Relationships Between Iodine and Some Trace Elements in Normal Thyroid of Males Investigated by Neutron Activation Analysis

Introduction

According to the World Health Organization (WHO), thyroid dis-eases rank second among endocrine disorders after diabetes mel-litus. More than 665 million people in the world have endemic goiter or suffer from other thyroid pathologies. At the same time, according to the same statistics, the increase in the number of thy¬roid diseases in the world is 5% per year [1]. It has been suggest¬ed that risk factors for the development of thyroid disorders may be numerous factors, including genetics, radiation, autoimmune diseases, as well as adverse environmental factors, such as an in¬crease in the content of various chemicals in the environment [2].

Trace elements (TE) are among these various chemicals, because their levels in the environment have increased significantly over the past hundred years as a result of the industrial revolution and the tremendous technological changes that have taken place in metallurgy, chemical production, electronics, agriculture, food processing and storage, cosmetics, pharmaceuticals and medicine. In connection with these changes, the levels and ratio of TE en-tering the human body from the outside have been significantly disturbed, compared with the conditions in which human societies have lived for many millennia.

More than 50 years ago, we formulated the postulate about the so¬matic TE homeostasis, which is now generally recognized [3]. Ac¬cording to this postulate, under evolutionary environmental condi¬tions, the mechanisms of homeostasis of organisms maintain the levels and ratios of TE in tissues and organs within certain limits. If the content of TE in the environment changes significantly, the mechanisms of somatic homeostasis may respond inadequately. Inadequate response of homeostasis mechanisms leads to changes in TE levels in tissues and organs, which, in turn, can affect their function and lead to the development of pathological conditions. The correctness of this conclusion was illustrated by us earlier on the example of the study of the role of TE in the normal and patho-physiology of the prostate [4-24]. It was shown, in particular, that a special role in the development of pathological transformations of the prostate is played by disturbances in the relationship be¬tween TE in the tissue and gland secretion. Moreover, it was found that changes in the relationship between TE can be used as highly informative markers of various prostate diseases, including malig¬nant tumors [25-39]. These findings stimulated our investigations of TE relationships in thyroid tissue in normal and pathological conditions.

There are many studies regarding TE content in human thyroid, us-ing chemical techniques and instrumental methods [40-52]. How¬ever, among the published data, no works on the relationship of TE in the normal human thyroid were found.

This work had three aims. The primary purpose of this study was to determine reliable values for the silver (Ag), cobalt (Co), chro-mium (Cr), iron (Fe), mercury (Hg), iodine (I), rubidium (Rb), an-timony (Sb), scandium (Sc), selenium (Se), and zinc (Zn) mass fractions in the normal thyroid of subjects ranging from children to elderly males using instrumental neutron activation analysis (INAA) and calculate individual values of I/Ag, I/Co, I/Cr, I/Fe, I/ Hg, I/Rb, I/Sb, I/Sc, I/Se, and I/Zn . The second aim was to com¬pare the Ag, Co, Cr, Fe, Hg, I, Rb, Sb, Sc, Se, and Zn mass frac¬tions in thyroid gland obtained in the study with published data. The final aim was to estimate the inter-correlations of TE contents and I/TE content ratios in normal thyroid of males and changes of these parameters with age. All studies were approved by the Ethical Committees of the Med-ical Radiological Research Centre, Obninsk.

All the procedures performed in studies involving human participants were in accor-dance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments, or with comparable ethical standards.

Materials and Methods

Samples of the human thyroid were obtained from randomly se-lected autopsy specimens of 73 males (European-Caucasian) aged 2.0 to 80 years. All the deceased were citizens of Obninsk and had undergone routine autopsy at the Forensic Medicine Depart-ment of City Hospital, Obninsk. The available clinical data were reviewed for each subject. None of the subjects had a history of an intersex condition, endocrine disorder, or other chronic disease that could affect the normal development of the thyroid. None of the subjects were receiving medications or used any supplements known to affect thyroid TE contents. The typical causes of sudden death of most of these subjects included trauma or suicide and also acute illness (cardiac insufficiency, stroke, embolism of pulmonary artery, alcohol poisoning). All right lobes of thyroid glands were divided into two portions using a titanium scalpel [53]. One tissue portion was reviewed by an anatomical pathologist while the other was used for the TE content determination. A histological exam- ination was used to control the age norm conformity as well as the unavailability of microadenomatosis and latent cancer.

After the samples intended for TE analysis were weighed, they were transferred to -20°C and stored until the day of transportation in the Medical Radiological Research Center, Obninsk, where all samples were freeze-dried and homogenized [54]. To determine the contents of the TE by comparison with a known standard, ali¬quots of commercial, chemically pure compounds were used [55]. Ten subsamples of the Certified Reference Material (CRM) IAEA H-4 (animal muscle) and IAEA HH-1 (human hair) were analyzed to estimate the precision and accuracy of results. The CRM IAEA H-4 and IAEA HH-1 subsamples were prepared in the same way as the samples of dry homogenized thyroid tissue.

The content of I was determined by INAA using short irradiation in a horizontal channel equipped with the pneumatic rabbit system of the WWR-c research nuclear reactor in Obninsk. The neutron flux in the channel was 1.7 × 1013n cm−2 s−1. A vertical channel of nu¬clear reactor WWR-c with a neutron flux of 1.3â?»1013 nâ?»cm-2â?»s-1 was applied to determine the content of Ag, Co, Cr, Fe, Hg, Rb, Sb, Sc, Se, and Zn by long irradiation. Details of sample preparation and used nuclear reactions, induced radionuclides, gamma-ener-gies and semiconductor spectrometry were presented in our earlier publications concerning TE contents in human scalp hair [56-57].

A dedicated computer program for INAA-SLR mode optimization was used [58]. All thyroid samples were prepared in duplicate, and mean values of TE contents were used in final calculation. Using Microsoft Office Excel, a summary of the statistics, includ¬ing, arithmetic mean, standard deviation, standard error of mean, minimum and maximum values, median, percentiles with 0.025 and 0.975 levels was calculated for TE contents and I/TE content ratios. Pearson's correlation coefficient was used in Microsoft Of¬fice Excel to calculate the relationship "age – TE mass fraction", as well as to identify inter-thyroidal relationships between different TE contents and between different TE content ratios.

Results

Table 1 depicts comparison of our data for ten TE in ten sub-sam-ples of CRM IAEA H-4 (animal muscle) and IAEA HH-1 (hu¬man hair) with the corresponding certified values of TE contents in these materials.

Table 1. INAA-LLR data of trace element contents in certified reference material IAEA H-4 (animal muscle) and IAEA HH-1 (human hair) compared to certified values ((mg/kg, dry mass basis)

Table 2 represents certain statistical parameters (arithmetic mean, standard deviation, standard error of mean, minimal and maximal values, median, percentiles with 0.025 and 0.975 levels) of the Ag, Co, Cr, Fe, Hg, I, Rb, Sb, Sc, Se, and Zn mass fractions, as well as I/Ag, I/Co, I/Cr, I/Fe, I/Hg, I/Rb, I/Sb, I/Sc, I/Se, and I/Zn mass fraction ratios in normal thyroid of males.

Table 2. Some statistical parameters of Ag, Co, Cr, Fe, Hg, I, Rb, Sb, Sc, Se, and Zn mass fraction (mg/kg, dry tissue) as well as I/Ag, I/Co, I/Cr, I/Fe, I/Hg, I/Rb, I/Sb, I/Sc, I/Se, and I/Zn mass fraction ratios in normal male thyroid (n=73)

The comparison of our results with published data for the Ag, Co, Cr, Fe, Hg, I, Rb, Sb, Sc, Se, and Zn contents in the human thyroid is shown in Table 3.

Table 3. Median, minimum and maximum value of means Ag, Co, Cr, Fe, Hg, Rb, Sb, Sc, Se, and Zn contents in normal human thyroid according to data from the literature in comparison with our results (mg/kg, dry tissue

M –arithmetic mean, SD – standard deviation, (n)* – number of all references, (n)** – number of samples. To estimate the effect of age on the TE contents and I/TE content ratios in normal thyroid of males Pearson's correlation coefficient was used (Table 4).

Table 4. Correlations between age (years) and trace element content (mg/kg, dry tissue), as well as between age and I/trace ele¬ment mass fraction ratios in the normal male thyroid (r – coefficient of correlation)

El - element, Statistically significant values: a p≤0.05, b p≤0.01, c p≤0.001.

The data of inter-thyroidal correlation (values of r – Pearson's coefficient of correlation) including all TE and I/TE content ratios identi-fied by us are presented in Tables 5 and 6, respectively.

Table 5. Intercorrelations of the chemical element mass fractions in normal male thyroid (r – coefficient of correlation)

                                        El – element, Significant values: ^a p≤0.05, ^b p≤0.01, ^c p≤0.001.

Table 6. Intercorrelations of the I/trace element mass fraction ratios in normal male thyroid (r – coefficient of correlation)

                                          Statistically significant values: ^a p≤0.05, ^b p≤0.01, ^c p≤0.001

Discussion

Good agreement of the Ag, Co, Cr, Fe, Hg, I, Rb, Sb, Sc, Se, and Zn contents analyzed by INAA with the certified data of CRMs IAEA H-4 and IAEA HH-1 (Table 1) indicates an acceptable accu-racy of the results obtained in the study for TE contents and I/TE content ratios in the normal male thyroid presented in Tables 2–6.

The content of TE was determined in all or most of the examined samples, which made it possible to calculate the main statistical parameters: the mean value of the mass fraction (M), standard de¬viation (SD), standard error of the mean (SEM), minimum (Min), maximum (Max), median (Med), and percentiles with levels of 0.025 (P 0.025) and 0.975 (P 0.975), of the Ag, Co, Cr, Fe, Hg, I, Rb, Sb, Sc, Se, and Zn mass fractions, as well as I/Ag, I/Co, I/Cr, I/Fe, I/Hg, I/Rb, I/Sb, I/Sc, I/Se, and I/Zn mass fraction ratios in normal thyroid of males (Table 2). The values of M, SD, and SEM can be used to compare data for different groups of samples only under the condition of a normal distribution of the results of deter¬mining the content of TE in the samples under study. Statistically reliable identification of the law of distribution of results requires large sample sizes, usually several hundred samples, and therefore is rarely used in biomedical research. In the conducted study, we could not prove or disprove the “normality” of the distribution of the results obtained due to the insufficient number of samples stud¬ied. Therefore, in addition to the M, SD, and SEM values, such statistical characteristics as Med, range (Min-Max) and percentiles P 0.025 and P 0.975 were calculated, which are valid for any law of distribution of the results of TE content in thyroid tissue.

Values obtained for Cr, Fe, Hg, Rb, Sb, Sc, Se, and Zn contents in the normal human thyroid (Table 3) agree well with median of mean values reported by other researches [40-52]. The obtained means for Ag and Co were almost one order of magnitude lower median of previously reported means but inside the range of means (Table 3). Data cited in Table 3 also includes samples obtained from patients who died from different non-endocrine diseases. A number of values for TE mass fractions were not expressed on a dry mass basis by the authors of the cited references. However, we calculated these values using published data for water (75%) [42] and ash (4.16% on dry mass basis) [59] contents in thyroid of adults. No published data referring to I/Ag, I/Co, I/Cr, I/Fe, I/ Hg, I/Rb, I/Sb, I/Sc, I/Se, and I/Zn mass fraction ratios in human thyroid was found.

With age, the I and Se content, as well as the I/Cr and I/Rb content ratio increase (Table 4). These characteristics can be used to esti¬mate the "biological age" of the male thyroid gland.

A significant direct correlation between the Ag and Co, Ag and Cr, Co and Cr, Cr and Rb, I and Sb, I and Se, Rb and Sc, Rb and Zn, Sb and Se mass fractions as well as an inverse correlation between I and Fe, Co and Hg, Cr and Hg, Hg and Sc, mass fractions was seen in male thyroid (Table 5).

Since no correlations were found between I and other TE, except for a direct correlation between I and Sb, I and Se an, as well as for inverse correlation between I and Fe, it would appear that the content of Ag, Co, Cr, Hg, Rb, and Zn in the thyroid gland is inde¬pendent of I content. However, this is not quite so. If we bring the content of the studied TE to the content of I (I/TE ratio), then there are close relationships between I/Ag, I/Co, I/Cr, I/Fe, I/Hg, I/Rb, and I/Zn. (Table 6). From this it follows that, at least, the levels of Ag, Co, Cr, Fe, Hg, Rb, Sb, Se, and Zn in the thyroid gland are in¬terconnected and depend on the content of I in it. Because I plays a decisive role in the function of the thyroid gland, the data obtained allow us to conclude that, along with I, such TE as Ag, Co, Cr, Fe, Hg, Rb, Sb, Se, and Zn, if not directly, then indirectly, are involved in the process of thyroid hormone synthesis.

Conclusion

The neutron activation analysis is a useful analytical tool for the non-destructive determination of TE contents in the thyroid tissue samples. This method allows at least determine means for Ag, Co, Cr, Fe, Hg, Rb, Sb, Sc, Se, and Zn (ten TE).

Our data reveal that the I and Se content, as well as the I/Cr and I/ Rb content ratio increase in the normal thyroid of male during a lifespan. Therefore, a goitrogenic and tumorogenic effect of exces¬sive I and Se level in the thyroid of old males and of disturbance in intrathyroidal I/Cr and I/Rb relationships with increasing age may be assumed. Furthermore, it was found that the levels of Ag, Co, Cr, Fe, Hg, Rb, Sb, Se, and Zn in the thyroid gland are inter-connected and depend on the content of I in it. Because I plays a decisive role in the function of the thyroid gland, the data obtained allow us to conclude that, along with I, at least such TEs as Co, Cr, Fe, Rb, Sb, Se, and Zn, if not directly, then indirectly, are involved in the process of thyroid hormone synthesis.

Acknowledgements

We are grateful to Dr. Yu. Choporov, Head of the Forensic Medi-cine Department of City Hospital, Obninsk, for supplying thyroid samples.

References

1. Wang H, Jiang Y, Song J, Liang H, Liu Y, Huang J, Tin P, Wu D, Zhang H, Liu {, Zhon D, Wei W, Lei L, Peng J, Zhang J. The risk of perchlorate and iodine on the incidence of thyroid tumors and nodular goiter: a case-control study in southeast-ern China. Environ Health. 2022; 21: 4.
2. Tang Z, Zhang J, Zhou Q, Xu S, Cai Z, Jiang G. Thyroid Can­cer "epidemic": a socio-environmental health problem needs collaborative efforts. Environ Sci Technol. 2020; 54(7): 3725–3727.
3. Zaichick V. Medical elementology as a new scientific disci­pline. J Radioanal Nucl Chem. 2006: 269: 303-309.
4. Zaichick V. A systematic review of the mercury content of the normal human prostate gland. Archives of Urology 2020; 3(2): 35-45.
5. Zaichick V. A systematic review of the cobalt content of the normal human prostate gland. J Clin Res Oncol. 2020; 3(1): 1-8.
6. Zaichick V. A systematic review of the phosphorus content of the normal human prostate gland. Applied Medical Research 2020; 7(2): 1-7.
7. Zaichick V. A systematic review of the antimony content of the normal human prostate gland. Journal of Hematology and Oncology Research 2021; 4(1): 17-27.
8. Zaichick V. A systematic review of the chromium content of the normal human prostate gland. Innovare Journal of Medi­cal Sciences 2021; 9(1): 1-6.
9. Zaichick V. A systematic review of the nickel content of the normal human prostate gland. Health Sciences 2020; 1(ID 234): 1-6.
10. Zaichick V. A systematic review of the aluminum content of the normal human prostate gland. Advances in Hematology and Oncology Research 2021; 4(1): 69-75.
11. Zaichick V. A systematic review of the lead content of the nor­mal human prostate gland. J Cancer Oncol Res. 2021; 2(1): 1-8.
12. Zaichick V. A systematic review of the arsenic content of the normal human prostate gland. International Journal of Medi­cine Sciences 2021; 3(1): 1-6.
13. Zaichick V. A systematic review of the calcium content of the normal human prostate gland. Iberoamerican Journal of Med-icine 2021; 3(1): 85-94
14. Zaichick V. A systematic review of the tin content of the nor­mal human prostate gland. Journal of Cellular & Molecular Oncology 2021; 3(1): 1-7.
15. Zaichick V. Barium levels in the prostate of the normal hu­man: a review. Universal Journal of Pharmaceutical Research 2021; 6(1): 52-60.
16. Zaichick V. A systematic review of the zinc content of the hyperplastic human prostate gland. Biomedical Research on Trace Elements 2020; 31 (3): 98-116.
17. Zaichick V. Beryllium content of the normal human prostate gland: A systematic review. Acta Scientific Medical Sciences 2021; 5(4): 78-85.
18. Zaichick V. Boron level in the prostate of the normal human: A systematic review. J Nano Nano Sci Rese. 2021; 1(2): 1-9.
19. Zaichick V. Bismuth level in the prostate of normal human: A systematic review. Int J Biopro Biotechnol Advance 2021; 7(1): 264-273.
20. Zaichick V. A systematic review of the cadmium content of the normal human prostate gland. World Journal of Advanced Research and Reviews 2021; 10(01): 258-269.
21. Zaichick V. A systematic review of the strontium content of the normal human prostate gland. Journal of Medical Re­search and Health Sciences (JMRHS) 2021; 4 (5): 1257-1269.
22. Zaichick V. Thallium content of the normal human prostate gland - A systematic review. Archives of Clinical Case Re­ports 2021; 2(5): 223-229.
23. Zaichick V. Vanadium content of the normal human prostate gland: A systematic review. Archives of Pharmacy Practice 2021; 12(3): 15-21.
24. Zaichick V, A systematic review of the zinc content of the normal human prostate gland. Biol Trace Elem Res. 2021; 199(10): 3593-3607.
25. Zaichick V, Zaichick S. Ratios of selected chemical element contents in prostatic tissue as markers of malignancy. Hema-tol Med Oncol. 2016; 1(2): 1-8.
26. Zaichick V, Zaichick S. Ratios of Zn/trace element contents in prostate gland as carcinoma’s markers. Cancer Rep Rev. 2017; 1(1): 1-7.
27. Zaichick V, Zaichick S. Ratios of Mg/trace element contents in prostate gland as carcinoma’s markers. SAJ Canc Sci. 2017; 2(1): 102.
28. Zaichick V, Zaichick S. Ratios of calcium/trace elements as prostate cancer markers. J Oncol Res Ther. 2017; 2017(4): J116.
29. Zaichick V, Zaichick S. Ratios of cobalt/trace element con­tents in prostate gland as carcinoma’s markers. The Interna­tional Journal of Cancer Epidemiology and Research 2017; 1(1): 21-27.
30. Zaichick V, Zaichick S. Ratios of cadmium/trace element con­tents in prostate gland as carcinoma’s markers. Canc Therapy & Oncol Int J. 2017; 4(1): 555626.
31. Zaichick V, Zaichick S. Ratios of selenium/trace element con­tents in prostate gland as carcinoma’s markers. J Tumor Med Prev. 2017; 1(2): 555556.
32. Zaichick V, Zaichick S. Ratios of rubidium/trace element con­tents in prostate gland as carcinoma’s markers. Can Res and Clin Oncology 2017; 1(1): 13-21.
33. Zaichick V, Zaichick S. Ratio of zinc to bromine, iron, ru­bidium, and strontium concentration in the prostatic fluid of patients with benign prostatic hyperplasia. Acta Scientific Medical Sciences 2019; 3(6): 49-56.
34. Zaichick V, Zaichick S. Ratio of zinc to bromine, iron, rubidi­um, and strontium concentration in expressed prostatic secre­tions as a source for biomarkers of prostatic cancer. American Journal of Research 2019; 5-6: 140-150.
35. Zaichick V, Zaichick S. Some trace element contents and ra­tios in prostatic fluids as ancillary diagnostic tools in distin­guishing between the benign prostatic hyperplasia and chron­ic prostatitis. Archives of Urology 2019; 2(1): 12-20.
36. Zaichick V, Zaichick S. Some trace element contents and ra­tios in prostatic fluids as ancillary diagnostic tools in distin­guishing between the chronic prostatitis and prostate cancer. Medical Research and Clinical Case Reports 2019; 3(1): 1-10.
37. Zaichick V, Zaichick S. Using prostatic fluid levels of zinc to strontium concentration ratio in non-invasive and highly accurate screening for prostate cancer. Acta Scientific Cancer Biology 2020; 4(1): 12-21.
38. Zaichick V, Zaichick S. Using prostatic fluid levels of zinc to iron concentration ratio in non-invasive and highly accurate screening for prostate cancer. SSRG International Journal of Medical Science 2019; 6(11): 24-31.
39. Zaichick V. Using prostatic fluid levels of rubidium and zinc concentration multiplication in non-invasive and highly ac­curate screening for prostate cancer. J Cancer Prev Curr Res. 2019; 10(6): 151â??158.
40. Zhu H, Wang N, Zhang Y, Wu Q, Chen R, Gao J, Chang P, Liu Q, Fan T, Li J, Wang J, Wang J. Element contents in or­gans and tissues of Chinese adult men. Health Phys. 2010; 98(1):61–73.
41. Vlasova ZA. Dynamics of trace element contents in thyroid gland in connection with age and atherosclerosis. Proceedings of the Leningrad Institute of Doctor Advanced Training 1969; 80: 135-144.
42. Katoh Y, Sato T, Yamamoto Y. Determination of multielement concentrations in normal human organs from the Japanese. Biol Trace Elem Res. 2002; 90(1-3): 57-70.
43. Salimi J, Moosavi K, Vatankhah S, Yaghoobi A. Investigation of heavy trace elements in neoplastic and non-neoplastic hu­man thyroid tissue: A study by proton – induced X-ray emis­sions. Iran J Radiat Res. 2004; 1(4): 211-216.
44. Tipton IH, Cook MJ. Trace elements in human tissue. PartII. Adult subjects from the United States. Health Phys.1963;9(2): 103-145.
45. Reddy SB, Charles MJ, Kumar MR, Reddy BS, Anjaneyulu Ch, Raju GJN, Sundareswar B, Vijayan V. Trace elemental analysis of adenoma and carcinoma thyroid by PIXE method. Nuclear Instruments and Methods in Physics Research Sec­tion B: Beam Interactions with Materials and Atoms 2002; 196(3-4): 333-339.
46. Ataulchanov IA. Age-related changes of manganese, cobalt, coper, zinc, and iron contents in the endocrine glands of fe­males. Problemy Endocrinologii, 1969; 15(2): 98-102.
47. Boulyga SF, Zhuk IV, Lomonosova EM, Kanash N, Bazha-nova NN. Determination of microelements in thyroids of the inhabitants of Belarus by neutron activation analysis using the k0-method. J Radioanal Nucl Chem. 1997; 222(1-2): 11-14.
48. Neimark II, Timoschnikov VM. Development of carcinoma of the thyroid gland in person residing in the focus of goiter endemic. Problemy Endocrinilogii 1978; 24(3): 28-32
49. Zabala J, Carrion N, Murillo M, Quintana M, Chirinos J, Sei-jas N, Duarte L, Brätter P. Determination of normal human intrathyroidal iodine in Caracas population. J Trace Elem Med Bio. 2009; 23(1): 9-14.
50. Boulyga SF, Becker JS, Malenchenko AF, Dietze H-J. Appli­cation of ICP-MS for multielement analysis in small sample amounts of pathological thyroid tissue. Microchimica Acta 2000; 134(3-4): 215-222.
51. Fuzailov YuM. Reaction of human and animal thyroids in the conditions of antimony sub-region of the Fergana valley. In: IX All-Union Conference on Trace Elements in Biology. Kishinev, 1981, 58-62.
52.   Kvicala J, Havelka J, Zeman J, Nemec J. Determination of some trace elements in the thyroid gland by INAA. J Radio­anal Nucl Chem. 1991; 149(2): 267-274.
53. Zaichick V, Zaichick S. Instrumental effect on the contami­nation of biomedical samples in the course of sampling. The Journal of Analytical Chemistry 1996; 51(12): 1200-1205.
54. Zaichick V, Zaichick S. A search for losses of chemical ele­ments during freeze-drying of biological materials. J Radio­anal Nucl Chem. 1997; 218(2): 249-253.
55. Zaichick V. Applications of synthetic reference materials in the medical Radiological Research Centre. Fresenius J Anal Chem. 1995; 352: 219-223.
56. Zaichick S, Zaichick V. The effect of age and gender on 37 chemical element contents in scalp hair of healthy humans. Biol Trace Elem Res. 2010; 134(1): 41-54.
57. Zaichick S, Zaichick V. (2011) The scalp hair as a monitor for trace elements in biomonitoring of atmospheric pollution. IJEnvH 2011; 5(1/2): 106-124.
58. Korelo AM, Zaichick V. Software to optimize the multiele­ment INAA of medical and environmental samples. In: Ac­tivation Analysis in Environment Protection. Dubna, Russia; Joint Institute for Nuclear Research, 1993, pp.326-332.
59. Schroeder HA, Tipton IH, Nason AP. Trace metals in man: strontium and barium. J Chron Dis. 1972; 25(9): 491-517