Irradiation of laboratory animals by neutron activated dust: development and application of the method – first results of international multicenter study

Manganese-56 (56Mn) was one of the dominant neutron-activated radionuclides during the first hours following the atomic-bombing of Hiroshima and Nagasaki. The radiation spectrum of 56Mn and the radiation emission from excited levels of 56Fe following 56Mn beta-decay include gamma-quanta, beta-particles, Auger electrons and X-rays. The dispersion of neutron activated 56Mn in the air can lead to entering of radioactive microparticles into the lungs. The investigation of spatial microdistribution of an internal dose in biological tissue exposed to 56Mn is an important matter with regards to the possible elevated irradiation of the lung alveoli and alveolar ducts. The Monte Carlo code (MCNP-4C) was used for the calculation of absorbed doses in biological tissue around 56Mn dioxide microparticles. The estimated absorbed dose has a very essential gradient in the epithelium cells of lung alveoli and alveolar duct: from 61 mGy/decay on the surface of simple squamous cells of epithelium to 0.15 mGy/decay at distance of 0.3 μm, which is maximal cell thickness. It has been concluded that epithelial cells of these pulmonary microstructures are selectively irradiated by low-energy electrons: short-range component of beta-particles spectrum and Auger electrons. The data obtained are important for the interpretation of biological experiments implementing dispersed neutron-activated 56Mn dioxide powder.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Microdistribution of internal radiation dose in biological tissues exposed to 56Mn dioxide microparticles

Stepanenko

Каприн

Иванов

et al. 2022

“…Calibration of AMPTEC, Inc., Gamma-Rad5 spectrometer was performed by using a standard source with a neutron-activated 56 Mn point source [ 10 ]. Shortly calibration procedure was as follows.…”

Section: General Description Of Experimental Studiesmentioning

confidence: 99%

Overview and analysis of internal radiation dose estimates in experimental animals in a framework of international studies of the sprayed neutron-induced 56Mn radioactive microparticles effects

Stepanenko

Каприн

Иванов

et al. 2022

The aim of overview is to present the pooled data of published internal dose estimates and the results of corresponding analysis of internal irradiation features of experimental mice and rats after exposure to sprayed neutron activated radioactive 56MnO2. These dose estimates were conducted in a framework of multicenter international study to investigate biological effects as a result of exposure to sprayed radioactive 56MnO2 microparticles. Radionuclide 56Mn (T1/2 = 2.58 h) is one of the main gamma-beta emitters during the first hours after neutron activation of soil following nuclear explosion. It was concluded that there are three groups of organs of mice and rats, the radiation doses of which differ by approximately an order of magnitude: the group with the highest radiation doses (large and small intestine, stomach, skin and lungs), the group with lowered radiation doses (eyes, esophagus, trachea), the group with the lowest radiation doses (liver, heart, kidneys). The radiation doses to organs are proportional to the activity of the sprayed radioactive powder. The distribution of internal radiation doses among organs of experimental mice of different strains but of the same age was practically the same in case of exposure to the same activity of sprayed 56MnO2 powder. Doses of internal irradiation of experimental mice substantially exceed the doses of internal irradiation of experimental rats exposed to the same activities of the sprayed 56MnO2 powder. The data presented in the overview can be helpful for further investigation and for interpretation of the biological effects of this type of irradiation.

“…In the case of microparticles, the exposure dose is highest when in close proximity to the microparticles, while in the case of solutions it is considered to be distributed, the same as external exposure [ 8 , 9 ]. However, the effects have only been briefly studied [ 10–12 ].…”

Section: Introductionmentioning

confidence: 99%

“…This is because the radiation dose rate increases inversely proportional to the square of the distance of the tissue to the radioactive microparticles. Calculations show that the dose rate can exceed tens of thousands of mGy in the vicinity of the microparticles [ 10–12 ], while the average dose is usually less than a few mGy.…”

Section: Introductionmentioning

confidence: 99%

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

Hoshi

2022

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.