Low-dose Extrapolation of Radiation-Related Cancer Risk

Draft document: Low-dose Extrapolation of Radiation-Related Cancer Risk
Submitted by Dr Judith Johnsrud, The Sierra Club
Commenting on behalf of the organisation

Please accept these comments on the ICRP Report “Low-Dose Extrapolation of Radiation-Related Cancer Risk.” They are offered for the Sierra Club in the United States. The Sierra Club, with more than 800,000 members, is devoted to protection and restoration of physical and human environments, and to the well-being of all forms of life. Thank you for an opportunity to comment on this document; and we trust that the ICRP will give the comments serious consideration. This report is informative, careful, balanced, useful, and a readable contribution to the literature on low-dose radiation and radiation-related cancer risk. (A glossary might help lay readers.) Although the report contains remnants of the heavily-criticized approaches to radiological protection that characterized the draft ICRP-2005 Recommendations (now being revised), this “Low-Dose” report deserves commendation. We hope it signals a permanent shift by regulators away from past assurances that low-dose radiation is entirely harmless, or that it’s good for you. Imperfect as the linear no-threshold (LNT) hypothesis may be if misapplied in the very low dose range, the Task Group authors reconfirm the LNT applicability to doses and dose-response for cancers. They stress that extrapolations downward from high-dose exposures may not be valid in the dose range below which past research was done. They repeatedly reject claims that a “safe” threshold dose level has been established below which there is no radiation-related risk of cancer. They rightly recommend the need for more research at very low dose levels, prudently cautioning it is possible, if unlikely, that some exposures may cause no damage, or even that some may impart some benefit. The reconfirmation and rejection are especially timely, after ICRP’s recent recommendation for adoption of a threshold dose level below which low-level radioactive materials and wastes could be exempted or excluded from regulatory control. (See Sierra Club and other comments on ICRP-2005 Recommendations.) After decades of failed attempts by the U.S. Nuclear Regulatory Commission to set a one millirem per year threshold dose standard, there is now indication that NRC is preparing to try again to adopt the long-discredited threshold concept. The Task Group is also commended for its emphasis on the importance of identification of DNA damage in inducing mutations, and of clustered lesions and chromosomal aberrations that may result from a single radiation track through a single cell. Analysis of the significance of genomic instability and bystander effects is particularly important at this time when both proposed revival of the commercial nuclear industry and renewed development and spread of nuclear weapons pose increasing radiation hazards worldwide. Despite the many praiseworthy aspects of this report, it is puzzling that the authors continue to support use on risk analysis in setting radiation protection standards and practices, particularly with respect to low-dose irradiation. Uncertainties noted about the accuracy of downward extrapolations from high to low doses should eliminate or restrain the use of risk analysis if it is applied without appropriate low-level radiation data to confirm low-dose applicability. The use of Hiroshima and Nagasaki Life Span Study data should also be ruled out of risk modeling, due to the absence from that data of those who failed to survive the first five years post-bombing when the Atomic Bomb Casualty Commission data collection began. The ABCC data are considered to be biased in favor of “healthy survivors” and not representative of the experience of the entire exposed population, which would include those who died in the first five post-war years. In addition, lack of inclusion of adverse effects of internal emitters also militates against reliance on existing risk models as reliable bases for standards-setting. Variations in a population in age, gender, genetic heritage, prior health, work conditions, other unmeasured or unique conditions, as well as all sources and levels of exposures -- all argue against reliance on risk assessment for deriving dose standards. To these reasons not to rely on risk analysis should be added the importance of the recent information on the role of a single radiation track on mutations, and of delayed effects, DNA damage, imperfect repair, genomic instability, and the bystander effect. Fundamentally, it is an individual, each one unique, who is the entity to be protected. The most, not least, sensitive individuals within exposed populations should be the objects of protection. For individual risks, due to both unexpressed assumptions and the methods used in risk analysis, that method cannot determine the nature or amount of risk that a given person is willing, or may be forced, to assume. There is a significant difference between development of best-estimate cancer risks recommended to a potential recipient of additive exposures, and the use of probabilistic risk analysis to develop regulatory exposure limits applied by licensees, or others, with no opportunity for recipients to refuse doses, even those that convey no benefit. The Task Group states clearly its recognition of the many shortcomings in risk analysis. It would be a regulatory improvement to drop risk analysis or limit it to appropriate applications, not the basis for all radiation protection. In Sierra Club’s comments for the ICRP-2005 Consultation, the Precautionary Principle was strongly recommended to the full Commission. Here, in the Executive Summary and Introduction, the Task Group has expressed its recognition of the inadequacies of risk assessment (Section 2.1). The full ICRP should act on the abundant information supplied in the report to recommend that instead of relying on risk analysis, regulators exercise utmost caution and minimize exposures from all sources of radiation that are additive to naturally-occurring background for the public, for medical, industrial, and research purposes, and for workers. As for classical epidemiology, those research methods are able to show patterns of association of cancer occurrences, including correlation of clusters that exceed expected incidence with sources of radiation exposures. But epidemiology has a low explanatory power for understanding the specific mechanisms of radiation injury. Recent research in radiation microbiology goes well beyond what classical epidemiology is capable of addressing, namely, those cancer patterns that may be positively correlated with the spatial presence of a nuclear facility. The newer research methods of microbiology are beginning to explain the mechanisms of the radiation damage -- how the damage occurs. The ability to identify single track impacts on single cells is a powerful indicator that no safe threshold dose level is likely to be found. Equally important is the capability of these research techniques to advance the understanding of transgenerational effects. In this report, emphasis is given only to cancer risks. Most genetic and all other impacts are ignored. Beyond the scope of this study, but of great importance to the public and to workers, would be the ability also to identify the non-fatal, non-cancer effects of low-dose and protracted low-dose radiation exposures. Fifteen years ago, the 1990 BEIR V Report had noted a role of radiation in heart disease and mental retardation. Post-Chernobyl, Russian researchers have described a broad range of radiation-related non-cancer impacts, including increased severity of infectious diseases of childhood; respiratory, gastrointestinal, and endocrinology disorders; and failure to thrive. All are detrimental to human health and should be considered in protective standards. The ICRP is encouraged to study non-cancer deleterious radiation impacts in development of dose standards. Also needed is further study of the relationships between radiation and the great assortment of lifestyle variations, which are barely touched on in the report. Even more important for protective standards is greater knowledge of interrelated -- synergistic -- relationships between and among exposures to radiation and to other contaminants – chemicals, pesticides, herbicides, heavy metals antibiotics, and a host of other toxic materials that are released into the biosphere. The risk-based regulatory practice of developing dose limits pollutant-by-pollutant masks the kinds and extent of the biological damage that may be experienced by individuals, or whole populations, who are exposed to mixtures of pollutants. Because so much in this report speaks to improved radiation protection, it was disheartening to reach the concluding portions (Section 6.4 and Chapter 7) that regress to discussion of continued reliance on linear extrapolation of risk estimates from high doses, tradeoffs of safety for economic benefits, “acceptable risk,” and learning to live with genetic damage that will continue to worsen. It is prudent to speculate that direct or recessive genetic damages will not be capable of correction and therefore all measures possible to reduce radiation exposures is the wise course of action. Recent news reports suggest that the next generations of humans may have a shortened life span, due to risky lifestyles and the effects of environmental contaminants. To these concerns, ICRP should add investigation of impairment of the immunological system, especially if we face ever more reliance on nuclear technologies and the generation, and release, of radioactive wastes. The ICRP should take notice that the last human generation to have been conceived and born prior to the splitting of the atom is now reaching the end of life. If recommendations of ICRP members’ predecessors have been inadequate, it will be future populations who will suffer the adverse consequences of our failure to assess correctly the biologic damage caused by increased exposures to radiation -- and undoubtedly in concert with many other pollutants as well. The degradation of future lives may or may not be avoidable. It is to be hoped that studies and status reports of a quality comparable with this “Low-dose” report will continue to move radiation protection decision-makers toward more restrictive controls over the many sources and uses of radioactive materials. We look forward to ICRP’s proposed research and reports on the impacts of ionizing radiation upon other forms of life, and hope that those studies will be conducted in a manner and with high quality comparable with this Task Group Report.