DOSE ASSESSMENT FOR INTAKE OF TRITIATED WATER IN HUMANS: ROLE OF TRITIUM INCORPORATION IN ORGANIC MATTER

Tritium is one of the factors of internal exposure of the humans both in occupational and public environments. It enters the body mainly as tritiated water through inhalation, with food, drinks and through the skin; part of tritium gradually transforms into the metabolised organically bound tritium as a result of biochemical reactions. The purpose of this study was to evaluate organically bound tritium contribution to the effective dose of an adult using the biokinetic model and real dosimetric data. The data of long term monitoring from 6 studies with 17 workers or volunteers following single intake of tritiated water in the body were selected from 9 publications (1968-1997). Three two-compartment models of tritium biokinetics were used in this study: recurrent model with gradual transformation of tritium from tritiated water into organically bound tritium and tritiated water excretion; model with instant transformation of tritium into organically bound tritium and tritiated water excretion; model with instant transformation of tritium into organically bound tritium and both tritiated water and organically bound tritium excretion (according to ICRP). The ICRP model doesn’t properly reflect the real tritiated water metabolism in the human body: second exponent of the tritiated water content in the body water and accumulation of the organically bound tritium fraction are absent. The organically bound tritium fraction composes 3% of tritiated water in ICRP model. It is significantly higher compared to two other models (0,4% and 0,8%). According to the first model the contribution of OBT fraction to the mean dose varied from 1,8 to 4,6% for individuals; mean value was 3,0 ± 0,9%. According to the second model the contribution of organically bound tritium fraction was slightly higher: 3,6 ± 1,1%, according to the ICRP model – 9%. The dynamic of excretion of tritium with urine can be described with double-exponential curves and provides the basis for two-compartment modeling. The recurrent model with tritiated water excretion was more adjusted to human physiology. Contribution of organically bound tritium to effective dose can be somewhat higher than that to absorbed dose defined in this work. The presented dose assessment system can be used when specified individual absorbed dose reconstruction in tissues is necessary following accidental intake of large tritium activities.

tritium, tritiated water, two-compartment model, organically bound tritium, dosimetry

1. Pinson E.A. Langham W.H. Physiology and toxicology of tritium in man. Journal of Applied Physiology,1957, Vol. 10, №1, pp. 108-126.

2. Balonov M.I. Dolgirev E.I., Likhtarev I.A. Exchange kinetics and dosimetry of tritium oxide in man for different routes of administration. Health Physics -1974, Vol. 27, №4, pp. 367-375.

3. Hill R.L. Johnson J.R. Metabolism and dosimetry of tritium. Health Physics, 1993, Vol. 65, №6, pp. 628-647.

4. Balonov M.I. Dosimetry and standardization of tritium. M., Energoatomizdat, 1983, 152 p. (In Russ)

5. Butler H.L. Leroy J.H. Observation of Biological Half-Life of Tritium. Health Physics, 1965, Vol. 11, pp. 283-285.

6. Rudran K. Significance of In Vivo Organic Binding of Tritium Following Intake of Tritiated Water. Radiation Protection Dosimetry, 1988, Vol. 25, №1, pp. 5-13.

7. Snyder W.S. Fish B.R., Bernard S.R. [Et al.] Urinary excretion of tritium following exposure of man to HTO – a two exponential model. Physics in Medicine and Biology, 1968, Vol. 13, №4, pp. 547-559.

8. Lambert B.E., H.B. Sharpe and K.B. Dawson. An accidential intake of tritiated water. Am Ind Hyg Assoc J 32(10): 682-686 (1971).

9. Henry P. Etude d’une contamination accidentelle par l’eau tritiee. Symposium on assessment of radioactive organ and body burdens. Proceeding of the International Atomic Energy Agency meeting; 1971 November 22; Stockholm, Sweden: Vienna; 1972. P.641-57. (in French).

10. Sanders S.M.J. and W.C. Reinig. Assessment of tritium in man. In: Diagnosis and Treatment of Deposited Radionuclides. ed. H.A. Kornberg, W.D. Norwood. Amsterdam: Excerpta Medica Foundation; c 1968. p.534-542

11. Trivedi A. Galeriu D., Richardson R.B. Dose contribution from metabolized organically bound tritium after acute tritiated water intakes in humans, Health Physics, 1997, Vol. 73, №4, pp. 579-586.

12. Minder W. Internal contamination with tritium. Strahlentherapie, 1969, Vol. 137, №6, pp. 700-704. (in German).

13. Moghissi A.A. Carter M.W., Bretthauer E.W. Further studies on the long-term evaluation of the biological half-life of tritium. Health Physics, 1972, Vol. 23, №6, pp. 805-806.

14. Balonov M. Bruk G., Zhesko T. Dosimetry and standardization of tritium in Russia. Fusion Technology, 1995, Vol. 28, pp. 809-813.

15. Balonov M.I., K.N. Muksinova and G.S. Mushkacheva. Tritium radiobiological effects in mammals: review of experiments of the last decade in Russia. Health Physics, 1993, Vol. 65, №6, pp. 713-726.

16. International Commission on Radiological Protection. Agedependent doses to members of the public from intake of radionuclides: Part 1. ICRP Publication 56. Ann ICRP 20(2): International Commission on Radiological Protection, Pergamon Press, Oxford; 1990.

17. International Commission on Radiological Protection. Agedependent doses to members of the public from intake of radionuclides: Part 2. Ingestion dose coefficients. ICRP Publication 67. Ann. ICRP 23: International Commission on Radiological Protection, Pergamon Press, Oxford; 1993.

18. International Commission on Radiological Protection. Agedependent doses to members of the public from intake of radionuclides: Part 4. Inhalation dose coefficients. ICRP Publication 71. Ann. ICRP. 25: International Commission on Radiological Protection, Pergamon Press, Oxford; 1995.

19. Takeda H. Kasida Y. Biological behavior of tritium after administration of tritiated water in the rat. Journal of Radiation Research, 1979, Vol. 20, №2, pp. 174-185.

20. Takeda H. Comparative metabolism of tritium in rat after single ingestion of some tritiated organic compounds versus tritiated water. Journal of Radiation Research, 1982, Vol. 23, №3, pp. 345-357.

21. International Commission on Radiological Protection. Basic anatomical and physiological data for use in radiological protection reference values. Translation of ICRP Publication 89, Ed. I.B. Keirim-Markus. М., Medkniga, 2007, 318 p. (In Russ)

22. International Commission on Radiological Protection. Report on the Task Group on Reference Man. Translation of the ICRP Publication 23, ed. Yu.D. Parfenov. М., Medkniga, 1977, 496 p. (In Russ)