Reduction of Radiocesium in Internal- and Surface-Contaminated Komatsuna (Brassica rapa var. perviridis) during Washing and Processing.

Radiocesium dynamics data during food processing are required for the realistic estimation of internal radiation content in food. Radiocesium contamination of leafy vegetables can occur externally due to the adhesion of fallout and/or resuspension from the air, and internally from soil via the root transport. Information regarding the dynamics of both surface and internal radiocesium contamination during food processing is required; however, such information for leafy vegetables is limited compared to other major agricultural products. In this study, the effect of washing on the removal of surface radiocesium contamination by resuspended materials and that of cooking (grilling, boiling, and microwave heating) on internal radiocesium contamination were investigated using komatsuna (Brassica rapa var. perviridis), a leafy vegetable. The surface-contaminated samples were experimentally grown in a difficult-to-return area in Fukushima Prefecture, which has not yet been decontaminated. The internally contaminated komatsuna were obtained after experimental cultivation in a greenhouse with soil containing 137Cs and no surface contamination. The concentration of 137Cs in surface-contaminated komatsuna was reduced to approximately half (processing factor: 0.55) after washing with water. However, the annual processing factor ranged from 0.12 to 0.95, suggesting that the growing environment and climatic conditions may affect the removal rate of radiocesium by washing. Internal contamination of 137Cs was removed by 23% and 14% by boiling and grilling, respectively, but no effect was observed for microwaving. Moreover, the concentration of 137Cs decreased by 0.66-fold after boiling, while it increased by 1.19- and 1.20-fold after grilling and microwaving, respectively. Therefore, boiling was found to be preferable than grilling or microwaving for radiocesium removal.

Input and output pathways determining potassium budgets in two paddy fields subjected to countermeasures against radiocesium in Fukushima, Japan.

Countermeasures to reduce radiocesium (134Cs and 137Cs) uptake by crops have been implemented in farmlands affected by the Fukushima nuclear accident in 2011. A widely practiced countermeasure is the application of potassium (K). Long-term soil K maintenance is a key issue due to the long physical half-life of 137Cs (30 years). Information on input and output pathways determining plant-available K budgets can provide a base for the development of maintenance strategies. Therefore, in this study we evaluated these pathways in paddy fields subjected to K fertilization as a countermeasure. We selected two fields with different soil textures and drainage conditions and quantified input and output via fertilization, irrigation, precipitation, straw return to soil, plant harvesting, surface runoff, and percolation during the cropping period in 2018. The major input pathways were fertilization, straw return, and irrigation due to a large inflow volume with spill-over irrigation. The major output pathways consisted of plant harvesting, surface runoff, and percolation. However, 85% of K in harvested plants was brought back by straw return; in practice, harvesting was a minor pathway. The K budgets during the study period were negative (-20 and -289 kg ha-1) and especially severe in clay loam soil with high output via percolation. This could probably be attributed to the low cation exchange capacity and high permeability from the low total C and clay contents. Losses via surface runoff stemmed from excessive irrigation volumes in both fields. Around 70% of the total K output via surface runoff and percolation was discharged before mid-summer drainage. Accordingly, controlling the irrigation volume during this period in addition to increasing cation exchange capacity and decreasing permeability may improve the negative budgets.

Observation of radioactive iodine ((131)I, (129)I) in cropland soil after the Fukushima nuclear accident.

During the early stages of the Fukushima nuclear accident, the temporal variations of (131)I deposited on the ground and of (131)I accumulated in cropland soil were monitored at a fixed location in Japan. Moreover, concentrations of long-lived radioactive iodine ((129)I) in atmospheric deposits and soil were measured to examine the feasibility of retrospectively reconstructing (131)I levels from the levels of accident-derived (129)I. The exceptionally high levels of (131)I in deposits and soil were attributed to rainfall-related deposition of radionuclides. In the crop field studied, the losses of deposited (131)I and (129)I due to volatilization were small. The atomic ratio (129)I/(131)I in the topsoil corresponded to the same ratio in deposits. The (131)I concentrations measured in the topsoil were very consistent with the (131)I concentrations reconstructed from the (129)I concentrations in the soil.

Evaluation of the cause of unexplained radiocaesium contamination of brown rice in Fukushima in 2013 using autoradiography and gamma-ray spectrometry.

The Great East Japan Earthquake on 11 March 2011, caused the release of radioactive materials from the Fukushima Daiichi Nuclear Power Plant (FDNPP), contaminating eastern Japan, particularly in part of Fukushima Prefecture. In 2012 and 2014, the radiocaesium concentration in brown rice did not exceed regulatory levels in Minamisoma City, Fukushima. However, in 2013, some radiocaesium concentrations in brown rice exceeded regulatory levels. In this work, autoradiograms showed that high radioactivity was present as contaminated spots on the panicles of rice and in brown rice in 2013. We evaluate the contribution of direct contamination to the radiocaesium concentration in brown rice and discuss the origin of radiocaesium contamination in brown rice using the (134)Cs/(137)Cs radioactivity ratio. Here, we show that the main cause of the unexplained radiocaesium contamination of brown rice in Minamisoma City in 2013 is the adherence of radioactive materials to the rice panicles, and these radioactive materials are associated with reactor units 2 or 3 of FDNPP.

The simulation of long-range transport of ¹³7Cs from East Asia to Japan in 2002 and 2006.

To evaluate the quantities of ¹³7Cs from past nuclear tests being transported to and deposited in Japan by naturally-occurring phenomena, the authors developed long-range transport models for ¹³7Cs considering Asian dust. The simulation using these models backed the observed recent increase of ¹³7Cs deposition along the coast of the Sea of Japan in early spring. For the sake of public safety, it is vital to ascertain whether an increase of radioactive deposition is caused by natural phenomena or a nuclear accident. The observations in recent years have suggested that dust and soil containing ¹³7Cs is transported from the regions around Inner Mongolia to Japan by the wind. In this paper, using observation data from the early spring of 2002 and 2006, the authors have found good agreement between the simulations and the measurements. The simulations reproduced the entrainment of ¹³7Cs and subsequent transport to Japan caused by strong winds associated with low pressure areas around the Inner Mongolian grasslands. The most likely cause of high-level ¹³7Cs deposition over northern Japan during March 2002 was ¹³7Cs associated with particles transported at low-altitude (1 km) and subjected to precipitation on the 22nd to 24th.

Contribution of Asian dust to atmospheric deposition of radioactive cesium ((137)Cs).

Both Asian dust (kosa) transported from the East Asian continent and locally suspended dust near monitoring sites contribute to the observed atmospheric deposition of (137)Cs in Japan. To estimate the relative contribution of these dust phenomena to the total (137)Cs deposition, we monitored weekly deposition of mineral particles and (137)Cs in spring. Deposition of (137)Cs from a single Asian dust event was 62.3 mBq m(-2) and accounted for 67% of the total (137)Cs deposition during the entire monitoring period. Furthermore, we found high (137)Cs specific activity in the Asian dust deposition sample. Although local dust events contributed to (137)Cs deposition, their contribution was considerably smaller than that of Asian dust. We conclude that the primary source of atmospheric (137)Cs in Japan is dust transported from the East Asian continent.

Deposition of atmospheric (137)Cs in Japan associated with the Asian dust event of March 2002.

Considerable deposition of (137)Cs was observed in the northwestern coastal area of Japan in March 2002. Since there were no nuclear explosions or serious nuclear accidents in the early 2000s, transport of previously contaminated dust appears to be the only plausible explanation for this event. In March 2002, there was a massive sandstorm on the East Asian continent, and the dust raised by the storm was transported across the sea to Japan. This dust originated in Mongolia and northeastern China, in an area distant from the Chinese nuclear test site at Lop Nor or any other known possible sources of (137)Cs. Our radioactivity measurements showed (137)Cs enrichment in the surface layer of grassland soils in the area of the sandstorm, which we attributed to accumulation as a result of past nuclear testing. We suggest that the grassland is a potential source of (137)Cs-bearing soil particles. Since the late 1990s, this area has experienced drought conditions, resulting in a considerable reduction of vegetation cover. We attribute the prodigious release of (137)Cs-bearing soil particles into the atmosphere during the sandstorm and the subsequent deposition of (137)Cs in Japan to this change.

Vertical distributions of persistent organic pollutants (POPs) caused from organochlorine pesticides in a sediment core taken from Ariake bay, Japan.

Persistent organic pollutants (POPs) of organochlorine pesticides such as dichlorodiphenyl trichloroethane (DDTs) and its metabolites, hexachlorobenzene (HCB), heptachlor, chlordane compounds (CHLs), aldrin, dieldrin, endrin, mirex and isomers of hexachlorocyclohexane (HCHs), were analyzed in sediment cores collected from Ariake Bay, Japan. Although Chikugo River has the largest flow in Ariake Bay, the total concentration of POPs in surface sediment was found in St.3, mouth of the Yabe River, where that level was two times higher than St.1, mouth of the Chikugo River. It could be assumed that the potential source of POPs contamination is relatively close to this study area. Relatively high residue levels of HCB, HCHs and DDTs in sediment core were found during the period from 1967 to 1970. In this layer, the HCB concentration investigated in sediment cores of Ariake Bay was maximum, 2.6 ng g(-1) dry weight and higher than that of Tokyo Bay and subsequently detected in deeper sediment cores. The ratio of (DDD+DDE)/SigmaDDTs was high in top sediments (0-2 cm). Although there was a concentration of DDTs in the top sediment, it was noticed that DDT emission did not cause direct input of DDT recently. The HCHs determined in upper sediment cores might be originated from long-range accumulation in environment after dispersing of technical-grade HCH. Moreover, the CHLs, dieldrin and heptachlor concentrations were detected and recently increased in sediment core. POPs in sediment cores of Ariake Bay based on the possibility of PCP contamination during the early 1960s were reflected.