The Carcinogenic Effect of Localized Fission Fragment Irradiation of Rat Lung

Abstract

In a preliminary investigation of 'hot particle' carcinogenesis uranium oxide particles were introduced into the lungs of rats either by intubation of a liquid suspension of the particles or by inhalation of an aerosol. Subsequently the animals were briefly exposed to slow neutrons in a nuclear reactor, resulting in localized irradiation of the lung by fission fragments emitted from 235U atoms in the oxide particles. The uranium used in the intubation experiments was either enriched or depleted in 235U. Squamous cell carcinomas developed at the site of deposition of the enriched uranium oxide in many cases but no lung tumours occurred in the rats with the depleted uranium oxide, in which the lung tissue was exposed to very few fission fragments. Only enriched uranium oxide was used in the inhalation experiments. Pulmonary squamous cell carcinomas occurred after the fission fragment irradiation but were fewer than in the intubation experiments. Adenocarcinomas of the lung were seen in rats exposed to uranium oxide without subsequent irradiation by neutrons in the reactor and in rats irradiated with neutrons but not previously exposed to uranium oxide. It is concluded that (i) fission fragments were possibly implicated in the genesis of the squamous cell carcinomas, which only developed in those animals exposed to enriched uranium oxide and neutrons and (ii) the adenocarcinomas in the rats inhaling enriched uranium oxide only were likely to have been caused by protracted irradiation of the lung with alpha-rays emitted from the enriched uranium.

Depleted and Natural Uranium: Chemistry and Toxicological Effects

“…A second animal study reported that adult rats having received DU oxide intratracheally cannula (1-3 g uranium oxide powder/10 ml distilled water) did not develop lung tumors, in contrast to rats injected with enriched uranium oxide (Batchelor, 1980). Lung tumors were attributable to the α rays emitted from the enriched oxide, resulting in a nonuniform distribution of radioactivity in the lung.…”

Depleted uranium—the growing concern

“…There was no mutagenic activity in control animals implanted with tantalum. On the other hand, Batchelor et al 24 introduced enriched and depleted uranium into the rat lung and found that enriched uranium caused carcinomas at the site of deposition, whereas no lung tumors occurred in the rats with depleted uranium oxide.…”