Modelling and experimental studies on the transfer of radionuclides to fruit

A review of 137Cs and 40K soil-to-plant transfer factors in tropical plants

In this work we critically assess the soil-to-plant transfer factors (TF) for ¹³⁷Cs and ⁴⁰K in edible fleshy organs of tropical plants that are often components of the human diet. Radionuclide concentrations in soil and plants were obtained from previous investigations developed in Brazil, after the Goiânia radiological accident occurred in 1987. Transfer factors were determined in specific plant compartments (main root, main stem, bark, old and new branches, twig, old and new leaves, mature and green edible organs) of tropical species such as lemon (Citrus aurantifolia), orange (Citrus sinensis), guava (Psidium guajava), chili pepper (Capsicum frutescens), pomegranate (Punica granatum), papaya (Carica papaya), banana (Musa paradisíaca), and manioc (Manihot esculenta). For ¹³⁷Cs, soil-to-fruit transfer factor ranged from 0.80 × 10^-2 (banana) to 3.65 × 10^-1 (pomegranate); for ⁴⁰K, this factor was from 4.42 × 10^-1 (orange) to 1.74 (chili pepper). Considering all the plant compartments analysed, the transfer factors for ⁴⁰K are between 24.5 (guava) and 90.5 (papaya) times higher than for ¹³⁷Cs. For both radionuclides, considerable differences in soil-to-plant transfer were found when new growing parts of the plant (green edible organ, leaf, and twig) are considered with respect to those older parts (mature edible organ, old leaf and branches). Considering all the species analyzed, the relationship TF(⁴⁰K)/TF(¹³⁷Cs) does not seem to follow a characteristic pattern. However, if we compare the value of this relationship for two organs of the same plant, the result is approximately constant, regardless of the species considered. This confirms earlier evidence that both radionuclides are similarly distributed in the different organs of the studied species. The differences in the transfer factors according to the ripening status of edible organs must be particularly considered when estimating the dose from ingestion of fruits and their derivatives in dose assessment models.

Variability of 137Cs and 40K soil-to-fruit transfer factor in tropical lemon trees during the fruit development period

In this investigation we evaluate the soil uptake of (137)Cs and (40)K by tropical plants and their consequent translocation to fruits, by calculating the soil-to-fruit transfer factors defined as F(v) = [concentration of radionuclide in fruit (Bq kg(-1) dry mass)/concentration of radionuclide in soil (Bq kg(-1) dry mass in upper 20 cm)]. In order to obtain F(v) values, the accumulation of these radionuclides in fruits of lemon trees (Citrus limon B.) during the fruit growth was measured. A mathematical model was calibrated from the experimental data allowing simulating the incorporation process of these radionuclides by fruits. Although the fruit incorporates a lot more potassium than cesium, both radionuclides present similar absorption patterns during the entire growth period. F(v) ranged from 0.54 to 1.02 for (40)K and from 0.02 to 0.06 for (137)Cs. Maximum F(v) values are reached at the initial time of fruit growth and decrease as the fruit develops, being lowest at the maturation period. As a result of applying the model a decreasing exponential function is derived for F(v) as time increases. The agreement between the theoretical approach and the experimental values is satisfactory.

Radionuclide transfer to fruit in the IAEA TRS 364 Revision

Information on the transfer of radionuclides to fruits was almost absent in the former TRS 364 "Handbook of parameter values for the prediction of radionuclide transfer in temperate environments". The revision of the Handbook, carried out under the IAEA Programme on Environmental Modelling for RAdiation Safety (EMRAS), takes into account the information generated in the years following the Chernobyl accident and the knowledge produced under the IAEA BIOMASS (Biosphere Modelling and Assessment) Programme in the years 1997-2000. This paper describes the most important processes concerning the behaviour of radionuclides in fruits reported in the IAEA TRS 364 Revision and provides recommendations for research and modelling.

Radionuclides in fruit systems: a review of experimental studies

Existing information on processes and parameters analysed in experimental studies on fruits was reviewed at the inception of the activities of the IAEA BIOMASS Fruits Working Group. Additional information on experimental studies, collected during the activities of the Group and not included in the Review, is presented and discussed in this paper. Studies on deposition of (14)CO2, CO(35)S and (3)H2O in the gas phase to apple, raspberry, strawberry and blackcurrant have filled gaps in knowledge of uptake of gaseous pollutants in fruit plants, quantifying processes of deposition, translocation and carry-over between seasons. Measurements over a period of six years on vine plants contaminated via leaves and soil by dry deposition of 137Cs and 90Sr have improved knowledge of the processes of direct deposition to fruit, translocation and carry-over of radionuclides from year to year. Additional information is given on soil to fruit transfer of U, Th and Pb for apple and mandarin grown under intensive agricultural conditions.