Determination of trace elements in Wistar rats bone by neutron activation analysis

The present study is part of the project: 'Study of uranium biodistribution in the food chain', with the aim of investigating the uranium transfer from soil to the human beings. Particularly in this experiment, the main idea is to investigate physiological alterations induced by intake of natural uranium in Wistar rats bone. The Wistar rats have been selected as a convenient animals for this study in function of the cost, handling and medico- legal implications. The experiment was performed with 15 male rats, 15 days old, assembled in groups with 2 animals each, and a control group with 3 animals. During two months they were kept in a temperature and air-controlled room and they were fed daily with chow doped with uranyl nitrate (except for the control group), at the following ppm concentrations of uranium per group: 20, 50 and 100. The control and measurements of the amount of ingested food and animal weight were carried out daily during the experiment. After that the animals were sacrificed and dissected. The samples of bones were calcinate, ground and homogenized and the ashes were analyzed by neutron activation analysis (NAA). Basically, the bone consists of 45 % of water, 35% mineral salts ( chiefly calcium and phosphorus ) and 20 % organic matter (chiefly collagen). Particularly, the inorganic fraction also contain small amounts of Sodium , Magnesium, Potassium and other trace elements. The procedure to identify and to determine the concentrations of these elements was the following: 50 mg of the ashed samples were weighed and sealed in polyethylene bags; aliquots of standard solutions the elements of interest, were pipette onto 1 cm2 pieces of Whatman No.40 filter paper, evaporated to dryness under an infrared lamp and were also sealed into polyethylene bags; samples and standards were irradiated at the IEA-R1 m nuclear reactor of IPEN/CNEN-SP. In order to determine short half live isotopes, the samples were irradiated at a thermal neutron flux of 5.1012n/ cm2.s for 3 minutes, and at a flux of 1012n/cm2.s, for 8 hours, to determine long half live isotopes. For uranium analysis, samples and standard were irradiated inside a Cadmium capsule. The samples and standard were analyzed with a gamma-spectrometer with Ge detector of high resolution (FWHM<1.87 keV at 1.32 MeV of 60 Co), mounted inside a lead shield hood in order to reduce the background radiation. The detector was operated with 671 ORTEC amplifier, in pile-up rejection mode. For Phosphors determinations, the beta particles of 32 P were measured by using a Geiger Muller detector. The concentration of the Al, As, Ca, Cl, Mg, Fe, K, Na, Rb, Sr, Zn and U for 20, 50 and 100 ppm, were determined and the results were discussed according to the uranium ingestion. Since bone is a major component of the skeletal system and about 99% of body calcium is found in side it we could compare the evaluation of Ca in the control group (normal value) with those group doped with uranyl nitrate. According to the results obtained no significant differences were observed among the values, especially for Ca and P, though an accumulation of Uranium in the bone was verified. (author)