Levels of naturally occurring radioisotopes in local and imported bottled drinking water available in Québec City, Canada

Consumption of local and imported bottled water in Canada has greatly increased during the past three decades. While the presence of natural radioactivity is often overlooked when dealing with the water quality of these bottled products, it could contribute substantially to the uptake of radionuclides especially when sourced from regions with higher radioactivity levels compared to where it is consumed. In this study, the activity of several naturally occurring radionuclides (i.e., 210Po, 226,228Ra, 230,232Th, 234,235,238U) were measured in bottled water available in Québec, Canada after sample pretreatment and analysis by either radiometric or mass spectrometry approaches. 230,232Th and 228Ra concentrations were below minimum detectable activity levels in all samples tested. Analytical results for 234U, 235U, 238U, and 226Ra showed concentrations that ranged from 0.38 to 115 mBq/L, (2.2-313) x 10-2 mBq/L, 0.48-58.4 mBq/L, and 1.1-550 mBq/L, respectively. 210Po was detected in only 5 samples and its activity ranged from 2 to 26 mBq/L. To determine variability in activity within brands, the same brands of bottled water were purchased during two consecutive years and analyzed. The possible radiological impact of the consumption of these types of water was assessed based on different drinking habit scenarios. Some of the imported water brands showed higher activity concentrations than local sources or tap water, suggesting that individuals drinking predominantly imported bottled water would receive a higher radiation dose than those who drink mainly local water.

Dose and Dose Rate-Dependent Effects of Low-Dose Irradiation on Inflammatory Parameters in ApoE-Deficient and Wild Type Mice

Anti-inflammatory low-dose therapy is well established, whereas the immunomodulatory impact of doses below 0.1 Gy is much less clear. In this study, we investigated dose, dose rate and time-dependent effects in a dose range of 0.005 to 2 Gy on immune parameters after whole body irradiation (IR) using a pro-inflammatory (ApoE-/-) and a wild type mouse model. Long-term effects on spleen function (proliferation, monocyte expression) were analyzed 3 months, and short-term effects on immune plasma parameters (IL6, IL10, IL12p70, KC, MCP1, INFγ, TGFβ, fibrinogen, sICAM, sVCAM, sE-selectin/CD62) were analyzed 1, 7 and 28 days after Co60 γ-irradiation (IR) at low dose rate (LDR, 0.001 Gy/day) and at high dose rate (HDR). In vitro measurements of murine monocyte (WEHI-274.1) adhesion and cytokine release (KC, MCP1, IL6, TGFβ) after low-dose IR (150 kV X-ray unit) of murine endothelial cell (EC) lines (H5V, mlEND1, bEND3) supplement the data. RT-PCR revealed significant reduction of Ki67 and CD68 expression in the spleen of ApoE-/- mice after 0.025 to 2 Gy exposure at HDR, but only after 2 Gy at LDR. Plasma levels in wild type mice, showed non-linear time-dependent induction of proinflammatory cytokines and reduction of TGFβ at doses as low as 0.005 Gy at both dose rates, whereas sICAM and fibrinogen levels changed in a dose rate-specific manner. In ApoE-/- mice, levels of sICAM increased and fibrinogen decreased at both dose rates, whereas TGFβ increased mainly at HDR. Non-irradiated plasma samples revealed significant age-related enhancement of cytokines and adhesion molecules except for sICAM. In vitro data indicate that endothelial cells may contribute to systemic IR effects and confirm changes of adhesion properties suggested by altered sICAM plasma levels. The differential immunomodulatory effects shown here provide insights in inflammatory changes occurring at doses far below standard anti-inflammatory therapy and are of particular importance after diagnostic and chronic environmental exposures.

Relative Biological Effectiveness and Non-Poissonian Distribution of Dicentric Chromosome Aberrations following Californium-252 Neutron Exposures of Human Peripheral Blood Lymphocytes

Cells exposed to fast neutrons often exhibit a non-Poisson distribution of chromosome aberrations due to the high ionization density of the secondary reaction products. However, it is unknown whether lymphocytes exposed to californium-252 (252Cf) spectrum neutrons, of mean energy 2.1 MeV, demonstrate this same dispersion effect at low doses. Furthermore, there is no consensus regarding the relative biological effectiveness (RBE) of 252Cf neutrons. Dicentric and ring chromosome formations were assessed in human peripheral blood lymphocytes irradiated at doses of 12-135 mGy. The number of aberrations observed were tested for adherence to a Poisson distribution and the maximum low-dose relative biological effectiveness (RBEM) was also assessed. When 252Cf-irradiated lymphocytes were examined along with previously published cesium-137 (137Cs) data, RBEM values of 15.0 ± 2.2 and 25.7 ± 3.8 were found for the neutron-plus-photon and neutron-only dose components, respectively. Four of the five dose points were found to exhibit the expected, or close to the expected non-Poisson over-dispersion of aberrations. Thus, even at low doses of 252Cf fast neutrons, when sufficient lymphocyte nuclei are scored, chromosome aberration clustering can be observed.

The bioavailability of ingested 26Al-labelled aluminium and aluminium compounds in the rat

The fractional uptake of ingested aluminium and aluminium compounds (aluminium citrate, aluminium nitrate, aluminium chloride, aluminium sulphate, aluminium hydroxide, aluminium oxide, aluminium metal, powdered aluminium pot electrolyte, acidic sodium aluminium phosphate (SALP), basic sodium aluminium phosphate (Kasal), sodium aluminium silicate and FD&C red 40 aluminium lake) from the gastro-intestinal tract of adult female rats was measured. This was determined by comparing retained body burden of 26Al at seven days post-admistration of an i.v. injection of 26Al-labelled aluminium citrate with that retained following the gastric admistration of 26Al-labelled test compounds as either solutions or suspended solid. The calculated percentage uptake of 26Al for all the aluminium solutions was similar: aluminium citrate 0.08%, aluminium chloride 0.05%, aluminium nitrate 0.05% and aluminium sulphate 0.21%. The uptake of 26Al administered as insoluble particulates was lower: 0.03% for aluminium hydroxide; 0.02% for aluminium oxide; 0.04% for powdered pot electrolyte; 0.12% for sodium aluminium silicate; and 0.09% for FD&C red 40 aluminium lake. For aluminium metal, SALP and Kasal the amount of 26Al present in the rats was insufficient to determine uptake and was less than 0.03%. The results produced for aluminium citrate, aluminium hydroxide and aluminium sulphate are close to those published for man.

Relative Biological Effectiveness and Non-Poissonian Distribution of Dicentric Chromosome Aberrations after Californium-252 Neutron Exposures of Human Peripheral Blood Lymphocytes

Cells exposed to fast neutrons often exhibit a non-Poisson distribution of chromosome aberrations due to the high ionization density of the secondary reaction products. However, it is unknown whether lymphocytes exposed to californium-252 (252Cf) spectrum neutrons, of mean energy 2.1 MeV, demonstrate this same dispersion effect at low doses. Furthermore, there is no consensus regarding the relative biological effectiveness (RBE) of 252Cf neutrons. Dicentric and ring chromosome formation was assessed in human peripheral blood lymphocytes irradiated at doses of 12-135 mGy. The number of aberrations observed were tested for adherence to a Poisson distribution and the maximum low-dose relative biological effectiveness (RBEM) was also assessed. When 252Cf-irradiated lymphocytes were examined along with previously published cesium-137 (137Cs) data, RBEM values of 15.0 ± 2.2 and 25.7 ± 3.8 were found for the neutron-plus-photon and neutron-only dose components, respectively. Four of the five dose points were found to exhibit the expected, or close to the expected non-Poisson over-dispersion of aberrations. Thus, even at low doses of 252Cf fast neutrons, when enough lymphocyte nuclei are scored, chromosome aberration clustering can be observed.

Administration of lower doses of radium-224 to ankylosing spondylitis patients results in no evidence of significant overall detriment

The use of low doses of radium-224 (224Ra) chloride for the treatment of ankylosing spondylitis was stopped following the discovery that patients treated with it had a higher than control incidence of leukaemia and other cancers. This was so even though the treatment resulted in decreased pain and increased mobility-both of which are associated with decreased mortality. It was decided to re-analyze the epidemiological data looking at all causes of death. The risk of leukaemia, solid cancer, death from non-cancer causes and from all causes in a study populations of men that received either the typical dose of 5.6 to 11.1 MBq of 224Ra, any dose of 224Ra or no radium were compared using the Cox proportional hazard model. For patients that received the typical dose of 224Ra agreed with the excess cancer was similar to that reported in previous studies. In contrast, these patients were less likely to die from non-cancer diseases and from all causes of death than the control patients. No excess mortality was also found in the population of all males that received the radionuclide. It is concluded that 224Ra treatment administered at low doses to patients with ankylosing spondylitis did not impact mortality from all causes. The study demonstrates the need to consider all causes of death and longevity when assessing health impacts following irradiation.

A Nontarget Mechanism to Explain Carcinogenesis Following α-Irradiation

This commentary highlights the published data on the metabolic processes that lead to the development of cancer following intakes of asbestos and chemical agents. Following exposure to both, the key initiating event is cell injury leading to cell death that may further lead to inflammation, fibrosis, and cancer. Since α-particle transits also kill cells, it is suggested that cell death and inflammation will also trigger carcinogenesis within tissues irradiated by these particles. Such an explanation would be consistent with the inflammation and fibrosis seen in tumor-bearing tissues irradiated by radon-222, radium-226, thorium-232, plutonium-239, and other α-emitting radionuclides. It would also provide an explanation for dose-related changes in latency and in the similar dose-responses for the same tissue in differently sized species.

In vivo animal studies help achieve international consensus on standards and guidelines for health risk estimates for chronic exposure to low levels of tritium in drinking water

Existing and future nuclear fusion technologies involve the production and use of large quantities of tritium, a highly volatile, but low toxicity beta-emitting isotope of hydrogen. Tritium has received international attention because of public and scientific concerns over its release to the environment and the potential health impact of its internalization. This article provides a brief summary of the current state of knowledge of both the biological and regulatory aspects of tritium exposure; it also explores the gaps in this knowledge and provides recommendations on the best ways forward for improving our understanding of the health effects of low-level exposure to it. Linking health effects specifically to tritium exposure is challenging in epidemiological studies due to high uncertainty in tritium dosimetry and often suboptimal cohort sizes. We therefore argued that limits for tritium in drinking water should be based on evidence derived from controlled in vivo animal tritium toxicity studies that use realistically low levels of tritium. This article presents one such mouse study, undertaken within an international collaboration, and discusses the implications of its main findings, such as the similarity of the biokinetics of tritiated water (HTO) and organically bound tritium (OBT) and the higher biological effectiveness of OBT. This discussion is consistent with the position expressed in this article that in vivo animal tritium toxicity studies carried out within large, multi-partner collaborations allow evaluation of a great variety of health-related endpoints and essential to the development of international consensus on the regulation of tritium levels in the environment. Environ. Mol. Mutagen. 59:586-594, 2018. © 2018 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Tritium ( 3 H) Retention In Mice: Administered As HTO, DTO or as 3 H-Labeled Amino-Acids

The objective of this study was to compare the biokinetics of injected H-labeled light (HTO) and heavy (DTO) water in CBA/CaJ mice and to compare the organ distribution and/or body content of H administered by chronic ingestion for 1 mo to C57Bl/6J mice, as either H-labeled water or H-labeled amino acids (glycine, alanine and proline). HTO and DTO were administered to CBA/CaJ mice by single intraperitoneal injection and body retention was determined for up to 384 h post-injection. Tritium-labeled water or H-labeled amino acids were given to C57Bl/6J mice ad libitum for 30 d in drinking water. Body content and organ distribution of H during the period of administration and subsequent to administration was determined by liquid scintillation counting. No differences were found between the biokinetics of HTO and DTO, indicating that data generated using HTO can be used to help assess the consequences of H releases from heavy water reactors. The results for H-water showed that the concentration of radionuclide in the mice reached a peak after about 10 d and dropped rapidly after the cessation of H administration. The maximum concentration reached was only 50% of that in the water consumed, indicating that mice receive a significant fraction of their water from respiration. Contrary to the findings of others, the pattern of H retention following the administration of a cocktail of the labeled amino acids was very little different from that found for the water. This is consistent with the suggestion that most of the ingested amino acids were rapidly metabolized, releasing water and carbon dioxide.

In vivo neutron activation study of the short-term kinetic behaviour of sodium and chlorine in the human hand

The time-dependent behaviour of sodium and chlorine was studied as a spinoff from a study of aluminum in the hand of subjects suffering from Alzheimer's disease and a control group, involving 15 Alzheimer's and 16 control subjects with an age range of 63-89 years. This was achieved using the in vivo neutron activation analysis system developed at McMaster University for the non-invasive measurement of aluminum, where a subject's hand is placed in a beam of accelerator-based thermalized neutrons, which activates elements by neutron capture. Following irradiation, the subject's hand is placed in a detection system comprising 9 NaI(Tl) detectors arranged in a 4π geometry to measure activated elements. The redistribution half-lives of the activation products ²⁴Na and ³⁸Cl from the hand were determined after correction for the physical half-life, by means of sequential analysis of the residual activity in the hand. The kinetic behaviours of sodium and chlorine were best characterized by an exponential function corresponding to the rapidly exchangeable pool. The mean redistribution half-lives from the hand for sodium and chlorine in the control subjects were 40.5  ±  17.4 min and 24.2  ±  8.5 min, respectively. For Alzheimer's disease subjects the mean redistribution half-lives were 58.2  ±  36.1 min for sodium and 33.6  ±  16.7 min for chlorine. There was no significant difference in chlorine and sodium redistribution half-lives between the Alzheimer's disease and control group subjects. These results are promising, given that the irradiation and counting protocol were optimized for the aluminum study, rendering them suboptimal for analyzing other elements and their rate of change with time. Further improvements include optimizing the irradiation protocol, longer counting times, and measuring the activity in the un-irradiated hand in various time intervals following irradiation.

Evaluation of Apoptosis with 99mTc-rhAnnexin V-128 and Inflammation with 18F-FDG in a Low-Dose Irradiation Model of Atherosclerosis in Apolipoprotein E-Deficient Mice

Low-dose radiation in apolipoprotein E-deficient (ApoE^-/-) mice has a protective effect with less subsequent atherosclerosis. Inflammation and apoptosis play major roles in the development of atherosclerosis. We evaluated the temporal pattern of the development of histologic atherosclerosis, inflammation with ¹⁸F-FDG, and apoptosis with ^99mTc-rhAnnexin V-128 at 3 time points.

METHODS

ApoE^-/- mice were fed a high-fat diet, exposed to low-dose ⁶⁰Co γ-radiation of 25 mGy at 2 mo of age, and evaluated within 1 wk (2-mo group), 1 mo (3-mo group), and 2 mo (4-mo group) from the time of radiation. Mice were divided into 3 subgroups and each received ¹⁸F-FDG, ^99mTc-rhAnnexin V-128, or no radiotracer for autoradiography. Mice underwent euthanasia and aortic root dissection. The extent of atherosclerosis was determined by en face and Oil red O imaging. Aortic arch inflammation (¹⁸F-FDG) and apoptosis (^99mTc-rhAnnexin V-128) were determined with digital autoradiography. Aortic sinus sections were stained with Sudan IV for assessment of lesion area and stage, antiCD68 antibody for inflammation and anti-cleaved-caspase 3 antibody for apoptosis.

RESULTS

The extent of aortic atherosclerosis increased from 2 to 3 mo and from 3 to 4 mo. Inflammation (CD68) decreased and apoptosis (anti-cleaved-caspase 3 antibody) increased in aortic sinus slices measured as percentage of lesion by 4 mo. With increasing lesion stage, lesion inflammation decreased and lesion apoptosis increased. Aortic arch inflammation (¹⁸F-FDG uptake) did not differ over time and did not correlate with average lesion stage. However, aortic arch apoptosis (^99mTc-rhAnnexin V-128) increased significantly by 4 mo and correlated with average lesion stage. There were no differences between the treatment subgroups (¹⁸F-FDG, ^99mTc-rhAnnexin V-128, or no radiotracer).

CONCLUSION

The temporal pattern of development of inflammation and apoptosis differ during the development of atherosclerosis in ApoE^-/- mice treated with low-dose radiation. Advanced lesions are characterized by increased apoptosis and either less or similar amounts of inflammation, shown on immunohistochemistry and autoradiography. Treatment with radiotracers had no significant effects on extent of atherosclerosis, inflammation, or apoptosis.

Low-dose irradiation affects expression of inflammatory markers in the heart of ApoE -/- mice

Epidemiological studies indicate long-term risks of ionizing radiation on the heart, even at moderate doses. In this study, we investigated the inflammatory, thrombotic and fibrotic late responses of the heart after low-dose irradiation (IR) with specific emphasize on the dose rate. Hypercholesterolemic ApoE-deficient mice were sacrificed 3 and 6 months after total body irradiation (TBI) with 0.025, 0.05, 0.1, 0.5 or 2 Gy at low (1 mGy/min) or high dose rate (150 mGy/min). The expression of inflammatory and thrombotic markers was quantified in frozen heart sections (CD31, E-selectin, thrombomodulin, ICAM-1, VCAM-1, collagen IV, Thy-1, and CD45) and in plasma samples (IL6, KC, MCP-1, TNFα, INFγ, IL-1β, TGFβ, INFγ, IL-10, sICAM-1, sE-selectin, sVCAM-1 and fibrinogen) by fluorescence analysis and ELISA. We found that even very low irradiation doses induced adaptive late responses, such as increases of capillary density and changes in collagen IV and Thy-1 levels indicating compensatory regulation. Slight decreases of ICAM-1 levels and reduction of Thy 1 expression at 0.025–0.5 Gy indicate anti-inflammatory effects, whereas at the highest dose (2 Gy) increased VCAM-1 levels on the endocardium may represent a switch to a pro-inflammatory response. Plasma samples partially confirmed this pattern, showing a decrease of proinflammatory markers (sVCAM, sICAM) at 0.025–2.0 Gy. In contrast, an enhancement of MCP-1, TNFα and fibrinogen at 0.05–2.0 Gy indicated a proinflammatory and prothrombotic systemic response. Multivariate analysis also revealed significant age-dependent increases (KC, MCP-1, fibrinogen) and decreases (sICAM, sVCAM, sE-selectin) of plasma markers. This paper represents local and systemic effects of low-dose irradiation, including also age- and dose rate-dependent responses in the ApoE^-/- mouse model. These insights in the multiple inflammatory/thrombotic effects caused by low-dose irradiation might facilitate an individual evaluation and intervention of radiation related, long-term side effects but also give important implications for low dose anti-inflammatory radiotherapy.

Further evaluations of the toxicity of irradiated advanced heavy water reactor fuels

The neutron economy and online refueling capability of heavy water moderated reactors enable them to use many different fuel types, such as low enriched uranium, plutonium mixed with uranium, or plutonium and/or U mixed with thorium, in addition to their traditional natural uranium fuel. However, the toxicity and radiological protection methods for fuels other than natural uranium are not well established. A previous paper by the current authors compared the composition and toxicity of irradiated natural uranium to that of three potential advanced heavy water fuels not containing plutonium, and this work uses the same method to compare irradiated natural uranium to three other fuels that do contain plutonium in their initial composition. All three of the new fuels are assumed to incorporate plutonium isotopes characteristic of those that would be recovered from light water reactor fuel via reprocessing. The first fuel investigated is a homogeneous thorium-plutonium fuel designed for a once-through fuel cycle without reprocessing. The second fuel is a heterogeneous thorium-plutonium-U bundle, with graded enrichments of U in different parts of a single fuel assembly. This fuel is assumed to be part of a recycling scenario in which U from previously irradiated fuel is recovered. The third fuel is one in which plutonium and Am are mixed with natural uranium. Each of these fuels, because of the presence of plutonium in the initial composition, is determined to be considerably more radiotoxic than is standard natural uranium. Canadian nuclear safety regulations require that techniques be available for the measurement of 1 mSv of committed effective dose after exposure to irradiated fuel. For natural uranium fuel, the isotope Pu is a significant contributor to the committed effective dose after exposure, and thermal ionization mass spectrometry is sensitive enough that the amount of Pu excreted in urine is sufficient to estimate internal doses, from all isotopes, as low as 1 mSv. In addition, if this method is extended so that Pu is also measured, then the combined amount of Pu and Pu is sufficiently high in the thorium-plutonium fuel that a committed effective dose of 1 mSv would be measurable. However, the fraction of Pu and Pu in the other two fuels is sufficiently low that a 1 mSv dose would remain below the detection limit using this technique. Thus new methods, such as fecal measurements of Pu (or other alpha emitters), will be required to measure exposure to these new fuels.

Childhood exposures to Rn-222 and background gamma radiation in the uranium provinces of south Kazakhstan and northern Kyrgyzstan

The project was undertaken in southern Kazakhstan and Kyrgyzstan. It was speculated that the radiation doses in these areas would be sufficiently high and dispersed to facilitate a case-control study where the radiation doses to leukaemia subjects/their siblings could be compared with those received by control children. As a precursor a pilot project was undertaken to confirm radiation exposures in the region. This was undertaken in association with regional childhood cancer treatment centres. Children from families affected by childhood leukaemia were monitored for 1 month for external γ-radiation dose and for exposure to radon gas. 28 children from families in Kazakhstan and from 31 families in Kyrgyzstan were monitored. The median measured radon in air concentration recorded in Kazakhstan was 123 Bq m(-3) and in Kyrgyzstan was 177 Bq m(-3). These represent 24-h average indoor/outdoor values. In the case of the γ-doses the mean annual dose was 1.2 mGy for Kazakhstan and 2.1 mGy for Kyrgyzstan. Overall, the results suggest that the populations studied receive similar annual radiation doses to those received by populations living in other areas with enhanced natural radioactivity and that further study of Kazakh and Kyrgyz populations would not facilitate a successful case-control study for childhood leukaemia.

Retention and excretion of ³H in rats following the intratracheal intubation of tritiated pump oil

Saturated hydrocarbon mineral oils in vacuum pumps used in ³H handling facilities often contain significant amounts of ³H (as much as several hundred GBq L⁻¹), and during maintenance the air around an open pump may contain MBq L of volatile and aerosol species. It follows that H-contaminated pump oils pose a workplace hazard-especially if inhaled deposits are retained in the lung. A long-term study (1-y duration) was undertaken to establish the retention time of ³H-pump oil in the lungs of rats. Excretion data was collected to establish the mechanism of oil clearance from the lung. Finally, liver data was collected both to indicate the levels of H in the rat body and to indicate either the presence or absence of the transfer of unmetabolized pump oil within cells from the lungs to liver. Within 1 d following intubation into the trachea, ∼16.5% of the emulsified pump oil had been rapidly mechanically cleared to feces, and 1.1%, present as HTO, or exchangeable H, was excreted in urine. 69.4% of the instilled dose remained in the lungs as the initial alveolar burden. Subsequently, H cleared from the lungs with a retention half-time of of 223 d. The lung burden was mostly cleared to feces-indicating that the pump oil droplets remaining in the lungs were behaving like insoluble particles, but the kinetics of clearance of particles and oil droplets may be different. Overall, it is concluded that inhaled H-pump oil should most likely be regarded as an insoluble particulate (ICRP Inhalation Type S) for the purposes of radiological protection dosimetry, but the possibility of Type M behavior cannot be excluded.

Toxicity of irradiated advanced heavy water reactor fuels

The good neutron economy and online refueling capability of the CANDU® heavy water moderated reactor (HWR) enable it to use many different fuels such as low enriched uranium (LEU), plutonium, or thorium, in addition to its traditional natural uranium (NU) fuel. The toxicity and radiological protection methods for these proposed fuels, unlike those for NU, are not well established. This study uses software to compare the fuel composition and toxicity of irradiated NU fuel against those of two irradiated advanced HWR fuel bundles as a function of post-irradiation time. The first bundle investigated is a CANFLEX® low void reactor fuel (LVRF), of which only the dysprosium-poisoned central element, and not the outer 42 LEU elements, is specifically analyzed. The second bundle investigated is a heterogeneous high-burnup (LEU,Th)O(2) fuelled bundle, whose two components (LEU in the outer 35 elements and thorium in the central eight elements) are analyzed separately. The LVRF central element was estimated to have a much lower toxicity than that of NU at all times after shutdown. Both the high burnup LEU and the thorium fuel had similar toxicity to NU at shutdown, but due to the creation of such inhalation hazards as (238)Pu, (240)Pu, (242)Am, (242)Cm, and (244)Cm (in high burnup LEU), and (232)U and (228)Th (in irradiated thorium), the toxicity of these fuels was almost double that of irradiated NU after 2,700 d of cooling. New urine bioassay methods for higher actinoids and the analysis of thorium in fecal samples are recommended to assess the internal dose from these two fuels.

Low-dose radiation exposure and protection against atherosclerosis in ApoE(-/-) mice: the influence of P53 heterozygosity

We recently described the effects of low-dose γ-radiation exposures on atherosclerosis in genetically susceptible (ApoE(-/-)) mice with normal p53 function. Doses as low as 25 mGy, given at either early or late stage disease, generally protected against atherosclerosis in a manner distinctly nonlinear with dose. We now report the influence of low doses (25-500 mGy) on atherosclerosis in ApoE(-/-) mice with reduced p53 function (Trp53(+/-)). Single exposures were given at either low or high dose rate (1 or 150 mGy/min) to female C57BL/6J ApoE(-/-) Trp53(+/-) mice. Mice were exposed at either early stage disease (2 months of age) and examined 3 or 6 months later, or at late stage disease (7 months of age) and examined 2 or 4 months later. In unirradiated mice, reduced p53 functionality elevated serum cholesterol and accelerated both aortic root lesion growth and severity in young mice. Radiation exposure to doses as low as 25 mGy at early stage disease, at either the high or the low dose rate, inhibited lesion growth, decreased lesion frequency and slowed the progression of lesion severity in the aortic root. In contrast, exposure at late stage disease produced generally detrimental effects. Both low-and high-dose-rate exposures accelerated lesion growth and high dose rate exposures also increased serum cholesterol levels. These results show that at early stage disease, reduced p53 function does not influence the protective effects against atherosclerosis of low doses given at low dose rate. In contrast, when exposed to the same doses at late stage disease, reduced p53 function produced detrimental effects, rather than the protective effects seen in Trp53 normal mice. As in the Trp53 normal mice, all effects were highly nonlinear with dose. These results indicate that variations in p53 functionality can dramatically alter the outcome of a low-dose exposure, and that the assumption of a linear response with dose for human populations is probably unwarranted.

Radiation doses received by adult Japanese populations living outside Fukushima Prefecture during March 2011, following the Fukushima 1 nuclear power plant failures

Data on the concentration of radionuclides in air for March following the reactor failures at the Fukushima NPP were available for Takasaki, Chiba and Tokyo. Gamma dose data for the same/close locations and for fixed locations in other prefectures were also obtained. Gamma dose data was used to calculate the cumulative gamma dose, during 2 weeks (15th-28th March) following the power plant failures. Corresponding doses were calculated for sites in other Japanese prefectures - except Fukushima Prefecture, for which equivalent monitoring data was not published. For Takasaki, Chiba and Tokyo air concentration data and ICRP dose coefficients were used to calculate inhalation committed effective doses (CED, E(50)) and thyroid equivalent doses (H) for adult members of the public. Average ratios of gamma dose to inhalation CED and inhalation CED from iodine isotopes to thyroid equivalent dose, determined for Takasaki, Chiba and Tokyo, were then used to predict these quantities for sites in other prefectures. Cumulative gamma dose profiles were used to identify dose increments that could be attributed to Fukushima releases within 11 prefectures (excluding Fukushima Prefecture). The most impacted of these were located in Gunma, Ibaraki, Tochigi and Saitama Prefectures - to the south of Fukushima - and in Miyagi Prefecture - to the north of Fukushima. Calculated total doses ranged from 16 μSv in Shizuoka (Shizuoka) to 400 μSv in Ibaraki (Mito). The total doses calculated for the major population centres of Tokyo and Chiba were 97 μSv and 80 μSv, respectively. For all prefecture locations the largest calculated contribution to total dose, during the period of assessment, was from inhalation (~80%). Estimated thyroid equivalent doses ranged from 5.9 mSv in Ibaraki to 200 μSv in Shizuoka. All total doses calculated were probably overestimates - since no allowances were made for shielding and shelter during the passage of radioactive clouds. Minor contributions to dose from the ingestion of contaminated food and water were not calculated.

Low-dose radiation exposure and atherosclerosis in ApoE⁻/⁻ mice

The hypothesis that single low-dose exposures (0.025-0.5 Gy) to low-LET radiation given at either high (about 150 mGy/min) or low (1 mGy/min) dose rate would promote aortic atherosclerosis was tested in female C57BL/6J mice genetically predisposed to this disease (ApoE⁻/⁻). Mice were exposed either at an early stage of disease (2 months of age) and examined 3 or 6 months later or at a late stage of disease (8 months of age) and examined 2 or 4 months later. Changes in aortic lesion frequency, size and severity as well as total serum cholesterol levels and the uptake of lesion lipids by lesion-associated macrophages were assessed. Statistically significant changes in each of these measures were observed, depending on dose, dose rate and disease stage. In all cases, the results were distinctly non-linear with dose, with maximum effects tending to occur at 25 or 50 mGy. In general, low doses given at low dose rate during either early- or late-stage disease were protective, slowing the progression of the disease by one or more of these measures. Most effects appeared and persisted for months after the single exposures, but some were ultimately transitory. In contrast to exposure at low dose rate, high-dose-rate exposure during early-stage disease produced both protective and detrimental effects, suggesting that low doses may influence this disease by more than one mechanism and that dose rate is an important parameter. These results contrast with the known, generally detrimental effects of high doses on the progression of this disease in the same mice and in humans, suggesting that a linear extrapolation of the known increased risk from high doses to low doses is not appropriate.

Determining the relative toxicity and RBE of internal emitters in animals

It is almost impossible to conduct a perfect study of the relative toxicity of the radiations produced by different radionuclides. This is because the results of such studies are commonly confounded by spatial and temporal differences in the distributions of dose produced by the radionuclides employed. In addition, the results of a study designed to overcome these problems (using matched radionuclides incorporated within fused clay particles) revealed additional characteristics of an ideal study. These included the use of sufficient numbers of animals to give the study statistical power; the derivation of all causes of death and of survival for the analysis; the use of relative risk, rather than crude incidence data, to determine toxicity ratios; the cautious use of relative biological effectiveness values derived from fitted curves; and the preferred use of relative toxicity values derived directly from the data.

Relative toxicity of (45)Ca beta-particles and (242)Cm alpha-particles following their intravenous injection into mice as radiolabelled FAP

PURPOSE

To determine the relative toxicity of alpha- and beta-radiations under conditions of controlled temporal and spatial dose distribution.

METHODS

Fused aluminosilicate particles were radiolabelled with either (45)Ca (a beta-emitter) or (242)Cm (an alpha-emitter). These were injected into CBA/Ca mice to give lifespan, whole-body doses of approximately 0.5, 1.0 or 1.5 Gy. Most animals were entered into a lifespan toxicity study, but some were killed for radiochemical analysis and autoradiography.

RESULTS

Twenty-seven tumour types were identified. The most common malignant tumours were: Mammary carcinoma; liver carcinoma; malignant lymphoma; uterine histiocytic sarcoma. Excess relative risk (strictly hazard ratio) was higher for radiation-induced carcinomas than for sarcomas. The carcinomas, but not sarcomas showed a reduction in relative risk at the highest radiation dose employed. This reduction was most easily attributed to a systemic effect. The highest relative toxicity measured was for liver carcinoma (5.9, 95% confidence intervals [CI] 2.4, 14) and the lowest for uterine carcinoma (0.6, CI 0.03, 9.7). Overall, the excess relative risk ratio for SURVIVAL WAS 1.9 (CI 1.1, 3.2), FOR ALL CARCINOMA WAS 2.3 (CI 1.7, 3.0) AND FOR ALL SARCOMA WAS 2.7 (CI 0.72, 10).

CONCLUSIONS

The 10-fold variability in the observed toxicity ratio for different tumour endpoints shows that tissue sensitivity is a more important determinant of relative toxicity than radiation quality. The use of single radiation-weighting (w(R)) factors for radiation risk prediction and for radiological protection dosimetry is inconsistent with scientific observation.

Americium, plutonium and uranium contamination and speciation in well waters, streams and atomic lakes in the Sarzhal region of the Semipalatinsk Nuclear Test Site, Kazakhstan

New data are reported on the concentrations, isotopic composition and speciation of americium, plutonium and uranium in surface and ground waters in the Sarzhal region of the Semipalatinsk Test Site, and an adjacent area including the settlement of Sarzhal. The data relate to filtered water and suspended particulate from (a) streams originating in the Degelen Mountains, (b) the Tel'kem 1 and Tel'kem 2 atomic craters, and (c) wells on farms located within the study area and at Sarzhal. The measurements show that (241)Am, (239,240)Pu and (238)U concentrations in well waters within the study area are in the range 0.04-87mBq dm(-3), 0.7-99mBq dm(-3), and 74-213mBq dm(-3), respectively, and for (241)Am and (239,240)Pu are elevated above the levels expected solely on the basis of global fallout. Concentrations in streams sourced in the Degelen Mountains are similar, while concentrations in the two water-filled atomic craters are somewhat higher. Suspended particulate concentrations in well waters vary considerably, though median values are very low, at 0.01mBq dm(-3), 0.08mBq dm(-3) and 0.32mBq dm(-3) for (241)Am, (239,240)Pu and (238)U, respectively. The (235)U/(238)U isotopic ratio in almost all well and stream waters is slightly elevated above the 'best estimate' value for natural uranium worldwide, suggesting that some of the uranium in these waters is of test-site provenance. Redox analysis shows that on average most of the plutonium present in the microfiltered fraction of these waters is in a chemically reduced form (mean 69%; 95% confidence interval 53-85%). In the case of the atomic craters, the proportion is even higher. As expected, all of the americium present appears to be in a reduced form. Calculations suggest that annual committed effective doses to individual adults arising from the daily ingestion of these well waters are in the range 11-42microSv (mean 21microSv). Presently, the ground water feeding these wells would not appear to be contaminated with radioactivity from past underground testing in the Degelen Mountains or from the Tel'kem explosions.

A novel size-selective airborne particle size fractionating instrument for health risk evaluation

Health risks associated with the inhalation of airborne particles are known to be influenced by particle size. Studies have shown that certain nanoparticles, with diameters <100 nm, have increased toxicity relative to larger particles of the same substance. A reliable, size-resolving sampler able to collect a wide range of particle sizes, including particles with sizes in the nanometre range, would be beneficial in investigating health risks associated with the inhalation of airborne particles. A review of current aerosol samplers used for size-resolved collection of airborne particles highlighted a number of limitations. These could be overcome by combining an inertial deposition impactor with a diffusion collector in a single device. Verified theories of diffusion and inertial deposition suggested an optimal design and operational regime. The instrument was designed for analysing mass distribution functions. Calibration was carried out using a number of recognized techniques. The sampler was tested in the field by collecting size-resolved samples of lead containing aerosols present at workplaces in factories producing crystal glass. The mass deposited on each screen proved sufficient to be detected and measured by an appropriate analytical technique. Mass concentration distribution functions of lead were produced. The nanofraction of lead in air varied from 10 to 70% by weight of total lead.

Introduction to arsenic contamination and health risk assessment with special reference to Bangladesh

The problem of arsenic contamination in the Bengal River Basin illustrates a classic conundrum in environmental health, namely, that development projects can have double effects: on one hand development of tube wells eliminated bacterial pathogens and on the other it exposed the population to poisoning from arsenic. Thus, in future development projects the full health risk of a project must be considered during the planning, implementation, and decommissioning phases (Caussy 2003b; Caussy et al. 2003b). If such a holistic approach would have been followed, the mass contamination in the Bengal River Basin, in which millions of people were and are exposed to unsafe levels of arsenic, could have been averted. Although definite knowledge gaps in applying risk assessment steps for arsenic contamination exist, arsenic clearly poses a serious health problem and economic consequences to the affected population of the Bengal River Basin. It is binding on the international community to alleviate the problem through remediation measures to reduce arsenic exposure. One Environmental Sustainability Millennium development goal is to increase the proportion of population with sustainable access to an improved water source (Bartram et al. 2005). Providing water with safe levels of arsenic to affected communities of the Bengal River Basin will directly contribute to improved community health.

Comparative Biokinetics of Trivalent Radionuclides with Similar Ionic Dimensions: Promethium-147, Curium-242 and Americium-241

Data on the distribution and redistribution patterns in the laboratory rat of three trivalent elements with a similar ionic radius have been compared. This showed that these distributions for the two ions with the same ionic radius (111 pm), i.e., those of promethium (a lanthanoid) and curium (an actinoid), were indistinguishable and that americium, with a slightly larger ion size (111.5 pm), behaved similarly. The results are consistent with the suggestion that ion size is the only important factor controlling the deposition and redistribution patterns of trivalent lanthanoids and actinoids in rats. The result is important because it suggests that the same radiological protection dosimetry models should be used for trivalent actinoids and lanthanoids, that human volunteer data generated for lanthanoid isotopes can be used to predict the behavior of actinoids with the same ion size, and that appropriate pairs of beta-particle-emitting lanthanoid and alpha-particle-emitting actinoids could be used to study the relative toxicity of alpha and beta particles in experimental animals.

Measurements of daily urinary uranium excretion in German peacekeeping personnel and residents of the Kosovo region to assess potential intakes of depleted uranium (DU)

Following the end of the Kosovo conflict, in June 1999, a study was instigated to evaluate whether there was a cause for concern of health risk from depleted uranium (DU) to German peacekeeping personnel serving in the Balkans. In addition, the investigations were extended to residents of Kosovo and southern Serbia, who lived in areas where DU ammunitions were deployed. In order to assess a possible DU intake, both the urinary uranium excretion of volunteer residents and water samples were collected and analysed using inductively coupled plasma-mass spectrometry (ICP-MS). More than 1300 urine samples from peacekeeping personnel and unexposed controls of different genders and age were analysed to determine uranium excretion parameters. The urine measurements for 113 unexposed subjects revealed a daily uranium excretion rate with a geometric mean of 13.9 ng/d (geometric standard deviation (GSD)=2.17). The analysis of 1228 urine samples from the peacekeeping personnel resulted in a geometric mean of 12.8 ng/d (GSD=2.60). It follows that both unexposed controls and peacekeeping personnel excreted similar amounts of uranium. Inter-subject variation in uranium excretion was high and no significant age-specific differences were found. The second part of the study monitored 24 h urine samples provided by selected residents of Kosovo and adjacent regions of Serbia compared to controls from Munich, Germany. Total uranium and isotope ratios were measured in order to determine DU content. (235)U/(238)U ratios were within +/-0.3% of the natural value, and (236)U/(238)U was less than 2 x 10(-7), indicating no significant DU in any of the urine samples provided, despite total uranium excretion being relatively high in some cases. Measurements of ground and tap water samples from regions where DU munitions were deployed did not show any contamination with DU, except in one sample. It is concluded that both peacekeeping personnel and residents serving or living in the Balkans, respectively, were not exposed to significant amounts of DU.

Relative toxicity of chronic irradiation by 45Ca beta particles and 242Cm alpha particles with respect to the production of lung tumors in CBA/Ca mice

Approximately 1800 female CBA/Ca mice were exposed by inhalation at three dose levels to beta particles from (45)Ca-labeled fused aluminosilicate particles (FAP), to alpha particles from (242)Cm-labeled FAP, or to carrier control FAP. Another group of mice inhaled no FAP and were designated as untreated cage controls. The FAP in combination with these radionuclides was used to achieve the same spatial and temporal distribution of alpha- and beta-particle dose within the irradiated mice. Some mice were killed to determine the clearance of radiolabeled FAP from their lungs, and the remainder were allocated to a life-span study. All animals were subjected to a detailed necropsy. To facilitate the identification of small tumors, the lungs were rendered transparent in methyl salicylate and examined under back illumination for the presence of lesions. Lung nodules and other microscopic lesions were excised for histological examination. The median survival of mice in all groups was approximately 910 days. The control animals lived longer than those that were irradiated, but it was difficult to determine a dose-response relationship for survival among the exposed mice. Benign adenomas and, less frequently, malignant adenocarcinomas were identified in all animal groups. The prevalence of these tumors was approximately 28.8% in the control mice, which is consistent with the results of other studies using the same strain of mouse. After exposure to radionuclide-labeled FAP, there was a significant dose-related increase in the prevalence of lung tumors in (242)Cm- (peak prevalence 55%) and (45)Ca-exposed (peak prevalence 48.6%) mice. The prevalence of tumors in the mice that received (242)Cm-labeled FAP was approximately twice that in the mice that inhaled (45)Ca-labeled FAP within the range of doses employed (0.55-4.69 Gy). Using the ratio of the slope of the linear component of the dose-response curves, the toxicity of the alpha particles relative to the beta particles was 1.5 (90% CI: 0.7, 9.0) for all adenomas and 9.4 (90% CI: 5.0, 23.0) for the less frequent adenocarcinomas. The relative toxicity for adenocarcinomas was found to decrease with increasing dose.

Tritium in well waters, streams and atomic lakes in the East Kazakhstan Oblast of the Semipalatinsk Nuclear Test Site

The concentration of tritium has been determined in well waters, streams and atomic lakes in the Sarzhal, Tel'kem, Balapan and Degelen Mountains areas of the Semipalatinsk Test Site. The data show that levels of tritium in domestic well waters within the settlement of Sarzhal are extremely low at the present time with a median value of 4.4 Bq dm(-3) (95% confidence interval:4.1-4.7 Bq dm(-3)). These levels are only marginally above the background tritium content in surface waters globally. Levels in the atomic craters at Tel'kem 1 and Tel'kem 2 are between one and two orders of magnitude higher, while the level in Lake Balapan is approximately 12,600 Bq dm(-3). Significantly, levels in streams and test-tunnel waters sourced in the Degelen Mountains, the site of approximately 215 underground nuclear tests, are a further order of magnitude higher, being in the range 133,000--235,500 Bq dm(-3). No evidence was adduced which indicates that domestic wells in Sarzhal are contaminated by tritium-rich waters sourced in the Degelen massif, suggesting that the latter are not connected hydrologically to the near-surface groundwater recharging the Sarzhal wells. Annual doses to humans arising from the ingestion of tritium in these well waters are very low at the present time and are of no radiological significance.

Source-term characterisation and solid speciation of plutonium at the Semipalatinsk NTS, Kazakhstan

New data on the concentrations of key fission/activation products and transuranium nuclides in samples of soil and water from the Semipalatinsk Nuclear Test Site are presented and interpreted. Sampling was carried out at Ground Zero, Lake Balapan, the Tel'kem craters and reference locations within the test site boundary well removed from localised sources. Radionuclide ratios have been used to characterise the source term(s) at each of these sites. The geochemical partitioning of plutonium has also been examined and it is shown that the bulk of the plutonium contamination at most of the sites examined is in a highly refractory, non-labile form.

The biological behaviour and bioavailability of aluminium in man, with special reference to studies employing aluminium-26 as a tracer: review and study update

Until 1990 biokinetic studies of aluminium metabolism and biokinetics in man and other animals had been substantially inhibited by analytical and practical difficulties. Of these, the most important are the difficulties in differentiating between administered aluminium and endogenous aluminium-especially in body fluids and excreta and the problems associated with the contamination of samples with environmental aluminium. As a consequence of these it was not possible to detect small, residual body burdens of the metal following experimental administrations. Consequently, many believed aluminium to be quantitatively excreted within a short time of uptake in all, but renal-failure patients. Nevertheless, residual aluminium deposits in a number of different organs and tissues had been detected in normal subjects using a variety of techniques, including histochemical staining methods. In order to understand the origins and kinetics of such residual aluminium deposits new approaches were required. One approach taken was to employ the radioisotope (67)Ga as a surrogate, but this approach has been shown to be flawed-a consequence of the different biological behaviours of aluminium and gallium. A second arose from the availability, in about 1990, of both (26)Al-a rare and expensive isotope of aluminium-and accelerator mass spectrometry for the ultra-trace detection of this isotope. Using these techniques the basic features of aluminium biokinetics and bioavailability have been unravelled. It is now clear that some aluminium is retained in the body-most probably within the skeleton, and that some deposits in the brain. However, most aluminium that enters the blood is excreted in urine within a few days or weeks and the gastrointestinal tract provides an effective barrier to aluminium uptake. Aspects of the biokinetics and bioavailability of aluminium are described below.

Human biokinetics of injected bismuth-207

A healthy male volunteer received an intravenous injection of 207Bi as citrate. Levels of the tracer in blood and in excretion samples, and its retention and distribution within the body, were investigated by appropriate radioactivity measurements. Levels in blood fell very rapidly, with only 1% of the injection remaining at 7 h and only ca. 0.1% at 18 days. There was rapid initial excretion, with 55% lost during the first 47 h, principally in urine; however, longer-term losses were much slower and 0.6% remained in the body at 924 days, when the contemporary rate of loss implied a half-life of 1.9 years. Integration of the retention pattern suggested that steady exposure to bismuth compounds could lead ultimately to a body content of approximately 24 times the daily systemic uptake. The largest organ deposit was in the liver, which after 3 days contained ca. 60% of the contemporary whole body content, consistent with reports of hepatotoxicity. These findings differ markedly from the metabolic model for bismuth proposed by the International Commission on Radiological Protection, which envisages a terminal half-life in the body of only 5 days and kidney as the site of highest deposition.

Accelerator mass spectrometry for the detection of ultra-low levels of plutonium in urine, including that excreted after the ingestion of Irish sea sediments

Currently, most methods for the quantitative assessment of (239)Pu have minimum detection levels (25 microBq for alpha-particle spectrometry) that are much higher than the levels of this isotope in many human bioassay and environmental samples. Accordingly, a priority has existed to develop methods that are more sensitive. Fission-track and ICP-MS methods have been used, but these can suffer either from an uncertain level of removal and/or recovery of uranium or from isobaric mass interferences. Accelerator mass spectrometry (AMS) has no such disadvantages, and its demonstrated detection limits for plutonium isotopes approach levels of attograms, equivalent to about 500 nBq for (239)Pu. This paper describes the application of AMS to the measurement of (239)Pu in urine produced by youths living in London (3.5 microBq day(-1)) and by adults (approximately 2-260 microBq day(-1)), some of whom were exposed occupationally. In addition, an experiment was undertaken to measure the fasted absorbed fraction of ingested plutonium after the ingestion of 15 g of Irish Sea sediment by a volunteer. The measured absorbed fraction was 4.5 x 10(-5). It is concluded that accelerator mass spectrometry is a suitable method for the ultra-trace detection of plutonium.

Revised organ partition of thorium-232 in thorotrast patients

Risk estimates for internally deposited alpha particles in humans, such as those for alpha-particle-induced leukemia, have been derived from data on the toxicity of (232)Th in patients injected with Thorotrast. Their derivation requires both epidemiological data and organ doses calculated from the volume of Thorotrast injected and a knowledge of its pattern of deposition within the body. However, accumulating evidence suggests that the organ partition of (232)Th that has commonly been used for dosimetry (i.e. liver:spleen:red bone marrow: others tissues = 59:29:9:3) is inaccurate. In the present study, the organ distribution of (232)Th has been recalculated using a revised averaging method and both published data and our own unpublished data. For the three major organs of deposition (liver, spleen and bone marrow), activity concentration data were selected from 27 published papers and data sets including 140 newly compiled Japanese cases. For organs of minor storage, both published data for 38 German and 24 Japanese autopsy cases and new data were used. The revised estimate of the relative partition of (232)Th among the above organs was 53:14:25:8. It follows that doses calculated to date are essentially correct for the liver but are too high for the spleen and about three times too low for the red bone marrow. This suggests that the risk of alpha-particle-induced leukemia, per unit of alpha-particle dose, in Thorotrast patients is about three times lower than previously thought.

Partition of thorium between organs of monkeys injected with thorotrast: implications for alpha-particle dosimetry

Risk estimates for alpha-particle-induced malignancies have been based mainly on studies of Thorotrast patients, but certain aspects of its deposition in the body have been at issue: the partition between the liver, spleen and red bone marrow, and the deposition at lower concentrations in other organs, such as muscle and fat, which may contribute to the risk. To supplement the existing data for humans, thorium concentrations were measured in the organs of two female monkeys 3-4 years after injection with Thorotrast. Relative deposits (liver:spleen:red bone marrow) were 54:6:41 and 75:4:21, in better agreement with the most recent observations in Thorotrast patients than with previous reports. Whereas the human testis had ranked among intermediate-level organs such as the adrenal glands and pancreas, the ovary of the monkey was among the organs with the lowest concentrations. The data suggest that risk factors for induction of malignancies by alpha-particle irradiation should be re-examined.

Uptake by man of aluminium in a public water supply

1. After overnight fasting, two young male adults each received a single oral dose of 100 Bq 26Al in tap water. Coincidence gamma-ray spectrometry and accelerator mass spectrometry were used to determine the 26Al content of excretion collections and of blood samples. 2. Close to 100% of the intake was recovered in faeces during the first 7 days. Gastro-intestinal uptake, determined by comparing urinary excretion with patterns previously established following intravenous administration of 26Al, averaged 0.22% in the two subjects. 3. Uptake fractions based on comparisons of blood concentration following ingestion and injection were much lower, but were judged to be unreliable. It is concluded that aluminium present in most water supplies is unlikely to contribute as much as 1% of a typical daily uptake of 10 microg from food.

Thorotrast distribution in monkey bone marrow at early and late times after injection

Thorotrast, a 25% colloidal suspension of 232ThO2, was formerly used as a radiographic contrast medium. Although epidemiological studies have shown that alpha particles emitted from 232Th and its decay products incorporated in the bone marrow cause leukemia, the use of these data for alpha particle induced leukemogenesis risk estimation has been criticized mainly for inhomogeneity of Thorotrast distribution. Four monkeys were injected with Thorotrast to investigate the degree of inhomogeneity in the thorium content of different bone marrow sites and the cellular localization of Thorotrast. Two were injected via an artery and two via a vein and sacrificed either at 1 wk or 3 to 4 y after injection. Microscopic, solid state autoradiography and back scatter electron imaging methods were applied to several bone sites to determine the degree of inhomogeneity. Quantification was performed using x-ray fluorescence for trabecular bone and bone marrow and neutron activation analysis for compact bones. At 1 wk Thorotrast was found to be distributed evenly in the red marrow; by 3 and 4 y conglomerates were seen which were restricted to macrophages. The monkey was found to be a good model for humans. The choice of injection route did not noticeably affect the Thorotrast distribution in bones of the skeletal system. Considering the even distribution of Thorotrast within the red bone marrow at early times after its injection, the inevitable diffusion of thorium progeny from the particles, the mobility of bone marrow macrophages, and the well established correction factor of self-absorption within conglomerates, these results suggest that data derived from Thorotrast patients are useful for risk estimation of alpha particle induced leukemia.

Variations in the concentration of plutonium, strontium-90 and total alpha-emitters in human teeth collected within the British Isles

Concentrations of plutonium-239, plutonium-240, strontium-90 and total alpha-emitters have been measured in children's teeth collected throughout Great Britain and Ireland. The concentrations of plutonium and strontium-90 were measured in batched samples, each containing approximately 50 teeth, using low-background radiochemical methods. The concentrations of total alpha-emitters were determined in single teeth using alpha-sensitive plastic track detectors. The results showed that the average concentrations of total alpha-emitters and strontium-90 were approximately one to three orders of magnitude greater than the equivalent concentrations of plutonium-239,240. Regression analyses indicated that the concentrations of plutonium, but not strontium-90 or total alpha-emitters, decreased with increasing distance from the Sellafield nuclear fuel reprocessing plant-suggesting that this plant is a source of plutonium contamination in the wider population of the British Isles. Nevertheless, the measured absolute concentrations of plutonium (mean = 5 +/- 4 mBq kg-1 ash wt.) were so low that they are considered to present an insignificant radiological hazard.

The bioavailability of 26Al-labelled aluminium citrate and aluminium hydroxide in volunteers

A study was undertaken to determine the fraction of ingested aluminium taken up by two male volunteers, following their ingestion of either aluminium citrate or aluminium hydroxide. In addition, the effects of simultaneous citrate ingestion on the gastrointestinal absorption of aluminium from its hydroxide was studied. Volunteers received three oral doses of 26Al-labelled aluminium compound in water. The doses were administered directly into the stomach using a paediatric feeding tube. Blood samples were collected from the volunteers at 1, 4 and 24 h after administration, and their daily output of urine and faeces was collected for 6 days. These samples were analysed for their 26Al content using either coincidence gamma-counting or accelerator mass spectrometry. The uptake of aluminium was greatest following its administration in the citrate form and was least following intake as the aluminium hydroxide suspension. The co-administration of citrate, with the aluminium hydroxide suspension, was found to enhance the levels of 26Al uptake in both volunteers. Using a urinary excretion factor based on the results of previous studies, the fractional aluminium uptake from each of the species was calculated: aluminium citrate, 5.23 x 10(-3); aluminium hydroxide, 1.04 x 10(-4); aluminium hydroxide with citrate, 1.36 x 10(-3).

Histopathology and 241Am microdistribution in skeletal USTER Case 246

Histopathology and qualitative autoradiography studies were undertaken on bone removed at autopsy from USTUR Case 246. The histopathology examination revealed extensive bone marrow peritrabecular fibrosis and decreased cellularity in most samples. In addition, histological indicators suggest that bone cell turnover was suppressed at most sites, although turnover was found to be essentially normal in a vertebral body sample. The autoradiographic studies showed that bone turnover that had occurred resulted in the redistribution of americium within bone. However, surface deposits of americium remained conspicuous at many sites, particularly those with low bone growth activity. A few percent of the americium was present in the bone marrow. The dosimetric and toxicology findings indicate that current assumptions about the metabolic behavior of bone-seeking radionuclides are likely to be unrealistically simplistic.

Inter-subject variability in the metabolism of aluminium following intravenous injection as citrate

1. Six healthy male volunteers received intravenous injections of 26Al as citrate. Accelerator mass spectrometry and gamma-ray spectrometry were used to determine levels of the tracer in blood and excreta at times up to 5-6 d. 2. There was a rapid clearance from blood (mean 2% of injection remaining after 1 d) and major loss in urine (59% up to 1 d), but 27 +/- 7 (s.d.)% was retained in the body at 5 d. Faecal excretion was negligible (1% up to 5 d). 3. The mean results accord with the early metabolic pattern in the single subject of a previous, more extensive study, who had retained 4% of the injection after 3 y. Together, the two studies point to the likelihood of large inter-subject differences in the long-term accumulation of dietary aluminium by populations receiving a given level of daily intake.

Human metabolism of aluminium-26 and gallium-67 injected as citrates

1. 26Al and 67Ga were given as citrates to a healthy male volunteer by intravenous injection. The retention of both tracers was studied by body radioactivity measurement. Levels in blood and excreta were determined by gamma-ray spectrometry and/or accelerator mass spectrometry. 2. More than half of the 26Al had left the blood after 15 min and the decline continued, leaving < 1% in blood after 2 d; the losses occurred both to renal excretion and through uptake by other compartments. Estimated excretion up to 13 d was 83% (urine) and 1.8% (faeces). Whole-body retention of 15% at 13 d declined to approximately 4% at 1178 d, when the daily reduction corresponded to a biological half-life of 7 y, suggesting that sustained intake of dietary aluminium may lead to a progressively increasing internal deposit. 3. The metabolism of 67Ga differed markedly from that of 26Al in all aspects studied.

Systemic deposits of thorium in thorotrast patients with particular reference to sites of minor storage

It is well established that injected Thorotrast is deposited in the liver, spleen, bone marrow, and lymph nodes, but accumulations in organs with lower macrophage activity have previously been given little attention. In this work, neutron activation analysis has been used to investigate concentrations of thorium in autopsy samples taken at sites of major and minor deposition in 24 Thorotrast patients. In the latter category, the highest values were found in the testis [40 x 10(-6) g/g(wet)], followed by those in the adrenal gland, gallbladder, lung, and pancreas. The resulting alpha-particle dose rates (mGy/year) are tentatively estimated to be 8.5 to the testis, 5.5 to the gallbladder, and 5.3 to the lung. These results may be relevant to the residual excess mortality among Thorotrast patients after diseases of the principal organs of deposition have been excluded; they also support previous indications that thorium deposited in pulmonary tissues is responsible for an important component of the total dose to the lung. In another context, our data may bear on the connection, postulated elsewhere, between exposure to alpha-particle emitters and elevated incidence of leukemia in the children of workers engaged in the reprocessing of nuclear fuel.

The prediction of the relative toxicities of radium 224 and of radium 226 in the bones of mice using Monte Carlo techniques

Toxicity studies using rodents have shown that the long-lived radium isotope radium 226 is about six times less toxic per unit of absorbed radiation dose to the skeleton than the short-lived isotope radium 224 with respect to the production of osteosarcoma. This difference in toxicity has been attributed to differences in the distribution of these isotopes. It has been suggested that 224Ra is more toxic than 226Ra because it decays on bone surfaces rather than within the volume of the bone mineral. However, in rodents many bone structures are small compared with the track length of the alpha particles and this explanation may be inadequate to explain the magnitude of the observed effect. Consequently, Monte Carlo calculations have been made to test the validity of the distribution-difference hypothesis. The results indicate that, for bone structures the size of those in mice, less than half of the observed difference in toxicity can be explained by considerations of the distribution of these radionuclides with respect to bone surfaces. Instead, it is suggested that the greater irradiation of trabecular than of cortical bone that is a characteristic of 224Ra is responsible for its enhanced toxicity.