A pair of recent reports from the UK and Germany found a relationship between childhood leukemia and proximity to nuclear facilities. The last major US analysis on this subject was completed in 1990 and found no correlation. That study is now outdated, say NRC researchers, and it had important limitations. It only looked at cancer deaths, as opposed to incidences, and analyzed groups of people by US counties, which vary widely in size and population density. It also did not consider populations around nuclear plants that began operating after 1982.
The question of whether cancer risks associated with living near a nuclear facility is of great interest to the public, especially those living closest to the facilities. Airborne and waterborne emissions of radioactive materials from the facilities’ normal operations (called effluents) can expose nearby populations to ionizing radiation, which could elevate the risk of cancer in the exposed populations.
Effluent release data may not be available and data quality may be poor for some nuclear facilities, especially during early years of facility operations. 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.
At the request of the U.S. Nuclear Regulatory Commission (USNRC) since September 2010, the United States National Academy of Sciences has been working on a comprehensive study of cancer risk in people living near U.S. Nuclear Regulatory Commission-licensed nuclear facilities.
During Phase 1 of this project, the 19-member committee, made up of epidemiologists, statisticians, and nuclear, environmental health and cancer experts, determined if the project is statistically feasible. They’ll have to overcome problems with analyzing the data, including background rates of cancer in the general population and loss of statistical power when looking at very small populations.
Should the U.S. Nuclear Regulatory Commission decide to proceed with epidemiologic studies of cancer risks in populations near nuclear facilities, the committee recommended two study designs:
- an ecologic study of multiple cancer types of populations living near nuclear facilities;
- a record-linkage based case-control study of pediatric cancers in children born near nuclear facilities.
The ecologic study should assess cancer incidence and mortality of relatively common cancer types in populations within approximately 50 kilometers (30 miles) of nuclear facilities for the operational histories of those facilities to the extent allowed by available data. A study zone of this size would incorporate both the most potentially exposed as well as essentially unexposed regions to be used for comparison purposes.
A sub-analysis should specifically be carried out for highly radiogenic cancers such as leukemia in children.
The study should examine associations between
(i) cancer and distance/direction from the nuclear facility and
(ii) cancer and estimated radiation dose, both at the census tract level.
The record linkage based case-control study should assess the association of childhood cancers (diagnosed at younger than 15 years of age)in relation to maternal residential proximity at the time of birth of the child under study, among those whose address at time of delivery was within a 50-kilometer radius of a nuclear facility.
The study period for individual facilities should be based on the quality and availability of cancer incidence information in each state. Controls born within the same 50-kilometer radius as the cases should be selected from birth records to match cases on birth year at a minimum.
Absorbed doses/dose surrogates should be based on address of the mother’s place of residence at time of delivery, as determined from birth records.
Need for a Pilot Study
The pilot study would focus on:
- Collecting effluent release and weather data for the 7 nuclear facilities.
- Development of a computer model to obtain dose estimates as a function of distance (0 to 50 kilometers from the plant) and direction for each of these seven facilities.
- Retrieving of cancer incidence and mortality data at the census tract level within 50 kilometers of these seven facilities to assess feasibility of the recommended ecologic study.
- Conferring with investigators who are conducting linkages of cancer and birth registration data to identify eligible cases of pediatric cancers and matched controls to assess feasibility of the recommended record based case-control study. Where such linkages are not already in place, link birth registration and cancer incidence data to identify eligible cases of pediatric cancers and matched controls.
In order to assess the feasibility of the recommended epidemiologic studies on a large scale and to estimate the required time and resources, the committee recommended that a pilot study be carried out.
The committee recommends that these six nuclear power plants and one fuel cycle facility become part of the pilot study:
- Dresden (Illinois),
- Millstone (Connecticut),
- Oyster Creek (New Jersey),
- Haddam Neck (Connecticut),
- Big Rock Point (Michigan),
- San Onofre (California),
- Nuclear Fuel Services (Tennessee)
These facilities are good candidates to evaluate study feasibility because they represent both currently operating and decommissioned facilities that started operation in different time points and with some variation in:
- the population size in close proximity,
- quality and maturity of cancer registration,
- level of complexity for registry’s research approval processes and research support.
Public meetings will take place all over the US and will be available by webcast to garner public comments on the study. Phase 1 will wrap up with a report and recommendations in early 2012. If deemed possible, the study will be carried out in Phase 2.
The report will be open for public comment for 60 days starting April 1, 2012.
Comments submitted about the report’s proposed methodologies will be used to inform the design of the next phase of study and will be placed in the project’s public access file, which can be made available to the public upon request.
Comments can be submitted via email to [email protected] or faxed to 202-334-3077.
The NRC requested that the study be performed in two phases. In Phase 1, NAS will determine whether the study request’s goals can feasibly be met in a technically defensible way– and if so, develop recommendations for phase 2 using scientifically sound processes for evaluating whether nuclear facilities pose a cancer risk.
The NRC has requested the NAS to consider several topics in the first phase.
1. Methodological approaches for assessing off-site radiation dose, including consideration of:
- The isotopes/radiation involved, how they could reach humans and how they interact with the human body.
- Availability, completeness, and quality of information on gaseous and liquid radioactive releases and direct radiation exposure from nuclear facilities
- Approaches for overcoming potential methodological limitations arising from the variability in radioactive releases over time and other confounding factors
2. Methodological approaches for assessing cancer risks including consideration of:
- Demographic characteristics of the study and control populations (e.g., all age groups, including children and nuclear facility workers)
- Geographic areas to use in the study (e.g., county, zip codes, census tracts, or annular rings around the facility at some nominal distances)
- Cancer types and endpoints (i.e., diagnosis, mortality)
- Availability, completeness, and quality of cancer diagnosis and mortality data
- Different health study designs and approaches
- Approaches for developing a scientifically sound study within known limitations such as changes in population characteristics over time.
Stage 1 Key Findings
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:
(1) Uneven availability and quality of data on cancer mortality and incidence;
(2) Uneven availability and quality of data on nuclear facility effluent releases (airborne and waterborne) from normal operations;
(3) Inability to reliably capture information on population mobility, risk factors, and potential confounding factors; and
(4) the low expected statistical power.
The first stage findings show that an assessment of cancer risks in populations near nuclear facilities could be carried out using several study designs, each of which has strengths and limitations for estimating cancer risks.
- Cancer death and incidence are tracked by individual states, and the availability and quality of data vary from state to state.
- Radioactive effluent release, direct exposure, and meteorology data, if available, can be used to obtain rough estimates of annual variations in dose as a function of distance and direction from nuclear facilities.
National Academies Press page where the public can download a free copy of the report and view other resources: