Radiocaesium Activity Concentrations in Wheat Grains in the Republic of Croatia for 1965–2003 and Dose Assessment

Results of systematic, long-term measurements of ¹³⁷Cs activities in wheat for the period 1965–2003 are summarized. Radiocaesum fallout activities affect wheat activity concentrations, the coefficient of correlation being 0.91. In the observed period, the highest activity of ¹³⁷Cs deposited by fallout, 6321 Bq m⁻², was recorded in 1986, i.e., in the year of Chernobyl accident, causing peak ¹³⁷Cs activity concentration in wheat of 38.0 ± 13.0 Bq kg⁻¹. After the Chernobyl nuclear accident the ¹³⁴Cs:¹³⁷Cs activity ratio in wheat was ≈0.5, and did not differ from the value found in other environmental samples. The transfer coefficient from ¹³⁷Cs fallout deposition to wheat was calculated to be 8.6 × 10⁻³ Bq y kg⁻¹ per Bq m⁻², indicating the low transfer of radiocaesium from fallout to wheat. The upper limit for the collective effective dose for the Croatian population due to ¹³⁷Cs and ¹³⁴Cs ingestion by wheat and wheat products consumption for period 1965–2003 was estimated to be 665 person-Sv, the upper limit for the annual collective effective dose in 2003 being only about 0.061 person-Sv.     

The contents and forms of solid-phase species of radioactive strontium and cesium in Taiwan soils

This study was to investigate the activities and contents of ¹³⁷Cs in the profiles of selected arable and forest soils in Taiwan and various solid-phase species of ⁸⁵Sr and ¹³⁷Cs in selected arable soils in Taiwan. The gamma (γ) ray spectra of the collected soil samples and some of the soils amended with ⁸⁵Sr and ¹³⁷Cs were measured. The data indicate that the arable soils from Sanhsing series, Sanhsing Township and Chuangwei series, Chuangwei Township, Ilan County, and from Tunglochuan series, Pinglin Township, Taipei County shows significantly higher radioactivity of ¹³⁷Cs (ND − 11.0 ± 0.2 Bq kg⁻¹). Furthermore, the radioactivity of ¹³⁷Cs in the mountain soils (1.24 ± 0.07 − 42 ± 1 Bq kg⁻¹) from Yuanyang Lake Nature Preserve among Ilan, Taoyuan, and Hsinchu Counties is the highest among the investigated mountain forest soils. This may be mainly attributed to the fact that Ilan County is located in the northeastern part of Taiwan and faces the northeastern and northern seasonal winds with lots of precipitation annually from mid-autumn through mid-spring next year and is receiving greater amount of fallouts yearly. Due to longer reaction period (≥3 y) of ¹³⁷Cs with soil components, ¹³⁷Cs was mainly in the forms bound to oxides and to organic matter in the soil amended with ¹³⁷Cs and in the soil contaminated with ¹³⁷Cs. On the contrary, due to shorter reaction period (<60 d) of ⁸⁵Sr with soil components, ⁸⁵Sr was mainly in exchangeable form and partially in the forms bound to carbonates and oxides in the soils amended with ⁸⁵Sr.     

RETRACTED ARTICLE: Biomonitoring fallout <Superscript>137</Superscript>Cs in resident and migratory fishes collected along the southern coast of India and assessment of dose

The globally distributed fallout radionuclide ¹³⁷Cs was monitored in 25 resident and 22 migratory fish species collected from some regions of west and east coast of southern India to establish a baseline data. The samples were collected during June 2008 to June 2009. Higher level of ¹³⁷Cs was noted in planktivorous fishes and lower level in herbivores. A significant variation in ¹³⁷Cs was observed between fishes with different feeding habits and different migratory pattern. Oceanodromic migratory fishes displayed higher cesium levels than other migratory types. Similarly, migratory fishes displayed higher ¹³⁷Cs concentration compared to resident fishes. The overall range of ¹³⁷Cs varied from 0.06 to 0.3 Bq/kg in fishes. The biological concentration varied from 55 to 250. The average external dose rate to fishes was calculated to be 2.7 × 10⁻⁷ μGy/h, while the internal dose rate varied from 8.50 × 10⁻⁶ to 5.27 × 10⁻⁵ μGy/h. The hazard quotient for fishes was found to be less than 1. The average intake of ¹³⁷Cs via fishes to the public was calculated to be 3.5 Bq/year and subsequently the committed effective dose was 0.05 μSv/year. The data obtained were less than global average and comparable to those of many regions.     

Long-term investigations of post-Chernobyl radiocaesium in fallout and air in North Croatia

The long-term behaviour of (137)Cs activity concentrations in air and fallout has been studied in the city of Zagreb for the post-Chernobyl period (1986-2006) as a part of an extended monitoring program of radioactive contamination of human environment in Croatia. Annual mean (137)Cs activity concentrations in air and annual total deposition fluxes (wet plus dry) decreased from 2.8 x 10(-4) Bq m(-3) in September 1986 to 3.0 x 10(-6) Bq m(-3) in last quarter of 2006 and from 6,410 Bq m(-2) year(-1) in 1986 to 2 Bq m(-2) year(-1) in 2006 respectively. By fitting the measured (137)Cs activity concentrations to the theoretical curve the ecological half-lives of (137)Cs in air and fallout were estimated with respective values of 0.46 and 0.54 years for immediate post-Chernobyl period, increasing to 5.52 and 3.97 years afterwards. Using the data on (137)Cs activity concentrations in air and fallout total caesium deposition velocity of (3.34 +/- 3.13) x 10(-2) ms(-1) was estimated with median value being 2.13 x 10(-2) ms(-1). Such relatively high (137)Cs deposition velocities compared with pre-Chernobyl ones, are characteristic for the post-Chernobyl period and, according to Stokes' settling law, indicate that the diameters of aerosol particles associated with (137)Cs originated from the Chernobyl accident are pretty large, i.e. >1 microm. (134)Cs/(137)Cs activity ratio in fallout and in air has been found to be similar to the theoretically predicted values, initial value being about 0.5 and decreasing according to differential radioactive decay. The similar ratio has been observed in most of the other environmental samples.     

Long-term transfer of global fallout 137Cs to cow’s milk in Iceland

The aim of this study was to provide improved information on the long-term transfer of global nuclear weapons ¹³⁷Cs fallout to cow’s milk in Iceland many years after deposition. The spatial variation in deposition was confirmed to be explained by precipitation. Soil samples showed a significant difference in ¹³⁷Cs deposition density between the main agricultural areas, with the South having the highest values, then the West and North and the lowest in the Northeast. There was no significant difference between the effective half-lives in ¹³⁷Cs activity concentrations in milk and milk powder from the main dairies in Iceland based on data for milk from 1990 to 2007 and for milk powder from 1986 to 2007. There was, however, a significant difference between the effective half-lives obtained for these two regions, 13.5?years for the Northern and 10.5?years for the Southern regions. These half-lives for global fallout are longer than those previously reported for similar time periods in other Arctic areas. The transfer of ¹³⁷Cs to cow’s milk was quantified for different agricultural regions using aggregated transfer coefficients (T _ag) for the period of peak global fallout soil inventory in 1965–1967. The values ranged from 2.8?×?10^?3 to 10.6?×?10^?3?m²?kg^?1. By 2001–2004, the T _ag values had only declined, in the main agricultural areas, to 0.6?×?10^?3–1.0?×?10^?3?m²?kg^?1. Long-term transfer rates to milk many years after deposition were high in Iceland compared with most other reported data. The transfer is potentially relevant for some of the contaminated areas around the Fukushima Nuclear Power Plant after the accident in March 2011 since limited information is available on uptake from Andosols and associated effective half-lives.     

Assessment of environmental radioactivity for Batman, Turkey

The province of Batman, located in southern Anatolia, has a population of approximately 500,000. To our knowledge, there exists no information regarding the environmental radioactivity in this province. Therefore, gamma activity measurements in soil, building materials and water samples and an indoor radon survey have been carried out in the Batman province. The mean activity concentrations of the natural radionuclides (²²⁶Ra, ²³²Th and ⁴⁰K) and a fission product (¹³⁷Cs) were 35 ± 8, 25 ± 10, 274 ± 167 and 12 ± 7 Bq kg^???1, respectively, in the soil samples. The concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the selected building materials ranged from 18 to 48 Bq kg^???1, 8 to 49 Bq kg^???1 and 68 to 477 Bq kg^???1, respectively. All the calculated radium equivalent (Ra_eq) activity values of the building material samples are lower than the limit of 370 Bq kg^???1, equivalent to a γ-dose of 1.5 mSv year^???1. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in tap waters collected from the study area were determined with mean specific activity concentrations of 42 ± 15, 35 ± 9 and 524 ± 190 mBq L^???1, respectively. Indoor radon measurements were made at 95 dwellings in Batman using a CR-39 detector. The radon concentration levels were found to vary from 23 to 145 Bq m^???3. The arithmetic mean of the measured radon concentration levels was found to be 84 Bq m^???3 with a standard deviation value of 23 Bq m^???3. The measurement results obtained in this study did not significantly differ from those taken in other parts of the country. The data generated in this study can be used to determine whether the Batman province is in a normal or high background radiation area and provides a valuable database for future estimations of the impact of radioactive pollution.     

Spatial variability of soil <Superscript>137</Superscript>Cs in the South Caspian region

In a comprehensive program of environmental radioactivity survey in South Caspian region,¹³⁷Cs inventories in soil has been measured at more than 50 sites in the Iranian northern province of Guilan. This has been the first wide-range survey of soil radionuclide inventories in the narrow band sensitive ecosystem of south Caspian shore. Radioactivity measurements were carried out using HPGe gamma-spectrometry system. The activity concentration of ¹³⁷Cs in surface soil exhibits a mean value of 17.6 ± 9.4 Bq kg⁻¹, with a range of 2.3–41.7 Bq kg⁻¹. In many sites, split-level sampling method has been applied down to a depth of 20 cm. There were found generally two profiles. Most profiles exhibit a negative exponential distribution, while others revealed a clear subsurface peak in 5–10-cm layer. Cesium deposition in the study area has been estimated to be in the range of 0.38–2.9 kBq m⁻² with a mean value of 1.7 kBq m⁻². Distribution patterns of ¹³⁷Cs concentration levels and deposition values have been estimated using Kriging interpolation method. Observed hotspots in deposition pattern coincide with areas of higher precipitation.     

226Ra, 232Th and 40K analysis in soil samples from some areas of Malwa region, Punjab, India using gamma ray spectrometry

The activity concentrations of soil samples collected from thirty different locations of Malwa region of Punjab were determined by using HPGe detector based on high-resolution gamma spectrometry system. The range of activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the soil from the studied areas varies from 18.37 Bq kg⁻¹ (Sangrur) to 53.11 Bq kg⁻¹ (Sitoguno), 57.28 Bq kg⁻¹ (Dhanola) to 148.28 Bq kg⁻¹ (Sitoguno) and 211.13 Bq kg⁻¹ (Sunam) to 413.27 Bq kg⁻¹ (Virk Khera) with overall mean values of 35 Bq kg⁻¹, 80 Bq kg⁻¹and 317 Bq kg⁻¹ respectively. The absorbed dose rate calculated from activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K ranges between 8.47 and 24.48, 35.68 and 92.38, and 8.74 and 17.11 nGy h⁻¹, respectively. The total absorbed dose in the study area ranges from 58.08 nGy h⁻¹ to 130.85 nGy h⁻¹ with an average value of 79.11 nGy h⁻¹. The calculated values of external hazard index (H_ex) for the soil samples of the study area range from 0.35 to 0.79. Since these values are lower than unity, therefore, according to the Radiation Protection 112 (European Commission. Radiation Protection 112 1999) report, soil from these regions is safe and can be used as a construction material without posing any significant radiological threat to population.     

Re-construction and updating our understanding on the global weapons tests 137Cs fallout

Global nuclear weapons tests fallout of 137Cs in the northern hemisphere has been documented in the UNSCEAR (United Nations Scientific Committee on the Effect of Atomic Radiation) reports. However, many questions have arisen during the past three to four decades; e.g. the water column inventory of 137Cs in the North Pacific Ocean was two to three time higher than the cumulative decay corrected fallout at the same latitude as stated in the UNSCEAR reports. Here we show more precise spatial distribution of global 137Cs fallout primarily on the basis of global measurements in rain, seawater and soil, as data from 10 degrees x 10 degrees grids. A typical feature of geographical distribution is that two high global 137Cs fallout areas exist in the northern hemisphere, where the highest 137Cs fallout was observed in the globe. These areas correspond to crossovers of areas where larger precipitation amounts were expected and where higher stratosphere-troposphere exchange was expected. Our new estimate of 765 +/- 79 PBq as global 137Cs fallout for the northern hemisphere is 1.4 times higher than that of 545 PBq in the UNSCEAR reports.     

Effects of Ageing and Microbial Component on Chemical Availability of 137Cs in a Long-term Experimental Site

A loamy soil contaminated with ¹³⁷CsCl 40 years ago was investigated by a sequential extraction technique to determine the effect of ageing on chemical availability of ¹³⁷Cs. The soil samples were sequentially extracted with H₂O, NH₄Ac, NH₂OH·HCl, H₂O₂, and HNO₃. Extractability of ¹³⁷Cs decreased in the order: HNO₃ > Residual > H₂O₂ > NH₄Ac > NH₂OH·HCl > H₂O. Only 0.94% in labile fractions (H₂O and NH₄Ac), while more than 96% was found in the strongly bound fraction (HNO₃ and residual). However, the activity percentage in labile fractions was increased to 1.34% after autoclaving treatment, while those in the other fractions did not significantly differ. This indicates that the microbial activity played a role in the ¹³⁷Cs retention. In the subsequent pot experiments with ryegrass and leek, specific activities in both plants were significantly higher in autoclaved soil than in non-autoclaved soil, and uptake of ¹³⁷Cs in the five cuts by ryegrass was 25% of the labile ¹³⁷Cs in the soil. In addition, a positive correlation was found between the amount of ¹³⁷Cs in labile fractions and that by plant uptake.     

The relationship of mineral and geochemical composition to artificial radionuclide partitioning in Yenisei river sediments downstream from Krasnoyarsk

Discharges from the Mining-and-Chemical Combine (MCC) of Rosatom, downstream from Krasnoyarsk, resulted in radioactive contamination of sediments of the River Yenisei. The concentration of artificial gamma-emitting radionuclides (¹³⁷Cs, ⁶⁰Co, ¹⁵²Eu, and ²⁴¹Am) was determined with the objective to analyze the migration processes leading to the transport of these radionuclides. The content of artificial radionuclides in the surface layers of the study area varied in wide ranges: ¹³⁷Cs—318–1,800 Bq/kg, ⁶⁰Co—87–720 Bq/kg, ¹⁵²Eu—12–287 Bq/kg and ²⁴¹Am—6–76 Bq/kg. There was a sequence of migration of radionuclides investigated in the surface layer of sediments that were collected in the near zone of influence of the MCC: ²⁴¹Am ≈ ¹⁵²Eu > ⁶⁰Co > ¹³⁷Cs. Radionuclide species have been found to be directly related to sediment structure and composition.     

Radiocaesium Activity Concentrations in Milk in the Republic of Croatia and Dose Assessment

Results of systematic measurements of radiocaesium activities in milk after the Chernobyl nuclear accident are summarized. ¹³⁷Cs fallout activity affects milk activity, the coefficient of correlation being 0.89. The ¹³⁷Cs activities in milk in Croatia are log-normally distributed, reflecting the exponential decrease of activity. After the Chernobyl nuclear accident the ¹³⁴Cs:¹³⁷ Cs activity ratio in milk was 0.5, and did not differ from that for other environmental samples. The dose due to radiocaesium ingestion by milk consumption was estimated for the Croatian population, the annual collective equivalent dose being approximately 205 manSv in 1986 and 1.5 manSv in 1994.     

Distribution of gamma-ray emitting radionuclides in the marine environment of the Burullus Lake: II. Bottom sediments

The sediment compartment has the ability to trap large amounts of radionuclides and to indicate the radiological impact of pollution. The present work shows the results obtained related to the concentrations of ¹³⁷Cs and natural radionuclides in sediment in the Burullus Lake, Egypt. The average values of ²²⁶Ra, ²³²Th, and ⁴⁰K in the bottom sediments collected from the east of the Burullus Lake ranged from 10.3 to 21.8 Bq/kg, from 11.9 to 34.4 Bq/kg, and from 268 to 401 Bq/kg, respectively. The study has shown that ⁴⁰K concentration is nearly uniform throughout the studied area while ²²⁶Ra and ²³²Th are more concentrated in the northeastern shore. Lake sediments showed contamination with ¹³⁷Cs (2.7–15.9 Bq/kg). The ¹³⁷Cs sediment activities indicated higher concentrations in the off-shore sites. Concentrations of all γ -ray emitting radionuclides except ⁴⁰K in water samples were below the detection limits. The ⁴⁰K sediment–water distribution coefficients of the near-shore samples were higher than the off-shore samples.     

Toxicodynamic modeling of 137Cs to estimate white-tailed deer background levels for the Department of Energy's Savannah River Site

The U.S. Department of Energy's (USDOE) Savannah River Site (SRS) is a former nuclear weapon material production and current research facility adjacent to the Savannah River in South Carolina, USA. The purpose of this study was to determine the background radiocesium (¹³⁷Cs) body burden (e.g., from global fallout) for white-tailed deer (Odocoileus virginianus) inhabiting the SRS. To differentiate what the background burden is for the SRS versus ¹³⁷Cs obtained from SRS nuclear activities, data were analyzed spatially, temporally and compared to other off-site hunting areas near the SRS. The specific objectives of this study were: to compare SRS and offsite deer herds based on time and space; to interpret comparisons based on how data were collected as well as the effect of environmental and anthropogenic influences; to determine what the ecological half-life/decay rate is for ¹³⁷Cs in the SRS deer herd; and to give a recommendation to what should be considered the background ¹³⁷Cs level in the SRS deer herd. Based on the available information and analyses, it is recommended that the determination of what is considered background for the SRS deer herd be derived from data collected from the SRS deer herd itself and not offsite collections for a variety of reasons. Offsite data show extreme variability most likely due to environmental factors such as soil type and land-use patterns (e.g., forest, agriculture, residential activities). This can be seen from results where samples from offsite military bases (Fort Jackson and Fort Stewart) without anthropogenic ¹³⁷Cs sources were much higher than both the SRS and a nearby (Sandhills) study site. Moreover, deer from private hunting grounds have the potential to be baited with corn, thus artificially lowering their ¹³⁷Cs body burdens compared to other free-ranging deer. Additionally, sample size for offsite collections were not robust enough to calculate a temporal decay curve with an upper confidence level to determine if the herds are following predicted radioactive decay rates like the SRS or if the variability is due to those points described above. Using mean yearly values, the ecological half-life for ¹³⁷Cs body burdens for SRS white-tailed deer was determined to be 28.79 years—very close to the 30.2 years physical half-life.     

Depth profiling of Pu, 241Am and 137Cs in soils from southern Belarus measured by ICP-MS and alpha and gamma spectrometry

The depth distribution of plutonium, americium, and 137Cs originating from the 1986 accident at the Chernobyl Nuclear Power Plant (NPP) was investigated in several soil profiles in the vicinity from Belarus. The vertical migration of transuranic elements in soils typical of the 30 km relocation area around Chernobyl NPP was studied using inductively coupled plasma mass spectrometry (ICP-MS), alpha spectrometry, and gamma spectrometry. Transuranic concentrations in upper soil layers ranged from 6 x 10(-12) g g(-1) to 6 x 10(-10) g g(-1) for plutonium and from 1.8 x 10(-13) g g(-1) to 1.6 x 10(-11) g g(-1) for americium. These concentrations correspond to specific activities of (239+240)Pu of 24-2400 Bq kg(-1) and specific activity of 241Am of 23-2000 Bq kg(-1), respectively. Transuranics in turf-podzol soil migrate slowly to the deeper soil layers, thus, 80-95%, of radionuclide inventories were present in the 0-3 cm intervals of turf-podzol soils collected in 1994. In peat-marsh soil migration processes occur more rapidly than in turf-podzol and the maximum concentrations are found beneath the soil surface (down to 3-6 cm). The depth distributions of Pu and Am are essentially identical for a given soil profile. (239+240)Pu/137Cs and 241Am/137Cs activity ratios vary by up to a factor of 5 at some sites while smaller variations in these ratios were observed at a site close to Chernobyl, suggesting that 137Cs is dominantly particle associated close to Chernobyl but volatile species of 137Cs are of relatively greater importance at the distant sites.     

Radioactive Contamination Control by Atmospheric Dispersion Assessment of Airborne Indicator Contaminants: Numerical Model Validation

In this work, a numerical model is proposed to estimate air concentration of released airborne radioactive contaminants ¹³¹I and ¹³⁷Cs. A Gaussian dispersion model is used to assess the atmospheric dispersion of radioactive contaminants released continuously from a nuclear power plant as a result of an accident. The model uses various input parameters such as source height, release rate, stability class, wind speed, and wind direction. The validation of the model was carried out by comparing its predicted values with published experimental data. The model was extensively tested by simulating several accidental situations. The main conclusion drawn from these tests is that for large downwind distances from the release point, the contaminant concentrations predicted by the model diverge drastically from measured data, while for short distances, the predicted values generally agree quite well with experimental data. The obtained activity concentrations range from 1.57?×?10² to 6.43?×?10³ Bq/m³ for ¹³¹I and from 3.18?×?10^?2 to 9.72?×?10² Bq/m³ for ¹³⁷Cs. The estimated standard deviation coefficients values range of 7.2 to 6847.7 m, and the maximum absolute error predicted by the model for these parameters was less than 5%.     

Anthropogenic plutonium in the North Jiangsu tidal flats of the Yellow Sea in China

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios were analyzed using a double-focusing SF-ICP-MS for sediment core samples obtained in 2007–2008 from the North Jiangsu tidal flats in the Yellow Sea in China. Particular attention was focused on the ²⁴⁰Pu/²³⁹Pu atom ratios in the sediment to identify the origins of Pu isotopes. The profiles of ^239+240Pu activities in the sediment cores are similar to those of the ¹³⁷Cs activities. The ²⁴⁰Pu/²³⁹Pu atom ratios in the tidal flats showed typical global fallout values, indicating that this area did not receive the possible early direct close-in fallout or oceanic current transported Pu from the Pacific Proving Grounds (PPG). If any, the contribution of the PPG source Pu to the total Pu inventory is negligible. This is different from the sediments in the Yangtze River estuary in the East China Sea, where the PPG source Pu contributed ca. 45 % to the total inventory. In addition, the observation of the global fallout origin Pu in the North Jiangsu tidal flats indicated that the nuclear power plant in the region was not causing any alteration/contamination to the ²⁴⁰Pu/²³⁹Pu atom ratios. The ^239+240Pu and ¹³⁷Cs activities/inventories in the sediment cores showed correlation to the mean clay sediment compositions (fine particles) in the tidal flats. Therefore, mud deposits are served as sinks for the anthropogenic radionuclides in the tidal flats and the Yellow Sea. Integrated with the previously reported spatial distributions of ^239+240Pu and ¹³⁷Cs activities in the surface sediments of the Yellow Sea, the mechanism of Pu transport with the ocean currents and the scavenging characteristics in the Yellow Sea were discussed.     

A Comparison of Aerial and Ground Level Measurements of 137Cs in the Marshall Islands

The purpose of this paper is to present and compare two independent sets of environmental gamma spectrometry measurements of¹³⁷ Cs collected nearly 14 years apart. One set of data was collected in 1978 by a contractor of the U.S. Department of Energy during an aerial radiological survey of the northern atolls of the Marshall Islands. That program used helicopter mounted sodium-iodide scintillation detectors; measurements were made from an altitude of 38 m. The second measurement program was conducted from early 1990 through late 1994 by the Republic of the Marshall Islands Government in a survey of the entire nation. This latter program used ground level in situ gamma spectrometry with high-purity germanium detectors. In this comparison, we highlight differences between the findings of the two studies and probable reasons for those differences, though we also discuss the effectiveness of the two techniques for monitoring the ionizing radiation environment. In the comparison of exposure rates from ¹³⁷Cs, fair agreement was noted after accounting for radioactive decay during the intervening years. Though the distributions were statistically different over their entire range, they were nearly identical above 1 R h^-1. There was considerable difference in the estimates of¹³⁷ Cs inventory; the difference was greater at low activity levels with the NaI measurements consistently larger than the in situ measurements. Reasons for this difference is attributed to three factors which differed between the two studies: (1) the assumed penetration of the cesium into the soil column, (2) the assumption of soil density, and (3) differences in the ability of the two different detector systems to reject interfering spectral contributions. Precise measurement of the lowest levels has implications for determining those atolls that exceeded the deposition of ¹³⁷Cs from global fallout. This issue is discussed in addition to a comparison of the findings from the two measurement programs.     

Radioactive fallout in the United States due to the Fukushima nuclear plant accident

The release of radioactivity into the atmosphere from the damaged Fukushima Daiichi nuclear power plant started on March 12th, 2011. Among the various radionuclides released, iodine -131 ((131)I) and cesium isotopes ((137)Cs and (134)Cs) were transported across the Pacific Ocean and reached the United States on 17-18 March 2011. Consequently, an elevated level of fission products (131)I, (132)I, (132)Te, (134)Cs and (137)Cs were detected in air, water, and milk samples collected across the United States between March 17 and April 4, 2011. The continuous monitoring of activities over a period of 25 days and spatial variations across more than 100 sampling locations in the United States made it possible to characterize the contaminated air masses. For the entire period, the highest detected activity values ranged from less than 1 m Bq m(-3) to 31 m Bq m(-3) for the particulate (131)I, and up to 96 m Bq m(-3) for the gaseous (131)I fraction.     

Plants as bio-monitors for Cs-137, Pu-238, Pu-239,240 and K-40 at the Savannah River Site

The Savannah River Site was constructed in South Carolina to produce plutonium (Pu) in the 1950s. Discharges associated with these now-ceased operations have contaminated large areas within the site, particularly streams associated with reactor cooling basins. Evaluating the exposure risk of contamination to an ecosystem requires methodologies that can assess the bioavailability of contaminants. Plants, as primary producers, represent an important mode of transfer of contaminants from soils and sediments into the food chain. The objective of this study was to identify local area plants for their ability to act as bio-monitors of radionuclides. The concentrations of cesium-137 ((137)Cs), potassium-40 ((40)K), (238)Pu and (239,240)Pu in plants and their associated soils were determined using γ and α spectrometry. The ratio of contamination concentration found in the plant relative to the soil was calculated to assess a concentration ratio (CR). The highest CR for (137)Cs was found in Pinus palustris needles (CR of 2.18). The correlation of soil and plant (137)Cs concentration was strong (0.76) and the R(2) (0.58) from the regression was significant (p = 0.006). This suggests the ability to predict the degree of (137)Cs contamination of a soil through analysis of the pine needles. The (238)Pu and (239,240)Pu concentrations were most elevated within the plant roots. Extremely high CR values were found in Sparganium americanum (bur-reed) roots with a value of 5.86 for (238)Pu and 5.66 for (239,240)Pu. The concentration of (40)K was measured as a known congener of (137)C. Comparing (40)K and (137)C concentrations in each plant revealed an inverse relationship for these radioisotopes. Correlating (40)K and (137)Cs was most effective in identifying plants that have a high affinity for (137)Cs uptake. The P. palustris and S. americanum proved to be particularly strong accumulators of all K congeners from the soil. Some species that were measured, warrant further investigation, are the carnivorous plant Utricularia inflata (bladderwort) and the emergent macrophyte Juncus effusus. For U. inflata, the levels of (137)Cs, (238)Pu, and (239,240)Pu (which were 3922, 8399, and 803 Bq kg(-1), respectively) in the leaves were extremely high. The highest (137)Cs concentration from the study was measured in the J. effusus root (5721 Bq kg(-1)).