This paper describes the merits and demerits of each technique utilized for determining the intakes of radioactive materials in workers with particular emphasis on the intake of thorium, uranium, and plutonium. Air monitoring at work places have certain flaws, which may give erroneous estimates of intake of the radionuclides. Bioassay techniques involve radiochemical determinations of radionuclides in biological samples such as urine, feces etc, and employing biokinetic models to estimate the intake from such measurements. Though, highly sensitive and accurate procedures are available for the determination of these radionuclides biokinetic models employed produce large errors in the estimate. In vivo measurements have fundamental problems of poor sensitivities. Also, due to non-availability of such facilities at most of the nuclear sites transporting workers at different facilities may cost a lot of financial resources. It seems difficult to defend in the court of law that determination of intake of radioactive material in workers by an individual procedure is accurate; at the best these techniques may be employed to obtain only an estimate of intake.
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.
The present paper deals with the following questions: Can a piece of any tissue or organ obtained at autopsies and/or biopsies be analyzed to predict the organ and/or body burden, initial exposures, and the committed dose equivalents to the workers or retired workers from exposures to thorium, uranium, and plutonium and what are the consequences of using such materials in predicting the initial exposures and the dose estimates? Based on the studies of the distribution of uranium and thorium in former uranium miners and millers, the distribution of plutonium in general population, and several other studies dealing with the distribution of actinides in man, it is reasonable to state that the utilization of tissue analyses for estimating the initial exposure to the workers may have serious limitations. The regulatory agencies must restrict the conditional utilization of tissue analyses in estimating exposures to the workers for thorium, uranium, and plutonium.
An analysis of the reliability of the ICRP's dose coefficients for intake of radionuclides, applied on the Human Respiratory Tract Dosimetry Model proposed in ICRP Publication No. 66 was carried out, with respect to the following variables: ventilation rates, time budget, total deposition, regional deposition for the four respiratory tract compartments (alveolar-interstitium, bronchioles, bronchi and extrathoracic), oral versus nasal breathing patterns, and variation in clearance rates of compartments. The analysis was done by calculating reliability factors defined as the square root of the ratio of larger to smaller dose coefficient calculated at the extreme values for the model parameter being tested, in intervals of values of the effective dose. Calculations for each of the variables were carried out for an adult, using these 12 radionuclides: 3H, 60Co, 90Sr, 95Zr, 106Ru, 125Sb, 131I, 137Cs, 210Pb, 226Ra, 238U and 239Pu. For AMAD = 0.1 mm the analysis associated with the total deposition in the compartments indicated a Reliability Category II. For AMADs = 1.0 and 10 mm the analysis associated with the deposition in the extrathoracic compartments indicated a Reliability Category II. For AMAD = 10 mm the deposition in the compartments of the tracheobronchial region also showed a Reliability Category II. Most results for all other parameters for the studied AMADs were found to be in Category I. The corresponding impacts on the uncertainties in the predicted bioassay results for these twelve radionuclides were also determined. This analysis is especially helpful when doses are estimated through bioassay measurements employing the ICRP Publication 66respiratory tract model.
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.
Authors:J. Lipsztein, D. Grynspan, B. Dantas, L. Bertelli, and M. Wrenn
The main objective of this paper is to point out problems associated with interpretation of bioassay monitoring in view of the existing biokinetic models. The exposure to thorium in Brazil is given in this paper as an example of the seriousness of the problem.
Authors:L. Costa, G. Paganetto, G. Bertelli, and G. Camino
The thermal decomposition of SbOCl, Sb4O5Cl2 and Sb8O11Cl2 has been studied by thermogravimetry with identification of the products resulting in the condensed phase by X-ray diffraction and infrared technique. It is shown that in nitrogen SbOCl undergoes progressive stepwise thermal disproportionation to Sb2O3 and SbCl3 with formation of Sb4O5Cl2 and Sb8O11Cl2 and as intermediates. It is thus confirmed that Sb3O4Cl, suggested to be formed instead of Sb8O11Cl2, is not an intermediate of this process. An identical mechanism is observed in air but with oxidation of Sb2O3 to Sb2O4.
Authors:L. Bertelli, A. Puerta, M. Wrenn, and J. Lipsztein
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.