The overview of neutron-induced 56Mn radioactive microparticle effects in experimental animals and related studies

Abstract

Investigation into the risks associated with radiation exposure has been carried out on those exposed to radiation in Hiroshima and Nagasaki, Semipalatinsk and other parts of the world. These risks are used as a guidance standard for the protection for radiation workers and the general public when exposed to radiation, and it sets upper regulatory limits for the amount of radiation exposure. However, the effects of internal exposure to radioactive microparticles have not been considered in these studies. These effects cannot be ignored since the exposure dose increases are inversely proportional to the square of the distance to the vicinity of the particles and can exceed tens of thousands of mGy. So far, only retrospective studies of people who have been exposed to radiation have been conducted, therefore we hypothesized that animal experiments would be necessary to investigate these effects. As a result, we found specific effects of radioactive microparticles. One particularly noteworthy finding was that internal exposure to radioactive microparticles resulted in pathological changes that were more than 20 times greater than those caused by the same level of external exposure. In contrast, there were other results that showed no such effects, and the reasons for this discrepancy need to be clarified. We also conducted RNA expression experiments and found that there was a difference between external exposure to 60Co gamma rays and internal exposure to 56Mn microparticles. In the future, we will need to study the mechanisms behind these findings. If the mechanism can be confirmed, it is expected to lead to the development of protective and therapeutic methods.

Comparative study of dose for different fluence of neutron

“…The IVG.1 M reactor is a research water-moderated heterogeneous thermal neutron reactor [1][2][3][4][5] with a beryllium reflector designed for radiation studies of samples of various materials used in reactor construction, nuclear power engineering and for performing experiments with irradiation of biological objects. Manganese dioxide is a finely dispersed powder weighing 100 mg with a particle size of about 3 microns [2][3][4][5][6]. Special construction for exposure of laboratory animals to sprayed powder 56 MnO 2 has been developed.…”

“…Experimental animals were exposed to 100 mg portion of sprayed radioactive manganese dioxide powder with various initial activities of 56 Mn -in the range from 8.0 × 10 7 Bq to 8.0 × 10 8 Bq -as it was planned in biological experiments [12][13][14]. There were six to nine experimental animals placed in each cage in dependence on biological experiments' plans [6][7][8][9][10][11][12][13][14][15] Tables 1 and 2 present the pooled information regarding values of internal irradiation among organs of mice from different strains after exposure to the sprayed neutron-activated 56 Mn dioxide powder with various levels of activity. As it follows from the Table 1, the doses of internal irradiation in organs and tissues resulting from exposure to sprayed 2.74 × 10 8 Bq activity of 56 Mn dioxide powder are not statistically different in different strains of mice.…”

Contribution of radioactive particles to the post-explosion exposure of atomic bomb survivors implied from their stable chromosome aberration rates

“…Although there are not a few epidemiological observations of the above-mentioned health effects of radioactive particles, there are few reports from animal experiments to explain these effects. As an only exceptional study, Hoshi and his team showed that there are notable, specific effects that have not been previously found for exposure to radioactive microparticles ( 39 ). They suggested that the health effects of exposure to radioactive particles can be 20 times greater than those of external exposure at the same absorbed dose, though the mechanism behind these results is yet to be investigated in future studies.…”