FINDING 1: There are several challenges for carrying out epidemiologic studies of cancer risks in populations near U.S. Nuclear Regulatory Commission-licensed nuclear facilities in the United States, including the following:
- Uneven availability and quality of data on cancer mortality and incidence at geographic levels smaller than a county. Cancer mortality and incidence are tracked by individual states, and the availability and quality of data varies from state to state. In general, cancer mortality data are available electronically from about 1970, but subject address at time of death is not captured until much later in some states. (In the absence of subject address at time of death, mortality data cannot be geocoded at levels of geographic interest for an epidemiologic study, such as census tracts.) Cancer incidence data of known quality are generally available from about 1995, although such data are available for earlier times in some states. These data include address at time of diagnosis and have been widely geocoded, although there are residual problems associated with post office boxes and rural delivery addresses.
- Uneven availability and quality of data on nuclear facility effluent releases. Effluent release data may not be available and data quality may be poor for some nuclear facilities. Effluent releases from many nuclear facilities were much higher in the past and their radionuclide compositions have changed over time. Uncertainties in dose estimates may be much higher in years when effluent releases were highest.
- Inability to reliably capture information on population mobility, risk factors, and potential confounding factors. There is no centralized source of information on residential histories or lifestyle characteristics of individuals who live in the United States. The U.S. Census provides decadal snapshots of some population characteristics, including population size and distribution with respect to age, race/ethnicity, gender, educational level, and income. However, data on population lifestyle risk factors, including exposure to cigarette smoking and access to healthcare, are limited to state-level health surveys and are not consistently available from state to state at the same level of resolution. Moreover, populations near nuclear facilities receive radiation doses from multiple sources that are unrelated to facility effluent releases, for example, doses from natural background radiation and medical radiation. There may be other risk factors and potential confounding factors, for example, exposures to toxic chemicals and unidentified lifestyle factors, that can influence cancer risks.