Reevaluation of the Committed Dose Equivalent from 232th and its Radioactive Progeny

Lee, Dewhey; Skrable, Kenneth W.; French, C.S.

doi:10.1097/00004032-199704000-00010

Cited by 3 publications

(2 citation statements)

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“…As already mentioned in the introduction, only personal breathing zone samples can be accepted as representative of real exposure. It should be remarked that newer calculations (Lee et al 1997) have indicated that the current health risk of thorium intake, as expressed in the dose coefficients, may have been overestimated.…”

Section: Discussionmentioning

confidence: 99%

Intakes of Thorium While Using Thoriated Tungsten Electrodes for TIG Welding

Ludwig¹,

Schwass²,

Seitz³

et al. 1999

Health Physics

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Thoriated electrodes are used in TIG welding. TIG welders, along with persons who grind thoriated electrodes and persons located near relevant welding and grinding sites, might be at risk of thorium intake. The isotopes of radiological relevance are 232Th, 230Th, and 228Th. The studies described in the literature do not provide a consistent picture of the actual hazards, and changes in European and German radiological protection laws have now made it necessary to determine the risks. To accomplish this, a field test was conducted under real working conditions in 26 different welding shops. The airborne activity generated through welding, and through grinding of electrodes, was measured using personal air samplers. Stationary samplers were also used. The filters' samples were evaluated by means of direct alpha spectrometry with proportional counting and by means of gamma spectrometry following neutron activation. The results clearly showed that considerable intake can occur during both alternating-current welding and electrode grinding, if no suction systems are used. The range of 232Th intakes to welders were estimated from 0.1 Bq y(-1) to 144 Bq y(-1) during welding and from 0.02 Bq y(-1) to 30.2 Bq y(-1) during grinding. In 6 of the 26 cases the recent annual limit on intake derived from the most recent ICRP publications was exceeded--in the worst case it was exceeded by a factor of 10--if it is assumed that the persons studied were not exposed workers (not routinely monitored for radiation exposure). When the significantly more restrictive German limits are applied, the amounts by which the limits were exceeded were even greater. Because many qualified welders have very long careers, the risks can thus be considerable. The paper also discusses parameters that influence exposure, and it presents a catalogue of recommended measures for dosage reduction.

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Section: Discussionmentioning

confidence: 99%

Intakes of Thorium While Using Thoriated Tungsten Electrodes for TIG Welding

Ludwig¹,

Schwass²,

Seitz³

et al. 1999

Health Physics

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“…Since most long-lived alpha emitters yield multiple, unstable daughters, dosimetry calculations for alpha-particle emitters require a theoretical framework to predict the dose to organs if the total dose also contains a contribution from the unstable intermediates. 1 In this work, a formalism that accounts for the effective biodistribution is presented. This effective biodistribution depends, among other factors, on the site at which the parent radionuclide decays, the known biodistribution of the daughters, and on the half-life of each radionuclide.…”

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confidence: 99%

A schema for estimating absorbed dose to organs following the administration of radionuclides with multiple unstable daughters: A matrix approach

Hamacher

Sgouros

1999

Medical Physics

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The dosimetry of alpha particle emitters requires that all decays, including those of unstable intermediates be included in the calculation. Such calculations are complicated by the potential differential biologic distribution of each of the intermediates. In this work we present a formalism which will account for the known biodistribution factors of the daughters and the resulting effective biodistribution which will depend upon the site at which the parent radionuclide decays. The number of decays or cumulated activity of a daughter radionuclide present in a particular tissue is estimated using a probability matrix which describes the likelihood of daughter decay in a particular tissue as a function of the decay site of the parent. An example of three initial compartments is provided to illustrate the use of this formalism. Such modeling may be used to evaluate the feasibility of using radionuclides whose decay includes alpha-emitting intermediates. Model validation and refinement will require an assessment of the fate of free, alpha-emitting intermediates in various biological milieus.

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Biokinetic modelling of natural thorium in humans by ingestion

Li¹,

Wahl²,

Oeh³

et al. 2006

Radiation Protection Dosimetry

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The retention of naturally occurring thorium (228Th, 230Th, 232Th) in model compartments and its daily urinary and faecal excretion after acute and chronic injections and ingestions were calculated for male and female subjects of six age groups based on the current age-dependent biokinetic model for thorium (Th) recommended by the International Commission on Radiological Protection (ICRP). The results are tabulated in a database. The calculated contents of 228,230,232Th in organs or tissues using their reference concentrations in foodstuffs for the European population are compared with autopsy data. The model prediction of 232Th in whole body for a 50-year-old unexposed person is 22 mBq, 86% of that in skeleton, 9.7% in other soft tissues, 3.4% in liver, 0.7% in kidneys and 0.01% in blood. The modelling predicts lower contents of the natural Th isotopes in whole body, especially in blood compared with measured data for the unexposed public. Modelled 232Th daily urinary excretions are 5 to 10 times less than bio-assay data from the authors' own laboratory.

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Reevaluation of the Committed Dose Equivalent from 232th and its Radioactive Progeny

Cited by 3 publications

References 0 publications

Intakes of Thorium While Using Thoriated Tungsten Electrodes for TIG Welding

Intakes of Thorium While Using Thoriated Tungsten Electrodes for TIG Welding

A schema for estimating absorbed dose to organs following the administration of radionuclides with multiple unstable daughters: A matrix approach

Biokinetic modelling of natural thorium in humans by ingestion

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