Measuring extremely low levels of daily urinary Th excretions in adult German population

Summary Exposure to thorium can be estimated by measuring its quantity excreted daily in urine. For this purpose, an adequately sensitive analytical method was developed and standardized, employing radiochemical neutron activation analysis (RNAA). The method was applied to measure pg levels of Th in urine samples from which its daily urinary excretion was quantified. It was possible to achieve a limit of detection (LOD) of 10 pg Th (0.04 μBq) in urine samples. The daily urinary excretion of Th was measured in a group of 15 adult German subjects who were not occupationally exposed to Th. The daily urinary excretion ranged between 0.49-3.65 ng^. d^-1, with the geometric mean of 1.29 ng Th^. d^-1. This daily urinary excretion of Th provides an important baseline data against which the occupational exposure of workers could be assessed.     

Estimation of uranium in bioassay samples of occupational workers by laser fluorimetry

A newly established uranium processing facility has been commissioned at BARC, Trombay. Monitoring of occupational workers is essential to assess intake of uranium in this facility. A group of 21 workers was selected for bioassay monitoring to assess the existing urinary excretion levels of uranium before the commencement of actual work. Bioassay samples collected from these workers were analyzed by ion-exchange technique followed by laser fluorimetry. Standard addition method was followed for estimation of uranium concentration in the samples. The minimum detectable activity by this technique is about 0.2 ng. The range of uranium observed in these samples varies from 19 to 132 ng/L. Few of these samples were also analyzed by fission track analysis technique and the results were found to be comparable to those obtained by laser fluorimetry. The urinary excretion rate observed for the individual can be regarded as a ‘personal baseline’ and will be treated as the existing level of uranium in urine for these workers at the facility.     

Specific absorption parameters for uranium octoxide and dioxide applicable to the ICRP Publication 66 respiratory tract model

Literature data from in vivo chest measurements and urinary excretion rates of individuals exposed to U₃O₈ and UO₂ were used to compare the results predicted by different models with empirical observations in humans. As a result the use of the respiratory tract model proposed in ICRP Publication 66 with its default absorption parameters underestimates urinary excretion of inhaled U₃O₈ and UO₂. The new respiratory tract model also overpredicts the Fecal/Urine activity ratio, independently of the systemic model. For U₃O₈ and UO₂ the choice of systemic model has very little influence on the predicted urinary excretion of inhaled compounds. On the other way, the choice of the respiratory tract model does influence the predicted urinary excretion significantly. In this work specific absorption parameters for U₃O₈ and UO₂ were derived to be used in the respiratory tract model proposed in ICRP Publication 66. The predicted biokinetics of these compounds were compared with those derived for Type M and Type S compounds of uranium.     

A critical review of bioassay techniques for actinides in light of ICRP recommendations for monitoring workers

A critical review is presented of bioassay techniques for actinides in light of ICRP recommendations for monitoring workers. It is obvious that very sensitive techniques are required to meet these recommendations. Alpha spectrometry, the most commonly employed technique for measuring actinides in bioassay samples, has limited sensitivity. There are, however, certain techniques which are sensitive enough to meet the recommendations of ICRP, such as, fission track analysis for²³⁹Pu and²³⁵U, neutron activation analysis for²³²Th, mass spectrometry for a number of radionuclides, and many techniques for uranium. ICP-mass spectrometry does not have enough sensitivity to be implemented as a method of choice for the bioassay of actinides at present, however, it is quite promising.     

Modified respiratory tract model for uranium: Its implications on bioassay interpretations

The excretion of inhaled poorly transportable compounds of uranium relative to chest content has been measured in humans by a substantial number of measurements of urine, feces, andin vivo measurements over the chest. The use of these measurements have permitted us to compare the results predicted by the models with empirical observations in humans. The ICRP-30 model for inhaled class Y compounds of uranium along with the ICRP-30 systemic model, no matter what the particle size, grossly underpredicts urinary excretion over time than that observed in human occupationally exposed to poorly transportable compounds of uranium by inhalation. Conversely, if urinary excretion were to be used to estimate the contents of poorly transportable uranium compounds in the lung using ICRP-30 models, the results would be significantly overestimated. The new ICRP (ICRP-66) respiratory tract model also grossly underestimates urinary excretion of inhaled poorly transportable uranium compounds and exacerbates the problem, at least for the default values of the parameters of the model. A lung model derived from the original ICRP-30 lung model, which is named modified, has been proposed in this work. It predicts urinary excretion better, even though it is not entirely satisfactory in predicting urine/fecal ratio in excreta.     

Interpretation of bioassay measurements using different systemic models for plutonium

In vitro bioassay measurements for plutonium have been performed on a routine basis for many years. Since the biokinetic models have changed considerably and the dose limitation systems have become more restrictive, it is necessary to estimate the impact of these changes on the interpretation of bioassay measurements. This study is carried out for the plutonium systemic models proposed by the ICRP publications: ICRP-30, ICRP-48, and ICRP-56, using the excretion functions proposed by Langham, Durbin, and Jones. A quantitative comparison of dose estimates using the dose limitation systems proposed in the ICRP Publications 26 and 60 is also done. In order to evaluate the impact on the use of the new ICRP respiratory tract model, a comparative study of intake and dose estimates, using the new and the ICRP-30 respiratory tract models, was also done for the case of inhalation of plutonium compounds. These calculations are particularly important to provide means to compare doses when the occupational exposures lasted many years and the doses were assessed using different models and dose limitation systems.Since some countries are in the process of changing the dose limitation system from the recommendations of the ICRP-26 to the ICRP-60, or even from the ICRP-2 to the ICRP-26, a quantitative comparison of dose estimates will be shown. In order to evaluate the impact on the use of the new ICRP respiratory tract model, a comparative study of intake and dose estimates using the new and the ICRP-30 respiratory tract models will also be shown for the case of inhalation of plutonium compounds.     

Assessment of Iodine in the Diet of People Living Around a Nuclear Reprocessing Plant: Dose-Related Consequences of an Intake of 129I

It is important that in radioiodine dosimetry for low levels of daily intake, allowance must be made for the normal daily intake of stable iodine. This intake varies from one region to another, and variations are observed from one person to the next within a region, depending on eating habits. Measuring iodine in the urine over 24 hours can indirectly assess these variations. Analysis of the total iodine in the urine was carried out for 69 French people living in a temperate maritime region or in mainland France. This study justifies individual assessment of the coefficient of iodine transfer to the thyroid by means of this survey based on the urinary iodine analysis. The consequences for man of the release of ¹²⁹I around a nuclear reprocessing plant were analyzed by applying the methodology published previously by the authors. A software program based on the iodine biokinetic model recommended by the ICRP was used to calculate the daily urine excretion of ¹²⁹I for five different diets of total iodide in a ratio of 10^-4 for ¹²⁹I/¹²⁷I. This model makes it possible to set a practical detection limit of 20 mBq (0.003 µg). This approach is important from a practical point of view for health physicists involved in routine monitoring of workers in the nuclear field and members of the public exposed to radioiodine released into the environment.     

On the Use of ICP-MS for Measuring Plutonium in Urine

The analytical protocols currently used to measure plutonium in urinary excretion consist of radiochemical purification, the source preparation by electroplating and alpha spectrometry measurements. Such a procedure is of limited relevance to the individual monitoring of workers exposed to plutonium and mixed oxides. The use of ICP-MS, which takes much shorter counting time, was investigated with the aim of assessing the capabilities of this analytical tool for the determination of urinary excretion of plutonium. It has been shown that the detection level of 1 mBq·1^-1 could be achieved after a radiochemical purification process for a standard ICP-MS set-up.     

Immunochemical detection of metabolites of parent and nitro polycyclic aromatic hydrocarbons in urine samples from persons occupationally exposed to diesel exhaust

An immunochemical assay was developed for the detection of metabolites excreted in urine as a result of occupational exposure to PAHs and nitro-PAHs. These metabolites were analyzed in a competitive ELISA, using an existing antibody (4D5) that has been developed against 6-aminobenzo[a]pyrene coupled to bovine serum albumine (B[a]P-BSA). A solid phase extraction (SPE) work-up procedure was optimized by dilution of pooled urine samples from rats exposed to 1-NP, in human urine. The application was validated by comparison of test results with urinary excreted 1-hydroxypyrene (1-OH-P) levels in a study among 28 railroad workers. Excretion of urinary metabolites was determined over two consecutive workdays. The 24 h average excretion of metabolites as determined in the immunoassay was not related to levels of particulate matter in the breathing zones of workers, not to 1-OH-P excretion levels of the day of urine collection. However, it was significantly associated with the personal dust exposure of the day before (P<0.0001), suggesting slow excretion of urinary metabolites. Smoking habits caused minor interference (P<0.1).     

Urinary arsenic speciation by high-performance liquid chromatography/atomic absorption spectrometry for monitoring occupational exposure to inorganic arsenic

Total urinary arsenic determinations are often used to assess occupational exposure to inorganic arsenic. Ingestion of sea food can increase the normal background levels of total arsenic in urine by up to an order of magnitude, but this arsenic has relatively little toxicity; it is tightly bound as arsenobetaine. The excretion of inorganic arsenic and its metabolites dimethylarsenic acid (DMA) and monomethylarsonic acid (MMA) is not influenced by the consumption of arsenic from sea food. Specific measurements of DMA, MMA and inorganic arsenic provide a more reliable indicator or exposure than total urinary arsenic levels. An automated atomic absorption method involving high-performance liquid chromatographic separation of the arsenic species and continuous hydride generation is described for the determination of arsenite, arsenate, DMA and MMA at μg As l^?1 levels. The method is used to study normal urinary arsenic levels in laboratory staff and arsenic excretion by exposed workers.     

Thorium in human blood serum,clot, and urine comparison with ICRP excretion model

Neutron activation followed by a simple radio-chemical separation procedure was employed to determine the concentrations of thorium (²³²Th) in human blood serum, clot, and urine of normal subjects and three groups of occupationally exposed persons. The thorium concentrations in the blood serum, clot, and urine samples of the exposed groups were distinctly higher than those of the other study groups and were found to increase with increasing occupational length of the persons. Daily urinary excretion is correlated with serum thorium burden and it is estimated that the daily excreted thorium is about 15% of the thorium in the serum pool.     

Determination of uranium isotopes in urine samples from radiation workers using 232U tracer, anion-exchange resin and alpha-spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on the excretion rate of body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha-spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical method for the determination of U-isotopes in urine samples using anion-exchange resin and ²³²U tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of uranium along with calcium phosphate. Separation of U was carried out by Amberlite, IRA-400, anion-exchange resin. U-fraction was electrodeposited and activity estimated using tracer recovery by alpha-spectrometer. Eight routine urine samples of radiation workers were analyzed and consistent radiochemical tracer recovery was obtained in the range of 51% to 67% with a mean and standard deviation of 60% and 5.4%, respectively.     

Determination of plutonium isotopes in urine samples from radiation workers using <Superscript>236</Superscript>Pu tracer,anion exchange resin and alpha spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical method for the determination of Pu-isotopes in urine samples using anion exchange resin and ²³⁶Pu tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of plutonium along with calcium phosphate. Separation of Pu was carried out by Amberlite, IRA-400, anion exchange resin. Pu-fraction was electrodeposited and activity estimated using tracer recovery by alpha spectrometer. Twenty routine urine samples of radiation workers were analyzed and consistent radiochemical tracer recovery was obtained in the range 74–96% with a mean and standard deviation of 85 and 6% respectively.     

Absorption kinetics of uranium tri-n-butyl phosphate in the rat: Implications for occupational exposure

The absorption kinetics for uranium into blood after deposition as tri-n-butylphosphate (UTBP) in the rat lung were combined with human data on particle deposition and clearance from the ICRP Publication 66 respiratory tract model and information from the most recent ICRP biokinetic model for uranium to predict the consequences for exposure of workers. These predictions suggest that, (1) the biokinetics of UTBP are similar to those for a Type F compound as defined by ICRP, (2) the dose coefficient is essentially independent of the aerosol size and isotopic composition, (3) the mass of uranium equivalent to the ALI can vary by 13 fold depending upon the isotopic composition, (4) intakes of uranium as UTBP other than chronic intakes as highly enriched forms should be restricted on the basis of the chemical toxicity of uranium, (5) the assessment of intake by urine bioassay measurements should be interpreted with caution unless the exposure conditions are well defined and (6) severe kidney damage is unlikely at intakes corresponding to the ALI or daily limit.     

Recent developments in biokinetic models and the calculation of internal dose coefficients

In most cases the measurement of radioactivity in an environmental or biological sample will be followed by some estimation of dose and possibly risk, either to a population or an individual. This will normally involve the use of a dose coefficient (dose per unit intake value) taken from a compendium. In recent years the calculation of dose coefficients has seen many developments in both biokinetic modelling and computational capabilities. ICRP has recommended new models for the respiratory tract and for the systemic behavior of many of the more important elements. As well as this, a general age-dependent calculation method has been developed which involves an effectively continuous variation of both biokinetic and dosimetric parameters, facilitating more realistic estimation of doses to young people. These new developments were used in work for recent ICRP, IAEA and CEC compendia of dose coefficients for both members of the public (including children) and workers. This paper presents a general overview of the method of calculation of internal doses with particular reference to the actinides. Some of the implications for dose coefficients of the new models are discussed. For example it is shown that compared with data in ICRP Publications 30 and 54: the new respiratory tract model generally predicts lower deposition in systemic tissues per unit intake; the new biokinetic models for actinides allow for burial of material deposited on bone surfaces; age-dependent models generally feature faster turnover of material in young people. All of these factors can lead to substantially different estimates of dose and examples of the new dose coefficients are given to illustrate these differences. During the development of the new models for actinides, human bioassay data were used to validate the model. Thus, one would expect the new models to give reasonable predictions of bioassay quantities. Some examples of the bioassay applications, e.g., excretion data for the plutonium model, are discussed briefly.     

Determination of urinary S-phenylmercapturic acid, a specific metabolite of benzene, by liquid chromatography/single quadrupole mass spectrometry

A high-performance liquid chromatography/single quadrupole mass spectrometry (LC/MS) method is described for the determination of urinary S-phenylmercapturic acid (S-PMA), a specific metabolite of benzene. Urine samples were spiked with [13C6]S-PMA (used as the internal standard) and acidified; then they were purified by solid-phase extraction (SPE) on C18 cartridges. Analyses were conducted on a reversed-phase column by gradient runs with 1% aqueous acetic acid/methanol mixtures at different proportions as the mobile phase. The detector was used in electrospray negative ion mode (ESI-), the ions m/z 238 for S-PMA and 244 for [13C6]S-PMA being recorded simultaneously. The detection limit (for a signal-to-noise ratio = 3) was 0.2 microg/L, thus allowing for the measurement of background excretion of S-PMA in the general population. The use of the internal standard allowed us to obtain good precision (CV% values < 3%) and a linear calibration curve within the range of interest for monitoring occupational exposure to benzene (up to 500 microg/L). The method was applied to assay the metabolite concentration in a group of 299 workers (68 smokers and 231 non-smokers) occupationally exposed to relatively low levels of benzene (environmental concentration = 0.4-220 microg/m3, mean 11.4 microg/m3 and 236 non-exposed subjects (134 smokers and 102 non-smokers). The results clearly showed that smoking must be taken into account for the correct interpretation of the results of S-PMA measurements for the assessment of work-related benzene exposure. When only non-smokers were selected, the mean excretion of S-PMA was significantly higher in workers exposed to benzene (1.2 +/- 0.9 microg/g creatinine) than in the control group (0.7 +/- 0.6 microg/g creatinine) (p < 0.001), thus confirming the role of S-PMA as a biomarker of benzene on a group basis, even for relatively low exposure degrees.     

Use of animal studies for assessing intakes of inhaled actinide-bearing dusts

This paper reviews the methodology used in the execution and interpretation of animal studies (mostly conducted at NRPB) designed to provide guidance on limits of intake and the effectiveness of chest monitoring for persons exposed to various uranium, plutonium, americium, and thorium bearing dusts. The lung retention and transportability characteristics of the actinides in humans have been predicted by combining the absorption rates into blood calculated from the animal studies with particle transport rates from the alveolar region of the human lung. This approach is compatible with the application of the new ICRP respiratory tract model.The results of the animal experiments demonstrate the diversity of the absorption rates for the different chemical forms of the actinides and their disparity from the default values proposed by ICRP for Type F, M, and S compounds in the absence of specific data. The predicted lung retention kinetics of the actinides in humans provide the basis for assessing the validity of chest monitoring; for this purpose the most recent ICRP values for doses per unit intake and deposition in the alveolar region of the lungs have been taken into account. The results show that for some dusts, the data can be interpreted with confidence, while for others the method is impracticable or has considerable uncertainty. Overall, the results support the ICRP recommendation that material specific information is to be preferred for setting limits on intake and interpreting monitoring data.The paper concludes with suggestions for further work.     

Radioactivity of teeth in the follow-up of old contamination cases

The activity of plutonium and americium has been measured in teeth from two persons involved in an incident 25 years ago at Eurochemic. Assuming that the alpha activity of the teeth is representative of the activity of the skeleton an estimate of the systemic body burden is given and compared to the value obtained from the late urinary excretion using the Leggett-Eckerman excretion model. The results are compared with some data from US Transuranium and Uranium Registries.     

The application of electrodeposition techniques to flameless atomic absorption spectrometry. Part III. The determination of cadmium in urine.

Cadmium in urine can be determined by a simple flameless atomic absorption technique, in which the metal is electrolyzed onto a thin platinum wire, followed by electrical heating of the wire. The technique is compared with the well-established flame procedure, involving extraction with APDC into MIBK. The data obtained by the two techniques are in good agreement. Large individual variations occur in the urinary concentration of cadmium for workers suspected of cadmium exposure. The group mean values for these workers lie in the range 4–5 p.p.b.; mean values for unexposed control groups are around 1 p.p.b. On a group basis, the results indicate a significantly higher urinary excretion of cadmium for the workers than for the control groups.     

Separation and determination of <Superscript>241</Superscript>Am in urine samples from radiation workers using PC88-A and alpha spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This article deals with standardization of analytical method for the determination of ²⁴¹Am isotope in urine samples using Extraction Chromatography (EC) and ²⁴³Am tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of americium along with calcium phosphate. This precipitate after treatment is further subjected to calcium oxalate co-precipitation. Separation of Am was carried out by EC column prepared by PC88-A (2-ethyl hexyl phosphonic acid 2-ethyl hexyl monoester) adsorbed on microporous resin XAD-7 (PC88A-XAD7). Am-fraction was electro-deposited and activity estimated using tracer recovery by alpha spectrometer. Ten routine urine samples of radiation workers were analyzed and consistent radiochemical recovery was obtained in the range 44–60% with a mean and standard deviation of 51 and 4.7% respectively.