Soil-to-plant transfer factors of radioactive Ca, Sm and Pd isotopes Critical assessment of the use of analogies to derive best-estimates from existing non-specific data

International audience45Ca, 151Sm and 107Pd are three radionuclides present in low to intermediate in activity radioactive wastes for which no soil-to-plant Transfer Factors (TF) values are available to be used in biosphere models for Ecological Risk Assessment. In the absence of specific radioecological studies, this work reviews and analyzes the existing literature for stable isotopes of Pd, Sm and Ca in order to derive best estimates for TF values that could be used as Transfer Factors. Alternative methods of extrapolation are also critically assessed. The values have been classified according to climatic zone, plant class and soil type for each element. The overall geometric mean TF values (for all plants and conditions) was calculated as 8.4E-02 for Pd, for which the value of radioRu in TRS-472 is also available. The mean TF for Sm was 4.2E-04. This value was lower than the TF values for radioactive Ce that are proposed as alternative values for Sm in TRS-472. The former may be relevant for long term assessments and the latter could possibly used to describe the short term 151Sm post-release behaviour. The mean value for Ca is 2.3E-01 but varies considerably among plants of a given class due to the variety of plant Ca uptake behaviors. Alternatively, to limit this variability, Ca data content for dry plant matter, as analyzed using the phylogenetic method, could be used to derive TF values if the conservation of isotopic ratio of 45Ca to stable Ca in soils and in plants hypothesis is taken into account. The TF for Ca in sub-tropical zones is 10-fold lower than in temperate zones. There is a lot of data available about exchangeable Ca in soil, which mean that we could calculate an available TF. The analysis shows that Ca bioavailability is also a key factor within transfer. © 2014 Elsevier Ltd

Experimental quantification of radiocesium recycling in a coniferous tree after aerial contamination Field loss dynamics, translocation and final partitioning

International audienceAfter foliar interception of radioactive atmospheric fallout by forest trees, the short-term recycling dynamics of radiocesium from the tree to the soil as well as within the tree is a primary area of uncertainty in the modeling of the overall cycle. The partitioning of radiocesium transfers in a spruce tree exposed to aerial deposits was investigated during one growth season to reveal the dynamics and significance of underlying processes. The rate of radiocesium loss resulting from foliage leaching (wash-off) was shown to have a functional dependence on the frequency of rainy episodes in a first early stage (weathering 60% of initial contamination during 70 days) and on the amount of precipitation in a second stage (weathering 10% of initial deposits during the following 80 days). A classical single exponential decay model with offset and continuous time as predictor lead to a removal half-life t 1/2 of intercepted radiocesium of 25 days. During the growth season, the similar pattern of the internal 134 Cs content in new shoots and initially contaminated foliage confirmed that radiocesium was readily absorbed from needle surfaces and efficiently translocated to growing organs. In the crown, a pool of non-leachable 134 Cs (15–30%) was associated with the abiotic layer covering the twigs and needle surfaces. At the end of the growth season, 30% of the initial deposits were relocated to different tree parts, including organs like stemwood (5%) and roots (6%) not directly exposed to deposition. At the scale of the tree, 84% of the residual activity was assimilated by living tissues which corresponds to a foliar absorption rate coefficient of 0.25 year −1 for modeling purposes. According to the significant amount of radiocesium which can be incorporated in tree through foliar uptake, our results support the hypothesis that further internal transfers could supply the tree internal cycle of radiocesium extensively, and possibly mask the contribution of root uptake for a long time. © 2016 Elsevier Lt

Equation to predict the 137Cs leaching dynamic from evergreen canopies after a radio-cesium deposit

International audienceThe Fukushima Daiishi nuclear power plant (FDNPP) accident led to a massive radionuclide deposition mainly onto Japanese forest canopies. In our previous study, an improved double exponential (IDE) equation including rainfall intensity was proposed to estimate the 137Cs hydrological transport from evergreen canopies to the ground. This equation used two types of parameters, kinetic (k1 and k2) and leachable stock (A1 and A2). Those parameters have been estimated by adjusting them in the IDE equation in order to accurately describe the measured cumulative leached 137Cs from canopies (k1=4.2E-04-5.0E-04d-1, k2=1.2E-02-1.7E-02d-1, A1=62-99kBq/m2, A2=25-61kBq/m2).In this study, we linked the total leachable stock (Aleachable, a parameter of the IDE equation corresponding to A1+A2) to a physiological criteria (the canopy closure CC, which can be measured with a simple camera equipped with a fish-eye objective). Furthermore, the kinetic parameters measured for Japanese cedar (k1=5.0E-04d-1, k2=1.2E-02d-1, and r12=0.22 (r12=A1/A2) could also be used for two other coniferous species Japanese cypress and spruce. This suggests that these parameters could be constants for coniferous forests. © 2015 Elsevier Ltd

Role and uncertainty of foliar transfer in radiological impact assessments: State of the art and future actions

Sensitivity analyses have shown major role of foliar transfer for many radionuclides in the context of radiological impact assessments. A review of the published literature about foliar transfer focusing on translocation factors was carried out in order to constitute an updated database on one hand and to use the appropriate existing values of translocation parameters for modeling on the other. Translocation describes the distribution of radionuclides within the plant after foliar deposition and radionuclide absorption onto the surface of leaves. It mainly depends on elements and the plant growth stage. The collected data was derived from both in-field and greenhouse experiments. It was analysed to select those coming from a contamination simulating sprinkling irrigation or rain. This work not only allowed us to carry out a diagnosis on the values themselves but also enabled us to ascertain missing data needs. In order to compensate for the lack of data on important radionuclides concerning radioactive waste (129I, 36Cl, 79Se), experimental studies have been launched

Influence d'acides organiques sur la désorption de l'américium 241 et du neptunium 237 à partir d'un sol cultivé acide

Effect of organic acids on 241 americium and 237 neptunium desorption from an acidic cultivated soil. Naturally occurring organic substances have been recognised as one important factor affecting the behaviour in the environment of transuranic actinides. This experimental study aims at evaluating if some naturally occurring carboxylic acids (vanillic, citric, lactic, oxalic) would affect 241Am or 237Np availability in an acidic agricultural soil. Data show that these acids enhance the desorption of americium and neptunium from the soil, with a noticeable effect of citric acid. The fraction desorbed is multiplied by more than 10 for 0.1 M citric acid, and by 3 or 4 with other acids, in relation with the complexation of radionuclides with these acids. The desorption increases with molar concentration of the acids because of the decrease of pH in acidified soils, except for oxalic acid. The soil moisture conditions seem to affect the desorption results: the percentage desorbed is approximately 10 times lower for batch experiments (saturated conditions) than for centrifugation corresponding to unsaturated soil conditions. These preliminary data are mainly qualitative, but they show that it could be interesting to take into account more realistic physico-chemical conditions when measuring desorption ratios for cultivated soils

Root uptake by cultivated vegetables of radionuclides coming from contaminated algae used as organic manure in soil

In certain areas of the French Atlantic coast, algae of marine origin are used as organic fertilizer, particularly for vegetables cultivation. An experiment was carried out to estimate the transfers of radioactivity towards agricultural productions, which could result from this practice in the case where algae were contaminated. Algae (fucus vesiculosus) were cultivated in aquarium with seawater containing a mixture of radionucléides : 22Na, 60Co, 90Sr, 99Tc, 106Ru, 125Sb, 134, 137Cs, 238, 239+240Pu, 241Am, 244Cm. These algae were mixed, in a lysimeter, with a silty-sandy soil. Some vegetables, potatoes, lettuces, radishes, beans, tomatoes were cultivated on this manured soil. The soil to plant concentration ratios are given for the edible organs of the plants grown the year following the addition of algae in the soil and for cultures made several years later. On the other hand chemical extractions were performed to evaluate the bioavailable fraction of radionuclides in the soil

Root uptake by cultivated vegetables of radionuclides coming from contaminated algae used as organic manure in soil

In certain areas of the French Atlantic coast, algae of marine origin are used as organic fertilizer, particularly for vegetables cultivation. An experiment was carried out to estimate the transfers of radioactivity towards agricultural productions which could result from this practice in the case where algae were contaminated. Algae (fucus vesiculosus) were cultivated in aquarium with sea water containing a mixture of radionucléides: 22Na, 60Co , 90Sr, 99Tc , 106Ru , 125Sb, 134,137Cs , 238,239+240Pu, 241Am , 244Cm. These algae were mixed, in a lysimeter, with a silty-sandy soil. Some vegetables, potatoes, lettuces, radishes, beans, tomatoes were cultivated on this manured soil. The soil to plant concentration ratios are given for the edible organs of the plants grown the year following the addition of algae in the soil and for cultures made several years later. On the other hand chemical extractions were performed to evaluate the bioavailable fraction of radionuclides in the soil

Foliar interception of radionuclides in dry conditions A meta-analysis using a Bayesian modeling approach

International audienceUncertainty on the parameters that describe the transfer of radioactive materials into the (terrestrial) environment may be characterized thanks to datasets such as those compiled within International Atomic Energy Agency (IAEA) documents. Nevertheless, the information included in these documents is too poor to derive a relevant and informative uncertainty distribution regarding dry interception of radionuclides by the pasture grass and the leaves of vegetables. In this paper, 145 sets of dry interception measurements by the aboveground biomass of specific plants were collected from published scientific papers. A Bayesian meta-analysis was performed to derive the posterior probability distributions of the parameters that reflect their uncertainty given the collected data. Four competing models were compared in terms of both fitting performances and predictive abilities to reproduce plausible dry interception data. The asymptotic interception factor, applicable whatever the species and radionuclide to the highest aboveground biomass values (e.g. mature leafy vegetables), was estimated with the best model, to be 0.87 with a 95% credible interval (0.85, 0.89). © 2015 Elsevier Ltd