Root uptake of radionuclides following their acute soil depositions during the growth of selected food crops

Aggregated transfer factors of fresh Cs and Sr pollution to various vegetables from six common European soils - mesocosm experiment

Aggregated transfer factors (Tag) were identified for three common vegetables grown in six common European soils freshly contaminated by 134Cs and 85Sr. The experiment was carried out as a mesocosm experiment in pots with an average soil weight of 15.8 kg per pot. The vegetables were grown one after the other during one vegetation season, in the order lettuce, onion, and radish (the order usually applied in private gardens and small farms). Despite the fact that lettuce was grown in the most contaminated soil, it had the lowest Tag (in m2/kg) of both radionuclides (3.6E-4 for Cs, 2.0E-2 for Sr), while onion had 6.4E-3 for Cs and 3.2E-2 for Sr and radish had 1.9E-3 for Cs and 8.1E-2 for Sr. Potassium supply did not show any statistically significant effect on Cs Tag; there was a significant impact of K on the decrease in Sr Tag. The experiments indicated that Tag is more affected by plant species than by soil type; therefore, selection of plants with a lower capacity to uptake radionuclides may be an important measure to reduce food contamination and thus minimize the committed effective dose.

Parameter Values for Estimation of Internal Doses from Ingestion of Radioactive Fallout from Nuclear Detonations

ABSTRACT

This paper suggests values or probability distributions for a variety of parameters used in estimating internal doses from radioactive fallout due to ingestion of food. Parameters include those needed to assess the interception and initial retention of radionuclides by vegetation, translocation of deposited radionuclides to edible plant parts, root uptake by plants, transfer of radionuclides from vegetation into milk and meat, transfer of radionuclides into non-agricultural plants and wildlife, and transfer from food and drinking water to mother's milk (human breast milk). The paper includes discussions of the weathering half-life for contamination on plant surfaces, biological half-lives of organisms, food processing (culinary factors), and contamination of drinking water. As appropriate, and as information exists, parameter values or distributions are specific for elements, chemical forms, plant types, or other relevant characteristics. Information has been obtained from the open literature and from publications of the International Atomic Energy Agency. These values and probability distributions are intended to be generic; they should be reviewed for applicability to a given location, time period, or season of the year, as appropriate. In particular, agricultural practices and dietary habits may vary considerably both with geography and over time in a given location.

Distribution of 137Cs and 85Sr in selected Egyptian plants after foliar contamination

The transfer of ¹³⁷Cs and ⁸⁵Sr from fallout to plants was studied in two successive pot experiments. Five plant species (Oryza Sativa, Tritichum Vulgares, Vicia Faba, Sesamum Orientale and Trifolium Alexandrinum) were grown in pots containing sandy clay loam soil. For simulating foliar contamination, radioactive ¹³⁷Cs and ⁸⁵Sr solutions were sprayed once with different activity concentrations gently on the shooting system. After 8 weeks of radioactivity application to the above first four plants and 4 weeks to the last one, the total absorption of ¹³⁷Cs and ⁸⁵Sr and their distribution in different parts of the tested plants were determined. Most of the absorbed ¹³⁷Cs and ⁸⁵Sr accumulated in shoots with proportions ranged from 70.8 to 81.9% and from 88.9 to 95.0%, respectively for different plants. The absorbed ¹³⁷Cs and ⁸⁵Sr by grains/seeds followed that of shoots with values ranged from 11.9 to 19.2% and from 5 to 10.9%, respectively. The percentage of ¹³⁷Cs absorbed by roots ranged from 6.2 to 10.0% among different plants, while ⁸⁵Sr in roots of plants was below the minimum detectable activity of the detector. For Trifolium, most of the absorbed ¹³⁷Cs and ⁸⁵Sr accumulated in the first harvest (81.9 and 98.6%). The aggregated transfer factors (T_ag) of both radionuclides under foliar conditions were to a great extent similar. The average values of T_ag factors (m²kg^-1) of ¹³⁷Cs and ⁸⁵Sr, respectively, in rice grains were 3.4 × 10^-4 and 1.6 × 10^-4; in wheat grains were 4.2 × 10^-4 and 2.1 × 10^-4; in bean seeds were 4.9 × 10^-4 and 2.6 × 10^-4; and in sesame seeds were 2.8 × 10^-4 and 1.2 × 10^-4. Those T_ag factors of grains/seeds were substantially lower than those obtained with straw of the corresponding plant species.

Transfer factor of 137Cs and 90Sr to various crops in semi-arid environment

This study focuses on evaluating the transfer factor (F_v) of ¹³⁷Cs and ⁹⁰Sr from two basic soil types in the country, i.e. Aridisol and Inceptisol, to 18 common crops belong to six groups, i.e. cereals, leafy, non-leafy vegetables, tubers, leguminous fodder and leguminous vegetables. In addition, the variation of F_vs of ¹³⁷Cs and ⁹⁰Sr with crop components, growth stages of plants and the influence of mineral fertilisation were investigated. The experiments were performed in an open field and the results were expressed as geometric means. The data revealed that F_vs of both radionuclides were higher in Aridisol than Inceptisol for all crops by about 1.03-4.86 fold. F_vs of ⁹⁰Sr were more enhanced than those of ¹³⁷Cs by one or two orders of magnitude despite plant group and soil type, e.g. F_vs ranged 0.12-5.2 for ⁹⁰Sr and 0.0035-0.26 for ¹³⁷Cs in the vegetative portion of the crops. Among the six crop groups investigated, cereals gave the lowest F_vs for both radionuclides, which is compatible with the data reported worldwide. The average F_vs observed in cereal grains reached 0.001 for ¹³⁷Cs and 0.017 for ⁹⁰Sr, in Inceptisol. However, Jew-mallow (one of the major leafy vegetables in the country that is consumed throughout the year) reflected the highest F_vs for ¹³⁷Cs and ⁹⁰Sr, i.e. 0.11 and 2.44 in Inceptisol, respectively. Comparing F_vs of the radionuclides through the growing stages of the plants indicated enhanced values at the mid-season than harvest as a consequence of the decrease of the physiological activity of the plants towards maturation and dilution made by the increase of plant biomass; e.g. F_vs dropped to about 3.0 fold for ¹³⁷Cs and 2.2 for ⁹⁰Sr, in Aridisol. Mineral fertilisation of soil (for four crops, i.e. sorghum, barley, spinach and alfalfa) reduced F_vs for both radionuclides to an extent of 30% probably because of the competing action of their stable nutrient analogues NH₄⁺, K⁺ or Ca²⁺ or because of growth dilution. The data presented herein would form a baseline when decision of land-investment or phytoremediation is the preferable countermeasure for the management of ¹³⁷Cs and ⁹⁰Sr-contaminated soil in semi-arid environment.

Simulating the Transfer of Strontium-90 from Soil to Leafy Vegetables by Using Strontium-88

The transfer, from soil to Chinese cabbage and spinach, of radioactive strontium-90 released as a result of accidents in nuclear power stations was studied using a stable isotope of strontium, namely nuclide strontium-88 (⁸⁸Sr). The study led to an experimental model for assessing the hazard of radionuclide strontium-90 (⁹⁰Sr) entering the food chain and for predicting the risk to food safety. Chinese cabbage and spinach were grown in pots in a greenhouse and irrigated with deionized water containing known quantities of strontium. Based on the strontium content of that water, the plants were divided into five groups (treatments) and strontium content of the soil, and 30-day-old plants were determined by inductively coupled plasma atomic emission spectroscopy instrument (ICP-AES). Data on the strontium content of soil and plants enabled the development of a model using MATLAB, a mathematical software package, which included curve fitting and problem solving using regression equations and differential equations. Although strontium curves for leaves, stems, and roots of Chinese cabbage were not exactly the same, all showed a non-linear increase when compared with the increase in the content of strontium in soil. Strontium curves for leaves, stems, and roots of spinach were very similar and showed an initial increase followed by a decrease. Strontium concentrations in both Chinese cabbage and spinach were initially related to the concentrations of sodium and sulfur, the next two relevant nuclides being calcium and magnesium. The relationship between calcium and strontium in Chinese cabbage was different from that in spinach. By using ⁸⁸Sr to simulate the transfer of radionuclide ⁹⁰Sr from soil to a crop, the relevant data required to deal with accidental release of strontium can be obtained using a fitting curve and regression equations, thereby providing some experimental basis for evaluating the potential hazards posed by such accidents to the food chain.

Transfer factor of (90)Sr and (137)Cs to lettuce and winter wheat at different growth stage applications

The effect of clay soil contamination time on the transfer factors (Fvs) of (137)Cs and (90)Sr was investigated in four different growth stages of winter wheat and lettuce crops. The experiment was performed in an open field using lysimeters. The Fvs were the ratio of the activity concentrations of the radionuclides in crops to those in soil, both as dry weight (Bq kg(-1)). Significant difference of log-Fvs was evaluated using one-way Analysis of Variance (ANOVA). Basically, Fvs of (90)Sr were higher than those of (137)Cs, despite of the application stage or crop' variety. Higher Fvs for both radionuclides were observed for lettuce in comparison to winter wheat. Fvs of (90)Sr showed comparable trends for both crops with enhanced Fvs obtained when contamination occurred in early stages, i.e. 1.20 for lettuce and 0.88 and 0.02 for winter wheat, straw and grains, respectively. Despite the fluctuation noted in the pattern of Fvs for (137)Cs, soil contaminated at the second stage gave the highest Fvs for lettuce and grains, with geometric means of 0.21 and 0.01, respectively. However, wheat-straw showed remarkable increase in Fv for the latest contamination (ripening stage), about 0.06. It could be concluded that soil contamination at early growth stages would represent high radiological risk for the scenarios studied with an exception to (137)Cs in winter wheat-straw which reflected greater hazard at the latest application.

Soil-to-soybean transfer of (99)Tc and its underground distribution in differently contaminated upland soils

Pot experiments were performed in a greenhouse to investigate the soil-to-soybean transfer of (99)Tc in two different upland soils labeled with (99)TcO4(-) in two contrasting ways. One was to mix the soil with a (99)TcO4(-) solution 26 d before sowing (pre-sowing deposition: PSD), and the other was to apply the solution onto the soil surface 44 d after sowing (growing-period deposition: GPD). The soil-to-plant transfer was quantified with the transfer factor (TF, ratio of the plant concentration to the average of at-planting and at-harvest soil concentrations) or the aggregated transfer factor (TFag, ratio of the plant concentration to the deposition density). For both the depositions, the transfer of (99)Tc to aerial parts decreased in the order of leaf > stem > pod > seed. TF values (dimensionless) from the PSD were 0.22 and 0.27 (no statistically significant difference) for mature dry seeds in the respective soils, whereas a 600-fold higher value occurred for dry leaves. The post-harvest concentrations of the PSD (99)Tc in the top 20 cm soils as a whole were about half the initial concentrations. Around 25% of the total applied activity remained in the GPD soils after the harvest. The post-harvest depth profiles of the GPD (99)Tc in the two soils showed similar patterns of logarithmic activity decrease with increasing soil depths. Only 1.5-4.3% of the total applied activity was removed through the harvested biomass (seeds, pods and stems), and it was estimated that a great part of the total pant uptake returned to the soil through the fallen leaves. TFag values (m(2) kg(-1)) were about 2-4 times higher for the GPD than for the PSD. This finding and generally high root uptake of Tc may indicate that the use of empirical deposition time-dependent TFag data is particularly important for predicting the plant concentrations of Tc after its growing-period deposition.

Estimation of the committed radiation dose resulting from gamma radionuclides ingested with food

The objective of the study was to estimate the value of the radiation dose absorbed in consequence of consumption of popular food products for individual age groups. Potatoes, corn and sugar beet were selected for the study. Edible parts of these plants were collected in experimental fields of the KWS Lochów Polska Sp. z o.o. seeding company in Kondratowice (Poland). On the basis of the obtained study results, it can be stated that in consequence of consumption of the selected food products, people may receive increased doses from both natural and artificial radioactive isotopes. The doses calculated for several age groups do not show any health hazards in consequence of consumption of the tested food. One of the determined radionuclides was ¹³⁷Cs; however, its presence in the absorbed dose is lower than the doses from natural radioactive isotopes, in particular ⁴⁰K.

Translocation of (125)I, (75)Se and (36)Cl to edible parts of radish, potato and green bean following wet foliar contamination under field conditions

Specific translocation factor values (ftr) for (129)I, (79)Se and (36)Cl following foliar transfer are still missing from the IAEA reference databases. The translocation of the short-lived isotopes, (125)I, (75)Se, and (36)Cl, to radish, potato and green bean edible parts was measured under field conditions following acute and chronic wet foliar contamination at various plant growth stages in the absence of leaching caused by rain. The translocation factors obtained for (125)I ranged from 0.8 to 2.6% for radish, from 0.1 to 2.3% for potato and from 0.1 to 2.6% for bean. The translocation factors obtained for (75)Se ranged from 6.3 to 21% for radish, from 1.6 to 32.6% for potato and from 7.7 to 22.8% for bean (values similar to Cs or even higher). The translocation factors obtained for (36)Cl were close to those for (75)Se and ranged from 4.3 to 28.8% for radish, from 0.5 to 31.5% for potato and from 4.3 to 16.3% for bean. Iodide showed the lowest apparent mobility because of its preferential fixation in or on the leaves and a significant amount was probably volatilized. Selenite internal transfer was significant and possibly followed the sulfur metabolic pathway. Chloride was very mobile and quickly diffused throughout the plant. The translocation factors varied with the growth stage and depended on the development state of the edible tissue and its associated sink strength for nutrients and assimilates. For radish, translocation was high during the early vegetative stages. For potato, wheat and bean, a major peak in translocation was seen during the flowering growth stage and the concomitant growth of potato tubers. An additive effect of successive contamination events on translocated elements was shown in radish but not in bean and potato. The highest translocation value obtained for an acute contamination event was shown to be an adequate, conservative indicator of chronic contamination in absence of specific values. Due to the absence of rain leaching during the experiment this study probably provides translocation values among the highest that could be recorded.

134Cs transfer factors to green gram and soybean as influenced by waste mica

Greenhouse pot culture experiment was carried out to study the (134)Cs transfer factors from soils to green gram and soybean as influenced by waste mica application (@ 0, 10, 20, 40 g mica kg(-1) soil) and compared with muriate of potash (MOP) application (0.17 g kg(-1) soil). For the study, the soils were contaminated with (134)Cs radionuclide @ 37 kBq kg(-1) soil. The shoot biomass and K uptake by crops were significantly improved with waste mica application (@ 40 g kg(-1) soil). Compared to control, waste mica and MOP application significantly improved the yield, K content in plant and its uptake. Amongst the soils, crops grown in vertisol recorded higher shoot biomass compared to inceptisol and ultisol. Irrespective of the treatments, higher (134)Cs transfer factors were seen in ultisol (0.30) as compared to inceptisol (0.16) and vertisol (0.13). It was observed that higher the K concentration in soil and plant, lowered (134)Cs transfer to green gram and soybean. The study recommended that waste mica @ 20 g kg(-1) would be useful for checking the (134)Cs transfer factors from soils to green gram and soybean.

Transport behavior and rice uptake of radiostrontium and radiocesium in flooded paddy soils contaminated in two contrasting ways

In order to investigate the transport behavior and rice uptake of radiostrontium and radiocesium in flooded rice fields, lysimeter experiments with two paddy soils were performed in a greenhouse. A solution containing (85)Sr and (137)Cs was applied in two different ways - being mixed with the top soil 27 d before transplanting or being dropped to the surface water 1d after transplanting. Rice uptake was quantified with two kinds of transfer factor - TF(m) (dimensionless) and TF(a) (m(2)kg(-1)-dry) for the pre- and post-transplanting depositions, respectively. For brown rice, the TF(m) values of (85)Sr and (137)Cs differed between the soils by factors of 2 (1.6×10(-2) and 2.5×10(-2)) and 7 (2.2×10(-2) and 1.5×10(-1)), respectively. Corresponding factors by the TF(a) values were 2 (2.5×10(-4) and 4.4×10(-4)) for (85)Sr and 3 (1.1×10(-3) and 2.9×10(-3)) for (137)Cs. Straws had several times higher TF(m) and TF(a) values of (85)Sr than of (137)Cs. The surface-water concentrations were substantially higher for the TF(a) than for the TF(m), indicating the possibility of a much higher plant-base uptake for the TF(a). In the TF(a) soils, (137)Cs and, to a lesser degree, (85)Sr were severely localized towards the soil surface, probably leading to an increased root uptake. The activity loss due to plant uptake and water percolation was generally inconsiderable. Time-dependent K(d) values of (85)Sr measured in a parallel experiment ranged from 20 to 170, whereas (137)Cs had much higher K(d) values. The use of TF(a) values instead of TF(m) values turned out to be a reasonable approach to the evaluation of a vegetation-period deposition.