Radioactivity in human tissues

Transcription

1 Radioactivity in human tissues C.Papastefanou 1, M.Manolopoulou 1, L.Sihletidis 2 1 Atomic and Nuclear Physics Laboratory, Aristotle University of Thessaloniki, Thessaloniki, GR GREECE. papastefanou@physics.auth.gr, manolopoulou@physics.auth.gr 2 Laboratory of Pmeumonology, Aristotle University of Thessaloniki, Thessaloniki, GR GREECE. Abstract. The radioactivity in human tissues (lungs) obtained from the dead body of people who died by lung cancer in the region of Ptolemais, Northern Greece, where 16 units of 4 major coal-fired power plants are in operation, was studied. The specific activities of radioactive nuclides searched for in human tissues were not remarkable. The syndrome of lung cancer deaths at that area which showed an increase of 60% in the decade of as compared with that of the decade of might not be attributed to the escaping radioactivity from the coal-fired power plants into environment but in other reasons, as for example to various effluents in gaseous and or particulate form, which are the main pollutants discharged during the normal operation of the plants. 1. Introduction. It is well known that most types of lignites burned in coal-fired power plants (CPP) all over the world contain naturally occurring primordial radionuclides, particularly of the uranium-radium series, as well as the thorium series and potassium-40. The conventional fossil fueled plants discharge relatively greater quantities of radioactive materials into the atmosphere than nuclear powered plants of comparable size, during normal operation. A significant part of the radioactive nuclides escape from the stacks of CPPs and are discharged into environment as gases or fine particles [1-4]. In this way, coal burning might contribute significantly to the natural radioactivity of the CPP environment and remain a potential hazard to human health through intake via food and water and by inhalation. Radium-226 from such activity might be considering as an index of the environmental pollution on human beings. In the literature some papers have been appeared dealing with the radiation dose from coal-fired power plants and the associated risks. It was concluded that they result in relative risks during normal operation of the plants [5-9]. The purpose of this paper was to investigate by examining the radioactivity of human tissues in people living or working at Ptolemaida region, Northern Greece, where 16 units in 4 major coal-fired power plants are in operation (Fig.1) and to find out any association of lung cancer deaths with the radioactive effluents of the plants and the followed deposition onto the ground and vegetation. People living at Ptolemaida region believed that the syndrome of lung cancer, not only to workers at CPPs, is due to the environmental radioactivity associated with the operation of the coal-fired power plants.

2 FIG.1 A map of the valley of Ptolemaida, Northern Greece showing the location of the 4 coal-fired power plants (CPP). 2. Experimental procedure Seven human tissue samples were obtained from the dead body of people (men) who died by lung cancer in the region of Ptolemaida, Northern Greece, and latitudes: N, longitudes: E (Fig.2), population: according to the 2001 census of the Greek population. The age of men ranged between 56 and 70 years. Sampling was performed during the years , 8 years after the Chernobyl reactor accident (1986). The sampling of human tissues was performed at the Papanikolaou hospital at Thessaloniki suburban area, Northern Greece, by the Laboratory of Pneumonology, Aristotle University of Thessaloniki. The tissue samples were dried and then burned to ash. After that, the ash samples were mixed with active charcoal and then sealed appropriately for about one month [10] to reduce the leaching and to obtain radioactive equilibrium between radon and its decay products, as 8 half lives of Rn-222, the decay product of Ra-226, is 1 month. The samples were measured in a standard geometry of 40g plastic can and of 6cm diameter. The tissue samples were examined for radioactivity by γ-ray spectrometry using HPGe detectors of high resolution (1.9 kev at 1.33 MeV of Co-60) and high efficiency (42%).Uranium 238 was searched for via its decay product Th-234 (63 and 93 kev γ-rays) and Ra-226 was searched for via the 186 kev γ-ray. Potassium 40 was determined via the 1,460 kev γ-ray and Cs-137 fission yielded of Chernobyl origin was determined via the 662 kev γ-ray. The overall efficiency of the counting system was known to an accuracy of better than 5%. The spectrums collecting time was 120,000 seconds.

3 FIG 2. A map of Greece showing in the frame the region of interest in this study. 3. Results and Discussion Table I presents the activity concentrations in Bq. kg -1 of U-238, Ra-226, K-40 and Cs-137 in human tissues (lungs). U-238 was not detected. The low detection limit of U-238 in tissue samples was 67 Bq. kg -1. Radium was detected in one sample at the level of 1.4 Bq. kg -1. According to that level, the Ra- 226 content of the human body (70 kg standard person) estimated to be 98.7 Bq. A body burden (case of skeleton) of Bq (30-40 pci) of Ra-226 produces a dose to osteocytes of 60 µsv. y -1 (6 mrem. y -1 ) and a dose to bone marrow of 3 µsv. y -1 (0.3 mrem. y -1 ). The average natural tissue and or body burden of Ra-226 is 1.33 Bq (36 pci), while the maximum permissible body burden, MPBD of Ra-226 is 3700 Bq (0.1 µci) [11]. Potassium-40 concentrations ranged from 10.3 to 46.9 Bq. kg -1 (averaged 33.7 Bq. kg -1 ). The K-40 content of the human body ranged from 721 to 3283 Bq (averaged 2359 Bq) for the standard person (70 kg). That level of K-40 is about half of the typical normal body burden of 4440 Bq (0.12 µci) for standard person [11].

4 Table I. Activity concentrations (Bq. kg -1 ) in human tissues (lungs). Sample No. Ra-226 K-40 Cs-137 TISP TISP TISP TISP TISP TISP TISP Cesium-137 concentrations ranged from 0.24 to 0.57 Bq. kg -1 (averaged 0.35 Bq. kg -1 ). This level of Cs- 137 is negligible as the maximum permissible body burden, MPBD of Cs-137 is 1.1 MBq (30 µci) [11]. The presence of Cs-137 in human tissues 8 years after Chernobyl accident reflected cesium deposition from the period of the accident (26 April 1986). Indoor radon measurements in the Ptolemaida region during the years according to a radon survey showed increasing radon concentrations in dwellings and workplaces. In 1985, indoor radon concentrations ranged from 63 to 226 Bq. m -3 (averaged 108 Bq. m -3 ), while in 1986, indoor radon concentrations ranged from 23 to 123 Bq. m -3 (averaged 59 Bq. m -3 ) and in 1987, indoor radon concentrations varied between 15 to 154 Bq. m -3 (averaged 57 Bq. m -3 ) [12]. It must be noted that radon concentrations outdoors ranged from 3.63 to Bq. m -3 (averaged 9.09 Bq. m -3 ) [13]. The number of lung cancer deaths at that region showed an increase of 60% from the decade of to the decade of , according to the data of the Laboratory of Pneumonology, Aristotle University of Thessaloniki (Table II). Cancer deaths due to other reasons did not show any increase during the same period. Table II. Cancer deaths in the region of Ptolemaida, Northern Greece. Tissue Period Period Lungs Blood Digestive Abdomen Uterus-breast Brain Urinary Bones 3 2 Other Conclusions The specific activities of radionuclides searched for in human tissues (lungs) were not remarkable. The syndrome of lung cancer deaths appeared to the population living around the coal-fired power plants might not be attributed to the escaping radioactivity from the stacks of plants into environment but in other reasons, as for example to various effluents in gaseous and or particulate form, which are the main pollutants discharged during the normal operation of the plants [14]. The fact that people living at Ptolemaida region, Northern Greece, believed that the reason of the syndrome of lung cancer is due to the environmental radioactivity associated with the operation of the coal-fired power plants is not true as it was not confirmed by the data of this work.

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