Cancer Risks near Nuclear Facilities: The Importance of Research Design and Explicit Study Hypotheses
Wing, Steve, Richardson, David B., Hoffmann, Wolfgang, Environmental Health Perspectives
BACKGROUND: In April 2010, the U.S. Nuclear Regulatory Commission asked the National Academy of Sciences to update a 1990 study of cancer risks near nuclear facilities. Prior research on this topic has suffered from problems in hypothesis formulation and research design.
OBJECTIVES: We review epidemiologic principles used in studies of generic exposure--response associations and in studies of specific sources of exposure. We then describe logical problems with assumptions, formation of testable hypotheses, and interpretation of evidence in previous research on cancer risks near nuclear facilities.
DISCUSSION: Advancement of knowledge about cancer risks near nuclear facilities depends on testing specific hypotheses grounded in physical and biological mechanisms of exposure and susceptibility while considering sample size and ability to adequately quantify exposure, ascertain cancer cases, and evaluate plausible con founders.
CONCLUSIONS: Next steps in advancing knowledge about cancer risks near nuclear facilities require studies of childhood cancer incidence, focus on in utero and early childhood exposures, use of specific geographic information, and consideration of pathways for transport and uptake of radionuclides. Studies of cancer mortality among adults, cancers with long latencies, large geographic zones, and populations that reside at large distances from nuclear facilities are better suited for public relations than for scientific purposes.
KEY WORDS: childhood cancer, environmental epidemiology, ionizing radiation, methodology, nuclear power. Environ Health Perspect 119:417-421 (2011). doi:10.1289/ehp.1002853 [Online 10 December 2010]
The possibility that radiation releases from nuclear facilities could cause cancer in surrounding populations has been of interest for more than two decades. Epidemiologic studies of spatial variation in cancer incidence or mortality have been conducted to investigate effects of unplanned releases as well as routine operations. For example, a case--control study of cancer among children < 5 years of age found dial residence within 5 km of a nuclear facility was associated with a 61% [one-sided lower bound of the 95% confidence interval (CI), 26%] increased incidence of all cancer (Spix et al. 2008) and a 119% (lower bound of the 95% CI, 51%) excess risk of leukemia (Kaatsch et al. 2008a). A meta-analysis of geographic studies reported 23% (95% CI, 7-40%) higher incidence of leukemia among children 0-9 years of age living within 16 km of nuclear facilities (Baker and Hoel 2007). Other studies have compared risks among populations whose radiation doses have been estimated based on releases and transport of radiation or deposition of radionuclides. A study of thyroid disease among people who were exposed to radioactive iodine from the Hanford site in Washington State found that the risk of thyroid disease was similar regardless of the estimated doses from radioiodine (Davis et al. 2004), whereas a study of childhood leukemia after the Chernobyl accident, which classified radiation doses based on soil radioactivity and diet, reported an excess relative risk per gray of radiation of 32.4 (95% CI, 8.8-84.0) (Davis et al. 2006).
In April 2010 the U.S. Nuclear Regulatory Commission (NRC) asked the National Academy of Sciences (NAS) to analyze "radiogenic cancer mortality and total cancer mortality in populations living near past, present, and possible future commercial nuclear facilities for all age groups," and to conduct the same analyses for cancer incidence (Sheron 2010). Nuclear power, weapons, and fuel-cycle plants are to be included. Before beginning the full study in late 2011, the NAS is to conduct a scoping study to determine availability of data, feasibility of considering geographic units smaller than counties, and the best study design for assessing risks. The NRC request underscores the need to evaluate logical problems with previous studies of cancer around nuclear facilities and to consider the appropriateness of specific hypotheses and design options. …