Internal doses in experimental mice and rats following exposure to neutron-activated 56MnO2 powder: results of an international, multicenter study

Abstract

The experiment was performed in support of a Japanese initiative to investigate the biological effects of irradiation from residual neutron-activated radioactivity that resulted from the A-bombing. Radionuclide 56Mn (T1/2 = 2.58 h) is one of the main neutron-activated emitters during the first hours after neutron activation of soil dust particles. In our previous studies (2016–2017) related to irradiation of male Wistar rats after dispersion of 56MnO2 powder, the internal doses in rats were found to be very inhomogeneous: distribution of doses among different organs ranged from 1.3 Gy in small intestine to less than 0.0015 Gy in some of the other organs. Internal doses in the lungs ranged from 0.03 to 0.1 Gy. The essential pathological changes were found in lung tissue of rats despite a low level of irradiation. In the present study, the dosimetry investigations were extended: internal doses in experimental mice and rats were estimated for various activity levels of dispersed neutron-activated 56MnO2 powder. The following findings were noted: (a) internal radiation doses in mice were several times higher in comparison with rats under similar conditions of exposure to 56MnO2 powder. (b) When 2.74 × 108 Bq of 56MnO2 powder was dispersed over mice, doses of internal irradiation ranged from 0.81 to 4.5 Gy in the gastrointestinal tract (small intestine, stomach, large intestine), from 0.096 to 0.14 Gy in lungs, and doses in skin and eyes ranged from 0.29 to 0.42 Gy and from 0.12 to 0.16 Gy, respectively. Internal radiation doses in other organs of mice were much lower. (c) Internal radiation doses were significantly lower in organs of rats with the same activity of exposure to 56MnO2 powder (2.74 × 108 Bq): 0.09, 0.17, 0.29, and 0.025 Gy in stomach, small intestine, large intestine, and lungs, respectively. (d) Doses of internal irradiation in organs of rats and mice were two to four times higher when they were exposed to 8.0 × 108 Bq of 56MnO2 (in comparison with exposure to 2.74 × 108 Bq of 56MnO2). (e) Internal radiation doses in organs of mice were 7–14 times lower with the lowest 56MnO2 amount (8.0 × 107 Bq) in comparison with the highest amount, 8.0 × 108 Bq, of dispersed 56MnO2 powder. The data obtained will be used for interpretation of biological effects in experimental mice and rats that result from dispersion of various levels of neutron-activated 56MnO2 powder, which is the subject of separate studies.

Biological impacts on the lungs in rats internally exposed to radioactive 56MnO2 particle

“…To compare the effects of internal irradiation by 56 MnO 2 with the external irradiation’s effects, a group exposing to 60 Co-γ at 2 Gy, which is substantially higher than the predicted whole body doses by 56 MnO 2 , was also prepared. The dosimetry data indicated that the organ distribution of internal radiation in the present study was similar to the previous results 4 , suggesting good reproducibility in the 56 MnO 2 exposure process 5 . In general, thoracic external radiation exposure at high doses (> 8 Gy) induces radiation pneumonitis which eventually leads to pulmonary fibrosis in laboratory animals as well as in humans 6 – 9 .…”

“…The estimated accumulated doses of internal irradiation from 56 MnO 2 in each organ were previously described 5 . The absorbed doses of the internal irradiation of the lungs were 25 ± 3 (Mn56x1 group), 48 ± 9.0 (Mn56x2 group), and 65 ± 13 (Mn56x3 group), while the doses of internal irradiation of the whole body were 41 ± 8, 91 ± 3, and 100 ± 10 mGy, respectively.…”

“…The animal experiment design was previously described 5 , 31 . Specific pathogen-free male Wistar rats (10 weeks old) were purchased from the Kazakh Scientific Center of Quarantine and Zoonotic Diseases, Almaty, Kazakhstan.…”

“…Preparation and exposure of 56 MnO 2 powder and the internal dose estimation have been previously described 4 , 5 . Briefly, MnO 2 powder (Rare Metallic Co., Tokyo, Japan; particle diameters range, 1–19 µm) was activated by neutron beam in the Baikal-1 nuclear reactor at the National Nuclear Center, Kurchatov, Kazakhstan.…”

35 years after the Chernobyl NPP accident: methods of retrospective dosimetry in assessing of the consequences of large-scale uncontrolled radiation exposures, their subsequent development and application in oncoradiology (experience of A. Tsyb MRRC)

“…2). Распределение измеренной методом ОСЛ накопленной поглощённой дозы, D (мГр), по глубине кварцсодержащего образца черепицы крыши здания в Хиросиме -«свидетеля» атомной Радиобиологическая значимость бета-облучения от остаточной радиоактивности в отношении лиц, оказавшихся вблизи эпицентра вскоре после бомбардировки, изучается в настоящее время в ходе проводимых нами с международным участием экспериментов на лабораторных животных, подвергшихся воздействию диспергированного вещества, содержащего короткоживущий нейтрон-активированный бета-излучатель[35,36].…”