Military study on depleted uranium challenges radiation health risk models
Teams led by Dr Alexandra Miller at the US Armed Forces Radiobiology Research Institute (AFRRI) have been responsible for significant steps forward in our understanding over how DU interacts with tissues at the cellular level. This has included studies on DU’s genotoxicity, its mutagenicity and its ability to cause leukaemia. In Miller’s latest study, published this summer, they sought to determine whether DU also caused a recently discovered effect on cells – the Bystander Effect.
The Bystander Effect is a poorly understood phenomenon, whereby cells adjacent to cells affected by radiation are also damaged. The mechanisms through which this occurs are still being investigated but are presumed to relate to chemical signalling between cells. While it has also been found to be caused by some chemicals, the primary focus of research has been on radiation, and in particular alpha radiation. DU is an alpha radiation emitter so ICBUW and others have long argued that the potential for these effects should be taken into consideration in risk models from internal exposure – such as the inhalation of DU dust.
Miller’s study compared two carcinogenic metals – nickel and hexavalent chromium – with DU and also alpha radiation. The nickel and chromium controls did not trigger the Bystander Effect but both DU and the alpha radiation did. Her team also studied the medium that the cells were placed in, finding that it could not have been DU residues affecting the non-exposed cells but something else, possibly secreted by the damaged cells. Miller’s team suggested that: “The present finding of bystander effects induced by DU-exposed cells mediated through a secreted-extracellular factor may not only have significance as it supports the finding of radiation involvement in DU effects, but may have significant impact on the cancer risk assessment of DU exposure.”
The study challenges two common assumptions about DU’s health risks, the first, that the overarching threat is chemical toxicity, rather than radiation, and the second relates to the uncertainty in modelling the risks from internal radiation. The bulk of what informs radiation risk assessments is based on data from external exposures, with much less data available for modelling the risks from internal exposures. For the Bystander Effect, it means that a far larger number of cells may be damaged by each radiation event than previously thought.
The complexity of determining the health risks from internal exposures was highlighted last year in a report by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which found that: “…continued research and review is needed to assess the effects of internal exposures. Further work is required to understand the effects of uneven delivery of doses from internal emitters within tissues and cells relative to the uniform delivery of doses from external exposure to penetrating radiation.”
Ironically UNSCEAR had also addressed the health effects of DU, claiming that: “…no clinically significant pathologies related to exposure from depleted uranium were found in military personnel or members of the public”. Although given the absence of research on exposed civilian populations this is an unsurprising finding.
Radiation exposure from depleted uranium: The radiation bystander effect.