Radiocesium transfer into the fruit of deciduous fruit trees contaminated during dormancy

Abstract

Following the accident at the Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Plant (FDNPP), radiocesium ( 134 Cs + 137 Cs) concentrations in deciduous mature fruits were determined in orchards in the northern area of Fukushima Prefecture. At the time of the nuclear accident, most deciduous fruit trees were in the dormant stage prior to bud burst. To evaluate the relationship between radiocesium deposition in the soil and fruit contamination, radiocesium concentrations were measured from the 5-cm topsoil and from six fruit species across 17 orchards in 2011. The vertical distribution of radiocesium in the topsoil (0-30 cm in depth) and its spatial distribution in the 5-cm topsoil underlying the tree canopy of a peach, Prunus persica (L.) Batsh, orchard ("Akatsuki" cultivar) were also investigated. Significant correlations between the radiocesium concentration in the mature fruit and that in the 5-cm topsoil layer were observed for the 17 orchards as well as for the trees of the peach orchard. However, 93% of the 137 Cs found in the 30-cm soil core was retained within the top 3 cm of the soil in the peach orchard. Considering the profile of the root of this deciduous fruit tree, we assumed a negligible level of radiocesium uptake via the roots. However, the possibility of inward migration via the bark was undeniable, because some radiocesium adhered to the tree canopy before bud burst while depositing on the soil surface. Additionally, transfer factors for peach and grape, hybrid of Vitis labrusca L. and Vitis vinifera L., from young, uncontaminated trees cultivated with contaminated soil were lower than those previously reported.Key words: Fukushima Daiichi nuclear accident, inward migration via the bark, radiocesium in fruits, vertical distribution in orchard soil.

Decontamination Effects of Bark Washing with a High-pressure Washer on Peach [<i>Prunus persica</i> (L.) Batsch] and Japanese Persimmon (<i>Diospyros kaki</i> Thunb.) Contaminated with Radiocaesium during Dormancy

“…There were roots of undergrowth running through the topsoil at a high density because sod culture was applied in almost all orchards in Fukushima Prefecture. Therefore, radiocaesium contamination by root uptake was likely negligible during the accident year (Sato et al, 2015), the same as in a previous report in relation to the Chernobyl accident (AntonopoulosDomis et al, 1991). Deposits on the scaffold trunk of peach, cherry, apple, Japanese pear, and grape trees were recognized by measuring the radiation count rate using Geiger-Mueller survey meter at 1 cm distance from the bark surface at the top, side, and bottom sites on the scaffold limb 30 cm from a bifurcation on April 28, 2011 (Sato, 2012).…”

“…Small fruit volume may result in high 137 Cs content at an early stage. On the other hand, the 137 Cs concentration in fruits decreases by the dilution effect of assimilates transported into fruits in the ripening stage (Sato et al, 2015). In addition, the effects of bark washing on decreasing the Cs from leaves to fruits in the ripening stage (Carini and Bengtsson, 2001).…”

“…FW in the cortex including secondary phloem with cambium (Sato, 2012). The possibility of root uptake of 137 Cs was supposed to be extremely low in consideration of the interaction between the undergrowth roots and the soil profile of 137 Cs (Sato, 2014;Sato et al, 2015). It was therefore estimated that a large amount of radiocaesium inward migration via the bark had already occurred before the washing treatment was conducted.…”

Effect of Soil Surface Management on Radiocesium Concentrations in Apple Orchard and Fruit

“…In this study, the TFs, calculated using the radiocesium concentrations of the fruit and soil (0-15 cm) in the intertillage plots, were 0.013 in 2011, 0.0017 in 2012, 0.00050 in 2013, and 0.00031 in 2014. In the early years of 2011-2014, the TFs in apples may have been affected by the direct adhesion of fallout-derived radiocesium (Kusaba et al, 2015a, b;Sato, 2014;Sato et al, 2015); however, direct radiocesium adhesion might have had a smaller effect on the TF value in 2014. In 2014, the TF values of apples in this study are almost the same as those observed in herbaceous fruit.…”

“…AntonopoulosDomis et al (1991) demonstrated that the root uptake of radiocesium represented a small fraction of the total contamination of leaves and fruit of trees planted before the Chernobyl accident. Sato et al (2015) also suggested that the amount of radiocesium uptake via the roots of fruit trees was negligible after the FDNPP accident. On the other hand, Takata et al (2013) reported that, with a high concentration of radiocesium in the surface soil, the transfer rate of radiocesium from the soil to plants was higher in the shallow-rooted fruit tree fig than in the non-shallow-rooted fruit tree grape, suggesting that the radiocesium uptake via the roots of fruit trees could not be negligible under experimental conditions.…”