Long-term Excretion of Thorium with Faeces and Urine from TIG Welders after Continuos Occupational Handling of Thoriated Electrodes

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1 Long-term Excretion of Thorium with Faeces and Urine from TIG Welders after Continuos Occupational Handling of Thoriated Electrodes P. Ostapczuk 1, R. Hille 1, A Titze 2, N. Witkowski 1 1 Division of Safety and Radiation Protection, Forschungszentrum Jülich, D Jülich, Germany e- mail: p.ostapczuk@fz-juelich.de 2 Department of Safety-Engineering, Bergische University of Wuppertal, Gauss-Strasse 20, D Wuppertal, Germany Abstract. Sufficiently accurate knowledge of systemically stored thorium is necessary for determining the organ-specific and effective doses. Inhaled thorium is incorporated into the body (stored in the bodily organs) partly in an acute and partly in a chronic manner. In the case of long-term continuous inhalation, the systemic fractions of the stored thorium as well as of that excreted with the faeces and urine increase both absolutely and relatively. In order to quantify their effect, stool and urine samples from two TIG welders who had worked with thoriated electrodes for many years were collected quantitatively in three survey phases. The first two phases lasting 10 and 5 days, respectively, fell within the normal working period. The excretion rates, especially of the faeces, provide statistically reliable findings on inhalation at the place of work. The third phase lasting 7 days was scheduled at the end of a fairly long holiday. The time between the last working day and the first sampling day amounted to at least one week so that the excretion from the acute fractions had practically ceased. Previous studies had shown that for a representative determination of excretion rates with the faeces and urine quantitative samples had to be collected for at least five days. The samples were processed radiochemical. The activities of Th-232, Th-230 and Th-228 were determined by α- spectrometry. From ICRP lung models and biokinetic models, criteria and computational procedures were derived which were suitable for assigning the measured excretion rates for faeces and urine to the acute and systemic fractions. 1. Introduction Thorium is a naturally occurring element with industrial (lantern mantels, welding operations, preparation of refractories) and medical (Thortras imaging agent) applications [1]. The study of thorium in urine and faeces samples can give us the information about the amount of incorporated thorium by inhalation or ingestion. All of thorium isotopes are radioactive. 228 Th (t 1/2 = 1.91 y), 230 Th (t 1/2 = y),and 232 Th (t 1/2 = y) decay by emission of alpha particles. Studies of human populations by a number of investigators have provided some information on the distribution of thorium in the human body as the result of long-term chronic intake from environmental sources of thorium. All of these studies indicate that the skeleton is the major deposition site for thorium for persons exposed principally through inhalation as well as for persons exposed to environmental sources of thorium [1]. The International Commission on Radiological Protection (ICRP) has issued radiation protection recommendations for thorium [2]. The model is developed within a generic model framework adopted by the ICRP for application to a class of bonesurface-seeking radionuclides (Fig. 1). To this point, the generic model framework has been applied by the ICRP to thorium, plutonium, americium, curium, and neptunium. The content of Thoriumdioxide in Thoriated electrodes is about one to five percent. The aim of the work was to check the influence of the long time working with this kind of electrodes to the content of Thorium nuclides in urine and faeces samples. 2. Experimental 2.1. Samples From two TIG-Welders (test persons) and two mechanics (comparative persons) in a metal working company (about 50 co-workers) in the time from Monday 07:00 p.m. to Saturday 07:00 p.m. have 1

2 been collected 24-hours urine and faeces samples. All the urine samples were collected in 200 ml (for daily check) or in 2 L PE (for 24 hours urine) containers. 2.2.Equipment Personal air sampling (FSP, Gilian pumps with Casella - A - sampling head) was used to collect the fine particle over the working time on a cellulose nitrate filter with 8 µm mash by controlled volume flow of 2 l/min = 0,96 m 3 /8 h. The filter, urine, and faeces samples were chemical prepared and the activity of Th-228, Th-230 and Th-232 by alpha spectrometry determined. The calculation of excretion rates of Thorium with urine and faeces was based on [3, 4]. OTHER SOFT TISSUES INTERMEDIATE RAPID SLOW SKELETON BLOOD VOLUME SURFACE MARROW LIVER 2 VOLUME SURFACE MARROW KIDNEYS OTHER KIDNEY TISSUE LIVER 1 URINE URINARY BLADDER CINTENTS URINARY PATH GONADES GI TRACT CONTENTS FAECES FIG. 1. The ICRP`s generic framework for modelling the systemic biokinetics of a class of bonesurface-seeking elements, including thorium. 2.3 Chemicals For the digestion of all the samples nitric acid (suprapur, 65%, Merck), perchloric acid (p.a %, Merck) and hydrofluoric acid (p.a. 40%, Merck) were used Internal standard To control all the steps of thorium determination in urine samples before the processing a known amount of Th-229 was added to the sample. By filters and faeces the addition was done after burn of the sample. 2

3 2.5. Analytical procedure 24 hour urine sample were evaporated to dryness by heating and addition of nitric acid. The filter and faeces samples were burn in an ofen by 480 C over the night. The precipitate should be digested using a mixture of nitric, perchloric and hydrofluoric acid. After separation of thorium by precipitation and ionexchange (Dowex 1x8, mesh) the preparation of measuring sample was done by elctrodeposition. The counting time was s. 3. Results 3.1. Breathing air activity Analytical data for Th-228, Th-230 and Th-232 obtained by filtration the breathing air has been demonstrated in Tables I and II. About 50% of all data were below the detection limit. Table I. Breathing air activity for test persons measured by personal air sampler in the sampling week (volume flow: 2 l/min; filtration time: 07:00 15:00 each day; < = below the detection limit) Breathing air activity [mbq/m 3 ] Test person 1 (TP1) Test person 2 (TP2) Day Th-232 Th-230 Th-228 Th-232 Th-230 Th-228 Mo < Tu < < Wed < Th < <0.13 <0.30 Fr <0.07 < <0.12 <0.27 Table II. Breathing air activity for comparison persons measured by personal air sampler in the sampling week (volume flow: 2 l/min; filtration time: 07:00 15:00 each day; < = below the detection limit) Breathing air activity [mbq/m 3 ] Comparison person 1 (CP1) Comparison person 2 (CP2) Day Th-232 Th-230 Th-228 Th-232 Th-230 Th-228 Mo < <0.16 <0.16 <0.32 Tu <0.11 <0.09 <0.11 <0.30 Wed <0.14 < <0.27 Th <0.13 < <0.27 Fr. <0.10 <0.01 < <0.28 From presented data it is obvious that for the test person 1 and 2 higher values of Th nuclides in the breathing air were found than for comparison person 1 and Excretion measurements In Table III were presented the mean values (n = 5 days) for thorium excretion with urine and faeces. The activity found for Th-228 in faeces was significant higher than activity found for Th-230 and Th This trend was also seen for urine samples but the differences were not so significant. Also excretion values for test persons (TP1 and TP2) were higher than the excretion values for comparison persons (CR1 and CR2). 3

4 Table III. 5 days mean of excretion rate due urine and faeces Excretion rate [mbq/day] Faeces Urine Person Th-232 Th-230 Th-228 Th-232 Th-230 Th-228 TP1 13,2 9,8 54,4 0,21 0,28 0,39 TP2 15,2 11,2 81,7 0,40 0,83 0,35 CR1 5,6 6,4 43,5 0,10 0,08 0,22 CP2 4,4 5,1 51,2 0,07 0,34 0, Activity proportion of Th-232/Th-228 Fig. 2 present the proportion of Th-232/Th-228 in breathing air, faeces and urine samples from all four persons. Results for test person 1 (TP1) demonstrate the highest values for breathing air and urine samples. Test person 2 (TP2) demonstrated the highest value for faeces. 2 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 Th-232/Th-228 Breathing air Faeces Urine TP1 TP2 CP1 CP2 FIG. 2. Proportion of Th-232/Th-228 in breathing air, faeces and urine samples. In urine samples the proportion Th-232/Th-228 change from 0.1 to Higher values for faeces demonstrate probably the natural influence of the ingestion of Th-232 by food. For CP1 And CP2 similar values were observed also in breathing air. The high values for TP1 and TP2 indicate a incorporation of Th-232 by inhalation. 5. Discussion Data presented in Table 1 indicated, that for the TP1 a high values for Th-232 and Th-228 were found. For all other persons values below the detection limit or close to them have been determined. The result of calculated intake of Th nuclides by breathing air for TP1 and TP2 demonstrate the table IV. For all analysed Th nuclides the highest values were found for test person 1. This results support the 4

5 observations done in the factory: the TP1 has been working on more bad conditions that the test person 2. Table IV. Calculated intake for Th based on thorium activity in the breathing air, faeces and urine (constant intake, activity median aerodynamic diameter AMAD = 1 µm, class Y, exposure time for TP1 = days, respectively for TP2 = days. Person Thorium intake [mbq/day] Excretion Breathing air Faeces Urine Th-232 Th-230 Th-228 Th-232 Th-230 Th-228 Th-232 Th-230 Th-228 TP TP < From data presented in Table IV it can be seen that for TP1 a nearly good agreement between intake calculated based on breathing air and intake calculated on excretion data for faeces and urine. In case of TP2 the observed differences can be only explained by Th intake with the daily diet. REFERENCES 1. Glovert, S.E, Traubt, R.J., Grimm, C.A., Filby, R.H., Radiation Protection Dosimetry, 97: (2001) 2. ICRP (1995a). International Commission on Radiological Protection. Age-Depend Doses to Members if the Public from Intake of Radionuclides, Part. 3 ICRP Publication 69, Pergamon Press, Oxford, ICRP publication 30, Part 1-3. Report of the task group on reference mean International Commission on Radiological Protection Publication 23. Pergamon Press, Oxford ICRP publication 54. Individual Monitoring for Intakes of radionuclides by workers: Design and Interpretation. Pergamon Press, Oxford,