Comparative stochastic effects of alpha, beta or x-irradiation of the lung of rats

Impact of Local High Doses of Radiation by Neutron Activated Mn Dioxide Powder in Rat Lungs: Protracted Pathologic Damage Initiated by Internal Exposure

Internal radiation exposure from neutron-induced radioisotopes environmentally activated following atomic bombing or nuclear accidents should be considered for a complete picture of pathologic effects on survivors. Inhaled hot particles expose neighboring tissues to locally ultra-high doses of β-rays and can cause pathologic damage. ⁵⁵MnO₂ powder was activated by a nuclear reactor to make ⁵⁶MnO₂ which emits β-rays. Internal exposures were compared with external γ-rays. Male Wistar rats were administered activated powder by inhalation. Lung samples were observed by histological staining at six hours, three days, 14 days, two months, six months and eight months after the exposure. Synchrotron radiation—X-ray fluorescence—X-ray absorption near-edge structure (SR–XRF–XANES) was utilized for the chemical analysis of the activated ⁵⁶Mn embedded in lung tissues. ⁵⁶Mn beta energy spectrum around the particles was calculated to assess the local dose rate and accumulated dose. Hot particles located in the bronchiole and in damaged alveolar tissue were identified as accumulations of Mn and iron. Histological changes showed evidence of emphysema, hemorrhage and severe inflammation from six hours through eight months. Apoptosis was observed in the bronchiole epithelium. Our study shows early event damage from the locally ultra-high internal dose leads to pathogenesis. The trigger of emphysema and hemorrhage was likely early event damage to blood vessels integral to alveolar walls.

Effects of Internal Exposure to 56MnO2 Powder on Blood Parameters in Rats

Objective

The pathological effects of internal exposure to manganese dioxide-56 (⁵⁶MnO₂) radioisotope particles have been previously examined in rats. Here we further examine the effects of ⁵⁶MnO₂, focusing on changes in blood parameters.

Materials and Methods

Ten-week-old male Wistar rats were exposed to 3 doses of neutron-activated ⁵⁶MnO₂ powder, nonradioactive MnO₂ powder, or external 60Co γ-rays (1 Gy, whole body). On days 3 and 61 postexposure, the animals were necropsied to measure organ weights and clinical blood parameters, including red blood cell and white blood cell counts; concentrations of calcium, phosphorus, potassium, and sodium; and levels of alanine aminotransferase (ALT), aspartate aminotransferase, amylase, creatinine, urea, total protein, albumin, triglycerides, high density lipoprotein, total cholesterol, and glucose.

Results

In the ⁵⁶MnO₂-exposed animals, accumulated doses were found to be highest in the gastrointestinal tract, followed by the skin and lungs, with whole-body doses ranging from 41 to 100 mGy. There were no ⁵⁶MnO₂ exposure-related changes in body weights or relative organ weights. The ALT level decreased on day 3 and then significantly increased on day 61 in the ⁵⁶MnO₂-exposed groups. There were no exposure-related changes in any other blood parameters.

Conclusion

Although the internal doses were less than 100 mGy, internal exposure of ⁵⁶MnO₂ powder showed significant biological impacts.