Terms of Reference
It is now 22 years since the Chernobyl accident, and, while a number of reviews of the consequences of the accident have been made (see for example UN Chernobyl Forum, 2006, Cardis et al, 2006a, Williams and Baverstock 2006; Baverstock and Williams Env Health Persp 2006.), there is controversy over its consequences to date, and some variability in the assessment of the potential consequences in the future (Cardis et al, 2006b; Fairlie and Sumner, 2006; Greenpeace, 2006).
There are also differences of opinion over the course of action that should be taken in further studies of the health consequences of the Chernobyl accident. All recognize that the accident was unique in its type and scale, but some wish to concentrate on continuing studies of the most obvious health effects, particularly thyroid carcinoma, while others wish to look at emerging effects, and effects that they predict are likely to occur, such as a rise in the incidence of breast carcinoma. There is controversy, moreover, over the possible value of such studies in terms of radiation protection and open questions concerning their feasibility.
Studies of the atomic bomb exposures in Japan show the importance of late and unexpected consequences, such as cardiovascular complications detected more than 40 years later (Wong et al, 1993; Preston et al, 2003). Given these facts, and given that any investigations will take place against a background of claims and counterclaims from individuals and organizations that have a vested interest in either exaggerating or downplaying possible effects, it is necessary to devise a strategy for further Chernobyl research that takes these problems into account.
Any strategy must also recognize the need for the research to lead to outcomes that will meet three objectives:
- health improvement in those exposed to Chernobyl or to future nuclear accidents
- realistic assessment of present and future health consequences to aid health planning for those exposed after Chernobyl, and after future accidents; and
- improved understanding of radiation effects and help with future radiation protection measures.
These are wide-ranging objectives and we plan to build on existing reviews, new results and the knowledge and experience of experts rather than to undertake work directly. We aim to prepare a practical and cost-effective strategy combining large-scale surveillance of epidemiological studies with studies focused on specific areas.
While the health impact of the Chernobyl accident has been widely studied, particularly in the first decade after it occurred, it has not been comprehensively studied, as have, for example, the effects of the atomic bombings in Japan. Research on the outbreak of childhood thyroid cancer has been intensive, while claims about possible effects on the immune system have received little scientific attention outside the affected countries. Nevertheless the accident has proved uniquely illuminating in some aspects such as:
- the discovery of mini-satellite mutations inherited by children born after the accident but whose fathers were exposed (Dubrova et al, 1996, 2002);
- in providinº isotopes of iodine and factors which may modify this risk, including iodine deficiency and supplementation (Astakhova et al, 1998; Cardis et al, 2005; Jacob et al, 2006; Tronko et al, 2006);
- evidence of the non-threshold nature of radiation cataracts (Worgul et al, 2007).
The fact that no other radiation-related health effect has yet been clearly demonstrated does not mean that no increase has occurred or will occur in the future. Many of the studies conducted to date provide little information about radiation risks because of a number of methodological limitations. Further, based on the experience of other populations exposed to ionising radiation, a small increase in the relative risk of cancer, at least, is expected, even at the low to moderate doses received. In addition, because radiation-related diseases continue to occur decades after exposure, it is certainly too early to evaluate the full radiological impact of the accident (Cardis, 2007; Williams and Baverstock, 2006).
Although ionising radiation is one of the most studied carcinogens in our environment, much of the knowledge about its effects on human beings comes from studies of Japanese atomic bomb survivors exposed to external radiation and of patients who received very high doses for therapeutic purposes. Major questions in radiation protection today relate to the choice of models for transport of risk between populations with different background disease rates; for projection of risk over time; for extrapolation of risks following primarily external high dose and high dose-rate exposure to low dose and low dose-rate exposures (UNSCEAR, 2000, 2007; US NRC, 2006). This is particularly important for exposures resulting, as they did in the case of the Chernobyl accident, from a mixture of external and internal radiation, as current risk estimates for internally incorporated radio-nuclides are very uncertain (CERRIE, 2004).
Major questions also remain about the risk of non-cancer diseases following low levels of ionising radiation and concerning non-targeted effects of radiation (UNSCEAR, 2007; US NRC, 2006); indeed, the mechanistic dogma underlying the effects of ionising radiation has been challenged by the phenomena of genomic instability and bystander effect. At present no consensus has been reached on the underlying mechanisms for these non-targeted effects. New fundamental aspects of biology and genetics are, however, being explored at an unprecedented rate − in particular the importance of so called epigenetic factors in determining phenotype − and the Commission is investing heavily in research in this area.
Careful studies of populations exposed following the accident are therefore potentially able to provide important answers to some of these questions and to test hypotheses generated both in respect of mechanisms underlying radiation action and biology/genetics in general. As such, they may have important consequences for radiation protection in general, for action required following future nuclear emergencies, and, potentially, for monitoring and promoting the health of people exposed as a result of the Chernobyl accident.
To make the best use of this unique opportunity to increase our understanding of radiation effects, the current proposal is for the development of a long-term strategic plan for research into the health effects of the Chernobyl accident.
We are aiming at engaging stakeholders (general public, funding and international bodies) in assessing possible impact of proposed research on better understanding of effects of low dose and low dose rate radiation and implications for public health decision making.
Health consequences of the accident must be assumed to have occurred all over Europe (particularly in Belarus, the Russian Federation and Ukraine), although not necessarily at a level at which they could be detected, and are likely to continue to do so in the foreseeable future. No current multinational organisation is taking responsibility for monitoring disease trends or for building a strategic research agenda. An impartial review of the present position and a careful and critical assessment of the value of further studies are urgently needed.
Finally, a major expansion of nuclear power generation now seems likely in the coming decade, in Europe, as well as in countries with different safety cultures. The risk of accidents similar to the Chernobyl accident cannot be eliminated. Nuclear accidents have trans-boundary consequences and thus can lead to social and economic costs in neighbouring countries. National authorities will, in the event of an accident, be required to give assurances about the likely public health impact. Twenty-two years after the accident, unfortunately, the international response to the Chernobyl accident cannot be described as a success. The failure of the scientific community to reach a consensus over the likely extent of health damage has undoubtedly contributed to the psychosocial effect and has undermined the confidence of the general public in the safety of nuclear power generation.