Study of bioaccumulation and radiobiological effects of environmentally relevant level of Radium-226

Abstract

The primary aim of this thesis is to investigate the bioaccumulation of environmental level of Ra-226 in fish and the induced radiobiological effects. Elevated Ra-226 levels in the environment are of increasing concern because of its high radiotoxicity and long half-life. One in vivo study analyzed the accumulation of Ra-226 in fathead minnows exposed to environmental level of Ra-226 via ingestion. A second in vitro study focused on the biological effects of chronic low-dose radiation from Ra-226 and the induction of adaptive response. The main findings of the thesis revealed that the accumulation of Ra-226 in fish was not linear in relation to the dietary Ra-226 activity. The highest concentration factor was obtained from lowest food activity, and uptake was inversely proportional to the dietary Ra-226 concentrations. The fish fed with radioactive food showed some growth suppression compared to control. The results of the in vitro study indicated that chronic low-dose radiation from Ra-226 had an impact on the clonogenic survival of cells, but had no influence on the proliferation of cells. The reactions of CHSE/F (fish embryonic cells) and HaCaT (human epithelial cells) to chronic radiation from Ra-226 were different. After being cultured in medium containing Ra-226 over multiple generations, CHSE/F cells were sensitized by the radiation, while HaCaT cells were firstly sensitized and after several generations they showed the trend of getting adapted to the radiation. Furthermore, no adaptive response was induced by long-term low-dose radiation from Ra-226 when cells were subsequently exposed by acute high-dose challenge radiation, except for small adaptive responses at sporadic dose points. This thesis may provide information about the transfer and influence of low-dose Ra-226. It may motivate other studies to estimate the risks of internal alpha-emitters, to identify the influence of chronic radiation on different species, and to develop radiation protection guidelines.