Internal dose assessment of <Superscript>210</Superscript>Po using biokinetic modeling and urinary excretion measurement

The mysterious death of Mr. Alexander Litvinenko who was most possibly poisoned by Polonium-210 (²¹⁰Po) in November 2006 in London attracted the attention of the public to the kinetics, dosimetry and the risk of this high radiotoxic isotope in the human body. In the present paper, the urinary excretion of seven persons who were possibly exposed to traces of ²¹⁰Po was monitored. The values measured in the GSF Radioanalytical Laboratory are in the range of natural background concentration. To assess the effective dose received by those persons, the time-dependence of the organ equivalent dose and the effective dose after acute ingestion and inhalation of ²¹⁰Po were calculated using the biokinetic model for polonium (Po) recommended by the International Commission on Radiological Protection (ICRP) and the one recently published by Leggett and Eckerman (L&E). The daily urinary excretion to effective dose conversion factors for ingestion and inhalation were evaluated based on the ICRP and L&E models for members of the public. The ingestion (inhalation) effective dose per unit intake integrated over one day is 1.7 × 10⁻⁸ (1.4 × 10⁻⁷) Sv Bq⁻¹, 2.0 × 10⁻⁷ (9.6 × 10⁻⁷) Sv Bq⁻¹ over 10 days, 5.2 × 10⁻⁷ (2.0 × 10⁻⁶) Sv Bq⁻¹ over 30 days and 1.0 × 10⁻⁶ (3.0 × 10⁻⁶) Sv Bq⁻¹ over 100 days. The daily urinary excretions after acute ingestion (inhalation) of 1 Bq of ²¹⁰Po are 1.1 × 10⁻³ (1.0 × 10⁻⁴) on day 1, 2.0 × 10⁻³ (1.9 × 10⁻⁴) on day 10, 1.3 × 10⁻³ (1.7 × 10⁻⁴) on day 30 and 3.6 × 10⁻⁴ (8.3 × 10⁻⁵) Bq d⁻¹ on day 100, respectively. The resulting committed effective doses range from 2.1 × 10⁻³ to 1.7 × 10⁻² mSv by an assumption of ingestion and from 5.5 × 10⁻² to 4.5 × 10⁻¹ mSv by inhalation. For the case of Mr. Litvinenko, the mean organ absorbed dose as a function of time was calculated using both the above stated models. The red bone marrow, the kidneys and the liver were considered as the critical organs. Assuming a value of lethal absorbed dose of 5 Gy to the bone marrow, 6 Gy to the kidneys and 8 Gy to the liver, the amount of ²¹⁰Po which Mr. Litvinenko might have ingested is therefore estimated to range from 27 to 1,408 MBq, i.e 0.2–8.5 μg, depending on the modality of intake and on different assumptions about blood absorption.     

Reconstruction and forecast of doses due to ingestion of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr after the Chernobyl accident

The assessment doses due to ingestion of ¹³⁷Cs and ⁹⁰Sr for the population suffering from the Chernobyl accident was performed on the basis of the new mechanistic ecological model for assessment of radiological consequences of agricultural lands contamination (EMARC). The EMARC model allows estimation of internal doses based on ecological factors influencing the contamination of foodstuff, for the post-accidental years in the countries of the former Soviet Union. The EMARC model allows estimation of all quantities required in radiation hygiene practice. For example, the proposed analytical method may be used for both retrospective dose reconstruction and prospective estimates of annual dose and integrated “life-time” dose, for different age intervals. According to the EMARC model, estimated reference “life-time” doses for adults are between 7 and 269 μSv kBq⁻¹ m² for ¹³⁷Cs, and between 25 and 235 μSv kBq⁻¹ m² for ⁹⁰Sr. Maximal doses were estimated for persons who were 3, 9 and 11 years old, at the time of the accident and these doses exceed those for adults by a factors of 1, 5 for ⁹⁰Sr, and 1.4 for ¹³⁷Cs.     

<Superscript>131</Superscript>I age-dependent inhalation dose in Southern Poland from Fukushima accident

A general method for calculating doses absorbed from isotopes released in nuclear accidents is presented. As an example, this method was used to calculate doses for inhabitants of Southern Poland due to inhalation of ¹³¹I released due to the Fukushima nuclear plant accident. ¹³¹I activity measurements in the air of that region provided the basis for the study. The proposed model is based on a complex biokinetic model for iodine merging the Leggett model developed in 2010 with the human respiratory tract and gastrointestinal tract models recommended by the International Commission on Radiological Protection (ICRP). This model is described here, and it is demonstrated that resulting dose estimates are consistent with those obtained using the ICRP methodology. Using the developed model, total doses were calculated for six age groups of both genders, for gaseous and aerosol fractions alike. The committed effective dose, H ₅₀, for an adult man reached 16 nSv, which is lower than 0.001% of the background dose. The dose for the thyroid of an adult reached 0.33 μSv, which corresponds to circa 0.0007% of the dose to the population of Southern Poland after the Chernobyl nuclear plant accident.     

Biokinetics of <Superscript>90</Superscript>Sr after chronic ingestion in a juvenile and adult mouse model

The aim of our study was to define the biokinetics of ⁹⁰Sr after chronic contamination by ingestion using a juvenile and adult murine model. Animals ingested ⁹⁰Sr by drinking water containing 20 kBq l⁻¹ of ⁹⁰Sr. For the juvenile model, parents received ⁹⁰Sr before mating and their offspring were killed between birth and 20 weeks of ingestion. For the adult model, ⁹⁰Sr ingestion started at 9 weeks of age and they were killed after different ingestion periods up to 20 weeks. The body weight, food and water consumption of the animals were monitored on a weekly basis. Before killing and sampling of organs, animals were put in metabolic cages. ⁹⁰Sr in organs and excreta was determined by liquid scintillation β counting. Highest ⁹⁰Sr contents were found in bones and were generally higher in females than in males, and ⁹⁰Sr retention varied according to the skeletal sites. An accumulation of ⁹⁰Sr in the bones was observed over time for both models, with a plateau level at adult age for the juvenile model. The highest rate of ⁹⁰Sr accumulation in bones was observed in early life of offspring, i.e. before the age of 6 weeks. With the exception of the digestive tract, ⁹⁰Sr was below the detection limit in all other organs sampled. Overall, our results confirm that ⁹⁰Sr mainly accumulates in bones. Furthermore, our results indicate that there are gender- and age-dependent differences in the distribution of ⁹⁰Sr after low-dose chronic ingestion in the mouse model. These results provide the basis for future studies on possible non-cancerous effects during chronic, long-term exposure to ⁹⁰Sr through ingestion in a mouse model, especially on the immune and hematopoietic systems.     

Use of foliar Ca/Sr discrimination and <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and ⁸⁷Sr/⁸⁶Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the ⁸⁷Sr/⁸⁶Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios to trace Ca sources to plants.     

Activity concentrations of <Superscript>226</Superscript>Ra, <Superscript>228</Superscript>Th,and <Superscript>40</Superscript>K in different food crops from a high background radiation area in Bitsichi,Jos Plateau,Nigeria

One of the three goals of the United Nations for sustainable food security is to ensure that all people have access to sufficient, nutritionally adequate, and safe food. Decades of tin mining in the Bitsichi area of the Jos Plateau, Nigeria, have left a legacy of polluted water supplies, impoverished agricultural land, and soil containing abnormally high levels of naturally occurring radioactive elements. In order to ascertain the radiological food safety of the population, different crops that constitute the major food nutritive requirements were collected directly across farmlands in the area. The activity concentrations of ²²⁶Ra, ²²⁸Th, and ⁴⁰K were determined in the food and soil samples using γ-ray spectrometry. Additionally, in situ gamma dose rate measurements were performed on the farms using a pre-calibrated survey meter. The corresponding activity concentrations in the food crops ranged from below detection limit (BDL) to 684.5 Bq kg⁻¹ for ⁴⁰K, from BDL to 83.5 Bq kg⁻¹ for ²²⁶Ra, and from BDL to 89.8 Bq kg⁻¹ for ²²⁸Th. Activity concentrations of these radionuclides were found to be lower in cereals than in tubers and vegetables. As for the soil samples, activity concentrations of these radionuclides varied from BDL to 166.4 Bq kg⁻¹, from 10.9 to 470.6 Bq kg⁻¹, and from 122.7 to 2,189.5 Bq kg⁻¹ for ⁴⁰K, ²²⁶Ra, and ²²⁸Th, respectively. Average external gamma dose rates were found to vary across the farms from 0.50 ± 0.01 to 1.47 ± 0.04 μSv h⁻¹. Due to past mining activities, the soil radioactivity in the area has been modified and the concentration level of the investigated natural radionuclides in the food crops has also been enhanced. However, the values obtained suggest that the dose from intake of these radionuclides by the food crops is low and that harmful health effects are not expected.     

Measurement of activity concentrations of <Superscript>40</Superscript>K, <Superscript>226</Superscript>Ra and <Superscript>232</Superscript>Th for assessment of radiation hazards from soils of the southwestern region of Nigeria

Activity concentrations of the selected radionuclides ⁴⁰K, ²²⁶Ra and ²³²Th were measured in surface soil samples collected from 38 cities in the southwest region of Nigeria by means of gamma spectroscopy with a high-purity germanium detector. Measured activity concentration values of ⁴⁰K varied from 34.9 ± 4.4 to 1,358.6 ± 28.5 Bq kg⁻¹ (given on a dry mass (DM) basis) with a mean value of 286.5 ± 308.5 Bq kg⁻¹; that of ²²⁶Ra varied from 9.3 ± 3.7 to 198.1 ± 13.8 Bq kg⁻¹ with a mean value of 54.5 Bq kg⁻¹ and a standard deviation of 38.7 Bq kg⁻¹, while that of ²³²Th varied from 5.4 ± 1.1 to 502.0 ± 16.5 Bq kg⁻¹ with a mean value of 91.1 Bq kg⁻¹ and standard deviation of 100.9 Bq kg⁻¹. The mean activity concentration values obtained for ²²⁶Ra and ²³²Th are greater than the world average values reported by the United Nations Scientific Committee on Effects of Atomic Radiation for areas of normal background radiation. Radiological indices were estimated for the radiation/health hazards of the natural radioactivity of all soil samples. Estimated absorbed dose rates in air varied from 12.42 ± 2.25 to 451.33 ± 19.06 nGy h⁻¹, annual outdoor effective dose rates from 0.015 ± 0.003 to 0.554 ± 0.023 mSv year⁻¹, internal hazard index from 0.10 ± 0.03 to 3.02 ± 0.16, external hazard index from 0.07 ± 0.01 to 2.60 ± 0.11, representative level index from 0.19 ± 0.03 to 6.84 ± 0.29, activity index from 0.09 ± 0.02 to 3.42 ± 0.15, and radium equivalent activity from 26.95 ± 5.04 to 963.15 ± 41.87 Bq kg⁻¹. Only the mean value of the representative level index exceeds the limit for areas of normal background radiation. All other indices show mean values that are lower than the recommended limits.     

CD133<Superscript>+</Superscript>CD44<Superscript>+</Superscript> subgroups may be human small intestinal stem cells

The identification and separation of small intestinal epithelial stem cells are still on the preliminary stage. In this study, we planned to utilize immunohistochemistry, fluorescence-activated cell sorting (FACS) and RT-PCR to investigate the possibility of CD133 and CD44 as markers of human small intestinal epithelial stem cells. The expressions of CD133, CD44 and Lgr5 were studied by immunohistochemistry. Four subgroups of CD133⁺CD44⁺, CD133⁺CD44⁻, CD133⁻CD44⁺, CD133⁻CD44⁻ were sorted out through FACS and the expression level of Lgr5 gene was measured by RT-PCR and polyacrylamide gel electropheresis (PAGE) with sliver stained. Ten cases of samples were available for analyzing. By immunohistochemical staining, few cells with positive expressions of CD133, CD44 and Lgr5 were distributed in the bottom of crypts with the expression locations somewhat overlapped. The average percentage of CD133⁺CD44⁺ cells was 0.0580 ± 0.0403%, while the corresponding contents of CD133⁺CD44⁻ cells, CD133⁻CD44⁺ cells and CD133⁻CD44⁻ cells were 0.4000 ± 0.1225%, 0.7000 ± 0.2646% and 76.5600 ± 3.5529% respectively. Ten times of positive expressions of Lgr5 were detected in the CD133⁺CD44⁺ groups, while 9/10, 8/10 and 4/10 times for CD133⁺CD44⁻, CD133⁻CD44⁺ and CD133⁻CD44⁻ subgroups respectively. With the help of Quantityone 4.62 software, the densities of corresponding place to Lgr5 and reference gene were obtained. The density ratios of corresponding place to Lgr5 to reference gene were significant difference between subgroups (P < 0.001). By means of LSD method, the density ratios in CD133⁺CD44⁺ subgroups had statistical differences from the other subgroups (P < 0.05). We concluded CD133⁺CD44⁺ cells may be human small intestinal epithelial stem cells, which need further researches to confirm.     

Enhanced anti-tumor activity of interferon-alpha in SOCS1-deficient mice is mediated by CD4<Superscript>+</Superscript> and CD8<Superscript>+</Superscript> T cells

Interferon-alpha (IFN-α) is an immunomodulatory cytokine that is used clinically for the treatment of melanoma in the adjuvant setting. The cellular actions of IFN-α are regulated by the suppressors of cytokine signaling (SOCS) family of proteins. We hypothesized that the anti-tumor activity of exogenous IFN-α would be enhanced in SOCS1-deficient mice. SOCS1-deficient (SOCS1^−/−) or control (SOCS1^+/+) mice on an IFN-γ^−/− C57BL/6 background bearing intraperitoneal (i.p.) JB/MS murine melanoma cells were treated for 30 days with i.p. injections of IFN-A/D or PBS (vehicle). Log-rank Kaplan-Meier survival curves were used to evaluate survival. Tumor-bearing control SOCS1^+/+ mice receiving IFN-A/D had significantly enhanced survival versus PBS–treated mice (P = 0.0048). The anti-tumor effects of IFN-A/D therapy were significantly enhanced in tumor-bearing SOCS1^−/− mice; 75% of these mice survived tumor challenge, whereas PBS-treated SOCS1^−/− mice all died at 13-16 days (P = 0.00038). Antibody (Ab) depletion of CD8⁺ T cells abrogated the anti-tumor effects of IFN-A/D in SOCS1^−/− mice as compared with mice receiving a control antibody (P = 0.0021). CD4⁺ T-cell depletion from SOCS1^−/− mice also inhibited the effects of IFN-A/D (P = 0.0003). IFN-A/D did not alter expression of CD80 or CD86 on splenocytes of SOCS1^+/+ or SOCS1^−/− mice, or the proportion of T regulatory cells or myeloid-derived suppressor cells in SOCS1^+/+ or SOCS1^−/− mice. An analysis of T-cell function did reveal increased proliferation of SOCS1-deficient splenocytes at baseline and in response to mitogenic stimuli. These data suggest that modulation of SOCS1 function in T-cell subsets could enhance the anti-tumor effects of IFN-α in the setting of melanoma.     

Signaling Pathways in the Biphasic Effect of ANG II on Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> Exchanger in T84 Cells

The effect of ANG II on pH_i, [Ca²⁺]_i and cell volume was investigated in T84 cells, a cell line originated from colon epithelium, using the probes BCECF-AM, Fluo 4-AM and acridine orange, respectively. The recovery rate of pH_i via the Na⁺/H⁺ exchanger was examined in the first 2 min following the acidification of pH_i with a NH₄Cl pulse. In the control situation, the pH_i recovery rate was 0.118 ± 0.001 (n = 52) pH units/min and ANG II (10⁻¹² M or 10⁻⁹ M) increased this value (by 106% or 32%, respectively) but ANG II (10⁻⁷ M) decreased it to 47%. The control [Ca²⁺]_i was 99 ± 4 (n = 45) nM and ANG II increased this value in a dose-dependent manner. The ANG II effects on cell volume were minor and late and should not interfere in the measurements of pH_i recovery and [Ca²⁺]_i. To document the signaling pathways in the hormonal effects we used: Staurosporine (a PKC inhibitor), W13 (a calcium-dependent calmodulin antagonist), H89 (a PKA inhibitor) or Econazole (an inhibitor of cytochrome P450 epoxygenase). Our results indicate that the biphasic effect of ANG II on Na⁺/H⁺ exchanger is a cAMP-independent mechanism and is the result of: 1) stimulation of the exchanger by PKC signaling pathway activation (at 10⁻¹² – 10⁻⁷ M ANG II) and by increases of [Ca²⁺]_i in the lower range (at 10⁻¹² M ANG II) and 2) inhibition of the exchanger at high [Ca²⁺]_i levels (at 10⁻⁹ – 10⁻⁷ M ANG II) through cytochrome P450 epoxygenase-dependent metabolites of the arachidonic acid signaling pathway.     

Oxygen consumption rate and Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase activity in early developmental stages of the sea urchin <Emphasis Type="Italic">Paracentrotus lividus</Emphasis> Lam.

Changes in oxygen consumption rate and Na⁺/K⁺-ATPase activity during early development were studied in the sea urchin Paracentrotus lividus Lam. The oxygen consumption rate increased from 0.12 μmol O₂ mg protein⁻¹ h⁻¹ in unfertilized eggs to 0.38 μmol O₂ mg protein⁻¹ h⁻¹ 25 min after fertilization. Specific activity of the Na⁺/K⁺-ATPase was significantly stimulated after fertilization, ranging up to 1.07 μmol P_i h⁻¹ mg protein⁻¹ in the late blastula stage and slightly lower values in the early and late pluteus stages.     

Assessment of radiation exposure of murine rodents at the EURT territories

The study provides data on contemporary levels of radiation exposure of organs and tissues of murine rodents (several species of mice and voles) inhabiting the East-Ural Radioactive Trace. The estimation procedure involves the most advanced approach based on application of appropriate voxel phantom and biokinetic model. Input data for dose assessment are the results of measurements of skeletal ⁹⁰Sr activity concentration. Maximal internal dose to skeleton, accumulated during 45 days, is 303 mGy. Median internal dose rates on the last day before trapping were 0.83, 0.092 and 0.023 mGy/day for animals trapped at the sites with initial (1957) ⁹⁰Sr surface contamination >37 MBq/m², 18.5–37 MBq/m² and 0.074–18.5 MBq/m² respectively. Taking to account internal and external exposures, upper boundary of the ICRP Derived Consideration Reference Level (DCRL) is exceeded on the territory with maximal level of the initial ⁹⁰Sr surface contamination. On the territory with 18.5–37 MBq/m², whole body mean dose rates to murine rodents exceed the lower boundary of DCRL. On the areas with lower level of surface contamination, even the 90-th percentile of dose rate is below the DCRL.     

Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> exchange activity in the alkaliphile halotolerant cyanobacterium <Emphasis Type="Italic">Aphanothece halophytica</Emphasis>

The activity of Na⁺/H⁺ exchanger to remove toxic Na⁺ is important for growth of organisms under high salinity. In this study, the halotolerant cyanobacterium Aphanothece halophytica was shown to possess Na⁺/H⁺ exchange activity since exogenously added Na⁺ could dissipate a pre-formed pH gradient, and decrease extracellular pH. Kinetic analysis yielded apparent K _m (Na⁺) and V _max of 20.7 ± 3.1 mM and 3,333 ± 370 nmol H⁺ min⁻¹ mg⁻¹, respectively. For cells grown under salt-stress condition, the apparent K _m (Na⁺) and V _max was 18.3 ± 3.5 mM and 3,703 ± 350 nmol H⁺ min⁻¹ mg⁻¹, respectively. Three cations with decreasing efficiency namely Li⁺, Ca²⁺, and K⁺ were also able to dissipate pH gradient. Only marginal exchange activity was observed for Mg²⁺. The exchange activity was strongly inhibited by Na⁺-gradient dissipators, monensin, and sodium ionophore as well as by CCCP, a protonophore. A. halophytica showed high Na⁺/H⁺ exchange activity at neutral and alkaline pH up to pH 10. Cells grown at pH 7.6 under high salinity exhibited higher Na⁺/H⁺ exchange activity than those grown under low salinity during 15 days of growth suggesting a role of Na⁺/H⁺ exchanger for salt tolerance in A. halophytica. Cells grown at alkaline pH of 9.0 also exhibited a progressive increase of Na⁺/H⁺ exchange activity during 15 days of growth.     

Metagenome Cloning and Functional Analysis of Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> Antiporter Genes from Keke Salt Lake in China

Na⁺/H⁺ antiporters are ubiquitous membrane proteins and play a central role in cell homeostasis including pH regulation, osmoregulation, and Na⁺/Li⁺ tolerance in bacteria. The microbial communities in extremely hypersaline soil are an important resource for isolating Na⁺/H⁺ antiporter genes. A metagenomic library containing 35,700 clones was constructed by using genomic DNA obtained from the hypersaline soil samples of Keke Salt Lake in Northwest of China. Two Na⁺/H⁺ antiporters, K1-NhaD, and K2-NhaD belonging to NhaD family, were screened and cloned from this metagenome by complementing the triple mutant Escherichia coli strain KNabc (nhaA ⁻ , nhaB ⁻ , chaA ⁻) in medium containing 0.2 M NaCl. K1-NhaD and K2-NhaD have 75.5% identity at the predicted amino acid sequence. K1-NhaD has 78% identity with Na⁺/H⁺ antiporter NhaD from Halomonas elongate at the predicted amino acid sequence. The predicted K1-NhaD is a 53.5 kDa protein (487 amino acids) with 13 transmembrane helices. K2-NhaD has 73% identity with Alkalimonas amylolytica NhaD. The predicted K2-NhaD is a 55 kDa protein (495 amino acids) with 12 transmembrane helices. Both K1-NhaD and K2-NhaD could make the triple mutant E. coli KNabc (nhaA ⁻ , nhaB ⁻ , chaA⁻) grow in the LBK medium containing 0.2–0.6 M Na⁺ or with 0.05–0.4 M Li⁺. Everted membrane vesicles prepared from E. coli KNabc cells carrying K1-NhaD or K2-NhaD exhibited Na⁺/H⁺ and Li⁺/H⁺ antiporter activities which were pH-dependent with the highest activity at pH 9.5. Little K⁺/H⁺ antiporter activity was also detected in vesicles form E. coli KNabc carrying K1-NhaD or K2-NhaD.     

Natural variation in <Superscript>210</Superscript>Po and <Superscript>210</Superscript>Pb activity concentrations in the urine of Finnish population groups

A study to determine activity concentrations of ²¹⁰Pb and ²¹⁰Po in the urine of certain Finnish population groups was conducted, to investigate the variation in natural background level of urinary excretion. The study participants were divided into three groups mainly based on their diet. The first group comprised recreational fishermen and the second group represented people consuming more reindeer meat than an average Finn, while people using drinking water with very high activity concentrations of ²¹⁰Po were selected for the third group. The fourth group was a control group. The mean urinary excretion of ²¹⁰Po in groups 1 and 2 was 73 and 100 mBq d⁻¹, respectively. These values were higher than the value of the control group (20 mBq d⁻¹) and the mean values reported in the literature. The mean daily urinary excretion of ²¹⁰Pb in groups 1 and 2, 70 and 52 mBq d⁻¹, was also slightly higher than that in the control group (32 mBq d⁻¹). In contrast, the excretion rates of both ²¹⁰Po and ²¹⁰Pb for the members of group 3 were one to two orders of magnitude higher than those reported in the literature. This was clearly due to the elevated levels of natural radionuclides in their drinking water. The present study demonstrates the importance of possessing good knowledge of the background levels, in order to allow the determination of the additional exposure due, for example, to the malevolent use of radiation.     

The saturation of N cycling in Central Plains streams: <Superscript>15</Superscript>N experiments across a broad gradient of nitrate concentrations

We conducted ¹⁵NO₃⁻ stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed to measure nitrate (NO₃⁻) cycling dynamics. Mean ambient NO₃⁻ concentrations of the streams ranged from 0.9 to 21,000 μg l⁻¹ NO₃⁻–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which stream biota utilized available NO₃⁻-decreased along the gradient of increasing NO₃⁻. Observed functional relationships of biological N transformations (uptake and nitrification) with NO₃⁻ concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient of NO₃⁻ concentrations, but only accounted for ∼1% of total NO₃⁻ uptake. On average, 20% of stream water NO₃⁻ was lost to denitrification per km, but the percentage removed in most streams was <5% km⁻¹. Although the rate of cycling was greater in streams with larger NO₃⁻ concentrations, the relative proportion of NO₃⁻ retained per unit length of stream decreased as NO₃⁻ concentration increased. Due to the rapid rate of NO₃⁻ turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove N through denitrification is highly variable.     

Monte Carlo-based calculation of imaging plate response to <Superscript>90</Superscript>Sr in teeth: experimental validation of the required correction on sample thickness

Recently, a numerical method was proposed to correct the imaging plate (IP) response to ⁹⁰Sr concentration in tooth samples, depending on the sample thickness. This is important to quantify any ⁹⁰Sr concentration in teeth, which in turn is necessary to determine any ⁹⁰Sr incorporation of a person retrospectively. Although the final goal will be to evaluate the (inhomogeneous) spatial distribution of ⁹⁰Sr inside tooth samples precisely, the present study was restricted—as a first step—to the evaluation of ⁹⁰Sr in teeth assuming a uniform ⁹⁰Sr distribution. A numerical method proposed earlier was validated experimentally in the present study by measuring the IP response to standard sources of various thicknesses and ⁹⁰Sr concentrations. For comparison, the energy deposition of the β-rays emitted by ⁹⁰Sr in the IP—which is considered to be proportional to the IP luminescence signal—was calculated for the various sample thicknesses involved, by means of the MCNP-4C code. As a result, the measured IP response could be reproduced by the calculations within the uncertainties, depending on the thickness of the standard sources. Thus, the validity of the proposed numerical method to correct the IP response for sample thickness has successfully been demonstrated.     

Foliar and fungal <Superscript>15</Superscript> N:<Superscript>14</Superscript> N ratios reflect development of mycorrhizae and nitrogen supply during primary succession: testing analytical models

Nitrogen isotopes (¹⁵N/¹⁴N ratios, expressed as δ¹⁵N values) are useful markers of the mycorrhizal role in plant nitrogen supply because discrimination against ¹⁵N during creation of transfer compounds within mycorrhizal fungi decreases the ¹⁵N/¹⁴N in plants (low δ¹⁵N) and increases the ¹⁵N/¹⁴N of the fungi (high δ¹⁵N). Analytical models of ¹⁵N distribution would be helpful in interpreting δ¹⁵N patterns in fungi and plants. To compare different analytical models, we measured nitrogen isotope patterns in soils, saprotrophic fungi, ectomycorrhizal fungi, and plants with different mycorrhizal habits on a glacier foreland exposed during the last 100 years of glacial retreat and on adjacent non-glaciated terrain. Since plants during early primary succession may have only limited access to propagules of mycorrhizal fungi, we hypothesized that mycorrhizal plants would initially be similar to nonmycorrhizal plants in δ¹⁵N and then decrease, if mycorrhizal colonization were an important factor influencing plant δ¹⁵N. As hypothesized, plants with different mycorrhizal habits initially showed similar δ¹⁵N values (−4 to −6‰ relative to the standard of atmospheric N₂ at 0‰), corresponding to low mycorrhizal colonization in all plant species and an absence of ectomycorrhizal sporocarps. In later successional stages where ectomycorrhizal sporocarps were present, most ectomycorrhizal and ericoid mycorrhizal plants declined by 5–6‰ in δ¹⁵N, suggesting transfer of ¹⁵N-depleted N from fungi to plants. The values recorded (−8 to −11‰) are among the lowest yet observed in vascular plants. In contrast, the δ¹⁵N of nonmycorrhizal plants and arbuscular mycorrhizal plants declined only slightly or not at all. On the forefront, most ectomycorrhizal and saprotrophic fungi were similar in δ¹⁵N (−1 to −3‰), but the host-specific ectomycorrhizal fungus Cortinarius tenebricus had values of up to 7‰. Plants, fungi and soil were at least 4‰ higher in δ¹⁵N from the mature site than in recently exposed sites. On both the forefront and the mature site, host-specific ectomycorrhizal fungi had higher δ¹⁵N values than ectomycorrhizal fungi with a broad host range. From these isotopic patterns, we conclude:(1) large enrichments in ¹⁵N of many ectomycorrhizal fungi relative to co-occurring ectomycorrhizal plants are best explained by treating the plant-fungal-soil system as a closed system with a discrimination against ¹⁵N of 8–10‰ during transfer from fungi to plants, (2) based on models of ¹⁵N mass balance, ericoid and ectomycorrhizal fungi retain up to two-thirds of the N in the plant-mycorrhizal system under the N-limited conditions at forefront sites, (3) sporocarps are probably enriched in ¹⁵N by an additional 3‰ relative to available nitrogen, and (4) host-specific ectomycorrhizal fungi may transfer more N to plant hosts than non-host-specific ectomycorrhizal fungi. Our study confirms that nitrogen isotopes are a powerful tool for probing nitrogen dynamics between mycorrhizal fungi and associated plants.     

Foliar <Superscript>15</Superscript>N natural abundance indicates phosphorus limitation of bog species

Foliar δ¹⁵N, %N and %P in the dominant woody and herbaceous species across nutrient gradients in New Zealand restiad (family Restionaceae) raised bogs revealed marked differences in plant δ¹⁵N correlations with P. The two heath shrubs, Leptospermum scoparium (Myrtaceae) and Dracophyllum scoparium (Epacridaceae), showed considerable isotopic variation (−2.03 to −15.55‰, and −0.39 to −12.06‰, respectively) across the bogs, with foliar δ¹⁵N strongly and positively correlated with P concentrations in foliage and peat, and negatively correlated with foliar N:P ratios. For L. scoparium, the isotopic gradient was not linked to ectomycorrhizal (ECM) fractionation as ECMs occurred only on higher nutrient marginal peats where ¹⁵N depletion was least. In strong contrast, restiad species (Empodisma minus Sporadanthus ferrugineus, S. traversii) showed little isotopic variation across the same nutrient gradients. Empodisma minus and S. traversii had δ¹⁵N levels consistently around 0‰ (means of −0.12‰ and +0.15‰ respectively), and S. ferrugineus, which co-habited with E. minus, was more depleted (mean −4.97‰). The isotopic differences between heath shrubs and restiads were similar in floristically dissimilar bogs and may be linked to contrasting nutrient demands, acquisition mechanisms, and root morphology. Leptospermum scoparium shrubs on low nutrient peats were stunted, with low tissue P concentrations, and high N:P ratios, suggesting they were P-limited, which was probably exacerbated by markedly reduced mycorrhizal colonisations. The coupling of δ¹⁵N depletion and %P in heath shrubs suggests that N fractionation is promoted by P limitation. In contrast, the constancy in δ¹⁵N of the restiad species through the N and P gradients suggests that these are not suffering from P limitation.     

Plasma free amino acid kinetics in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) using a bolus injection of <Superscript>15</Superscript>N-labeled amino acids

To gain insight into the metabolic design of the amino acid carrier systems in fish, we injected a bolus of ¹⁵N amino acids into the dorsal aorta in mature rainbow trout (Oncorhynchus mykiss). The plasma kinetic parameters including concentration, pool size, rate of disappearance (R _d), half-life and turnover rate were determined for 15 amino acids. When corrected for metabolic rate, the R _d values obtained for trout for most amino acids were largely comparable to human values, with the exception of glutamine (which was lower) and threonine (which was higher). R _d values ranged from 0.9 μmol 100 g⁻¹ h⁻¹ (lysine) to 22.1 μmol 100 g⁻¹ h⁻¹ (threonine) with most values falling between 2 and 6 μmol 100 g⁻¹ h⁻¹. There was a significant correlation between R _d and the molar proportion of amino acids in rainbow trout whole body protein hydrolysate. Other kinetic parameters did not correlate significantly with whole body amino acid composition. This indicates that an important design feature of the plasma-free amino acids system involves proportional delivery of amino acids to tissues for protein synthesis.