Protective actions in the late phase intervention criteria and decision-making

Full text: In the past 15 years, the Chernobyl and Goiania accidents resulted in extensive postemergency phase response. Large amounts of 137Cs were released to the environment during these accidents, leading to a prolonged or quasi-prolonged exposure of the affected populations. The experiences gained from these accidents and others have revealed a need for an updated and fully complete system of decision-making an implementation of long-term countermeasures. In the post-release phase it is expected that a reasonably complete picture of radiation and contamination levels and affected areas in the environment is available. In this phase the dominant risks originate from radioactive materials deposited on the ground, mainly from external exposure and ingestion of contaminated foodstuffs. Measured surface contamination density can thus be used to estimate doses from both the external and ingestion exposure pathways and can therefore be used to make decisions about the introduction of countermeasures. The major countermeasures in the late phase of a nuclear or radiological accident where long-lived radionuclides have been dispersed in the environment are relocation/resettlement, foodstuff restrictions, agricultural countermeasures and cleanup of contaminated land. An overview of these late phase countermeasures is given in the paper. In addition, recommendations from the international radiation protection organizations ICRP, IAEA and from the EU on late phase countermeasures are presented together with the background for their derivation. An important aim of late phase countermeasures is to reduce the likely numbers of cancers as much and as effectively as reasonably possible. However, the total health consequences from long-term exposure situations, and of any countermeasures subsequently implemented, include more than the injuries and increased risks directly attributable to radiation exposure. Stressors, such as the perception of the hazard posed by radiation in the environment and enforced changes of lifestyle, may lead to increases in psychological strain in the effected population. Such increases may in turn lead directly or indirectly to increased illness, and the final decision on the nature and scale of late phase countermeasures should include considerations of reducing both radiological and non-radiological hazards and risks. Decisions on countermeasures to mitigate the consequences in the late phase of a nuclear or radiological accident include factors or attributes describing benefits from the countermeasure and those describing harm. In analysing the inputs to the decision, it is necessary to decide on the relative importance of each factor. There has been essentially a broad acceptance internationally of the principles for intervention. However, it has not been possible to reach agreement for the purpose of defining a net benefit, on the exact weighting to be attached to each of the attributes influencing the decision to take a protective action. Major attributes would include those related to radiological protection, and those related to social and psychological issues. Some of these attributes are discussed in the paper and the role of radiation protection in the final decision-making process is addressed. The current scientific consensus on radiation protection is based an objective assessments of the health risks associated with radiation exposure and on radiological protection attributes of various exposure situations. lt should; however, be recognized that this consensus on recommendations of radiation protection should be seen as a decision-aiding tool, and that these recommendations would be used as input to the final decision-making process together with other relevant protection attributes. Unresolved issues on the introduction of late phase countermeasures have been identified to include the interaction between radiological and non-radiological attributes in decision-making. Both radiological and non-radiological factors will influence the level of protection actions being introduced. Social-psychological countermeasures are a new category of action, in the sense that social protection philosophy has not yet been developed to fully include their application after a nuclear or radiological accident. lt is concluded in the paper that optimisation of the overall health protection is not a question of developing radiation protection philosophy to fully include socio-psychological factors. lt is rather a question of including these factors - in parallel with the radiological protection factors - in cooperation between radiation protection experts and e.g. experts in social and psychological sciences under the responsibility of the decision-maker. The overall optimization of the total health protection, i.e. the final decision on the introduction of long-term countermeasures is thus the sole responsibility of the decision-maker. A number of further conclusions have been made in the paper on the role of the radiation protection community in decision-making, the issuing of numerical guidance on intervention levels for late phase countermeasures from the international radiation protection organisations and the illusory goal to arrive at internationally accepted intervention levels based on an overall 'optimization' of protection, which includes all the relevant protection attributes, both the radiological and the non-radiological attributes. Finally, it is concluded that further research - more focused than hitherto - is needed before any tools for an overall optimization of protection in the late phase can be operational. (author)