Foliar lead uptake by lettuce exposed to atmospheric fallouts

Metal uptake by plants occurs by soil−root transfer but also by direct transfer of contaminants from the atmosphere to the shoots. This second pathway may be particularly important in kitchen gardens near industrial plants. The mechanisms of foliar uptake of lead by lettuce (Lactuca sativa) exposed to the atmospheric fallouts of a lead-recycling plant were studied. After 43 days of exposure, the thoroughly washed leaves contained 335 ± 50 mg Pb kg−1 (dry weight). Micro-X-ray fluorescence mappings evidenced Pb-rich spots of a few hundreds of micrometers in diameter located in necrotic zones. These spots were more abundant at the base of the central nervure. Environmental scanning electron microscopy coupled with energy dispersive X-ray microanalysis showed that smaller particles (a few micrometers in diameter) were also present in other regions of the leaves, often located beneath the leaf surface. In addition, submicrometric particles were observed inside stomatal openings. Raman microspectrometry analyses of the leaves identified smelter-originated Pb minerals but also secondary phases likely resulting from the weathering of original particles. On the basis of these observations, several pathways for foliar lead uptake are discussed. A better understanding of these mechanisms may be of interest for risk assessment of population exposure to atmospheric metal contamination

Weather-dependent change of cesium, strontium, barium and tellurium contamination deposited as aerosols on various cultures

Various types of plants (wheat, bean, lettuce, radish and grass) were contaminated by dry deposition of radioactive aerosols (137Cs, 85Sr, 133Ba and 123mTe) in order to supplement the radioecological data necessary for operational post-accidental codes. A few days after deposition, rainfalls were applied to these cultures to evaluate the influence of some characteristics of the rain on the contamination of the culture over time. On the other hand, for wheat and bean, the influence of the humidity condition of the foliage at the contamination time was considered. For a given plant species at a given vegetative stage, the four radionuclides were intercepted in an identical way. The interception varied from 30% for bean (young sprout) to 80% for lettuce (near maturity). The global transfer factor values were dependent on both the radionuclides and the plant species; nevertheless, a higher value was obtained for cesium, regardless of the plant and the rainfall (from 0.006 m2 kgfresh-1 for wheat-grains - contaminated at the shooting stage - or for bean-pods - contaminated at the pre-flowering stage - to 0.1 m2 kg fresh-1 for a whole lettuce). The analysis of the results allowed us on the one hand, to extract parameter values of the foliar transfer directly usable in operational codes, in particular those relating to barium and tellurium, unknown until then, and on the other hand, to lay the foundations of a future, more mechanistic model, taking into account the foliar processes in a finer way. © 2005 Elsevier Ltd. All rights reserved

Contamination of terrestrial gastropods, Helix aspersa maxima, with 137Cs, 85Sr, 133Ba and 123mTe by direct, trophic and combined pathways

137Cs, 85Sr, 133Ba and 123mTe contaminations of terrestrial gastropods, Helix aspersa maxima, by direct deposition, labelled food ingestion or combined (trophic and direct pathways) exposure were carried out under laboratory conditions. The aim of this study was to compare the three contamination pathways: direct, trophic and combined, in terms of individual mortality, radionuclide uptake, depuration and distribution in the tissues. An initial group of 30 snails (2 years old) was exposed to radioactive aerosols during a 20-h period. These aerosols were assumed to be representative of those that would be released during a nuclear accident occurring in a PWR. A second group of 50 snails (same age) was submitted to an ingestion of commercial food contaminated by the same aerosols, twice a week for 21 days (flour at a feeding rate of about 0.2 g). A third group of 40 snails was submitted to a combined exposure: exposure to radioactive aerosols (20 h), followed by ingestion of flour contaminated by the same aerosols, twice a week for 21 days. No significant difference between the three groups and a reference group of 10 snails was observed, neither in growth nor in mortality. Concerning the direct pathway, at the end of direct deposition (about 1 day after the beginning), cesium was the most bioavailable element, distributed rather homogeneously throughout the whole body (13% of the total Cs in all organs excepting the digestive system and 28% in the muscle). Strontium was measured in the shell (about 70%). Barium was found in the muscle (20%) and in the shell (65%). Tellurium was mainly present in the shell (70%) and in the digestive system (20%). After 21 days of depuration, the faeces eliminated 42% of the Te. As for contamination by ingestion, Te mainly accumulated in the digestive system (72% of Te present in the total body), Ba accumulated in the muscle (75%) and Sr in the shell (70%). Concerning contamination by combined pathways, at the end of the 21-day exposure, the 4 radionuclides had the same tendency as direct deposition. However, the effect of the trophic pathway was significant: it causes an 18% increase of Sr in the shell and an 7% increase of Cs in the digestive system in comparison to direct deposition, resulting in a final 86% in the shell and 27% in the digestive system. © 2006 Elsevier Ltd. All rights reserved

Transfert du radiocésium du sol vers la plante : une étude en lysimètre

14 ref.National audienc

Evolution of cesium and strontium contamination deposited on vines

Vine plant contamination by means of dry aerosols (Cs-137 and Sr-90) was carried out on two large scale lysimeters taken from an on-site vine plantation (limestone silty loamy soil) in order to forecast, both short and long term consequences of an accident occurring at a pressurised water reactor on some common agricultural products. Initial contamination (of the soil and the plant) was performed at two vegetative stages : one at the "late flowering" stage for one lysimeter, the other at the "beginning of ripening" stage for the second lysimeter. A total but non-lethal defoliation test was carried out on one vine plant in order to estimate the efficiency of this countermeasure method in reducing contamination at harvest. The influence of rain during the vegetative stages was analysed. For the first 6 years following deposition, root absorption of two radionuclides was examined : the consequences of initial contamination on different parts of the plant (bunches, leaves and shoots) were assessed as a function of time after each harvest. Monitoring of migration in soil and bioavailability was also undertaken. Correlation tests between the activities found in the plants and the behaviour of radionuclides in soil (bio-availability of the stable and radioactive elements, migration of radio-nuclides) were performed

Foliar transfer into the biosphere: Review of translocation factors to cereal grains

A review of the published literature about foliar transfer radionuclides to cereal grains was carried out with a special interest for translocation factors. 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 were derived from both in-field and greenhouse experiments. They were analysed in order to select those coming from a contamination simulating a sprinkling irrigation or a rain. The data set contains 307 values. For each radionuclide the translocation factor values were sorted according to 5 characteristic stages of the cereal vegetative cycle: leaf development-tillering, stem elongation, earing-flowering, grain growth and ripening. Wheat, barley and rye have been treated together, independently of rice. For mobile elements such as cesium, the translocation factor is maximum when the contamination occurred at the earing-flowering stage. For less mobile elements such as strontium this maximum occurred for a foliar contamination at the grain growth stage. This review enabled us to propose the most probable value as well as the range of variation of translocation factors for some radionuclides according to the cereal vegetative cycle. Moreover, from these results, a radionuclide classification is proposed according to three mobility groups. © 2008 Elsevier Ltd. All rights reserved

Contamination of terrestrial gastropods Helix aspersa Maxima with

Contaminations of the terrestrial gastropods Helix aspersa maxima by direct deposition or labelled food ingestion of 137Cs, 85Sr, 133Ba and 123mTe were carried out under laboratory conditions. The aim of this study was to compare the two contamination pathways: direct and trophic, in terms of individual mortality and radionuclide uptake, depuration and tissular distribution. A first group of 30 snails (2-years old) was exposed to radioactive aerosols during a twenty-hour period. These aerosols were assumed to be representative of those that would be released during a nuclear accident occurring in a PWR. A second group of 40 snails (same age) was submitted to an ingestion of food contaminated by the same aerosols, twice-a-week for 10 days (flour at a feeding rate of about 0.2g). During the 21 day-observation period, a comparison between the two groups and the reference group (not contaminated by radionuclides) was performed. No significant difference between the three groups was observed in the growth or in the mortality. One day after deposition, cesium was the most bioavailable element, distributed rather homogeneously through the whole body (from 13 to 28% of the total Cs in organs other than the digestive system and the muscle, respectively). Strontium accumulated in the shell (about 70%). Barium was found in the muscle (20%) and the shell (65%). Tellurium was mainly present in the shell (70%) and in the digestive system (20%). After a few days, this element was mostly present in the faeces. As regards contamination by ingestion, it was mainly accumulated in the digestive system

Foliar contamination of plants with aerosols of

Two types of plants (lettuce and radish) were contaminated by dry deposition of radioactive aerosols (137Cs, 85Sr, 133Ba and 123mTe). Due to the rain efficiency in decreasing radiological contamination of crops, a rain scenario was applied on the two types of plants. These experiments aimed at improving the prediction of the consequences on agricultural products of a nuclear accident occurring on a PWR, and at improving the understanding of the different processes occurring between contamination and harvest. For a plant species at a given stage of its growth cycle, the interception of the four radionuclides was found to be identical and varied from 68% for radish to 75% (at the middle of ripeness stage) or 78% (at the mature plant stage). Using a conceptual model, the predominance between the two processes - washing-off the leaves and absorption through the leaves cuticles allowing translocation - was evidenced. For Cs, Sr and Ba, for both the lettuce and the radish, washing-off on the foliar cover was the most significant during the first rain. The absorption process inside the plant became dominant only from the third rain event. Tellurium had a particular behaviour: it was non-mobile and stayed put on the leaves. The values of the washing-off and absorption coefficients were estimated. The global transfer factor values were dependant on both the radionuclides and the plant species; nevertheless, a higher value was obtained for cesium, regardless of the plant and the rainfall (from 0.06 m2.kg$_{\scriptsize\textrm{fresh}}$-1 for radish to 0.1 m2.kg$_{\scriptsize\textrm{fresh}}$-1 for a whole lettuce)

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

Effects of radionuclide and rainfall characteristics on field loss parameters of grass

The decrease of foliar activity in vegetation after its initial contamination by foliar deposition is termed "field loss" (Chamberlain, 1970). This work investigated further laboratory data concerning field loss of 134Cs, 137Cs, 85Sr, 133Ba and 123mTe deposited on grassland (Madoz-Escande et al., 2005). Treatments consisted in rainfall scenarios cumulating 14 mm per week, combining two levels of intensity (8 or 30 mm/h) and two levels of frequency/precocity (late once or early twice-a-week). The time course of field loss was monitored in the edible tissues which were sampled by mowing between the rainfalls. Data were analyzed with an offset exponential loss model which is applicable to chronic contamination and is consistent with approaches adopted in radiological assessment models. Its parameters were estimated by the maximum-likelihood method, and their accuracy was determined by nonparametric boostrap. Radionuclide and rainfall conditions significantly affected the estimated rate (λ1) and extent (A1) of field loss. Field loss rate (λ1) and nonentrainable fraction (1 - A1) varied by a factor 1.5-3. Cesium was very mobile but persistent. On the contrary Tellerium was found less labile, but eventually was almost completely eliminated. Strontium and Barium had intermediate behaviors. Field loss was more efficient for moderate late once-a-week rainfalls (8 mm/h). Higher rainfall intensity reduced more the radionuclides losses than higher rainfall frequency/precocity. This paper reports statistically relevant effects that should be considered for more realistic assessments. © 2009 Elsevier Ltd. All rights reserved