Incidence of lymphoid neoplasms among atomic bomb survivors by histological subtype, 1950 to 1994.

Epidemiological data have provided limited and inconsistent evidence on the relationship between radiation exposure and lymphoid neoplasms. We classified 553 lymphoid neoplasm cases diagnosed between 1950 and 1994 in the Life Span Study cohort of atomic bomb survivors into World Health Organization subtypes. Mature B-cell neoplasms represented 58%, mature T-cell and natural killer (NK)-cell neoplasms 20%, precursor cell neoplasms 5%, and Hodgkin lymphoma (HL) 3%, with the remaining 15% classified as non-Hodgkin lymphoid (NHL) neoplasms or lymphoid neoplasms not otherwise specified. We used Poisson regression methods to assess the relationship between radiation exposure and the more common subtypes. As in earlier reports, a significant dose response for NHL neoplasms as a group was seen for males but not females. However, subtype analyses showed that radiation dose was strongly associated with increased precursor cell neoplasms rates, with an estimated excess relative risk per Gy of 16 (95% Confidence interval: 7.0, >533) at age 50. The current data based primarily of tissue-based diagnoses suggest that the association between radiation dose and lymphoid neoplasms as a group is largely driven by the radiation effect on precursor cell neoplasms while presenting no evidence of a radiation dose response for major categories of mature cell neoplasms, either B- or T-/NK-cell, or more specific disease entities (diffuse large B-cell lymphoma, plasma cell myeloma, adult T-cell leukemia/lymphoma) or HL.

Recent insights into trends of thyroid cancer incidence in Lithuanian population exposed to Chernobyl fallout early in life.

In the last three decades, an increase in thyroid cancer incidence has been observed worldwide, as well as in Lithuania. Although the rise was linked to overdiagnosis, the role of lifestyle and environmental factors, including exposure to ionizing radiation, cannot be excluded. In our retrospective study, we aimed to assess the association between the average age-specific thyroid dose due to the radioactive iodine uptake during childhood and adolescence from the Chernobyl fallout in Lithuania, and the trends of incidence of thyroid cancer from 1991 to 2015 in different regions. Averaged age-dependent thyroid doses were estimated for every municipality based on radioiodine activity in milk, reconstructed from available 131I activity measurements in the grass. Thyroid cancer incidence rates were calculated for the entire population and for two age at the time of exposure groups: 0-19 years and 0-9 years. Thyroid cancer relative risk (RR) was estimated for three municipality-specific thyroid dose (for 0-year-old babies) categories: less than 100 mGy (reference group), 100-199 mGy, and ≥200 mGy. Over the study period (1991-2015), a total of 5664 cases of thyroid cancer were registered in the entire Lithuanian population; 817 cases in the age group from 0 to 19 years at the time of the Chernobyl accident, and 266 cases in the age group from 0 to 9 years. Age-standardized thyroid cancer incidence rates have notably increased since 2000, peaked in 2009 (especially in females), and then slightly decreased and stabilized. The estimated average municipality-specific age-dependent thyroid doses ranged from 270 mGy in western Lithuania to 1.5 mGy in central and northern Lithuania. For the age group of 0-19 years at the time of the accident, in the period 1991-1995, the thyroid cancer relative risk was significantly increased (RR 3.91; 95 % CI: 1.27-10.29, p=0.01) in the highest dose category, compared to the lowest (although based on a small number of cases). For the age group 0-9 years at the time of the accident, a tendency of increased RR in the highest dose category appeared in the most recent period, 2011-2015. Our observations need to be confirmed by further following trends of thyroid cancer incidence in the cohort of 0-19-year-old Lithuanians at the time of the Chernobyl accident.

Plutonium Signatures in a Dated Sediment Core as a Tool to Reveal Nuclear Sources in the Baltic Sea.

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvären bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, 240Pu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 ± 0.31)·10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 ± 0.11)·10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958).

An overview of plutonium isotopes in soils, China: Distribution, spatial patterns, and sources.

Plutonium (Pu) is an anthropogenic radionuclide which has drawn significant attentions due to its radiotoxicity, and the sources of plutonium linked with nuclear accidents and contaminations. The 240Pu/239Pu atom ratio is source dependent and can be used as a fingerprint to determine the sources of radioactive contaminant. However, the distribution and sources of plutonium in soils of China have not yet been systematically studied at a national scale up to date. The distribution, spatial patterns, and sources of plutonium in soils of China were discussed in this work. The concentrations of 239,240Pu are in the range of 0.002-4.824 mBq/g with a large variation, and the 239,240Pu concentrations in surface soils increase with the increasing latitude, which affects by multi-factors such as organic matter and particle size, etc. The inventories of 239,240Pu are in the range of 7.31-554 Bq/m2. The weighted average of 240Pu/239Pu atom ratios (0.180 ± 0.004) in all surface samples is good agreement with the ratio of global fallout (0.180 ± 0.014) of the nuclear weapons tests, this indicate that the major source of plutonium in China is global fallout. However, among some sites, distinctly lower 240Pu/239Pu atom ratio compared to the global fallout values were observed in the northwest China, indicating a significant contribution from other source besides the global fallout. Furthermore, the spatial clustering patterns of hot spots (high values) and cold spots (low values) for plutonium showing the clear associations with nuclear tests, especially the Chinese Lop Nor nuclear weapons tests (CNTs) and the Semipalatinsk nuclear weapons tests (STS). Radioactive material including plutonium from the STS or CNTs was transported by the prevailing westerlies to the northwest China. This review about the fingerprints and distribution of plutonium in soils of China will help researchers to establish a reference database for future radiation risk assessment and environmental radioactive management.

Modeling the Dynamic Behavior of Radiocesium in Grazing Reindeer.

Radiocesium contamination in Norwegian reindeer and the factors influencing contamination levels have been studied for more than 50 years, providing significant amounts of data. Monitoring contamination in reindeer is of utmost importance for reindeer husbandry and herders in Norway and will need to be studied for many years because of the persistent contamination levels due to the 1986 Chernobyl fallout. This paper presents a novel dynamic model that takes advantage of the large data sets that have been collected for reindeer monitoring to estimate 137Cs in reindeer meat at any given time. The model has been validated using detailed 137Cs data from one of the herds most affected by the fallout. The model basis includes detailed 137Cs soil data from aerial surveys, GPS-based knowledge of reindeer migration, and local soil-to-vegetation 137Cs transfer information. The validation exercise shows that the model satisfactorily predicts both short- and long-term changes in 137Cs concentrations in reindeer meat and suggests that the model will be a useful tool in estimating seasonal changes and evaluating possible remedial actions in case of a future fallout event.

On the ordered nature of redistribution of technogenic elements in undisturbed elementary landscape-geochemical systems of the temperate zone on the example of the Chernobyl 137Cs fallout.

The study is aimed at identifying patterns in distribution of pollutants in the elementary landscape-geochemical systems (ELGS) of the temperate zone. The study used 137Cs as a tracer, which allows a highly detailed analysis of the nature of the heterogeneity of secondary migration in the toposequence: summit-slope-closing depression, treated as the elementary landscape-geochemical system. The study site was located in the Bryansk region in the Chernobyl abandoned area with an initial level of 137Cs contamination exceeding 1480 kBq/m2 (40 Ci/km2). An original technique of repeated 137Cs measurements along cross-sections accompanied by topographic survey and soil cores sampling has been applied. The obtained results showed a complete absence of constant increase of 137Cs concentration downslope but revealed a steady regular variability of 137Cs activity of a cyclical type. Given uniformity of the initial 137Cs fallout within a small-sized plot, variation of 137Cs due to its secondary distribution in ELGS was 2-2.7-fold according to field gamma-spectrometry data which corresponded to the radionuclide contamination density of the top 20-cm layer of the soil containing 96-99% of the total radionuclide amount (correlation between the parameters equaled to r0.01 = 0.782, n = 20). A specifically regular structure obviously formed under the set of radionuclide water migration processes seems to be inherent in all systems of the studied type. The results obtained are believed to be of both theoretical and practical importance, since they can contribute to making decisions on the precise monitoring of zones of technogenic accumulation, as well as solving fundamental problems of soil formation and its restoration after technogenic pollution.

Spatial geochemical differentiation of the iodine-induced health risk and distribution of thyroid cancer among urban and rural population of the Central Russian plain affected by the Chernobyl NPP accident.

The main goal was to study the spatial distribution of thyroid cancer (THYC) among the population of urban and rural settlements of four regions of Russia, which were characterized by different contents of stable iodine in soils and exposed to radioactive fallout of 131I from the Chernobyl NPP. Using GIS technologies, zoning of territories for the deficiency of 127I and pollution with 131I was performed. The resulting risk maps were compared with the THYC distribution. The association between the spatial distribution of the total (natural and man-made) risk assessment and the incidence of THYC at the district level tended to have a higher positive correlation (r = 0.505, p < 0.001, n = 94) compared with the correlation of the latter parameter with a fallout density of 131I (r = 0.468, p < 0.001). After latent period, the incidence of THYC among residents of urban settlements of the Bryansk region was considerably higher than in rural, the difference increasing with time. The correlation between the assessed total risk and THYC distribution in risk zones was significant and higher in the rural areas than in the urban ones. A tendency for a negative significant correlation (r = - 0.55, p = 0.01) between daily iodine intake (based on the main components of the diet) and THYC cases among the rural population was found. A definite difference in the influence of geochemical environmental factors on the distribution of THYC among urban and rural populations deserves more detailed study to prevent this disease.

The Hiroshima A-Bomb Black Rain and the Lifespan Study; A Resolution of the Enigma.

The Japanese Lifespan Study (LSS) of the A-Bomb survivors is the principal basis of the current legal radiological framework. Evidence provided for the first time here shows that internal exposure to radiologically significant quantities of Uranium-234 contained in sub-micron particle rainout from the un-fissioned weapon warhead, the Black Rain, is a missing exposure in the LSS analysis. It is argued that this is responsible for a background excess cancer risk in all the LSS dose groups. This, together with epidemiological evidence based on unexposed controls falsifies the LSS cancer vs. dose regression coefficients for internal exposure.

Reliability of thyroid doses due to 131I intake exceeding 5 Gy in a cohort of Belarusian children exposed to Chernobyl fallout.

High thyroid doses due to Iodine-131 (131I) intake among individuals exposed in childhood and adolescence to Chernobyl fallout raise questions about their reliability and their impact on the analysis of the radiation-related risk of thyroid cancer and other thyroid diseases in the exposed population. In the present study, an in-depth examination was conducted of thyroid doses from 131I intake over 5 Gy calculated for 131 subjects of the Belarusian-American cohort of individuals exposed after the Chernobyl accident. Thyroid doses in this cohort study were estimated based on individual radiation measurements of 131I thyroidal activity and detailed questionnaire data on individual behavior and consumptions of locally produced foodstuffs. Therefore, these doses provide the best basis for assessing reliability. The analysis showed that the result of direct thyroid measurement was mistakenly assigned to three out of 131 study subjects (2.3% of the total), and, therefore, the instrumental thyroid dose for these individuals cannot be correctly estimated. This study confirmed with a high degree of confidence the reliability of thyroid doses due to 131I intake exceeding 5 Gy that were calculated for the Belarusian-American cohort members.

Hematological malignancies in Ukraine in post-Chernobyl era: sources of data and their preliminary analysis.

The major sources of the data on the hematological malignancies in the post-Chernobyl period in the regions of Ukraine differing by the levels of the residual contamination with radionuclides have been analyzed. According to the data collected from the primary hematological facilities in Ukraine in 2010-2017, the incidence of lymphoid neoplasms from mature B cells, acute myeloid leukemia, and multiple myeloma in the most contaminated regions was higher than in the less contaminated ones. For the first time, the relative contribution of the several specific types of leukemia in the total diagnosed hematological malignancies has been analyzed throughout 1997-2017 based on the in-house database compiled by the Reference Laboratory of RE Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, the National Academy of Sciences of Ukraine. In 2011-2017, the Reference Laboratory provided the diagnostic studies in about 26% of all Ukrainian patients with tumors of hematopoietic and lymphoid tissues (34% of patients with different forms of acute and chronic leukemia). The increased proportion of acute myeloid leukemia and chronic lymphocytic leukemia in the total diagnosed cases of overall leukemia in the patients from contaminated regions has been demonstrated following Chernobyl accident.

Endemic diseases of geochemical origin and methodological approaches toward their prevention and elimination.

A new approach to the study of diseases of geochemical origin is presented, which is based on the hypothesis that all such geochemical endemias were not possible in conditions of virgin biosphere and are products of human civilization. Two genetically different types of endemic diseases of geochemical origin are distinguished, each having a specifically spatial structure: (1) diseases of natural origin due to natural element deficiency or excess in the particular zones or areas; (2) diseases of anthropogenic origin related to chemical transformation of the environment in the course of agricultural or industrial production. Anthropogenically provoked diseases of geochemical nature always occur in conditions of already formed natural geochemical heterogeneity. As each type of the endemic disease has a peculiar structure of spatial distribution, the present health risk can be mapped as a genetically two-layer structure, characterizing deviation of the existing geochemical conditions from those ideal for specific species. Parameters of geochemical conditions, which are ideal for humans and domesticated species, should be sought within the areas with undisturbed soil cover, where these species have been formed in their present form. The hypothesis is tested on example of thyroid diseases observed in iodine-deficient areas affected by a nuclear accident with 131I fallout. The developed approach is believed to serve as a practical tool for monitoring and prevention of endemic diseases of geochemical origin.

Belarusian in utero cohort: A new opportunity to evaluate the health effects of prenatal and early-life exposure to ionising radiation.

In April 1986, the Chernobyl nuclear accident resulted in wide-scale contamination of Belarus with significantly elevated levels of radioiodine isotopes, mainly iodine-131 (131I), and long-lived radiocaesium isotopes, mainly caesium-137 (137Cs). Various groups of the population were affected by exposure to ionising radiation, including pregnant women and their foetuses. This paper describes the methods and results related to the establishment of a cohort of 2965 Belarusian people exposed in utero due to Chernobyl fallout. The cohort consists of individuals whose mothers resided in the most radioactively contaminated areas in Belarus at the time of the accident. Prenatal and postnatal doses to the thyroid due to intake of 131I, external irradiation and ingestion of radiocaesium isotopes were estimated for all cohort members. Ongoing research on this unique cohort will provide important information on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocaesium isotopes, for which available epidemiological data are scant.

Averting cumulative lifetime attributable risk (LAR) of cancer by decontamination of residential areas affected by a large-scale nuclear power plant fallout: time aspects of radiological benefits for newborns and adults.

The averted cumulative lifetime attributable risk (LAR), the residual dose and highest ground deposition of 137Cs complying with a reference dose level of 20 mSv yr-1 to an individual returning after one year to an area contaminated by unfiltered releases of fission products from a nuclear power plant (NPP) were evaluated by applying an existing exposure model designed to compute age- and gender-dependent time-integrated LAR. The model was applied to four types of nuclear fallout scenarios, partly based on data from the Chernobyl and Fukushima releases and from theoretical source terms from Swedish NPPs. For rapid decontamination measures that achieve a 50% relative reduction in external dose rate within 1 year, compliance with the reference level 20 mSv yr-1 can be attained for an initial 137Cs ground deposition of up to 2 MBq m-2 with relaxed food restrictions. This compliance can be attained at even higher ground deposition (up to 4.5 MBq m-2) if using the strict food restrictions employed in Japan after 2011. Considering longer than 1 year return times it was also found that the benefit of implementing decontamination decreases rapidly with time (2-3 years half-time), especially if the fallout has a high initial 134Cs to 137Cs activity ratio and if the ecological half-time of the external dose rate is short (<5 years). Depending on fallout scenario the averted cumulative LAR for newborn girls by decontamination that is achieved after 5 years is only between 6% and 11% of that obtained by evacuation alone during the same time, indicating a rather limited radiological benefit of decontamination if delayed more than a few years. We conclude that decision makers and emergency response planners need to consider that protracted decontamination measures may have limited radiological benefit compared with evacuation in terms of averted future cancer cases, albeit it may have other societal benefits.

Long term investigation of 137Cs in chicken meat and eggs from northwest Croatia.

This paper presents the results of long-term investigations of 137Cs activity concentrations in chicken meat and eggs from northwest Croatia for the period 1987-2018. The research has been done as a part of monitoring program of radioactive contamination in Croatia. The highest activity concentrations in both of these foodstuffs were measured in 1987 and have been decreasing exponentially ever since. The Fukushima-Daiichi accident in 2011 did not cause any increase of 137Cs activity concentrations. The ecological half-life for 137Cs was estimated to be 8.0 and 8.4 years for chicken meat and eggs respectively. The correlation between 137Cs in fallout and chicken meat as well as between 137Cs in fallout and eggs is very good, the respective correlation coefficients being 0.79 and 0.72, indicating that fallout was the main source of 137Cs contamination in both foodstuffs. The estimated effective doses received by adult members of the Croatian population due to the intake of radiocaesium by chicken meat and egg consumption for the overall observed period are very small, 2.0 and 0.6 µSv respectively. Therefore, chicken meat and chicken egg consumption was not a critical pathway for the transfer of radiocaesium to humans.

Activity of 90Sr in Fallout Particles Collected in the Difficult-to-Return Zone around the Fukushima Daiichi Nuclear Power Plant.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released abundant radioactive particles into the surrounding environment. Herein, we analyzed the activity of 90Sr in these particles to estimate the contribution of this radionuclide to the overall radiation exposure and shed light on the processes that occurred during the accident. Seven radioactive particles were isolated from the dust and soil samples collected from areas surrounding the FDNPP, and the minimum/maximum 137Cs activities were determined as 224/4,100 Bq. Based on the size, specific activity, and 134Cs/137Cs activity ratios, we concluded that six of the seven radioactive particles were released from the Unit 1 reactor, while one particle was released from the Unit 3 reactor by a hydrogen explosion. Strontium-90 was detected in all radioactive particles, and the minimal/maximal 90Sr activities were determined as 0.046/1.4 Bq. 137Cs/90Sr activity ratios above 1000 were observed for all seven particles, that is, compared to 137Cs, 90Sr had negligible contribution to the overall radiation exposure. The 137Cs/90Sr activity ratios of the radioactive particles were similar to those of terrestrial environmental samples and were higher for particles released from the Unit 1 reactor than for samples collected from the Unit 1 reactor building, which indicates possibility of additional 90Sr-rich contamination after release of the particles.

Long-term Investigations of 134Cs and 137Cs Activity Concentrations in Honey from Croatia.

This paper presents the results of long-term post-Chernobyl investigations of 134Cs and 137Cs activity concentrations in multifloral and chestnut honey sampled in northwest Croatia. For both radionuclides, the activity concentrations peaked in May 1986, decreasing exponentially until the mid-1990 s, when they fell under the detection limit for both radionuclides. After the Fukushima-Daiichi accident in 2011, the presence of both radionuclides in honey was detected once again. The ecological half-life was estimated to be 1.67 and 1.45 years for 137Cs and 134Cs, respectively. The correlation between 134Cs and 137Cs activity concentrations in fallout and honey was very good, indicating fallout to be the main source of honey contamination. The observed 134Cs/137Cs activity ratio in honey was similar to the ratio found in other environmental samples. The estimated collective effective doses for the Croatian population incurred by honey consumption indicate that honey was not a critical pathway for the transfer of 134Cs and 137Cs from fallout to humans.

Long-Term Consequences of the Chernobyl Radioactive Fallout: An Exploration of the Aggregate Data.

Policy Points Policymakers should invest more on researching the long-term health effects of low-ionizing radiation exposure, as we are far from reaching a consensus on a topic that is of enormous importance for public health and safety. Public policies such as those limiting the import of contaminated food from areas hit by a radioactive disaster or those regulating the resident population's access to such areas should follow a precautionary approach. Neoplasm diagnosis and medical care should be designed in order to take into account the possible role of long-term, low-dose radiation exposure. Health care policies should provide effective screening and prevention strategies with a specific focus on the regions that were hit most severely by the Chernobyl nuclear fallout. Health care expenditure should be targeted, taking into account the geographical dispersion of the fallout in order to attenuate its possible effect on neoplasm incidence. CONTEXT: This study investigates the association between the radioactive 137 Cesium fallout originated by the 1986 Chernobyl nuclear accident and dispersed over Western Europe, as a result of a combination of radioactive cloud passage days and rainy days over a 10-day period, and long-term health patterns and related costs. Since the half-life of 137 Cesium is 30.17 years, part of the radioactivity in the affected regions is still present today, and it is usually still detected in the food chain, although at lower concentration levels. METHODS: We match longitudinal data on neoplasm incidence over the time span 2000-2013 in a number of European regions not immediately adjacent to Chernobyl with the randomly distributed levels of cesium deposition after the nuclear disaster in order to assess whether we can detect an association with the long-term health effects on the European population through a random effects model. FINDINGS: Considering 3 levels of fallout deposition-low, medium, and high-hospital discharges after treatment for neoplasms are, respectively, 0.36, 0.44, and 0.98 discharges over 100 inhabitants higher compared to regions with no fallout, with the population average being around 1.7 hospital discharges by neoplasms over 100 inhabitants. We checked the robustness of our findings to a number of tests including a placebo simulation and different model specifications. CONCLUSIONS: Radioactive fallout is positively associated with a higher incidence of hospital discharges after treatment for neoplasms almost 30 years after its release, with larger effects in regions where the radioactivity was more intense. Our estimates are comparable to the findings of the largest-scale study on the long-term health effects of continuous low levels of radiation exposure among workers in the nuclear industry and suggest that more research is needed on this topic, given its enormous importance for public health and safety.

Increased prevalence of essential hypertension in areas previously exposed to fallout due to nuclear weapons testing at the Semipalatinsk Test Site, Kazakhstan.

This study examines the association between environmental radiation exposure and essential hypertension in a series of investigated geographical districts adjacent to the Semipalatinsk nuclear test site in Kazakhstan. The sample consists of 2000 volunteers participants in screening examinations in three administrative districts close to the nuclear test site, which was carried out as part of the Government Programs on Environmental Health Hazard. The cross-sectional study compares prevalence ratios in a population sample with long-term exposure in the low and intermediate dose range. Age-adjusted odds ratios for hypertension were found significantly increased with higher exposure groups. After accounting for main cardiovascular risk factors into the model and stratifying by gender, the prevalence odds ratios for radiation remained significantly increased, with a significant dose-response effect observed for some but not all subgroups. The results support existing evidence of cardiovascular health effects of radiation exposure and of persisting environmental health issues that require attention in both epidemiological surveys and healthcare provision.

Introducing the concept of the isodose for optimisation of decontamination activities in a radioactive fallout scenario.

In the recovery phase after a radioactive release incident, it is important to be able to focus decontamination operations on the areas that contribute most to the radiation dose. Monte Carlo simulations were applied to determine the shielding effect of a building against radiation from various directions, also giving information on the dose contributions at various locations inside the building from specific areas outside. The concept of the isodose was developed to optimise decontamination activities, and was applied as isodose lines to define the smallest areas that lead to a certain dose reduction through decontamination of areas surrounding the building. The shape and position of the isodose lines depend on the building's geometry, wall thickness, and material, and on the observation point inside the building. Calculations have been made with a surface resolution of 1 m2 for four observation points in a modular building, assuming depositions of 137Cs and 60Co on the ground surface and on the roof, as well as 1 cm below the ground surface to represent ground penetration. For example, a ten times as large area would have to be decontaminated to increase the dose reduction from 10% to 30%, if it is assumed that all the contamination is located at a depth of 1 cm.

Plutonium Isotopes (239-241Pu) Dissolved in Pacific Ocean Waters Detected by Accelerator Mass Spectrometry: No Effects of the Fukushima Accident Observed.

The concentration of plutonium (Pu) and the isotopic ratios of 240Pu to 239Pu and 241Pu to 239Pu were determined by accelerator mass spectrometry (AMS) in Pacific Ocean water samples (20 L each) collected in late 2012. The isotopic Pu ratios are important indicators of different contamination sources and were used to identify a possible release of Pu into the ocean by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. In particular, 241Pu is a well-suited indicator for a recent entry of Pu because 241Pu from fallout of nuclear weapon testings has already significantly decayed. A total of 10 ocean water samples were prepared at the Radiochemie München of the TUM and analyzed at the Vienna Environmental Research Laboratory (VERA). Several samples showed a slightly elevated 240Pu/239Pu ratio of up to 0.22 ± 0.02 compared to global fallout (240Pu/239Pu = 0.180 ± 0.007), whereas all measured 241Pu-to-239Pu ratios were consistent with nuclear weapon fallout (241Pu/239Pu < 2.4 × 10-3), which means that no impact from the Fukushima accident was detected. From the average 241Pu-to-239Pu ratio of 8-2+3 ×10-4 at a sampling station located at a distance of 39.6 km to FDNPP, the 1-σ upper limit for the FDNPP contribution to the 239Pu inventory in the water column was estimated to be 0.2%. Pu, with the signature of weapon-grade Pu was found in a single sample collected around 770 km off the west coast of the United States.