parameters for distances from 0 to 1 km. For emission–measurement distances above 1 km, differences appear between the trends deduced from our measurements and those of the Briggs-urban model: it will be necessary to acquire data at greater distances, 2000 m and more, to verify and validate these trends. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric transport plays an important role in the transfer of pollutants to ecosystems. During such transport, the atmospheric aerosol is one of the key factors in terms of deposition. Over 18 months, we studied the concentrations of Zn, Pb, Ni, Cd, Hg in air and precipitations in a wetland site in the north west of France. The objective of this study was to characterise the quantities transferred by dry and wet deposition. An eddy correlation technique was used to measure dry deposition velocities and determine the dry deposition fluxes from atmospheric concentration. In this site, wet deposition is almost always preponderant, except for Pb and Cd over several months. Measurements in the air and in rainwater are low and show that the site is protected from important anthropogenic influences, with levels that can be considered as background levels. In terms of deposition fluxes, the configuration of the site and the meteorological conditions (low wind speeds, low thermal fluxes) lead to low dry depositions. Wet depositions, although more important are also relatively low compared to the literature, directly linked to the pluviometry during the study period. [Copyright &y& Elsevier]

The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011 led to an unprecedented direct input of artificial radioactivity into the marine environment. The Institute for Radioprotection and Nuclear Safety was requested by the French authorities to investigate the radioecological impact of this input, in particular the potential contamination of products of marine origin used for human consumption. This article describes the close link between the responses provided and the availability of the data, as well as their nature and ability to meet the requirements of expert investigation. These responses were needed: (i) to evaluate the inputs of radionuclides into the marine environment, (ii) to understand their dispersion in seawater, and (iii) to estimate their transfer to the biota and sediments. Three phases can be distinguished which characterise these processes during the accident and post-accident periods. The first phase corresponds to an emergency phase during which no measurements were available on samples from the marine environment. It involved the formulation of hypotheses based solely on the expertise of the Institute for Radioprotection and Nuclear Safety. The second phase started when the Japanese authorities provided measurements of the concentrations of radionuclides in seawater. Although these data were not yet adapted to addressing the problems of radioecology, the scenarios could then be refined and the estimates developed in more detail. During the third phase, the accumulation of data over the course of time made it possible to study the phenomena in an appropriate way. The chronology of the events shows that it is essential to have (i) significant measurements of concentration from samples collected in the various matrices of the marine environment, regularly updated and sufficiently well-documented, (ii) samples of seawater collected at the earliest opportunity as close as possible to the damaged site to characterise the source term, and (iii) a numerical tool allowing rapid modelling of the dispersion of radionuclides in seawater, as well as their transfer to sediments and the biota, ultimately for the purpose of estimating the dose to humans. [ABSTRACT FROM AUTHOR]

Abstract: The French Institute for Radiological Protection and Nuclear Safety (IRSN), in collaboration with VEOLIA (French environmental services company), conducted experimental campaigns to study atmospheric dispersion around an Energy Recycling Unit (EUR). The objectives were to study dispersion for an elevated release in a rural environment and to compare results with those of models. The atmospheric dispersion was studied by SF6 tracer injection into a 40 m high stack. Maximum values of experimental Atmospheric Transfer Coefficients (ATCmax) and horizontal dispersion standard deviations (σ h) were compared to predictions from a first generation Briggs gaussian model as well as results from the latest generation ADMS 4.1 gaussian model. In neutral atmospheric conditions, the Briggs and ADMS models are in good agreement with experimental data in terms of ATC and σ h. In unstable condition, for σ h, both ADMS and Briggs models slightly overestimate the data for winter and summer conditions. In unstable conditions, ADMS and Briggs models overestimated ATCmax. The statistical evaluation of the models versus experimental data shows neither models ever meets all of the criteria for good performance. However, statistical evaluation indicates that the ADMS model is more suitable for neutral condition, and that the Briggs model is more reliable for summer unstable conditions. [Copyright &y& Elsevier]

Abstract: A sequential extraction protocol has been used to determine the solid-phase partition of 210Po and 210Pb in anoxic marine sediment from the roads of Cherbourg (France) in the central English Channel. Measurements were also obtained in pore waters, in which 210Po activities range between 1 and 20mBqL−1 and 210Pb activities between 2.4 and 3.8mBqL−1, with highest activities in the topmost layer. These activities are higher than in seawater, suggesting that sediment act as a source of both 210Po and 210Pb for overlying water. The 210Po profile in the pore waters is apparently correlated with those obtained for Fe, Mn and SO4 2 −, suggesting an influence of early diagenetic processes on the 210Po solid-liquid distribution. In the sediment, 210Po is predominantly bound to organic matter or chromium reducible sulphides, and residuals (clay minerals and refractory oxides). Our results indicate that 210Po is not significantly bound to AVS, i.e. acid volatile sulphides: bioturbation could play a role by the early redistribution of 210Po bound to acid volatile sulphides in the sediment. 210Po, 210Pb and Pb exhibit differences in terms of distribution, probably due to a different mode of penetration in the sediment. This work provides information on solid and liquid distribution of 210Po and 210Pb in marine sediment. These data are very scarce in the litterature. [Copyright &y& Elsevier]

Atmospheric transport and dispersion were investigated during the CAPITOUL campaign using measurements of sulphur hexafluoride (SF6) tracer. Six releases of SF6 tracer were performed (March 9–11 and July 1–3, 2004) in the same suburban area of Toulouse conurbation, during the Intensive Observing Periods (IOP) of CAPITOUL. Concentration data were collected both at ground-level along axes perpendicular to the wind direction (at distances ranging between 280 m and 5000 m from the release point), and above the ground at 100 m and 200 m height using aircraft flights. Meteorological conditions were all associated with daytime anticyclonic conditions with weak winds and convective clear and cloudy boundary layers. A meso-scale dispersion modelling system, PERLE, developed at Meteo-France for environmental emergencies in case of atmospheric accidental release, was evaluated in terms of meteorology and dispersion, for the different tracer experiments, in its operational configuration. PERLE is based on the combination of the non-hydrostatic meso-scale MESO-NH model, running at 2 km horizontal resolution, and the Lagrangian particle model SPRAY. The statistical meteorological evaluation includes two sets of simulations with initialisation from ECMWF or ALADIN. The meteorological day-to-day error statistics show fairly good Meso-NH predictions, in terms of wind speed, wind direction and near-surface temperature. A strong sensitivity to initial fields concerns the surface fluxes, crucial for dispersion, with an excessive drying of the convective boundary layer with ALADIN initial fields, leading to an overprediction of surface sensible heat fluxes. A parameterization of dry and shallow convection according to the Eddy-Diffusivity-Mass-Flux (EDMF) approach (Pergaud et al. 2008) allows an efficient mixing in the Convective Boundary Layer (CBL) and improves significantly the wind fields. A statistical evaluation of the dispersion prediction was then performed and shows a realistic behaviour of the system, with a good location of the concentration maxima. But the lateral spread of the plumes is quasi-systematically underestimated, mainly in July, even when meteorological conditions are well reproduced. In the same way, higher integrated concentration values are slightly overestimated. The remove of the EDMF scheme in Meso-NH artificially improves the horizontal dispersion, underlying compensating errors. Sensitivity tests performed on the Lagrangian time scales in the coupling Meso-NH-SPRAY have been conducted. But they don’t solve the shortcoming and lead to the conclusion that SPRAY could have some difficulties to correctly reproduce the mixing for daytime thermal convection. [ABSTRACT FROM AUTHOR]

Measurements of 210Po were carried out in various marine matrices (mussels, oysters, seaweed, fish, and abalones) and in seawater at several points along the French coast, over a period of 2 years (2003–2005). These measurements contribute to a better knowledge of this element, since few recent data exist for the French coast. Marked seasonal variations have been revealed in some species and there are differences according to the way of life of these species. Activities in mussels (Mytilus edulis) and oysters (Crassostrea gigas) are similar and varying between 90 and 600Bqkg−1 (d.w.). Activities in macroalgae (Fucus serratus) are lowest, between 4 and 16Bqkg−1 (d.w.). In oyster, abalone (Haliotis tuberculata) and fish (Solea solea, Sparus sp.), the strongest activities are measured in the digestive glands, the gills and the gonads. 210Po/210Pb ratios in all cases have values of more than one for all species. From a significant number of measurements, CFs were calculated for seaweed (between 4.6×103 and 5.0×103) and for molluscs, with highest CFs (>105) found for the digestive gland and gills of the oysters, the digestive gland of the abalones and the liver of fish. Finally, the activities measured have made it possible to estimate the internal dose from chronic exposure due to 210Po received by the marine organisms (0.05μGh−1 for macroalgae, between 0.70 and 1.5μGh−1 for mussels and oyster), and the contribution of seafood to the dose received by humans (46–129μSvy−1). [Copyright &y& Elsevier]