Radiocesium Activity Research Articles

Temporal variations of 7Be, 40K, 134Cs and 137Cs in epiphytic lichens (genus Usnea) at the Sakhalin and Kunashir islands after the Fukushima accident

Temporal variations of radionuclide levels in the epiphytic Usnea sp. lichens from the two islands Sakhalin and Kunashir, the Sakhalin region, Russia have been evaluated using the already published (2011–2013) and new experimental data (2015). A total of 62 lichen samples were measured using high purity germanium γ-ray detectors and multichannel analyzers. In the period 2011–2015, activity concentrations of the anthropogenic radionuclides 134Cs and 137Cs and the natural radionuclides 7Be and 40K were found to be in the range of (<0.53)–41.3, 0.55–50.6, 99–603 and 35–95 Bq kg–1 on dry weight, respectively. The activity concentrations of 134Cs and 137Cs in lichens were statistically significantly higher at Kunashir than at Sakhalin. The present-day levels of radiocesium activity concentrations in lichens are low: < 6 Bq kg–1 for 137Cs and <1 Bq kg–1 for 134Cs. A decline in the annual median 137Cs activity concentrations in lichens from 2011 to 2015 corresponds to a biological half-life of 1.2 y for Kunashir and 1.1 y for Sakhalin. The activity concentrations of 137Cs and 134Cs in lichens were strongly correlated (r=0.978, P<0.01) and the 134Cs biological half-life value of 1.2 y in the period 2011–2013 was similar to the corresponding 137Cs biological half-life value. The soil-tolichens aggregated transfer factor, Tag, for 134Cs at time t=0 after the Fukushima accident is calculated as 0.56 m2 kg–1 at Sakhalin and 0.31 m2 kg–1 at Kunashir. In contrast to radiocesium, the natural radionuclides 7Be and 40K did not show clear time-dependent variations in the Usnea lichens. No correlation was found between 7Be and 40K as well as between 40K and cesium radioisotopes. However, positive and statistically significant (P<0.05) correlations were obtained between 7Be and cesium radioisotopes. High abundance of the Usnea sp. lichens in the study area and large values of Tag for radiocesium in the lichens make these organisms suitable candidates for detection of low levels of airborne radioactive contamination of the environment.

Temporal changes of radiocesium in irrigated paddy fields and its accumulation in rice plants in Fukushima

About half of the total paddy field area, which is the dominant agricultural land in Fukushima Prefecture, was contaminated by radiocesium released by the Fukushima Daiichi Nuclear Power Plant accident. In this study, we investigated the temporal changes of radiocesium in soil, irrigation water, and rice plant in two adjacent rice paddies, with and without surface-soil-removal, in Fukushima Prefecture for over three years (2012–2014) after the nuclear accident. Our results showed that radiocesium migrated into 24–28 cm soil layers and that the activity concentration of radiocesium in paddy soils showed a significant reduction in 2014. The newly added radiocesium to paddies through irrigation water contributed only a maximum value of 0.15% and 0.75% of the total amount present in control and decontaminated paddies, respectively, throughout the study period. The radiocesium activity concentration in suspended sediment in irrigation water exponentially decreased, and the effective half-lives (Teff) for 137Cs and 134Cs were 1.3 and 0.9 years, respectively. Additionally, the average suspended sediment concentration in irrigation water increased between 2012 and 2014, suggesting that enhanced soil erosion had occurred in the surrounding environment. Radiocesium accumulation in rice plant also decreased with time in both paddies. However, the concentration ratio of radiocesium for rice plant in the decontaminated paddy increased compared with control paddy, despite approximately 96% of fallout radiocesium removed in paddy soil. Further analysis is required to clarify the reasons of high concentration ratio of radiocesium for rice plant in the decontaminated paddy.

Radiocaesium activity concentrations in parmelioid lichens within a 60 km radius of the Fukushima Dai-ichi Nuclear Power Plant

Radiocaesium activity concentrations (134Cs and 137Cs) were measured in parmelioid lichens collected within the Fukushima Prefecture approximately 2 y after the Fukushima Dai-ichi Nuclear Power Plant accident. A total of 44 samples consisting of nine species were collected at 16 points within a 60 km radius of the Fukushima Dai-ichi Nuclear Power Plant. The activity concentration of 134Cs ranged from 4.6 to 1000 kBq kg−1 and for 137Cs ranged from 7.6 to 1740 kBq kg−1. A significant positive correlation was found between the 137Cs activity concentration in lichens and the 137Cs deposition density on soil (n = 44), based on the calculated Spearman's rank correlation coefficients as r = 0.90 (P < 0.01). The two dominant species, Flavoparmelia caperata (n = 12) and Parmotrema clavuliferum (n = 11), showed strong positive correlations, for which the r values were calculated as 0.92 (P < 0.01) and 0.90 (P < 0.01) respectively. Therefore, Flavoparmelia caperata and Parmotrema clavuliferum are suggested as biomonitoring species for levels of radiocaesium fallout within the Fukushima Prefecture.

Reducing radioactive cesium transfer from sawdust media to Pleurotus ostreatus fruiting bodies

The Fukushima Daiichi nuclear power plant was damaged, and radionuclides such as 137Cs were spread into the environment. Three years have passed since the accident, and ingestion of foods contaminated with radioactive material through the food chain is a health hazard of concern. Mushrooms are known for absorbing radionuclides, and methods for reducing fruiting body radioactivity are needed. We investigated radiocesium transfer activities and methods of reducing radiocesium transfer from sawdust media into fruiting bodies using Pleurotus ostreatus. Fruiting body radiocesium activity increased linearly with increasing media radioactivity. The radiocesium activities of fruiting bodies cultivated in different sawdust media were 0.2–0.9-fold (on wet-weight basis) and 1.3–3.7-fold (on dry-weight basis) higher than those of sawdust media, showing that transfer rates vary with cultivation conditions. From the reducing fruiting body radiocesium activity tests by medium additives, Prussian blue was effective and nanoparticle insoluble Prussian blue was more efficient than soluble Prussian blue. However, nanoparticle insoluble Prussian blue is more expensive than soluble Prussian blue. If mushroom growers use Prussian blue, it will be necessary to determine the type and the additional amounts that correspond to used strains, consumer needs, commercial value and cost.

Spatial patterns and ratios of ¹³⁷Cs, ⁹⁰Sr, and Pu isotopes in the top layer of undisturbed meadow soils as indicators for contamination origin.

Spatial distribution of activity concentrations of (137)Cs, (90)Sr, and (239,240)Pu in the top layer of undisturbed meadow soils was compared between two regional transects across Lithuania: one in the SW region, more affected by the Chernobyl radioactive fallout, and the other in the NE region. Radiochemical, γ-, α-, β-, and mass spectrometric methods were used to determine the radionuclide activity. Our results validate that higher activity concentrations in the top soil layer were present in the SW region, despite the fact that sampling was performed after 22 years of the Chernobyl Nuclear Power Plant (NPP) accident. Using the activity concentration ratio (137)Cs/(239,240)Puglobal, the contribution of the Chernobyl NPP accident to the total radiocesium activity concentrations in these meadow soils was evaluated and found to be in the range of 6.5-59.1%. Meanwhile, the activity concentration ratio (238)Pu/(239,240)Pu showed that Chernobyl-derived Pu occurred at almost half of the sampling sites. The locations with maximal values of 47% of Chernobyl-derived Pu material were close to northeastern Poland, where deposition of most of non-volatile radioisotopes from the Chernobyl plume was determined.

Radiocaesium activity concentrations in macrofungi from Galicia (NW Spain): Influence of environmental and genetic factors

Radiocaesium (137Cs) is an artificial radionuclide that can be captured from the soil through the mycelium of fungi. However, in Spain there are few data on its presence in edible mushrooms. 137Cs activity concentrations were determined using 54 samples of wild and cultivated mushrooms and 18 samples of soil, all of them collected in Galicia (NW Spain) during 2010. Samples were analyzed by gamma spectroscopy with a High-Purity Germanium (HPGe) detector. The average activity concentration of 137Cs in wild mushrooms was 249.2Bqkg−1 dry weight (dw) and about 24.9Bqkg−1 fresh weight (fw). Genetic factors (species) influenced the uptake of 137Cs, highlighting Hydnum repandum as the greatest accumulator of all wild species (1016.4Bqkg−1 dw), while cultivated species showed much lower levels (1.6Bqkg−1 fw). Accumulation was also favored by fungal mycorrhizal ecology, whose mycelium was distributed in contaminated soil horizons. The mean levels detected in soils were 14Bqkg−1 fw. Although some species behaved as bioexclusors of radiocaesium, the transfer factors (TF) suggest that mushrooms preferentially bioaccumulate 137Cs. No sample reached the limit of 600Bqkg−1 fw (about 6000Bqkg−1 dw) indicated in the European legislation. In conclusion, the consumption of mushrooms harvested from the investigated areas poses no toxicological risk to human health due to radiocaesium.

煎茶の仕上げ加工において分級された茶葉および茎に含まれる放射性セシウム濃度

Radiocesium release following the accident at the Fukushima Dai-ichi Nuclear Power Plant, operated by the Tokyo Electric Power Company, caused severe contamination of new tea plant shoots in many prefectures in eastern Japan in 2011. Consequently, many studies to reduce the radiocesium levels in tea have since been conducted. In this study, we investigated the radiocesium activity in tea leaves and stems classified through the refining process. The radiocesium activity in stems was 14% and 23% higher than those in ara-cha (unrefined tea) and tea leaves classified through the refining process, respectively. However, stems only make up approximately 10% of ara-cha, and thus only a minimal reduction of radiocesium activity in sen-cha can be expected by removing stems during the refining process.

Changes in radiocesium activities with new shoots growth of tea (Camellia sinensis (L.)) plants

Changes in radiocesium activities with new shoots growth of tea (Camellia sinensis (L.)) plants

Numerical model analysis of radioactive cesium concentrations in marine organism—For radiocesium activity concentrations in the Tokyo Bay after the Fukushima Daiichi Nuclear Power Station accident—

Numerical model analysis of radioactive cesium concentrations in marine organism—For radiocesium activity concentrations in the Tokyo Bay after the Fukushima Daiichi Nuclear Power Station accident—

Exposure of a herbivorous fish to 134Cs and 137Cs from the riverbed following the Fukushima disaster

Ayu Plecoglossus altivelis, a herbivorous fish, is an important fishery resource and key component of the foodweb in many Japanese streams. Radionuclide contamination of this species is likely transferred to higher trophic levels, include humans, in the food chain. After the Fukushima accident in March 2011, ayu were exposed to highly contaminated silt while feeding on algae attached to the riverbed stones. To understand the route by which herbivorous fish are exposed to radionuclides, the activity concentrations of sum of 134Cs and 137Cs (radiocesium) were analyzed in riverbed samples (algae and silt) and in the internal organs and the muscle of ayu in five river systems in the Fukushima Prefecture between summer 2011 and autumn 2013. Although there was a positive correlation between the radiocesium activity concentrations in the muscle and the internal organs of ayu, the median activity concentration in the muscle was much lower than those in the internal organs. The activity concentrations of radiocesium in the riverbed samples and the internal organs and the muscle of ayu were correlated with contamination levels in soil samples taken from the watershed upstream of the sample sites. The results of the generalized linear mixed models suggest that the activity concentrations in both the internal organs and the muscle of ayu declined over time. Additionally, the activity concentrations in the internal organs were correlated with those in the riverbed samples that were collected around the same time as the ayu. The activity concentrations in the muscle were correlated with ayu body size. Our results suggest that ayu ingest 134Cs and 137Cs while grazing silt and algae from the riverbed, and a part of the 134Cs and 137Cs is assimilated into the muscle of the fish.

Quantitation of Japanese cedar pollen and radiocesium adhered to nonwoven fabric masks worn by the general population.

In the spring of 2012, a year after the Fukushima Daiichi nuclear disaster, radiocesium-contaminated Japanese cedar pollen may have caused internal exposure to the general population by inhalation. To determine if pollen had been contaminated through uptake of radiocesium by Japanese cedars and was therefore contributing to inhalation doses, the authors measured radiocesium and Japanese cedar pollen adhered to masks worn by 68 human subjects residing in eastern Japan, including Fukushima prefecture, for 8 wk in the spring of 2012. The maximum cumulative Cs and Cs radioactivities on masks worn by an individual were 21 ± 0.36 Bq and 15 ± 0.22 Bq, respectively, and the estimated effective dose during the 8 wk was 0.494 μSv. The average estimated effective dose during the 8 wk was 0.149 μSv in Fukushima prefecture and 0.015 μSv in other prefectures, including Tokyo metropolitan. The correlation between radiocesium activity and the Japanese cedar pollen count was moderate. However, imaging-plate and light microscopy observations showed that the main source of radiocesium adhered to masks was fugitive dust.

Radiocesium distribution in bamboo shoots after the Fukushima nuclear accident.

The distribution of radiocesium was examined in bamboo shoots, Phyllostachys pubescens, collected from 10 sites located some 41 to 1140 km from the Fukushima Daiichi nuclear power plant, Japan, in the Spring of 2012, 1 year after the Fukushima nuclear accident. Maximum activity concentrations for radiocesium 134Cs and 137Cs in the edible bamboo shoot parts, 41 km away from the Fukushima Daiichi plant, were in excess of 15.3 and 21.8 kBq/kg (dry weight basis; 1.34 and 1.92 kBq/kg, fresh weight), respectively. In the radiocesium-contaminated samples, the radiocesium activities were higher in the inner tip parts, including the upper edible parts and the apical culm sheath, than in the hardened culm sheath and underground basal parts. The radiocesium/potassium ratios also tended to be higher in the inner tip parts. The radiocesium activities increased with bamboo shoot length in another bamboo species, Phyllostachys bambusoides, suggesting that radiocesium accumulated in the inner tip parts during growth of the shoots.

Radioactivity measurements in soils surrounding four coal-fired power plants in Serbia by gamma-ray spectrometry and estimated dose

The study of spatial distribution of activity concentration of 238U, 226Ra, 210Pb, 232Th, 40K, and 137Cs radionuclides in the surface soil samples (n = 42) collected in the vicinity of four coal-fired power plants in Serbia is presented. Radioactivity measurements in soils performed by gamma-ray spectrometry showed values [Bqkg-1] in the range: 15-117 for 238U, 21-115 for 226Ra, 33-65 for 210Pb, 20-69 for 232Th, 324-736 for 40K, and 2-59 for 137Cs. Surface soil radio-activity that could have resulted from deposition of radionuclides from airborne discharges or resuspension of ash from disposal sites showed no enhanced levels. It was found that variation of soil textural properties, pH values, and carbonate content influenced activity levels of natural radionuclides while radiocesium activities were associated with soil organic matter content. Modification of some soil properties was observed in the immediate vicinity (&lt;1 km) of power plants where the soil was more alkaline with coarser particles (0.2-0.05 mm) and carbonates accumulated. Calculated average values of the absorbed gamma dose rate and annual external effective dose originating from the terrestrial radionuclides were 69.4 nGy/h and 0.085 mSv, respectively.

Horizontal distribution of Fukushima-derived radiocesium in zooplankton in the northwestern Pacific Ocean

Abstract. The magnitude of the 9.0 Tohoku earthquake and the ensuing tsunami on 11 March 2011, inflicted heavy damage on the Fukushima Dai-ichi nuclear power plant (FNPP1). Fission products were emitted, falling over a broad range in the Northern Hemisphere, and water contaminated with radionuclides leaked into the ocean. In this study, we described the horizontal distribution of the Fukushima-derived radiocesium in zooplankton and in seawater in the western North Pacific Ocean (500–2100 km from the FNPP1) 10 months after the accident. 134Cs and 137Cs were detected in zooplankton and seawater from all the stations. Because of its short half-life, the 134Cs detected in our samples could only be derived from the FNPP1 accident. The highest 137Cs activity in zooplankton was the same order of magnitude as it was one month after the accident, and average activity was one or two orders of magnitude higher than 137Cs activities observed before the accident around Japan. Horizontally, the radiocesium activity concentrations in zooplankton were high at around 25° N while those in surface seawater were high at around the transition area between the Kuroshio and the Oyashio currents (36–40° N). We observed subsurface radiocesium maxima in density range of the North Pacific Subtropical Mode Water and the occurrence of many diel vertical migratory zooplankton. These suggested that the high activity concentrations in the subtropical zooplankton at around 25° N were connected to the subsurface radiocesium and active vertical migration of zooplankton. However, the high activity concentrations of radiocesium in subsurface seawater did not necessarily correlate with the higher radiocesium activity in zooplankton. Activity concentrations of radiocesium in zooplankton might be influenced not only by the environmental radiocesium activity concentrations but also by other factors, which are still unknown.

Distribution of the Fukushima-derived radionuclides in seawater in the Pacific off the coast of Miyagi, Fukushima, and Ibaraki Prefectures, Japan

Abstract. The activities of artificial radionuclides in seawater samples collected off the coast of Miyagi, Fukushima, and Ibaraki Prefectures were measured as part of a monitoring program initiated by the Japanese Ministry of Education, Sports, Science and Technology immediately after the Fukushima Dai-ichi Nuclear Power Plant accident. The spatial and temporal distributions of those activities are summarized herein. The activities of strontium-90, iodine-131, cesium-134 and -137 (i.e. 90Sr, 131I, 134Cs, and 137Cs) derived from the accident were detected in seawater samples taken from areas of the coastal ocean adjacent to the power plant. No 131I was detected in surface waters (≤ 5 m depth) or in intermediate and bottom waters after 30 April 2011. Strontium-90 was found in surface waters collected from a few sampling stations in mid-August 2011 to mid-December 2011. Temporal changes of 90Sr activity in surface waters were evident, although the 90Sr activity at a given time varied widely between sampling stations. The activity of 90Sr in surface waters decreased slowly over time, and by the end of December 2011 had reached background levels recorded before the accident. Radiocesium, 134Cs and 137Cs, was found in seawater samples immediately after the accident. There was a remarkable change in radiocesium activities in surface waters during the first 7 months (March through September 2011) after the accident; the activity reached a maximum in the middle of April and thereafter decreased exponentially with time. Qualitatively, the distribution patterns in surface waters suggested that in early May radiocesium-polluted water was advected northward; some of the water then detached and was transported to the south. Two water cores with high 137Cs activity persisted at least until July 2011. In subsurface waters radiocesium activity was first detected in the beginning of April 2011, and the water masses were characterized by σt (an indicator of density) values of 25.5–26.5. From 9–14 May to 5–16 December 2011, the depths of the water masses increased with time, an indication that deepening of the isopycnal surfaces with time can be an important mechanism for the transport of radiocesium downward in coastal waters. During 4–21 February 2012, the water column became vertically homogeneous, probably because of convective mixing during the winter; the result was nearly constant values of radiocesium activity throughout the water column from the surface to the bottom (~200 m depth) at each station.

Distribution of Artificial Radionuclides in Abandoned Cattle in the Evacuation Zone of the Fukushima Daiichi Nuclear Power Plant

The Fukushima Daiichi Nuclear Power Plant (FNPP) accident released large amounts of radioactive substances into the environment. In order to provide basic information for biokinetics of radionuclides and for dose assessment of internal exposure brought by the FNPP accident, we determined the activity concentration of radionuclides in the organs of 79 cattle within a 20-km radius around the FNPP. In all the specimens examined, deposition of Cesium-134 (134Cs, half-life: 2.065 y) and 137Cs (30.07 y) was observed. Furthermore, organ-specific deposition of radionuclides with relatively short half-lives was detected, such as silver-110m (110mAg, 249.8 d) in the liver and tellurium-129m (129mTe, 33.6 d) in the kidney. Regression analysis showed a linear correlation between the radiocesium activity concentration in whole peripheral blood (PB) and that in each organ. The resulting slopes were organ dependent with the maximum value of 21.3 being obtained for skeletal muscles (R2 = 0.83, standard error (SE) = 0.76). Thus, the activity concentration of 134 Cs and 137Cs in an organ can be estimated from that in PB. The level of radioactive cesium in the organs of fetus and infants were 1.19-fold (R2 = 0.62, SE = 0.12), and 1.51-fold (R2 = 0.70, SE = 0.09) higher than that of the corresponding maternal organ, respectively. Furthermore, radiocesium activity concentration in organs was found to be dependent on the feeding conditions and the geographic location of the cattle. This study is the first to reveal the detailed systemic distribution of radionuclides in cattle attributed to the FNPP accident.

Anthropogenic Radionuclides in Japanese Food: Environmental and Legal Implications

The Japanese government ordered the analysis of thousands of foods after the Fukushima nuclear accident to ascertain compliance with regulatory limits for anthropogenic radionuclides in food. Four hundred and forty-five samples obtained until 31 December 2011 from 11 prefectures exceeded the regulatory limits that were in force until 31 March 2012. The possibility of these 445 samples representing localized areas of high radiocesium concentration was investigated. The objective of this study was to determine the radiocesium activity ratio ((134)Cs/(137)Cs) in foods from each geographic area to possibly identify the radioactive signature of the four different reactors (i.e., four independent sources) in the distinct regions. The average (134)Cs/(137)Cs activity ratio was 0.98 ± 0.01 for all samples. However, no statistically significant deviations from this value could be confirmed in the various regions. Therefore, we conclude that the releases from reactor No. 4 (carrying a significantly smaller activity ratio) are assumed to be small when compared with the other three reactor releases. The individual radioisotopic signatures of reactors No. 1, 2, and 3 could not be identified in various Japanese regions using the food samples, indicating integral radiocesium contamination from these sources. Subsequent releases of fission products from the reactors (e.g., after possible criticalities reported in October 2011) proved to have no impact on the radiocesium activity ratio. A discussion of the development of the regulatory limits in Japan and Europe with regard to the current limits and radiological food safety are also included.

Fluvial discharges of radiocaesium from watersheds contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident, Japan

A large amount of radiocaesium, 134Cs and 137Cs, was released to the atmosphere and Pacific Ocean from the Tokyo Electric Power Company's Fukushima Dai-ichi Nuclear Power Plant (FDNPP) that was damaged by the tsunami caused by the Tohoku earthquake on 11 March 2011. Radiocaesium deposited on the ground is now the most important consideration in assessing the risk to people in the vicinity of the FDNPP and remediating the contaminated area. Transfer of radiocaesium from the ground through rivers is an important factor in the downstream contamination of irrigation waters, paddy fields, lakes, and the sea. We estimated the transport of radiocaesium through two small rivers, the Hiso River and Wariki River, that traverse mountainous areas in Fukushima Prefecture. Areal depositions of radiocaesium in their watersheds (catchments) were high (1–3 MBq m−2). Water samples were collected from the rivers twice during each of two baseflow and two flood stages in 2011 and analysed for radiocaesium in particulate and dissolved forms. The radiocaesium concentrations depended strongly on the rates of water discharge. Maximum activities of radiocaesium in the samples from the Hiso River and Wariki River when there was precipitation or flooding (July and September) were 25 ± 0.31 and 35 ± 0.25 Bq L−1, respectively. Particulate radiocaesium during periods of flooding contributed over 90% of the total radiocaesium activity in the samples. The discharge of radiocaesium from the catchments during 2011 was estimated to be 0.5% and 0.3% of the total amount of radiocaesium deposited on the catchments of the Hiso River and Wariki River, respectively. It is considered that the most of the radiocaesium deposited in the catchment remains on the soil surface.

Distribution of 137Cs and 134Cs in the North Pacific Ocean: impacts of the TEPCO Fukushima-Daiichi NPP accident

Impact of the TEPCO Fukushima-Daiichi NPP accident, FNPP1, to the North Pacific Ocean occurred through two pathways, namely direct release and atmospheric deposition to wide ocean surface. We collected more than 100 seawater samples in the North Pacific Ocean in April and May 2011 by seven commercial ships as VOS. Since the sample volume was 2 l each, we measured radiocaesium activity at Ogoya Underground Facility to obtain reliable activity. 137Cs was detected at all stations and 134Cs was detected at most of the stations in the North Pacific Ocean. The 137Cs activity ranged from around 1 to 1,000 Bq m−3 with activity ratios of 134Cs/137Cs close to 1 which is a signature of radiocaesium originated from the FNPP1 accident. At east of the International Date Line north of 40°N in the Pacific Ocean in April 2011, the 134Cs activity ranged from 2 to 12 Bq m−3.

Radiocesium contaminations of 20 wood species and the corresponding gamma-ray dose rates around the canopies at 5 months after the Fukushima nuclear power plant accident

Radiocesium (134Cs + 137Cs) deposition from the Fukushima nuclear power plant accident was measured in 20 woody plants (12 evergreen and 8 deciduous species) grown in Abiko (approximately 200 km SSW from the NPP). Leaves (needles) and twigs were sampled from each of three foliar positions (top, middle, and bottom) in the plant canopy in early August 2011. At the time, soils around the plants were also sampled, and gamma radiation dose rates were measured at each sampling position. The average radiocesium activity in the observed leaves of the evergreen species was 7.7 times that in the leaves of the deciduous species. Among the observed evergreen coniferous species, the activity in pre-fallout-expanded leaves was 2.4 times that in the post-fallout-expanded leaves. Notably, a distinct variation in the activity among the evergreen coniferous species could be observed for the post-fallout-expanded leaves but not for the pre-fallout-expanded leaves. Although these differences depend on whether the leaves had expanded at the time of the fallout, it is probable that a considerable amount of radiocesium was translocated to newly developed leaves at a species-specific rate. In addition, it was demonstrated that dose rates around woody plants were not consistent with the prevailing prediction that general dose rates correspondingly decrease with monitoring height from the ground. Thus, the dose rates in the top foliar layer of the deciduous species decreased more than predicted, whereas those in the top foliar layer of the coniferous species did not decrease. This may be due to differences in the balance between the attenuation resulting from a shielding effect of the plant bodies and the higher radiocesium accumulation in the leaves.