Individual Thyroid Dose Estimates for a Case-Control Study of Chernobyl-Related Thyroid Cancer Among Children of Belarus???part Ii. Contributions From Long-Lived Radionuclides and External Radiation

Abstract

Significant quantities of long-lived radionuclides were released to the environment during the Chernobyl nuclear power plant accident in 1986. These radionuclides contributed to radiation doses due to ingestion of contaminated foods and external exposure from the ground deposition that resulted. The contributions of these exposure pathways to thyroid doses received by subjects of an epidemiologic study of children from Belarus are evaluated and presented. The analysis shows that ingestion of the long-lived radionuclides, primarily radiocesium, typically contributed a small percentage of the total thyroid dose received by the study subjects. The median and mean fractional contributions were 0.76 and 0.95%, respectively. The contribution of external exposure to the thyroid dose was generally larger and more variable, with median and mean contributions of 1.2 and 1.8% of the total thyroid doses, respectively. For regions close to the reactor site, where radionuclide deposition was highest, the contributions of radiocesium ingestion and external exposure were generally lower than those of the short-lived radioiodine isotopes (132I and 133I) and their precursors (132Te). In other areas, the contributions of these two pathways were comparable to those of the short-lived radioiodines. For all subjects, intakes of 131I were the primary source of dose to the thyroid.

Radiation exposure to the population of Europe following the Chernobyl accident

“…Contribution of that exposure pathway varied on dietary habits of population of different ages and in general was responsible for up to 80-95% of the total dose. (27,28) (open squares), Belarus (23) (open circles), the Czech Republic (34) (crosses), Finland (36) (closed squares) and Norway (46) (closed circles).…”

“…The methods of dose estimation were tailored to the types of radiation data available in each particular country. Local experts provided dose estimates for Belarus, Ukraine and the Russian Federation, where extensive work has been undertaken developing and validating methods for dose reconstruction (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) . For less affected European countries, information on country-specific radiation data and dose estimates was either obtained from local experts: Bulgaria, the Czech Republic, Finland, Lithuania and Switzerland; and/or from published data: Austria (24)(25)(26)(27)(28) , Belgium (29) , Bulgaria (30) , Croatia (31,32) , the Czech Republic (33,34) , Estonia (35) , Finland (36) , France (37) , Greece (38,39) , Hungary (40) , Italy (41,42) , Lithuania (43,44) , Norway (45,46) , Serbia and Montenegro (47) , Slovakia (48,49) , Sweden (50) , Switzerland (51) and the United Kingdom …”

“…For later years, the dietary intake of 137 Cs was assumed to decrease exponentially with a half-time of 1.7 y up to 1993 and with a half-time of 7.8 y starting from year 1993. Figure 1 shows the time-dependence of dietary intake of 137 Cs activity used in dose reconstruction (solid line) and that observed in Austria (27,28) , Belarus (23) , the Czech Republic (34) , Finland (36) and Norway (46) . As can be seen from Figure 1, the accepted time-dependence of dietary intake of 137 Cs agrees with that observed in those countries.…”

“…For some countries, data on deposition of 99 Mo, (23) 154 (55) 0. (23) 61 (55) 0. (60) 110 (61) 0.07-0.14 1.6 0.45 7.6-11 6.7-10 0.54 0.41-0.63 Russia, Kaluga Oblast (60) 14.2 (61) (60) 41 (61) (60) 67 (61) (14) 136 Cs, 141 Ce, 144 Ce and 239 Np were also available and used for the reconstruction of external doses.…”

“…Dosimetry models used for dose reconstruction included empirical and semiempirical approaches that are based on the relationships between environmental contamination and measured levels of radionuclides in humans, and ecological models that describe the processes of transfer of radionuclide activities from ground deposition to the human body. Input data used for dose reconstruction in these countries included hundreds of thousands of results of measurements of 131 I in human thyroids performed in 1986 (9,15,21,30,34) ; and 137 Cs body burdens, as well as, 137 Cs in milk and other foodstuffs (10,13,14,19,23,33,(62)(63)(64) . Majority of these measurements were carried out in the most contaminated states.…”