Relationship between radiocaesium in muscle and physicochemical fractions of radiocaesium in the stomach of wild boar

137Cesium (137Cs) assessment in wild boars from northwestern Italy

Radionuclide contamination is a serious health issue caused by nuclear experiments and plant accidents, as seen for the Chernobyl and Fukushima nuclear plants. Italy has been especially interested in northwestern alpine regions, as have several other nations. The aim of this work was to indagate 134Cs and 137Cs contamination in wild boars, which were considered bioindicators sampled in the Chisone/Germanasca Valley and the Pellice Valley districts (Piedmont, Italy) in two hunting seasons (2014 and 2016). In the 2014 season, only the livers of the animals (n = 48) were sampled, whereas in 2016, five different anatomical sampling sites were sampled for each animal (n = 16). The analyses were conducted in an accredited laboratory (Agenzia Regionale per la Protezione dell'Ambiente-ARPA) by the aid of an HPGe detector (Ortec) with a relative efficiency of 50%. In general, the contamination levels registered in 2014 were under the detection limit for 134Cs and low for 137Cs (Chisone/Germanasca valley: min: 0.0, max: 23.9 median 11.0 Bq/kg vs Pellice valley: min 0, max: 31.7, median: 9.6 Bq/kg) and no health concern can be supposed. In the first-year samples, the liver showed a negative correlation between age and contamination level. In the second year of sampling, low levels were confirmed (min: 3.1 Bq/kg, max: 113.3; median 17.7 Bq/kg). Multiple sampling from the same animal showed that the diaphragm (median = 27.7 Bq/kg) kidney (27.4) and tongue (27.6) were more contaminated than the liver (17.7) and spleen (15.3). Moreover, a linear mixed model revealed a negative organ-by-age interaction, meaning that interorgan differences in contamination level were greater in younger (5-11 months) than in older (18-36 months) animals. Different feeding habits can be the explanation. Our paper shows that muscle sites (diaphragm and tongue) can be useful for radionuclide pollution surveillance in wild boar populations and that younger animals show more interorgan variability in contamination levels than older animals. More investigations are needed to confirm this correlation and to fulfill the request for more data to achieve better risk assessment.

Half-century trends of radioactivity in fish from Danish areas of the North Sea, Kattegat, and Baltic Sea

This work reports comprehensive time-series datasets over the past 50 years for natural (210Po) and anthropogenic (134Cs and 137Cs) radionuclides in three fish species (cod, herring and plaice) from Danish marine areas covering the North Sea, Kattegat, and Baltic Sea. Impact from the global fallout of atmospheric nuclear weapons testing, radioactive discharges from the European nuclear reprocessing plants and release from Chernobyl accident are clearly detected in the fish samples. While 210Po concentrations in each fish species demonstrated comparable levels across the three regions without notable temporal trends, significantly higher median 210Po concentration was observed in the lower trophic level fish, namely herring and plaice, compared to cod. In contrast, 137Cs concentrations in all three species steadily decrease over time after the Chernobyl-attributed peaks in late 1980s in the entire study area, whereas 137Cs always demonstrated higher concentrations in cod than herring and plaice. Our calculated concentration factors (CFs) for 137Cs in this work indicate that the mean CFs for 137Cs over the past 50 years are significantly different across the three species, following the order of cod < herring < plaice. Based on the time-series data, ecological half-lives (Teco) of 137Cs in fish from Danish marine areas were estimated to evaluate the long-term impact of anthropogenic radioactive contamination in different regions. Our results indicate no significant difference in Teco across different fish species, whereas the weighted mean Teco for fish in the Baltic Sea (29.3 ± 3.9 y) is significantly longer than those of the North Sea (9.8 ± 0.9 y) and Kattegat (11.7 ± 1.2 y), reflecting the strong 'memory effect' of the Baltic Sea due to its slow water renewal. However, the dose assessment demonstrates that the contribution of the natural radionuclide 210Po to ingestion dose from fish consumption is 1-2 order of magnitude higher compared to that of 137Cs.

Imaging Plate Autoradiography for Ingested Anthropogenic Cesium-137 in Butterfly Bodies: Implications for the Biological Impacts of the Fukushima Nuclear Accident

The Fukushima nuclear accident in March 2011 caused biological impacts on the pale grass blue butterfly Zizeeria maha. At least some of the impacts are likely mediated by the host plant, resulting in "field effects". However, to obtain the whole picture of the impacts, direct exposure effects should also be evaluated. Here, we examined the distribution of experimentally ingested anthropogenic cesium-137 (¹³⁷Cs) in adult butterfly bodies using imaging plate autoradiography. We showed that ¹³⁷Cs ingested by larvae was incorporated into adult bodies and was biased to females, although the majority of ingested ¹³⁷Cs was excreted in the pupal cuticle and excretory material during eclosion. ¹³⁷Cs accumulation in adult bodies was the highest in the abdomen, followed by the thorax and other organs. These results suggest that ¹³⁷Cs accumulation in reproductive organs may cause adverse transgenerational or maternal effects mediated by reactive oxygen species (ROS) on germ cells. ¹³⁷Cs accumulation was detected in field individuals collected in September 2011 and September 2016 but not in May 2011, which is consistent with the abnormality dynamics known from previous studies. Taken together, these results contribute to an integrative understanding of the multifaceted biological effects of the Fukushima nuclear accident in the field.

Time dependence of 137Cs contamination in wild Japanese monkeys after the Fukushima Daiichi nuclear accident

Over the 10 years immediately after the Fukushima Daiichi nuclear accident, we measured the changes in the muscle ¹³⁷Cs concentration (Bq/kg) of wild Japanese monkeys living in Fukushima City, which is located approximately 70 km from the Fukushima Daiichi Nuclear Power Plant. The muscle¹³⁷Csconcentration, which was observed at a maximum of 13,500 Bq/kg immediately after the accident, had decreased to several hundred Bq/kg 10 years later. The muscle ¹³⁷Cs concentration was significantly related to the soil contamination levels (10,000-30,000, 30,000-60,000, 60,000-100,000, and 100,000-300,000 Bq/m²), sex, age class (immature, mature), body weight (> 5000 g, 5000-10,000 g, < 10,000 g), and seasons (the cold period from December to April, the warm period from May to November).The value of muscle ¹³⁷Cs concentration and the aggregated transfer factor (T_ag: calculated by dividing muscle ¹³⁷Cs concentration [Bq/kg] by soil ¹³⁷Cs deposition density at the capture site [Bq/m²]) apparently decreased with time for several years. However, post hoc pairwise comparisons showed no difference from 2017 to 2020, and the accumulation of ¹³⁷Cs in muscle may continue for some time.

Exemplifying the “wild boar paradox”: dynamics of cesium-137 contaminations in wild boars in Germany and Japan

Wild boars (Sus scrofa) are notorious for accumulating high contamination levels of 137Cs in their meat. Publicly available data of 137Cs contamination levels in wild boars from 2011 to 2019 were used to determine some radioecological characteristics in Germany (affected by Chernobyl-fallout, 1986) and Japan (affected Fukushima, 2011). The effective half-life of 137Cs in wild boar meat was much longer in Germany (7.3 y) than in Japan (2.6 y), respectively. Wild boars in Germany thus show much more persistent contamination levels than other game or forest animals. This unusual behavior has been termed “wild boar paradox.” In German wild boars, the data sets reveal a distinct geographical and seasonal dependence with higher activity concentrations in winter than in summer. In Japan, contamination levels only exhibit a distinct decline behavior.

Radiocesium accumulation and germline mutations in chronically exposed wild boar from Fukushima, with radiation doses to human consumers of contaminated meat

Genetic effects and radioactive contamination of large mammals, including wild boar (Sus scrofa), have been studied in Japan because of dispersal of radionuclides from the Fukushima Dai-ichi Nuclear Power Plant in 2011. Such studies have generally demonstrated a declining trend in measured radiocesium body burdens in wildlife. Estimating radiation exposure to wildlife is important to understand possible long-term impacts. Here, radiation exposure was evaluated in 307 wild boar inhabiting radioactively contaminated areas (50-8000 kBq m^-2) in Fukushima Prefecture from 2016 to 2019, and genetic markers were examined to assess possible germline mutations caused by chronic radiation exposures to several generations of wild boar. Internal Cs activity concentrations in boar remained high in areas near the power plant with the highest concentration of 54 kBq kg^-1 measured in 2019. Total dose rates to wild boar ranged from 0.02 to 36 μGy h^-1, which was primarily attributed to external radiation exposure, and dose rates to the maximally exposed animals were above the generic no-effects benchmark of 10 μGy h^-1. Using the estimated age of each animal, lifetime radiation doses ranged from <0.1 mGy to 700 mGy. Despite chronic exposures, the genetic analyses showed no significant accumulation of mutation events. Because wild boar is an occasional human dietary item in Japan, effective dose to humans from ingesting contaminated wild boar meat was calculated. Hypothetical consumption of contaminated wild boar meat from radioactively contaminated areas in Fukushima, at the per capita pork consumption rate (12.9 kg y^-1), would result in an average effective annual dose of 0.9 mSv y^-1, which is below the annual ingestion limit of 1 mSv y^-1. Additionally, a consumption rate of about 1.4 kg y^-1 of the most contaminated meat in this study would not exceed annual ingestion limits.

Environmental transfer parameters of strontium for soil to cow milk pathway for tropical monsoonal climatic region of the Indian subcontinent

The radionuclide transfer between compartments is commonly described by transfer parameters representing the ratio of concentrations of an element in two compartments for equilibrium conditions. This is a comprehensive study on the soil-to-grass transfer factor (Fv) and grass-to-cow milk transfer coefficient (Fm) for stable strontium (Sr) for soil-grass (pasture)-cow (Bos taurus) milk environmental pathway under field conditions for a high rainfall tropical monsoonal climatic region of the Indian subcontinent. The study was conducted in the vicinity of the Kaiga nuclear power plant (NPP), situated ~ 58 km inland of the West Coast of the Indian subcontinent. A grass field was developed exclusively for this study, and two cows of the native breed were raised to graze on it. The soil, grass, and milk were analyzed to evaluate the Fv and the Fm values for the stable Sr. For comparison, several pasture lands and the cows raised by the villagers and a dairy farm were also studied. The Fv values were in the range 0.18-8.6, the geometric mean (GM) being 1.8. The correlations of Fv values with a range of physicochemical parameters are presented. The GM values for Fm were 2.2 × 10-3 d L-1 and 7.2 × 10-3 d L-1 for the two cows raised for this study, 2.6 × 10-3 d L-1 for those raised by the villagers, and 4.2 × 10-3 d L-1 for the dairy farm. The site-specific Fm value for the region was determined as 3.2 × 10-3 d L-1. The concentration ratio (CR), defined as the ratio of Sr concentration in milk to that in feed under equilibrium conditions, exhibited less variability (1.8 × 10-2-5.4 × 10-2) among the three categories of cows.

Monitoring of radioactive cesium in wild boars captured inside the difficult-to-return zone in Fukushima Prefecture over a 5-year period

Following the Fukushima Daiichi Nuclear Power Plant accident in 2011, tissue samples from wild boar (Sus scrofa) outside the evacuation zone (difficult-to-return zone, DRZ) tended to show high activity concentrations of cesium-137 (¹³⁷Cs). Understanding the ¹³⁷Cs dynamics of wild boar populations inside the DRZ is necessary because they affect ¹³⁷Cs dynamics and wild boar management in areas outside the DRZ. Since few detailed, long-term studies have been conducted inside the DRZ, we measured ¹³⁷Cs activity concentrations in 221 wild boar muscle samples obtained from wild boar caught inside the DRZ and surrounding areas over a 5-year period. Our results showed that the ¹³⁷Cs activity concentration in wild boar from inside the DRZ were higher than those in wild boar outside this zone. No significant difference was observed between muscle and soil ¹³⁷Cs levels, but significant correlations were observed between muscle ¹³⁷Cs activity concentrations and body length and body weight in the low-activity-concentration season, but not between all seasons and the high-activity-concentration seasons. It is considered that the size effects observed during the low-activity-concentration season may be due to factors related to metabolism and changes in food habit. This is the first long-term survey of ¹³⁷Cs in wild boar inside the DRZ.

Ecological half-life of radiocesium in white-tailed deer on the Department of Energy's Savannah River Site: What can a half century of field monitoring tell us?

This paper estimates the ¹³⁷Cs ecological half-life of white-tailed deer inhabiting the Department of Energy's Savannah River Site (SRS) based on sex and age using data collected over a 51-year time-period. With a physical half-life of 30.2 yr, the biological half-life for the deer herd is considerably shorter because of the isotope's biochemical mimicry of K+ inside the body. Leveraging this long-term dataset and robust sample size, we compared the long-term half-century estimates to shorter decadal increments. The simple exponential decay model for the entire 51-year sampling period predicted an ecological half-life of 23.15 years. When breaking the sample data into decadal increments ¹³⁷Cs body burden had complex temporal dynamics with predicted half-lives ranging from 9.25 to 32.33 years. Exponential decay for the entire 51-year sampling period for models evaluated by sex, age, sex*age to determine how these variables influence the predictability in the mean depuration rate, the ecological half-lives were between 21 and 23 years for all permutations, except for fawns that had a half-life no different than the physical half-life of the isotope itself. Differential habitat use and competition most likely explains why both yearling and adult females consistently had higher body burdens than males over the 51-year time period, showing how dynamic this radioisotope is in biological systems. This study is one of the most robust long-term datasets in the world (n = 42,412) that is specifically focused on monitoring the uptake and depuration of ¹³⁷Cs in a wild species.

Differentiating Fukushima and Nagasaki plutonium from global fallout using 241Pu/239Pu atom ratios: Pu vs. Cs uptake and dose to biota

Plutonium (Pu) has been released in Japan by two very different types of nuclear events - the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive ²⁴¹Pu/²³⁹Pu atom ratios. In contrast, other typically-used Pu measures (²⁴⁰Pu/²³⁹Pu atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of ~0.4%-2% in the 0-5 cm soils, ~0.3%-3% in earthworms, and ~1%-10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the ^134,137Cs uptake appears to be highly influenced. Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher ²³⁹Pu and was distinguished by both ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of ²⁴¹Pu/²³⁹Pu atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu.