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15 Evaluating Health Risks in Communities near Nuclear Facilities A. James Ruttenber Department of Preventive Medicine and Biometrics, University of Colorado School of Medicine, Denver, CO 80217

Recent critical reviews of published epidemiologic studies sug­ gestthat these studies are not capable of evaluating causal re­ lationsbetween exposure and disease in communities near nu­ clear facilities. In the United States the combination of dose reconstruction and risk assessment is being tried as an alter­ nate method for assessing health risks. This chapter reviews the limitations of epidemiologic studies, outlines the process of dose reconstruction and risk assessment, and describes a number of dose reconstruction projects underway in the United States.

FACILITIES AROUND THE WORLD

INiuCLEAR are subjected to intense public scrutiny regarding health risks from past, current, and future operations. Over the years the most popular response to public concern by public health researchers was to conduct epidemiologic studies in populations near these facilities. This approach resulted in numerous studies of disease rates in these communities (Figure 1). Taken separately or as a group, these epidemiologic studies do not provide much clarity regarding the relation between nuclear plants and health risks. Dose reconstructions and risk assessments are being conducted by independent scientists for communities near nuclear facilities in the United States in an attempt to estimate health risks more accurately 0065-2393/95/0243-0201$08.00/0 © 1995 American Chemical Society

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Figure 1.

Cancer studies in populations near nuclear facilities.

than with epidemiologic studies. Similarly, such techniques are used to evaluate health risks from the Chernobyl reactor explosion in the former Soviet Republics and in Eastern European countries. This chapter summarizes the weaknesses of epidemiologic studies of populations around nuclear facilities and describes how modern techniques of dose reconstruction and risk assessment can be used to help clarify health risks.

How Useful Are Epidemiologic Studies? A recent review of epidemiologic studies around nuclear facilities indicates that most studies were not able to establish or reject causal relations between exposure and disease in nearby communities (I). Commonly, these studies failed to establish dose-response relations between environmental exposure and disease—perhaps the most important of the criteria used to demonstrate causal relations (2). The major reason the dose-response analyses were inadequate was the absence of reliable estimates of exposure or dose. Most epidemiologic studies estimate exposure with a combination of physical distance and geopolitical boundaries. A common practice is to draw a series of concentric circles around a nuclear facility and base exposure on whether geopolitical units, such as counties or administrative districts, are within these circles. Another popular approach is to use the linear distance from a nuclear facility to the ad-^ dress of a research subject as an indicator of exposure status.

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These measures are inadequate for two reasons: (1) the dynamics of ecosystems do not follow political boundaries, and distance is only one of the many factors that contribute to exposure; and (2) the location of the residence of a research subject at the time a disease is diagnosed may not be the same as the residence location for the period when the disease was induced by an environmental exposure. Studies of the dispersal of radionuclides and the distribution of radiation doses from the Three Mile Island (TMI) nuclear power plant accident (3, 4), the early operations of the Hanford nuclear facility (57), and the Chernobyl nuclear power plant accident (8) showed that the distribution of radiation doses, as estimated from models and environmental measurements, did not conform to concentric circles. In fact researchers studying the health impacts of the T M I accident proposed that distance from a nuclear facility can be used as a measure of stress in the population following a nuclear accident, not exposure to ionizing radiation (9). In a study of cancer in counties near nuclear facilities in the United States (JO), four of the nine counties selected as the unexposed controls for the Hanford nuclear facility in southeastern Washington actually received exposure from Hanford via both atmospheric and food chain pathways (5-7). Such an error in classification usually makes false-negative results more likely than false-positive ones. Another problem common to epidemiologic studies is low statistical power—a measure of the probability that a finding of no association between exposure and disease is actually correct. Statistical power increases with the size of the population in a study, the size of disease risk associated with the magnitude and duration of exposure, and the prevalence of the disease of interest in the unexposed population. Because nuclear facilities are usually located in rural areas and because offsite exposures are generally low, most epidemiologic studies have predictably low power. It is important, therefore, to report the statistical power of such studies if no association is found between exposure and disease—a practice that is rare in the scientific literature. The results from studies with low power or from studies with power that is not reported should not be interpreted as evidence for no effect between exposure and disease. An example of this problem is the aforementioned study of cancer mortality in counties near nuclear facilities in the United States (JO). This study found no suggestion of a risk in counties near nuclear facilities and concluded that, if any excess cancer risk was present, it was too small to be detected with the methods employed. Although the authors acknowledged that they did not prove the absence of any effect, they did not report the power of their study so that readers

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could estimate the likelihood of accepting a null hypothesis when it should have been rejected. The reported exposures around nuclear facilities during normal operating conditions usually produce low risks for cancer in surrounding communities, and these populations are usually too small to reliably assess disease, even with the best of epidemiologic techniques. These limitations can be predicted before beginning a study and should not be used as excuses for not being able to interpret results. Using epidemiologic studies to screen for health risks and to guide future research is a flawed strategy. Because of the limited statistical power of epidemiologic studies, negative findings cannot reliably rule out the presence of health risks. Moreover, multiple studies with flawed or limited methods are no more convincing than a single study with a good design—particularly in the field of radiation biology where such studies must be compared with a number of well-designed ones. The criteria scientists use for establishing causal relations (2, J J) do not include recognizing quantity as superior to quality. The fact that the scientific community has not accepted the results from existing community studies supports this assessment. In spite of the many studies identifying disease increases in populations near nuclear facilities (i), the health risks are still being debated. Moreover, the evidence from community epidemiologic studies supporting the risks from nuclear facilities is not convincing enough to be used by the national and international agencies responsible for evaluating and setting radiation protection standards. On the other hand, multiple analyses showing no risk do not convince the public or scientists of the absence of any risk. In the case of the study of all nuclear facilities in the United States (10), critics can easily agree with the authors' own stated limitations. It is interesting to note that the one positive finding in this study—a slight but significant elevation in the incidence of leukemia around the Millstone nuclear power plant in New London County, Connecticut—has spurred additional epidemiologic analysis in communities around this facility, while the nuclear facility with the most convincing evidence for offsite exposure and health risk—the Hanford facility during its early operational years (5—7, 12)—showed no epidemiologic evidence of increased health risks in surrounding communities (10). The primary reason epidemiologic studies are difficult to interpret is because they usually set out to evaluate simultaneously two alternatives to the null hypothesis: (1) environmental exposures are higher than reported, and (2) the risks from radiation are higher than currently acknowledged. For studies that have not explicitly measured exposure, it is impossible to determine which of the two hypotheses

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is supported by evidence of increased disease in communities around nuclear facilities. In spite of the limitations of epidemiologic studies of populations around nuclear facilities, scientists and the public still advocate their use. Some argue that even more studies of these communities are needed to help clear up the debate about whether nuclear facilities present health risks to the public: After an initial report of a cluster of childhood leukemia near one nuclear plant in northern England, subsequent investigations revealed that there is a consistent pattern in the United Kingdom of a small but elevated risk of leukemia for children living near nuclear establishments. These clusters differ from many others investigated in that a source of environmental contamination exists near the initial cluster, and it is possible to identify other similar sources of contamination elsewhere for further hypothesis testing. Identifying several similar sources of environmental contamination and examining for consistent increases in disease rates around them may, in general, be more likely to yield interprétable epidemiologic results than in-depth studies of isolated clusters. In doing this, however, clear prior hypotheses need to be specified before the investigation begins (13). In summary, advocates for epidemiologic studies take two positions: (1) the studies, no matter how limited by methodology, help determine whether additional research is needed; and (2) although a single study may not produce convincing results, many studies around different nuclear facilities, analyzed separately or combined, will improve our knowledge of health risks from these facilities.

Dose Reconstruction and Risk Assessment: Useful Alternatives to Epidemiologic Studies Dose reconstruction provides estimates of health risk based on estimates of radiation exposure that depend, in part, on the distribution of radionuclides in the environment. Quantitative information about radiation exposure from nuclear facilities to persons living around them helps solve the three biggest problems of epidemiologic studies: doseresponse analysis, misclassification bias, and low statistical power. The steps in dose reconstruction are outlined in Figure 2. The type of dose reconstruction described in this chapter involves state-

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Review Production and Environmental Monitoring Data

Identify Radionuclides and Chemicals That May Pose Health Risks

Collect and Review Production and Monitoring Data for Selected Agents

i With Models and Environmental Data, Make Preliminary Estimate of Risk For Each Agent

For Agents Producing the Highest Risks, Develop Databases and Models For Making Best Estimates of Dose and Risk

Compare Dose and Risk Estimates With Environmental Data and Estimate Their Uncertainty

Τ

Present Final Dose Estimates and Their Uncertainties

Figure 2.

Dose reconstruction: the major steps.

of-the-art techniques applied to site-specific conditions and is far more detailed than techniques of dose estimation used for many risk as­ sessments, such as those for compliance with the Resource Conser­ vation and Recovery Act (RCRA) and the Comprehensive Environ­ mental Response, Compensation, and Liability Act (CERCLA) (14). I will use the terms dose estimation and dose evaluation to apply to these less detailed approaches and the term dose reconstruction for more detailed analyses. The first step in a dose reconstruction is a thorough review of production and environmental monitoring data to identify radio­ nuclides and chemicals that may pose health risks. Environmental monitoring data, appropriately collected and analyzed, are the best for reconstructing doses. Because such data usually are not available, par-

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ticularly for early years of operation, dose reconstruction must rely heavily on models of radionuclide movement in the environment. These models usually depend on a source term—the quantity of radioactive material released to the environment over a defined period of time. Source terms are estimated by extensively reviewing data from production records, recordings from stack monitoring, and mass-balance analysis, a technique that compares quantities of starting materials with the quantities of finished products. The radionuclides and chemicals that may provide off-site exposures are then assessed with screening models that assume conditions that maximize doses and risk estimates to the public in order to select the ones that require more detailed modeling and uncertainty analysis. The screening process can involve different levels of effort, depending on the particular site and on trie availability of funds. One popular approach is to establish a level of risk below which there is little concern. Doses from chemicals and radionuclides that result in risks above this level receive more careful analysis, while those producing lower risks receive less attention. The models used in dose reconstruction incorporate the latest advances in modeling techniques and rely on large data sets obtained by in-depth investigations. The increased availability of large microcomputers and advanced software has stimulated improvement in, and access to, state-of-the-art models. These models are designed to describe atmospheric dispersion of agents based on local and regional weather patterns, terrain, and the release characteristics of the facility. Models are also available for the surface, groundwater, and food chain transport of radionuclides and chemicals. Dose reconstructions can be performed for toxic chemicals as well as for radionuclides, although the risk for cancer per unit dose is usually computed differently for chemicals than for radionuclides. Furthermore, there is little guidance in the scientific literature for determining the combined risk from chemicals and radionuclides. In order to be meaningful from a public health standpoint, the doses estimated in the reconstruction process are converted to estimates of disease risk. This conversion is accomplished by multiplying the doses by estimates of disease risk per unit dose, which are available in the scientific literature for cancer, genetic damage to offspring from radiation exposure, and some acute and chronic diseases caused by chemical exposures. When using dose reconstruction results for assessing health risks, extensive analyses of the combined uncertainty from all variables are required to establish the upper and lower bounds for risk as well as to estimate the median risk for the exposed group (15).

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Independent Scientific Oversight and Public Involvement In the past, nuclear facilities usually did not provide the public with verifiable data on health and environmental impacts. Therefore, a large effort is required for confirming the data used to reconstruct doses to the public (14). When doses from nuclear facilities were reported they usually were prepared by the operators of the facilities and often were tainted by assumptions and language that conveyed a bias toward minimizing health risks. Moreover, these dose reports were usually based on simplistic models with few estimates of uncertainty. They also lacked peer review of procedures and results and had no public review. In some cases—particularly for weapons facilities in the United States, Great Britain, France, and the former Soviet Republics—important data documenting health risks to the public and to workers were classified for purported security reasons, and official reports to the public from agencies and scientists with knowledge of the classified material misrepresented health risks to be far lower than they actually were (16-18). In order for the results of a dose reconstruction to be acceptée} by the public and the general scientific community, each step should be planned, carried out, and reviewed by members of the public and by independent scientists. Many of the dose reconstructions now underway for Department of Energy (DOE) facilities in the United States are performed with ongoing independent scientific review by panels composed of scientists and representatives of the public. Although some of these dose reconstructions do not involve the public to the greatest extent possible, they are overseen by the public and independent scientists to a degree never before seen. Since dose reconstructions for nuclear weapons facilities may require some data that are still classified, extensive efforts should be made to identify classified material that may be relevant to dose estimates and to declassify these data whenever possible. In most cases scientists and members of the public involved in recent dose reconstructions for the D O E facilities demand that all data be accessible for review by the public and independent researchers, often requiring extensive declassification efforts. Risk estimates can be made from reconstructed doses for specific areas around a nuclear facility and for particular periods in time. It is therefore possible to identify groups in the exposed population with the highest risk for disease. Such data are also important for determining the feasibility of epidemiologic studies. An example of this approach is the feasibility analysis performed for the study of thyroid neoplasia in persons exposed to I releases from the Hanford nuclear facility (12). In this analysis only preliminary data were available and 131

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worst-case conditions were used to estimate statistical power. Because worst-case doses were used, feasibility was evaluated for a range of risks below the maximum, thereby adjusting for overestimates of dose that may erroneously raise statistical power. The data from this analysis suggested that an epidemiologic study was feasible, and these data were also used in designing an epidemiologic study, which is now underway. The initial worst-case dose estimates also helped to justify a thorough analysis of doses from early Hanford operations—the Hanford Environmental Dose Reconstruction (HEDR) project (19). Preliminary dose estimates from the H E D R project helped epidemiologists identify those who were at highest risk for thyroid neoplasia—children who consumed milk from cows that grazed on contaminated pastures. The question of whether to conduct a dose reconstruction or an epidemiologic study may be one of timing rather than the superiority of one procedure over another. In the United States many federal and state agencies have decided to conduct dose reconstruction before epidemiologic analysis. This decision was made after determining that, in the many instances where epidemiologic studies preceded dose analysis, both additional epidemiologic analysis and dose reconstruction were ultimately required. The relative merits of these two approaches are summarized in Table I.

Dose Reconstruction Projects in the United States The best examples of state-of-the-art dose reconstructions are those underway at selected D O E facilities (Table II). These studies were initiated in response to public concern over health risks arising from the entire operational histories of the facilities. To assess health risks from these sites, dose reconstructions were chosen instead of epidemiologic studies for two reasons: (1) usually, epidemiologic studies designed and conducted without dose and statistical power estimates were not interprétable; and (2) dose reconstructions provide estimates of health risk that can stand alone or be used to design future epidemiologic studies. Nevada Test Site. Many efforts were made to estimate radiation doses from the atmospheric weapons tests conducted at the Nevada Test Site (NTS). Most recently the D O E sponsored the Off-site Radiation Exposure Review Project (ORERP), which estimated internal and external exposures for persons who lived near the NTS. The ORERP developed a number of databases with information on fallout deposition. Although the project was monitored by a scientific advi-

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Table I. Dose Reconstruction and Epidemiology: A Comparison Epidemiologic Dose Comparison Reconstruction Study Time Identify periods of high and low Ν exposure Y Estimate exposures for past, Ν current, and future operations Y Space Identify areas impacted by offsite releases Identify areas exposed to different agents Identify pathways for exposure Identify areas in need of cleanup Disease risk Rank risks from multiple sources Estimate cumulativeriskfrom exposures Estimate risks for specific populations Estimate disease rates in study population NOTE:

Y is yes;

N

Y

M

Y Y Y

M

Y

M

Y

Y

Y

M

N

Y

Ν Ν

is no; M is maybe.

sory committee, which included independent scientists, most research was conducted by D O E scientists and contractors and had no public oversight. The data from the ORERP were used in more comprehensive dose reconstructions conducted in conjunction with epidemiologic studies of childhood leukemia and thyroid disease, sponsored by the National Cancer Institute (20, 21). These studies employed extensive checks on D O E data and rigorous evaluations of models. Estimates of uncer­ tainty were also reported with the doses.

Three Mile Island.

Following the accident at the TMI nuclear

power facility, many different groups initiated projects to estimate doses received by the public (22). The majority of these studies were con­ ducted in the first year or two after the accident, and four compre­ hensive reports were prepared by governmental agencies (23-26). In addition, a thorough and independent dose reconstruction was commissioned by the T M I Fund (3). The atmospheric dispersion data from this reconstruction were used in an epidemiologic study of cancer incidence (4), but actual radiation doses were not employed in this analysis. Because the doses predicted by the model were relatively small, relative atmospheric concentrations predicted by the model were

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Young and Yalow; Radiation and Public Perception Advances in Chemistry; American Chemical Society: Washington, DC, 1995.

Atmosphere, food chain, surface water Atmosphere, food chain, aquifer, surface water

Multiple radionuclides and chemicals

Multiple radionuclides and chemicals

Savannah River site

aquifer

surface

1988 (DOE) 1992 (CDC) 1992 [RR, FS] (DOE) 1992 [RR, FS] (CDC)

Year Started (Sponsor) 1979 (DOE) 1979 (multiple) 1985 (DOE) 1990 (CDC) 1988 (DOE) 1991 (CDC) 1989 (DOE)

"Projects other than complete dose reconstructions are identified with []: RR = records review; and FS = feasibility study.

I, plutonium

Fission products,

Idaho National Engineering Laboratory Oak Ridge Reservation 131

Plutonium, chemicals

surface

Rocky Flats

131

aquifer,

Pathway Atmosphere, food chain Atmosphere Atmosphere, food chain, surface water Atmosphere, food chain, water Atmosphere, food chain, water Atmosphere, food chain,

Major Exposures Fission products Radioactive noble gases and iodine Uranium oxide particles, radon, other radionuclides I, fission products

Facility Nevada test site Three Mile Island Fernald Feed Materials Production Center Hanford

Table II. Dose Reconstruction Projects in the United States 0

h-*

S.

Ci

I

!

ο

n

ft

M Ζ W W SA

c

ϋι

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RADIATION AND PUBLIC PERCEPTION

used instead of doses. This approach was designed to look for health effects that might be associated with higher releases that were not correctly or honestly reported by official sources and for effects that might be due to synergism between radiation and chemicals released during the accident. This technique is unique and provides a way to conduct exposure-response analysis without detailed knowledge of the quantity of radionuclides released to the environment.

Fernald Feed Materials Production Center.

Efforts to es-

timate off-site radiation doses from the Fernald Feed Materials Production Center (FM PC) began in 1986 in response to a request to the Centers for Disease Control (CDC) for an epidemiologic study of residents around the F M PC. The request was based on evidence of large off-site releases of uranium over the operational history of the plant, which produced uranium oxides and metal ingots from uranium ore concentrates or other uranium-containing materials. The F M P C also processed thorium and stored uranium ore that released radon to the atmosphere around the site. Instead of conducting an epidemiologic study immediately, the C D C first recommended a dose reconstruction in order to determine the region of potential exposure, to estimate possible radiation doses to the public in this area, and to provide data for determining the feasibility of an epidemiologic study. The D O E , along with staff from the F M P C and other contractors, began a dose reconstruction study in 1986. There were many delays in this project, and there were also many inconsistencies in estimates of the quantities of uranium that were released, as reported in draft versions of the research. In 1989, after discovering a substantial underestimate in the source term for uranium, there was clear evidence that so many errors had been made in the D O E estimates that the final product would not be believed by the public. In 1990 the C D C contracted with the Radiological Assessment Corporation (RAC) to conduct a thorough dose reconstruction. The completion date is planned for 1994. Draft reports for this project have been released (27-29), and the methodology has been reviewed favorably by a committee of the National Academy of Sciences (30). Oversight has been provided through advisory groups of technical experts and by periodic meetings between RAC scientists, the C D C , and the community around the F M P C . Hanford. In 1986 the states of Washington and Oregon, with the assistance of the C D C and under the sponsorship of the Nez Perce Tribe, the Yakima Indian Nation, the Confederated Tribes of the Umatilla Indian Reservation, and the Indian Health Service, estab-

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lished the Hanford Health Effects Review Panel to evaluate the possible human health effects associated with the past, current, and future operations of Hanford. The panel was also directed to assess the feasibility and utility of conducting epidemiologic studies around Hanford. Following a freedom of information request for classified documents about the early operations of Hanford filed by local citizens groups and in compliance with a State of Washington request for the D O E to cooperate with the review of Hanford health risks, several hundred previously classified documents were made public in 1987. Scientists from the State of Washington and the C D C reviewed and summarized these data and made preliminary worst-case estimates of the radiation doses that could have resulted from these exposures. After reviewing these data the Hanford Health Effects Review Panel recommended that more detailed dose estimates be developed for persons living near Hanford during the years of highest radiation release. In 1988 the D O E established a dose reconstruction project for Hanford—the H E D R project. With the help of representatives of area universities, the D O E selected an oversight panel, which then elected to closely supervise the work of D O E contractors rather than merely provide peer review. In 1991 the C D C assumed responsibilities for funding the H E D R project under its new responsibility for managing and conducting energy-related epidemiologic health research, as specified in a memorandum of understanding between the D O E and the Department of Health and Human Services. The H E D R project relies heavily on modeling the atmospheric dispersion of all radionuclides released to the environment. It also incorporates analyses of dairy and agricultural practices to estimate doses to the thyroid from I and will incorporate data on fish consumption and recreational activities to estimate doses received from radionuclides in the Columbia River. This project is also employing stateof-the-art techniques to model the spatial distribution of doses that could have resulted, as well as to estimate the range of doses received by exposed groups, based on the combined uncertainty of all model parameters. The H E D R project will provide dose estimates from all types of radiation exposure for individual members of the public, based on history of residence and life-style. These data can be used to estimate cancer risks for individuals in the region surrounding Hanford and will be employed in an epidemiologic study of thyroid neoplasia that is being conducted by the C D C and the Fred Hutchinson Cancer Research Center in Seattle, Washington (19). 131

Rocky Flats. In 1989 the D O E funded the Colorado Department of Health (CDH) to assess health risks around the Rocky Flats

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facility, which produced plutonium components and other products for nuclear weapons. The C D H relied heavily on the lessons learned from the dose reconstruction at Hanford to establish a multiphased dose reconstruction process with an independent oversight panel. Phase I of the Rocky Flats Toxicologic Review and Dose Reconstruction Project, which was completed in the spring of 1993, was a review of chemicals and radionuclides that possibly were released off-site and a ranking of agents based on risks for cancer in the exposed public (14). Data on source terms and exposed populations were then developed for a detailed dose reconstruction. Phase II of this project, begun in 1993, will involve extensive modeling of releases to the environment, validation of these models with historical and current environmental measurements, and analysis of the uncertainty in dose and risk estimates. These data will also be used to assess the feasibility of epidemiologic studies.

Idaho National Engineering Laboratory.

In 1990 the D O E

completed a historical dose evaluation of the Idaho National Engineering Laboratory (INEL)—a facility that tested nuclear reactors and other devices and processed spent fuel from the U.S. Navy's nuclear submarines. This analysis was less comprehensive than the dose reconstructions underway at Hanford, Fernald, and Rocky Flats for the following reasons: (1) it did not include chemicals; (2) it did not evaluate groundwater contamination, which is a possible route of exposure; (3) it estimated doses for realistic worst-case conditions but did not provide estimates of uncertainty for these doses; and (4) it was performed by the D O E and its contractors and was not reviewed by the public or independent scientists while it was being conducted. Because of these deficiencies, which were highlighted by an independent peer review panel convened by the D O E and another independent review panel formed by the state of Idaho, the state requested a more complete dose reconstruction to be performed by the C D C . The C D C began the data collection and evaluation phase of this project in the fall of 1992. At the time of this writing, neither the state of Idaho nor the C D C had provided for adequate public oversight for this project.

Other D O E Facilities.

The D O E funded the Tennessee De-

partment of Health to conduct a feasibility study for health-related research at its facilities in Oak Ridge, Tennessee. A review of records that could be used in a dose reconstruction project was started in 1992, overseen by a panel of citizens, scientists, and governmental representatives. Data from this project indicate that a detailed dose

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reconstruction is technically feasible, and work on this project will begin in 1994. In 1991 the C D C was given the responsibility for conducting analyses of health effects in populations around all D O E facilities through a memorandum of understanding with the D O E . Under this arrangement the C D C began a similar initial evaluation for the Savannah River site in South Carolina in the fall of 1992. To date neither the state of South Carolina nor the C D C has established ongoing, independent oversight for this project. The C D C is also considering the need for reconstruction efforts around other D O E facilities.

Conclusion The utility of dose reconstruction for quantifying and explaining health risks will be decided by the success or failure of the studies now underway at Hanford, Fernald, and Rocky Flats. Already, it is clear that dose reconstructions are expensive and time-consuming, ranging in cost between 3 and 10 million dollars or more per site and requiring from 5 to 10 years to complete. At the conclusion of the aforementioned studies, results will be interpreted by public health experts and the feasibility of epidemiologic studies will be evaluated. Based on the reasons discussed earlier, it is likely that epidemiologic studies will be deemed infeasible at one or more of these facilities. Although past experience has not shown epidemiologic studies to produce convincing conclusions, it is not yet clear whether the public will be satisfied with risk estimates based solely on data from dose reconstructions. The public may demand epidemiologic studies regardless of their feasibility. Also unclear is whether federal public health agencies will continue to support epidemiologic studies under such conditions, as funds are not available to study every possible disease around every nuclear facility—particularly with well-designed studies that may cost a few million dollars each and take from 5 to 10 years to complete. What is clear is that the dose reconstructions currently underway in the United States are setting new standards for conducting environmental health research, with regard both to improving analytical techniques and to involving the public and independent scientists in the research process. Hopefully, the advances being made in these dose reconstructions will be applied to other areas of environmental health, such as risk assessment for Superfund sites. It is encouraging that epidemiologists and public health policy makers recognize the usefulness of dose reconstruction and that they seem to agree that these studies are necessary regardless of whether

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epidemiologic studies are initiated. The value of dose reconstruction will also be recognized at the conclusion of any epidemiologic study that is performed, as that study's results will have to be interpreted for a wider population than those selected for study, and only by using data from a dose reconstruction w ill such interpretation be possible.

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21. Kerber, R. Α.; Till, J. E.; Simon, S. L.; Lyon, J. L.; Thomas, D. C.; Preston-Martin, S.; Rallison, M. L.; Lloyd, R. D.; Stevens, W. JΑΜΑ, J. Am. Med. Assoc. 1993, 270, 2076-2082. 22. Beyea, J. A Review of Dose Assessments of Three Mile Island and Rec­ ommendations for Future Research; Three Mile Island Public Health Fund: Philadelphia, PA, 1984. 23. Auxier, J. A. et al. Report of the Task Group on Health Physics and Dosimetry to the President's Commission on the Accident at Three Mile Island; The Kemeny Commission: Washington, DC, 1979. 24. Rogovin, M.; Frampton, G. Three Mile Island: A Report to the Com­ missionersand to the Public;U.S.Nuclear Regulatory Commission Spe­ cial Inquiry Group: Washington, DC, undated. 25. U.S. Nuclear Regulatory Commission; Investigation into the March 28, 1979 Three Mile Island Accident(NUREG-0600);Washington, DC, 1979. 26. Ad Hoc Dose Assessment Group; Population Dose and Health Impact of the Accident at the Three Mile Island Nuclear Station (NUREG-0588); U.S. Nuclear Regulatory Commission: Washington, DC, 1979. 27. RAC (Radiological Assessments Corporation); Task 1: Identification of Re­ lease Points at the Feed Materials Production Center; Report prepared for Fernald Dosimetry ReconstructionProject;RAC: Neeses, SC, 1991. 28. RAC (Radiological Assessments Corporation); Fernald Dosimetry Recon­ structionProject Tasks 2 and 3: Radionuclide Source Terms and Uncer­ tainties;RACReportCDC-5;RAC:Neeses, SC, 1993. 29. RAC (Radiological Assessments Corporation); Fernald Dosimetry Recon­ struction Project Task 4: Environmental Pathways—Models and Valida­ tion; RAC Report CDC-3; RAC: Neeses, SC, 1993. 30. Committee on an Assessment ofCDCRadiation Studies; Report of the Committee on an Assessment of CDC Radiation Studies: Dose Recon­ struction for the Fernald Nuclear Facility; National Academy Press: Washington, DC, 1992. RECEIVED for review October 2, 1992. ACCEPTED revised manuscript April 12, 1993.

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