PUBLIC HEALTH ASSESSMENT

Quantitative Risk Assessment and Uncertainty/Sensitivity Analyses

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The failure of ATSDR to acknowledge the presence and magnitude of individual risk from radiation is inconsistent with ATSDR practice for other known human carcinogens. This long-standing concern has been raised before the ORRHES and the ATSDR by many members of the Oak Ridge community and others. ATSDR has remained persistently non-responsive in this matter.

I believe that it would be appropriate for the range of risks associated with doses below the ATSDR cancer comparison values to be discussed and acknowledged.

The ATSDR draft PHA concludes that there is no health hazard from exposure to past, present, or future releases, but does not discuss or disclose the levels of individual risks of radiogenic cancer incidence that are associated with these exposures. The impression that there is no concern at doses below the specified cancer Comparison Values (CVs) for radiation exposure is misleading.

A distinction needs to be made between levels of exposure likely to produce statistically significant relative risks in an epidemiological study and levels of exposure that constitute significant relative and excess lifetime risks to individuals. Discussion of individual risks of cancer is notably lacking in the PHA, even though the quantification of excess risk, with uncertainty, was the main focus of the Oak Ridge Dose Reconstruction Task 4 Report.

In the Oak Ridge Dose Reconstruction Task 4 Report, the upper limits of the 95% credibility interval of the excess lifetime risk range from 1.6 to 4 chances in ten thousand at Kingston, and from 5.4 chances in ten thousand to 3.8 chances in one thousand at Jones Island on the Clinch River (see Table 13.D.1 of Apostoaei et al, 1999). The lower credibility limits approach or exceed a risk of one in one hundred thousand at all locations.

ATSDR recognizes that every radiation dose, action, or activity may have an associated risk. The fact that we did not previously present details on individual risk for radiation in the public health assessment is not inconsistent with ATSDR practice, as suggested by the commenter, because to develop conclusions we use a dose methodology in our assessments.

In the public health assessment process, techniques similar to those of the quantitative risk assessment methods (i.e., generating quantitative "risk estimates"), such as those used in the Task 4 of the Tennessee Department of Health's Reports of the Oak Ridge Dose Reconstruction (Task 4 report), may be used primarily as a screening tool to rule out clearly the existence of public health hazards or as a way of understanding regulatory concerns. If, however, exposure at a site exceeds one or more media-specific comparison values (dose-based comparison values or quantitative risk estimates), the public health assessment process proceeds with a more in-depth health effects evaluation. ATSDR scientists conduct a health effects evaluation by carefully examining site-specific exposure conditions about actual or likely exposures; conducting a critical review of available toxicological, medical, and epidemiologic information to ascertain the substance-specific toxicity characteristics (levels of significant human exposure); and comparing an estimate of the amount of chemical exposure (i.e., dose) to which people might frequently encounter at a site to situations that have been associated with disease and injury. This health effects evaluation involves a balanced review and integration of site-related environmental data, site-specific exposure factors, and toxicological, radiological, epidemiologic, medical, and health outcome data to help determine whether exposure to contaminant levels might result in harmful effects. The goal of the health effects evaluation is to decide whether harmful effects might be possible in the exposed population by weighing the scientific evidence and by keeping site-specific doses in perspective. The output is a qualitative description of whether site exposure doses are of sufficient nature and magnitude to trigger a public health action to limit, eliminate, or study further any potential harmful exposures. The PHA report presents conclusions about the actual existence and level of the health threat (if any) posed by a site. It also recommends ways to stop or reduce exposures.

The conclusions and recommendations are based on the professional knowledge and judgment of the health assessment team members. Because, however, of uncertainties regarding exposure conditions and because of adverse effects associated with environmental levels of exposures, definitive answers on whether health effects actually will or will not occur are not possible. That said, providing a framework that puts site-specific exposures and the potential for harm in perspective is possible and is one of the primary goals of the public health assessment process.

For this PHA, ATSDR added an appendix (Appendix F) to discuss risk terminology, radiation risk, and risk limits in detail. The appendix also explains the differences between ATSDR public health assessments and EPA risk assessments and shows the method for converting the doses in this PHA to risk numbers. Please note that although ATSDR does not base its public health conclusions on these risk numbers, they are presented in this PHA to provide for the community detailed information on risk.

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The excess lifetime risk levels associated with ATSDR's cancer CVs for radiation are much higher than the risk levels ATSDR uses in its evaluation of other human carcinogens. For exposures to other human carcinogens, ATSDR usually considers risks in the range of one chance in ten thousand to one chance in one million to warrant more detailed investigation.

For non-cancer producing toxic substances, ATSDR typically applies a series of safety factors to the lowest observed adverse effects level to derive an exposure level that can be considered to have a minimum risk. For exposure to radiation, the majority of scientific opinion is that there is no threshold dose below which the risk from exposure can be considered to be zero.

The risk range cited is the typical risk range used by the U.S. Environmental Protection Agency (EPA) in its evaluations of contaminants in the environment. Many of these evaluations may not necessarily be based on health, but entirely on risk assessments. The ATSDR Cancer Policy Framework, adopted in 1993, addresses many factors that must be evaluated in analyzing environmental exposures. ATSDR recognizes that at present no single generally applicable procedure for exposure assessment is available, and therefore exposures to carcinogens are best assessed on a case-by-case basis, with an emphasis on exposure prevention.

There are subtle differences in ATSDR's process of evaluating chemicals and radiation such as dose to individual organs, age-specific dose coefficients, and other metabolic differences as discussed in several ICRP publications. In its 1989 Report 96 (titled: Comparative Carcinogenicity of Ionizing Radiation and Chemicals), the National Council on Radiation Protection and Measurements (NCRP) stated that less than 30 chemicals were known to be cancer-inducing in humans and of those, in most it was not possible to define a dose-incidence relationship except generally. Also, there is much more uncertainty in chemical metabolism, the possibility of additive or synergistic effects between or among chemicals, potency, and dosimetry than in radiation evaluations. The NCRP stated that risk assessment for chemicals is "generally more uncertain than risk assessments for radiation." Because of these statements by the NCRP, ATSDR does not, in the true sense of the comment, evaluate radiation in the similar manner as it evaluates chemicals.

In this public health assessment, ATSDR compares annual doses to the 100 mrem/year dose limit of the International Commission on Radiological Protection (ICRP), the NCRP, and the U.S. Nuclear Regulatory Commission (NRC), as well as ATSDR's minimal risk level (MRL). ATSDR compares lifetime doses to the agency's radiogenic cancer comparison value of 5,000 mrem over 70 years, which is based on peer-reviewed literature and other documents developed to review the health effects of ionizing radiation. These values, used as screening tools during the public health assessment process, are levels below which adverse health effects are not expected to occur. If the screening indicates that past or current doses exceed our comparison values, then we would conduct further in-depth health evaluation.

ATSDR incorporated safety margins when it developed its screening values for radiation exposures. The approach ATSDR uses to derive MRLs, such as those in the Toxicological Profile for Ionizing Radiation, was developed with the EPA. The screening value includes the use of a no observed adverse effect level (NOAEL) or a lowest observed adverse effect level (LOAEL) as well as three or more situation-specific uncertainty factors; when multiplied, these factors give a total uncertainty factor generally ranging from 1 to 1,000 based on the studies used. Furthermore, the ATSDR legislative authority, as discussed many times, limits ATSDR to evaluate exposures based on observable and tolerable adverse health effects. If adverse health effects are not observed in an epidemiological study, then the doses used in the study should be considered tolerable.

ATSDR's radiogenic comparison value of 5,000 millirem over 70 years incorporates the linear no-threshold (LNT) model for evaluating public health hazards associated with exposure to radiation. It assumes a total lifetime dose (70 years of exposure) above background that is considered safe in terms of cancer induction. In addition to the LNT model, ATSDR also incorporates a margin-of-dose (MOD) approach into this comparison value. During an evaluation, if ATSDR determines that further investigation is needed, scientific literature associated with radiological doses and dose estimates, particularly those related to adverse health effects, is reviewed. Then, ATSDR compares the dose estimates from scientific literature to site-specific dose estimates. Thus, ATSDR uses the LNT model to determine when a more detailed site-specific evaluation is necessary, and uses the MOD approach to develop realistic information for communities regarding what is known and unknown about radiation levels at a particular site.

An independent expert panel convened to review ATSDRs site-specific approaches used to evaluate past, current, and future radiation risks to communities surrounding the Oak Ridge Reservation concluded that this combination of approaches (LNT and MOD) is appropriate for ATSDR to use to determine radiation levels at which health effects actually occur. The panel found that ATSDRs use of the MRL of 100 millirem and radiogenic cancer comparison value of 5,000 millirem were appropriate screening values. If extrapolated over 70 years assuming constant exposure, the radiogenic cancer comparison value dose estimate would be about 71 millirem per yeara level the panel determined to be protective of public health in terms of cancer and noncancer risks. The panel also concluded that ATSDRs approach considers evidence for both individual organs and whole-body doses (effective doses), noting that a whole-body dose could not be developed without accounting for doses to single organs. Further, the panel determined that ATSDRs method of distinguishing dose levels from risk levels was acceptable because ATSDR incorporated risk and LNT explicitly and implicitly when calculating doses.

In the words of one peer reviewer regarding ATSDRs radiogenic cancer comparison value, The general consensus is that the linear non-threshold hypothesis is scientifically reasonable for the purpose of radiation protection. The recent NCRP comprehensive review and UNSCEAR [United Nations Scientific Committee on the Effects of Atomic Radiation] evaluations do not find any alternative model to be better, including one with a threshold. While epidemiology is not capable of detecting risks in the low dose domain, under say 10,00020,000 millirem, there are cellular experiments and theoretical reasoning that support a linear response.

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Needless to say, the ATSDR could have avoided considerable negative criticism among scientists knowledgeable in the estimation of radiogenic cancer risk if the Agency had produced a quantitative estimate of cancer risk, instead of relying on crude estimates of epidemiological limits of detection in human epidemiological studies and making a policy decision that epidemiological limits of detection for radiogenic cancers in human cohorts are appropriate as surrogates for a limit of public health concern.

The independent external peer reviewers were satisfied with the results expressed in dose in this public health assessment (see Appendix H for the peer reviewer comments and ATSDR's responses). This comment is interesting, considering that risk estimates are based on the "crude estimates of epidemiological limits of detection." ATSDR's policy decision was reviewed by an external independent peer review panel comprised of radiation scientists and epidemiologists (see the response to comment 42 for more information on the findings of the peer review panel). The agency also solicited comments from reviewers at the National Cancer Institute and the International Epidemiology Institute. The peer reviewers were satisfied with ATSDR's approach.

In the words of one peer reviewer, a highly respected radiation epidemiologist, "The general consensus is that the linear non-threshold hypothesis is scientifically reasonable for the purpose of radiation protection. The recent NCRP [National Council on Radiation Protection and Measurements] comprehensive review and UNSCEAR [United Nations Scientific Committee on the Effects of Atomic Radiation] evaluations do not find any alternative model to be better, including one with a threshold. While epidemiology is not capable of detecting risks in the low dose domain, under say 10,000–20,000 mrem, there are cellular experiments and theoretical reasoning that support a linear response."

In response to a dose versus risk issue, this expert also stated that "Radiation protection is based on limiting dose to the public and to workers. Thus international and national committees make recommendations and national policy and regulatory bodies make judgments as to the allowable doses for the population. Dose limits are roughly based on risk of adverse health effects, and in the case of exposure to ionizing radiation it is primarily the cancer risk at low doses that is of concern. Heritable effects (genetic effects in future generations) have not been demonstrated in humans and are now believed to be much lower than originally suspected based on experimental studies."

Further, the issue with applying a "quantitative" risk coefficient to any dose is that one can calculate any risk and this is "perceived" as a true value. As stated in the ATSDR Cancer Framework Policy, "This artificial appearance of precision can lead decision makers to rely heavily on numerical risk estimates. Although ATSDR recognizes the utility of numerical risk estimates in risk analysis, the Agency considers these estimates in the context of the variables and assumptions involved in their derivation and in the broader context of biomedical opinion, host factors, and actual exposure conditions." For additional information, please review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html.

For this PHA, ATSDR nonetheless added an appendix (Appendix F) to discuss risk terminology, radiation risk, and risk limits in detail. The appendix also explains the differences between ATSDR public health assessments and EPA risk assessments and shows the method for converting the doses in this PHA to risk numbers. Please note that ATSDR does not base its public health conclusions on these risk numbers; they are presented here to provide the community with detailed information on risk.

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Page 6, Line 2: ATSDR needs to remain instep with the EPA in the methodology for performing risk assessments for DOE sites.

It is EPA and CERCLA (Comprehensive Environmental Response Compensation and Liability Act) and not ATSDR that has the regulatory authority to stipulate the proper methodology to be used to perform radiological risk assessments.

ATSDR needs to follow EPA's lead of using CERCLA slope factors for radionuclides, and not the 'millirem approach' in its estimation of risks from the ingestion of radioactively contaminated fish. In case ATSDR is uniformed about how to do this please refer to an EPA publication that documents the proper selection of risk assessment tools to be used in the evaluation of a radioactively contaminated stream. EPA 904-R-97-010. Title: Compendium of Issues surrounding the levels of contaminants contained in fish collected in tributaries leaving the Savannah River Site (SRS) and associated risk from exposure to those levels of contaminants. It was this risk assessment that documented a hazard with radioactive contamination of fish in the Savannah River (located between Georgia and South Carolina and downstream from another DOE facility, the Savannah River Site in Akin, SC. The characterization of these environmental releases of hazardous chemical (both radioactive and non-radioactive) from SRS directly resulted in a Fish Advisory being issued to advise the public of associated health risks. This joint effort of EPA, DOE, Georgia, and South Carolina added significant value to these agencies' joint efforts to protect the public health. ATSDR should use this laudatory state and federal collaboration as a case study in how to proceed in a constructive fashion in their work with stakeholders downwind and downstream of the DOE ORR.

Page 93, Table 15. Estimated Whole Body Radiation Does For Current Lower Watts Bar Reservoir Exposure Pathways. Refer to the comment concerning need to use 'slope factors,' and not 'millirems' in performing CERCLA risk analyses for ingested radionuclides.

Page 100, Table 20. Estimated Radiation Doses From Current Consumption of Fish. Refer to comment for Page 90, Table 13. This PHA is becoming increasingly complicated because of ATSDR's intransigence in not utilizing the standard methodology specified in EPA CERCLA RAGs for risk analyses of ingested radionuclides.

ATSDR needs to better inform itself by consulting with available guidance on EPA's Superfund Web sites to obtain information on how to perform a risk analysis that can meet the muster of CERCLA. After all ATSDR is supposed to already know this and should not have to be informed of this from stakeholders. Better, ATSDR should immediately consult with its sister federal agency, specifically the EPA Southeastern Regional Office of EPA in Atlanta, GA as to how was it that the EPA was able to facilitate an interstate fish advisory for the Savannah River because of offsite radioactive releases from the Savannah River site (SRS), near Akin, SC. Also, consult the EPA's OLS (Online Library System) at the following website: www.epa.gov/natlibra/ols.htm and use the search terms Savannah River Fish. This search will give you the details of a risk assessment for radioactively contaminated fish. ATSDR should use a comparable approach, one consistent with current EPA CERCLA RAGs, to produce a more valid PSA for communities downstream from DOE ORR.

Here is the OLS citation and call number for EPA 904/R-96/006 as it appears online: Main Title Potential human health effects of ingesting fish which are taken from locations near the Savannah River site (SRS). Publisher US Environmental Protection Agency, Region 4. Year Published 1996. OCLC Number 36482354. Report Number EPA 904/R-96/006. Holdings LIBRARY CALL NUMBER EKAM. RA602.F5P6. Owner Libraries EKA Region 4 Library/Atlanta, GA. Holding Modified LIBRARY Date Modified EKA 19970314. Place Published Atlanta, GA. Bib Levl m. OCL Time Stamp 19970304154240. Cataloging SOURCE OCLC/T. Language ENG. PUB Date Free Form May 1996. Collation var. paging chiefly table 28 cm. Notes "EPA 904/R-96/006" "May 1996".

Subject Added Net Health risk assessment-Savannah River Region (Ga. And S.C.); Fish as food-Contamination-Savannah River Region (Ga. And S.C.); Water quality – Savannah River Region (Ga. And S.C.). CORP Au Added Net United States. Environmental Protection Agency. Region IV ; United States. Department of Energy; United States. Environmental Protection Agency. Region IV; United States. Department of Energy. OCLC Rec Leader 00953nam 2200241Ka 45010.

Stakeholders know this volume is an easy to read guide on how to perform their own risk analysis of radioactively contaminated fish. This guide should prove useful in performing a comparable risk analysis of fish downstream from DOE ORR, from Clinch River Mile 1 (CRM1) to at least to the TVA Mocassin Bend embayment.

The radionuclide fish tissue is reality extractable from the OREIS database and can be easily analyzed according to the method in the EPA report.

This guide could also be used to map hot spot fishing holds throughout the TVA dendritic system fro Oak Ridge, TN to Paducah, KY. The TVA has an online, interactive, map of the TVA tributaries for all seven states of the system, and the necrotic locations are easily identified. Also, TVAs three nuclear pants are pinpointed as well: Browns Ferry, Sequoia, and Watts Bar. The Web site for this very useful map of the area(s) potentially impact by these radioactively contaminated fish is available online at: www.tva.gov/sites/sites_ie2.htm.

Page 102, Table 21. Summary of Public Health Implications From ATSDRs Evaluation of Past and Current Exposure to Radionuclides Released to the Clinch River/Lower Watts Bar Reservoir. The 'millirem' approach that ATSDR is persisting to utilize here is not in sync with current EPA RAGs guidance for doing risk analyses. Redo all of these analyses using current EPA RAGs guidance. Potentially exposed stakeholders will definitely be doing their own risk analyses of these exposures. These risk analyses will be using the now standard EPA approach cited above that uses, for example, pCi/gm of radionuclides in fish. These stakeholders will not be using the 'millirem' approach that ATSDR persists in using because it is too easy to discount each incremental cumulative radiation exposure one at a time as being inconsequential. ATSDR should be doing so too so that it can catch up with the stakeholders own assessments.

In addition to the OREIS fish data, ASER also has robust fish data in its data volume which can be accessed at http://www.ornl.gov/sci/env_rpt/ . To get to the data volume you need to scroll down to the index and the data bookmark is typically near the bottom for each year. All fish data are given in picocuries per gram. (1 pCi = 3.75E-02 Bequerels [Bq]). This is another good reason that ATSDR must move to using the standard EPA 'slope factor' approach, which measures exposure dose in pCi – not millirems (mrem). If ATSDR persists in using the dated mrem approach in performing its exposure assessment it will be out of sync with both standard EPA practice and those stakeholders doing their own 'alternative' risk analyses.

Also, the OREIS biota/fish data date all the way back to 1985. A plethora of fish data for stakeholders interested in detailed data – or in doing risk calculation and statistics on their own ATSDR should reasonably anticipate that there will be plenty of 'alternative' stakeholder-developed risk analyses of WOC releases. How will ATSDR contend with these foreseeable developments if it is not using the same methodology that stakeholders will be using?

Page 108, Line 17. ATSDR is utilizing methodology, which is not consistent to the legal requirements of CERCLA. ATSDR must use standard EPA Risk Assessment Guidelines (RAGs) for ingested radionuclides. These ingested radionuclides are to be treated the same as all other chemical carcinogens. These ingested radionuclides are not to be cranked into the dated approach of simply comparing 'millirems' of exposure to a hypothetical annual dose for an 'average' citizen.

ATSDR is ostensibly a 'client' federal agency for EPA, and EPA is one of its 'customer' federal agencies – also partnering with DOE and DOD. All three federal agencies contribute millions of dollars to fund ATSDR through interagency transfer of tax dollars. Why is ATSDR so unresponsive to using standard EPA Risk Assessment Guidelines (RAGs) for ingested radionuclides?

The citizens of Oak Ridge and the citizens of all downwind and downstream potentially impacted communities will do their own research to come up with valid risk analyses if they have to, and ATSDR should realize that we are fully capable of protecting our own public health. (Comments received on the initial release PHA dated December 2003.)

No mention is made of the EPA regulatory standards for public exposure to radiation, which includes the Safe Drinking Water Act of 4 mrem per year, or the fact that EPA generally regards cumulative individual risks to maximally exposed individuals on the order of one chance in ten thousand (approximately equal to about 100 mrem cumulative whole body dose over a 30 year exposure period) to merit consideration for remedial action. For carcinogenic chemicals, excess lifetime risks to maximally exposed individuals from between one chance in ten thousand and one chance in one million may be considered for remedial action at contaminated sites, but usually some form of action is taken when these risks exceed one chance in ten thousand.

ATSDR and EPA have distinct purposes and goals that necessitate different types of assessments, as explained in ATSDR''s Public Health Assessment Guidance Manual (http://www.atsdr.cdc.gov/HAC/PHAManual/toc.html), EPA's Risk Assessment Guidance for Superfund – Human Health Evaluation Manual, and in A Citizen's Guide to Risk Assessments and Public Health Assessments at Contaminated Sites (written jointly by ATSDR and EPA Region IV; see http://www.atsdr.cdc.gov/publications/CitizensGuidetoRiskAssessments.html).

An ATSDR health assessment is a mechanism to provide the community with information on the public health implications of a specific site, identifying populations for which further health actions or studies are needed. The health assessment might also make recommendations for actions necessary to protect public health. An EPA baseline risk assessment is used to support the selection of a remedial measure at a site. An overview of the public health assessment process ATSDR uses to evaluate whether people will be harmed by hazardous materials is available at: http://www.atsdr.cdc.gov/training/public-health-assessment-overview/html/index.html. A comprehensive guide to the Superfund risk assessment process is available from EPA on the Internet at: http://www.epa.gov/superfund/health/risk/index.htm .

To understand why in the public health assessment process ATSDR scientists use doses (instead of the quantitative baseline risk assessments conducted by regulatory agencies, such as EPA) it is important to understand the intentional differences between ATSDR's health assessments and EPA's risk assessments. The public health assessment is different from a risk assessment in its purpose, its goals, the exposures evaluated, and the use of information. The table below outlines the primary differences between an ATSDR public health assessment and an EPA baseline risk assessment.

ATSDR Public Health Assessment vs. EPA Baseline Risk Assessment

Public Health Assessment

The public health assessment process serves as a triage for evaluating the public health implications of exposure to environmental contamination and for identifying appropriate public health actions for particular communities. PHAs are used to identify off-site populations 1) who are exposed to hazardous substances; 2) to determine how and when they were exposed; 3) to determine whether these past, present, or future exposures are likely to lead to illness; and 4) to recommend follow-up public health actions to address the exposure and ensure the protection of public health. The public health assessment process, which may lead to a variety of public health actions, serves as a mechanism through which the agency responds to site-specific community health concerns.

In the public health assessment process, similar techniques to those of the quantitative risk assessment methods (i.e., generating quantitative "risk estimates") may be used primarily as a screening tool to clearly rule out the existence of public health hazards or as a way of understanding regulatory concerns. If, however, exposure at a site exceeds one or more media-specific comparison values (dose-based comparison values or quantitative risk estimates), the public health assessment process proceeds with a more in-depth health effects evaluation. ATSDR scientists conduct a health effects evaluation by carefully examining site-specific exposure conditions about actual or likely exposures; conducting a critical review of available toxicological, medical, and epidemiologic information to ascertain the substance-specific toxicity characteristics (levels of significant human exposure); and by comparing an estimate of the amount of chemical exposure (i.e., dose) to which people might frequently encounter at a site to situations that have been associated with disease and injury. This health effects evaluation involves a balanced review and integration of site-related environmental data, site-specific exposure factors, and toxicological, radiological, epidemiologic, medical, and health outcome data to help determine whether exposure to contaminant levels might result in harmful effects. The goal of the health effects evaluation is to decide whether harmful effects might be possible in the exposed population by weighing the scientific evidence and by keeping site-specific doses in perspective. The output is a qualitative description of whether site exposure doses are of sufficient nature and magnitude to trigger a public health action to limit, eliminate, or further study any potential harmful exposures.

The PHA presents conclusions about the actual existence and level of the health threat (if any) posed by a site. It also recommends ways to stop or reduce exposures. The conclusions and recommendations are based on the professional knowledge and judgment of the health assessment team members. Because, however, of uncertainties regarding exposure conditions and adverse effects associated with environmental levels of exposure, definitive answers on whether health effects actually will or will not occur are not possible. But providing a framework that puts site-specific exposures and the potential for harm in perspective is possible. In fact, it is one of the primary goals of the public health assessment process.

Baseline Risk Assessment

The quantitative baseline risk assessment (the framework of the EPA human health evaluation) is a numerical analysis used to determine whether levels of chemicals at hazardous waste sites pose an unacceptable risk as defined by regulatory standards and requirements. The risk assessment process is used by regulators as part of site remedial investigations to support risk management decisions and to define remedial actions involving hazardous site cleanup strategies (the determination of permit levels for the discharge, storage, or transport of hazardous waste; the establishment of clean-up levels; and the determination of allowable levels of contamination) that ensure overall protection of human health and the environment. Remedial plans based on a quantitative risk assessment represent a prudent public health approach—that of prevention.

The EPA risk assessment provides an estimate of theoretical risk from possible current or future exposures and considers all contaminated media regardless of whether exposures are occurring or are likely to occur. For cancer effects, risks are expressed as probabilities. For noncancer effects, exposure levels are compared to pre-established levels deemed to be safe. The quantitative risk estimates are not, however, intended, to predict the incidence of disease or measure the actual health effects in people resulting from hazardous substances at a site. The estimated predictions are based on statistical and biological models that include a number of protective assumptions about exposure and toxicity to ensure protection of the public. By design, they are conservative predictions that generally overestimate risk. For this reason, risk estimates are very useful in deciding the extent to which a site needs to be cleaned up (and to what levels) to protect public health adequately.

Risk assessment involves estimating exposure doses based on conservative (protective) standard (or default) exposure and toxicity assumptions (which often overestimate health risk) to ensure that remedial actions are amply safe and protective of health. Therefore, people will not necessarily be affected even if they are exposed to materials at dose levels higher than those estimated by the risk assessment. EPA's quantitative risk assessments, which are used for regulatory purposes, do not provide perspective on what the risk estimates mean in the context of the site community and do not measure the actual health effects that hazardous substances have on people.

Conclusions

For its evaluation of past exposures to X-10 radionuclide releases via White Oak Creek, ATSDR used a dose methodology and considered the 50^th percentile estimates provided in Task 4 of the Tennessee Department of Healths Reports of the Oak Ridge Dose Reconstruction (available at http://www2.state.tn.us/health/CEDS/OakRidge/WOak1.pdf ). The Task 4 team, on the other hand, used a risk model and the upper 95^th percentile dose and risk levels. Nonetheless, even using different approaches, we came to the same basic conclusions as described below.

According to page 15-4 of the Task 4 report, "The radiological doses and excess lifetime cancer risks estimated in this report are incremental increases above those resulting from exposure to natural and other anthropogenic sources of radiation. Nevertheless, for the exposure pathways considered in this task, the doses and risks are not large enough for a commensurate increase in health effects in the population to be detectable, even by the most thorough of epidemiological investigations. In most cases, the estimated organ-specific doses are clearly below the limits of epidemiological detection (1 to 30 cSv [centisieverts]) for radiation-induced health outcomes that have been observed following irradiation of large cohorts of individuals exposed either in utero, as children, or as adults." "...it is unlikely that any observed trends in the incidence of disease in populations that utilized the Clinch River and Lower Watts Bar Reservoir after 1944 could be conclusively attributed to exposure to radionuclides released from the X-10 site, even though this present dose reconstruction study has potentially identified increased individual risks resulting from these exposures."

Also, the Task 4 report was reviewed by the Oak Ridge Health Agreement Steering Panel (ORHASP)—a panel of experts and local citizens appointed to direct and oversee the Oak Ridge Health Studies. On page 12 of the ORHASPs final report titled Releases of Contaminants from Oak Ridge Facilities and Risks to Public Health (available at http://www2.state.tn.us/health/CEDS/OakRidge/ORHASP.pdf ), the panel determined that Although the White Oak Creek releases caused increases in radiation dose, the calculated exposures were small, and less than one excess cancer is expected.

On page 147 of the final public health assessment, "ATSDR concludes that exposures to X-10 radionuclides released from White Oak Creek to the Clinch River and to the Lower Watts Bar Reservoir are not a health hazard. Past and current exposures are below levels associated with adverse health effects and regulatory limits. Adults or children who have used, or might continue to use, the waterways for recreation, food, or drinking water are not expected to have adverse health impacts due to exposure. ATSDR has categorized those situations as posing no apparent public health hazard from exposure to radionuclides related to X-10. This classification means that people could be or were exposed, but that their level of exposure would not likely result in adverse health effects."

Thus, even though ATSDR used a dose methodology and considered the 50^th percentile estimates, while the Task 4 team used a risk model and the upper 95^th percentile dose and risk levels, we came to the same basic conclusion. ORHASP found that less than one excess cancer case would be expected to occur as a result of exposure to X-10 radionuclide releases via White Oak Creek; ATSDR concluded that this exposure posed no apparent public health hazard.

That said, for this PHA ATSDR added an appendix (Appendix F) to discuss risk terminology, radiation risk, and risk limits in detail. The appendix also explains the differences between ATSDR public health assessments and EPA risk assessments and shows the method for converting the doses in this PHA to risk numbers. Please note that ATSDR does not base its public health conclusions on these risk numbers; they are presented in this PHA only to provide detailed information on risk for the community.

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Page 106, Line 5. This is ridiculous. ATSDR, an advisory federal agency, is supposed to work hand-in-glove with EPA, a regulatory federal agency, to protect the public health of stakeholders downwind, downstream, and down-aquifer form DOE ORR. Yet ATSDR persists in not using standard EPA risk assessment guidance in developing its WOC 'Public Health Assessment.'

ATSDR states flatly: "Currently, there are not federal regulations pertaining to the ingestion of radiological contaminated food." This is a very ignorant statement, which is not factual. ATSDR needs to use the following reference, which includes guidance of the risk analysis of radioactive contaminants for all possible routes of exposure, including fish:

Main Title Risk Assessment Guidance for Superfund. Volume 1. Human Health Evaluation Manual (Part B, Development of Risk-Based Preliminary Remediation Goals [PRGs]). Corp Author Environmental Protection Agency, Washington, DC. Office of Emergency and Remedial Response. Publisher Dec 91 Year Published 1991 Report Number OSWER-9285.7-01B; Stock Number PB92-963333 Subjects Hazardous materials; Public health; Pollution Control; Toxicity; Exposure; Investigations; Objectives; Selection; Decision making; Superfund; Remedial response Holding. Chapter 4 of this volume, RISK-BASED PRGs FOR RADIOACTIVE CONTAMINANTS, is the one that ATSDR need to acquit itself with because this is the reference that EPA and other stakeholders in the community are using. ATSDR, and stakeholders as well, can access this reference online at the following website: http://www.epa.gov/oswer/riskassessment/ragsb/pdf/chapt4.pdf .

ATSDR needs to desist from its fallacious assertions of 'No Risk' when it is not even using standard EPA risk analysis guidelines. Consequently, this entire WOC PHA is fatally flawed and should be immediately redrafted using the standard EPA guidance cited above.

(Comment received on the initial release PHA dated December 2003.)

Please see the response to comment 44 regarding ATSDR's policy on performing risk assessments. Also, for this PHA, ATSDR added an appendix (Appendix F) to discuss risk terminology, radiation risk, and risk limits in detail. The appendix also explains the differences between ATSDR public health assessments and EPA risk assessments and shows the method for converting the doses in this PHA to risk numbers. Please note that ATSDR does not base its public health conclusions on these risk numbers; they are presented in this PHA only to provide detailed information on risk for the community.

The referenced statement, "Currently, there are no federal regulations pertaining to the ingestion of radiological contaminated food," was removed during subsequent revisions and is not included in the final PHA. It is nonetheless important to note that this is not, as this comment states, a "very ignorant statement, which is not factual." Guidance documents refer to ingestion of radiologically contaminated food, but these are not the same as federal regulations. In contrast to federal regulations, guidance documents, while they may offer suggested guidelines, are not legally enforceable.

ATSDR is not sure what is referenced in the comment that "ATSDR needs to desist from its fallacious assertions of 'No Risk.'" As mentioned in the response to comment 44, ATSDR does not perform risk assessments; we conduct public health assessments. Further, neither previous versions of this PHA nor the final version mention "no risk." . As explained previously (see response to comment 27), ATSDR bases its conclusions on estimated doses compared to health guidelines (e.g., MRL) where observable health effects have been observed—not on theoretical risk for possible exposures whether they are occurring or are likely to occur. Therefore, ATSDR would not make a "no risk" conclusion. Instead, in this final PHA, ATSDR concludes that "Exposures to X-10 radionuclides released from White Oak Creek to the Clinch River and to the Lower Watts Bar Reservoir are not a health hazard. Past and current exposures are below levels associated with adverse health effects and regulatory limits. Adults or children who have used, or might continue to use, the waterways for recreation, food, or dinking water are not expected to have adverse health impacts due to exposure. ATSDR has categorized those situations as posing no apparent public health hazard from exposure to radionuclides related to X-10."

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Why doesn't ATSDR choose to give EPA, as its customer agency, a product here that EPA is demanding? Could it be that ATSDR is more interested in low-balling DOE's risk estimates by hacking out lower risk estimates by using the FDA 'millirem' vis-à-vis the PA PRGs?

ATSDR should not go searching for some way out of 'discovering' that fishers downstream of WOC may be in harm's way. In fact, there may be serious potential human health effects from ingesting fish taken from many locations downstream of WOC. The citizens of Oak Ridge, Kingston, Spring City, and all other downstream communities from DOE ORR demand a better product from ATSDR, and one consistent with the legal requirements of CERCLA. (Comment received on the initial release PHA dated December 2003.)

Please refer to the response to comment 44 regarding the intentional differences between ATSDR's health assessments and EPA's risk assessments. In 1980, Congress established ATSDR, part of the U.S. Department of Health and Human Services, under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also referred to as Superfund. This law was established so that funding would be available to identify and clean up hazardous waste sites throughout the country. While EPA and individual states regulate the investigation and clean up of the sites, since 1986 ATSDR has been required by law to conduct a public health assessment at each site on EPA's National Priorities List.

Also to clarify, this commenter refers to ATSDR using "DOE's risk estimates" in this public health assessment, which is not true. This public health assessment uses data and doses from Task 4 of the Tennessee Department of Health's Reports of the Oak Ridge Dose Reconstruction (Task 4 report) and documents associated with the report to evaluate past exposures. For current exposures, ATSDR uses data collected from 1988 to 1994 as presented in ATSDR's 1996 Lower Watts Bar Reservoir Health Consultation, including environmental sampling data from the 1980s and 1990s that had been collected and assembled by DOE, TVA, and various consultants, as well as data from TVA's 1993 and 1994 annual radiological environmental reports for the Watts Bar Nuclear Plant. ATSDR also used data collected from 1989 to the present (2003) in the Oak Ridge Environmental Information System. For future exposures, ATSDR based its evaluation on current exposures and doses related to releases from White Oak Creek, data on current contaminant levels in the Clinch River and Lower Watts Bar Reservoir, institutional controls in place to monitor contaminants in these water bodies, and consideration of the possibility that remedial activities could release radionuclides to White Oak Creek.

Thus, as required by law under CERCLA, ATSDR prepared a public health assessment to evaluate these various exposure scenarios. Using the data mentioned above, ATSDR calculated dose estimates for past, current, and future off-site exposures to X-10 radionuclide releases to the Clinch River and Lower Watts Bar Reservoir via White Oak Creek. Given ATSDR's independent evaluation, we determined that past, current, and future uses of these watersheds do not pose a health hazard for people who have used or might continue to use these waterways for food, drinking water, or recreation.

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Pages 120-121: ATSDR limits health outcome evaluation to disease occurrence in a population. ATSDR seems to ignore the fact that, even though the population around the Clinch River was not exposed to levels that would lead to a statistically significant increase in the number of disease cases, some individuals may have been subject to non-negligible risk. It is important that ATSDR quantify the risk of disease for different categories of individuals in addition to quantification of the risk in the population. Examples of such categories are:

Anglers who fished close to White Oak Creek and who consumed relatively large amounts of the fish they caught.

Children living in the area. Children are more radiosensitive than adults. This aspect has not been explicitly addressed in the SENES Oak Ridge, Inc., Task 4 Report. It would be useful for ATSDR to address this issue. Note that the exposures in the first two decades of releases (1944-1953 and 1954-1963) are significantly larger than exposures in the next two decades (1964-1973, 1974-1991), as described in the SENES Task 4 report.

Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency does however recognize the importance of EPA risk assessment and risk analysis to determine whether levels of chemicals at hazardous waste sites pose an unacceptable risk as defined by regulatory standards and requirements. Risk analysis also helps regulatory officials make decisions in support of cleanup strategies that will ensure overall protection of human health and the environment. ATSDR acknowledges that conservative safety margins are built into EPA risk assessments and that these assessments do not measure the actual health effects that hazardous chemicals at a site have on people. For additional information, please review the framework policy at http://www.atsdr.cdc.gov/cancer.html.

Current ATSDR policy does not allow for the use of risk coefficients in determining public health impacts. The issue with applying a "quantitative" risk coefficient to any dose is that one can calculate any risk, and this is "perceived" as a true value. As stated in the ATSDR Cancer Framework Policy, "this artificial appearance of precision can lead decision makers to rely heavily on numerical risk estimates. Although ATSDR recognizes the utility of numerical risk estimates in risk analysis, the Agency considers these estimates in the context of the variables and assumptions involved in their derivation and in the broader context of biomedical opinion, host factors, and actual exposure conditions." The agency acknowledges that at present no single generally applicable procedure for exposure assessment is available, and therefore exposures to carcinogens must be assessed on a case-by-case or context-specific basis.

For additional information, please review the framework policy at http://www.atsdr.cdc.gov/cancer.html.

Nonetheless, for this PHA ATSDR added an appendix (Appendix F) to discuss risk terminology, radiation risk, and risk limits in detail. The appendix also explains the differences between ATSDR public health assessments and EPA risk assessments and shows the method for converting the doses in this PHA to risk numbers. Please note that ATSDR does not base its public health conclusions on these risk numbers; they are presented in this PHA only to provide for the community detailed risk information.

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I was immediately concerned with the fact it appears that no uncertainty estimates are given on reconstructed doses and no information is given on the cancer risks of past exposure. Instead, the report makes simple comparisons against doses that ATSDR calls "cancer comparison values" that are given with the intent that they represent a dose level below which there should be no public concern for past exposure to radiation.

Our own past work in historic dose reconstruction at Oak Ridge has been misrepresented by ATSDR. It has failed to acknowledge the uncertainty in doses that we reconstructed for reference individuals and instead has chosen to focus only on median estimates. It has inappropriately averaged relatively high annual doses that occurred during the early years of operation over a lifetime of 70 years to give the impression that annual doses were merely small fractions of natural background.

The implications of such uncertainties need to be forthrightly acknowledged by ATSDR, even if they consider the upper credibility limits to be conservative. Since ATSDR has not demonstrated that the parameters, and hence the dose distributions, derived in the Task 4 report were conservative, it is all the more critical that the PHA include this consideration.

ATSDR evaluated the need for an uncertainty analysis as outlined in NCRP Commentary 14 titled A Guide for Uncertainty Analysis in Dose and Risk Assessments Related to Environmental Contamination. In essence, the use of conservative and biased screening calculations indicated the possible resulting dose would be clearly below a regulatory limit. "Conservative screening calculations are designed to provide a risk estimate that is highly unlikely to underestimate the true dose or risk. Therefore, a more detailed analysis will likely demonstrate that the true risk is even less."

The document states that screening can be considered among the first steps in conducting an uncertainty analysis, as this roughly defines the upper and lower bounds of a distribution of exposed populations or individuals. If these screening calculations are to be used successfully, a decision point has to be determined to establish the boundary at which no further analyses are necessary. According to NCRP Commentary 14, "For example, for dose reconstruction, the National Academy of Sciences has suggested that an individual lifetime dose of 0.07 Sv be used as a decision criterion for establishing the need for more detailed investigation (NAS/NRC 1995 [National Research Council. 1995. Radiation dose reconstruction for epidemiologic uses. Committee on an assessment of CDC radiation studies. Board on Radiation Effects Research, Commission on Life Sciences. Washington, DC: National Academy of Sciences.])." A value of 0.07 Sv is equivalent to 7 rem or 7,000 mrem—a value that is 40% higher than ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years. Thus, ATSDR's screening value is more conservative than the criteria suggested by the National Academy of Sciences as reported by the NCRP.

For information on the difference between EPA risk assessment and ATSDR performing public health assessments, please see the response to comment 44. Further, for this PHA, ATSDR added an appendix (Appendix F) to discuss risk terminology, radiation risk, and risk limits in detail. The appendix also explains the differences between ATSDR public health assessments and EPA risk assessments and shows the method for converting the doses in this PHA to risk numbers. It is important to note that ATSDR does not base its public health conclusions on these risk numbers; they are presented in this PHA to provide for the community detailed information on risk.

Use of the upper bound value artificially increases the risk, as the calculated uncertainty in many cases is at least an order of magnitude or greater than the 50^th percentile value. ATSDR uses the central values in this public health assessment because they provide the most realistic doses for potential exposures to radionuclides in the Clinch River and Lower Watts Bar Reservoir. Central estimates are used because they describe the risk or dose for a typical, realistic individual. When considering central estimates, half of the potential doses will fall above and half will fall below the estimate. Therefore, an individual's actual dose would most likely be closer to the central value than near the high or low end of the range of dose estimates. In fact, ATSDR's external reviewers who evaluated documents associated with the Oak Ridge Dose Reconstruction recommended emphasizing the central estimate rather than the upper and lower bounds of the dose distribution.

The method the commenter describes is a first approximation of the annual dose. This method is generally used by many agencies, including the U.S. Environmental Protection Agency (EPA), the U.S. Department of Energy (DOE), and the U.S. Nuclear Regulatory Commission (NRC) in determining the accumulated dose in the first year following an intake. This issue was discussed at several Exposure Evaluation Work Group meetings (EEWG, formerly known as the Public Health Assessment Work Group [PHAWG]) and at the Oak Ridge Reservation Health Effects Subcommittee (ORRHES) meetings where the screening process was discussed. The reason for dividing the total dose by 48 years was to establish a first approximation of the dose, as this would allow for comparison to the 100 mrem/year dose limit recommended for the public by the ICRP, the National Council on Radiation Protection and Measurements (NCRP), the NRC, and ATSDR. ATSDR approximated the annual whole-body dose for each pathway by applying weighting factors to the Task 4's estimated 50^th percentile organ-specific doses, adjusting for a 1-year exposure, and summing the adjusted organ doses across each pathway. The first approximation value of 4.0 mrem/year for past exposures is 25 times less than the 100 mrem/year dose limit recommended for the public. Because this approximated value is so much lower than the dose limit recommended for the public during the screening-level evaluation, no further actions were necessary. Had the approximation shown an annual dose close to 100 mrem/year, ATSDR would have re-assessed the evaluation and conducted further investigation.

In the Task 4 report the authors state they used measured concentrations when available. If however, these data were not available, estimations were made via the use of modeled parameters. As discussed in Chapter 4 of the task report, these estimations were subjective probability distributions. Given the nature of the subjective analyses, ATSDR believes these to be conservative in nature and application.

A quantitative uncertainty analysis, as discussed in NCRP Commentary 14, "usually requires that the state of knowledge about the uncertain components of the mathematical model be described by probability distributions." If this knowledge is unavailable, then professional judgment is used to evaluate the site-specific parameters. NCRP Commentary 14 also states that if the results of an assessment indicate that doses are below regulatory limits, then a quantitative uncertainty analysis may not be necessary. The Task 4 report used conservative parameters (similar to worst-case) to estimate risks and doses from past exposures to X-10 radionuclides released to White Oak Creek. ATSDR calculated doses using the findings of the Task 4 report and obtained estimated doses well below conservative, regulatory limits.

NCRP Commentary 14 also states that following an uncertainty analysis, if the 95^th percentile exceeds a standard or regulatory limit and the 50^th percentile is less than the standard or regulatory limit, then additional evaluations may be recommended (page 23). ATSDR performed this additional evaluation and concluded that the more reasonable result was that the doses received from the intake of potentially contaminated foods (i.e., the pathway yielding the highest doses) were below regulatory limits and below levels of a public health hazard. Even if doses from all other pathways evaluated were combined with the ingestion pathway, the doses were still sufficiently low and were below levels where tolerable and observable adverse health effects would be expected.

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Reflecting on the Community Concerns and Communications Work Group (CCCWG) minutes for June 14, 2005, it is clear that further discussion on the subjects of criteria, the review of draft public health assessments, and the need for uncertainty analysis, is warranted and should be beneficial.

In addition, the statement is made in NCRP Commentary 14 that the National Academy of Sciences (NAS) has suggested that an estimated individual lifetime (whole body) dose below which further investigation is not necessary is 7000 mrem.

There is a difference between a dose so low that a statistically significant epidemiological relative risk is not expected, and a dose below which the risk to the general public can be considered to be negligible. The failure of an epidemiological study to determine statistically significant relative risks is not sufficient to conclude "no health hazard" at lower doses. It is well understood amongst professionals in radiation epidemiology and radiation risk assessment that epidemiology by itself can never prove the null.

For epidemiological investigations, a recommendation based on the highest dose attained, must take into account age at time of exposure, gender, and number of individuals exposed, uncertainty in exposure, and the inter-individual differences in exposure, before determining whether or not an epidemiological study will or will not have sufficient statistical power to detect an effect. For the ATSDR PHA, the risk below the limits of epidemiological detection should be disclosed with uncertainty. Anything else is censorship of information.

ATSDR evaluated the need for an uncertainty analysis as outlined in the National Council on Radiation Protection and Measurements' (NCRP) Commentary 14 titled A Guide for Uncertainty Analysis in Dose and Risk Assessments Related to Environmental Contamination. In essence, the use of conservative and biased screening calculations indicated the possible resulting dose would clearly be less than a regulatory limit. "Conservative screening calculations are designed to provide a risk estimate that is highly unlikely to underestimate the true dose or risk. Therefore, a more detailed analysis will likely demonstrate that the true risk is even less."

The PHA states that screening can be considered among the first steps in conducting an uncertainty analysis, as this roughly defines the upper and lower bounds of a distribution of exposed populations or individuals. If these screening calculations are to be used successfully, a decision point has to be determined to establish the boundary at which no further analyses are necessary. According to NCRP Commentary 14, "For example, for dose reconstruction, the National Academy of Sciences has suggested that an individual lifetime dose of 0.07 Sv be used as a decision criterion for establishing the need for more detailed investigation (NAS/NRC 1995 [National Research Council. 1995. Radiation dose reconstruction for epidemiologic uses. Committee on an assessment of CDC radiation studies. Board on Radiation Effects Research, Commission on Life Sciences. Washington, DC: National Academy of Sciences.])." A value of 0.07 Sv is equivalent to 7 rem or 7,000 mrem—a value that is 40% higher than ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years. Thus, ATSDR's screening value is more conservative than the criteria suggested by the National Academy of Sciences as reported by the NCRP.

ATSDR recognizes that every radiation dose, action, or activity may have an associated risk. Given our evaluation in this public health assessment, ATSDR concludes that exposures to X-10 radionuclides released from White Oak Creek to the Clinch River and to the Lower Watts Bar Reservoir are not a health hazard. Past and current exposures are below levels associated with adverse health effects and regulatory limits. Adults or children who have used, or might continue to use, the waterways for recreation, food, or drinking water are not expected to have adverse health impacts due to exposure. ATSDR has categorized those situations as posing no apparent public health hazard from exposure to radionuclides related to X-10. This classification means that people could be or were exposed, but that their level of exposure would not likely result in any adverse health effects.

But this public health assessment does not imply that an inability to detect effects is the same as no risk of exposure. This is clearly evident by the use of the no apparent public health hazard conclusion category in this public health assessment. ATSDR uses this category in situations in which human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but where the exposure is not expected to cause any harmful health effects. Radiation exposure is possible; still, such exposure is not expected to result in observable and tolerable health effects.

EPA-conducted risk assessments are useful in determining safe regulatory limits and prioritizing sites for cleanup. Risk assessments provide estimates of theoretical risk from possible current or future exposures and consider all contaminated media, regardless of whether exposures are occurring or are likely to occur. These quantitative risk estimates are not intended, however, to predict the incidence of disease or to measure the actual health effects in people resulting from hazardous substances at a site. By design, these risk estimates are conservative predictions that generally overestimate risk. Risk assessments do not provide a perspective on what the risk estimates mean in the context of the site community and do not measure the actual health effects that hazardous substances have on people.

ATSDR uses the public health assessment process to evaluate the public health implications of exposure to environmental contamination and to identify the appropriate public health actions for particular communities. ATSDR scientists conduct a health effects evaluation 1) by carefully examining site-specific exposure conditions about actual or likely exposures; 2) by conducting a critical review of available toxicological, medical, and epidemiologic information to ascertain the substance-specific toxicity characteristics (levels of significant human exposure); and 3) by comparing an estimate of the amount of chemical exposure (i.e., dose) to which people might frequently encounter at a site to situations that have been associated with disease and injury. This health effects evaluation involves a balanced review and integration of site-related environmental data, site-specific exposure factors, and toxicological, radiological, epidemiologic, medical, and health outcome data to help determine whether exposure to contaminant levels might result in harmful effects. The goal of the health effects evaluation is to decide whether harmful effects might be possible in the exposed population by weighing the scientific evidence and by keeping site-specific doses in perspective. The output is a qualitative description of whether site exposure doses are of sufficient nature and magnitude to trigger a public health action to limit, eliminate, or further study any potential harmful exposures. The PHA presents conclusions about the actual existence and level of the health threat (if any) posed by a site. It also recommends ways to stop or reduce exposures.

For detailed information on risk, please see Appendix F in the final PHA.

In this public health assessment, ATSDR compares annual doses to the 100 mrem/year dose limit of the International Commission on Radiological Protection (ICRP), the NCRP, and the U.S. Nuclear Regulatory Commission (NRC), as well as ATSDR's minimal risk level (MRL). ATSDR compares lifetime doses to the agency's radiogenic cancer comparison value of 5,000 mrem over 70 years, which is based on peer-reviewed literature and other documents developed to review the health effects of ionizing radiation. These values, used as screening tools during the public health assessment process, are levels below which adverse health effects are not expected to occur. If the screening indicates that past or current doses exceed our comparison values, then we would conduct further in-depth health evaluation.

When ATSDR developed its screening values for radiation exposures, safety margins were incorporated. The approach ATSDR uses to derive MRLs, such as those in the Toxicological Profile for Ionizing Radiation, was developed with the U.S. Environmental Protection Agency (EPA). The screening value includes the use of a no observed adverse effect level (NOAEL) or a lowest observed adverse effect level (LOAEL) as well as three or more situation-specific uncertainty factors. When multiplied, these factors give a total uncertainty factor generally ranging from 1 to 1,000, based on the studies used. Furthermore, as discussed many times, the ATSDR legislative authority limits ATSDR to the evaluation of exposures based on observable and tolerable adverse health effects. If adverse health effects are not observed in an epidemiological study, then the doses used in the study should be considered tolerable.

ATSDR's radiogenic comparison value of 5,000 millirem over 70 years incorporates the linear no-threshold (LNT) model for evaluating public health hazards associated with exposure to radiation. It assumes a total lifetime dose (70 years of exposure) above background that is considered safe in terms of cancer induction. In addition to the LNT model, ATSDR also incorporates a margin-of-dose (MOD) approach into this comparison value. During an evaluation, if ATSDR determines that further investigation is needed, it reviews scientific literature associated with radiological doses and dose estimates, particularly those related to adverse health effects. ATSDR then compares the dose estimates from scientific literature to site-specific dose estimates. Thus, ATSDR uses the LNT model to determine when a more detailed site-specific evaluation is necessary, and uses the MOD approach to develop realistic information for communities regarding what is known and unknown about radiation levels at a particular site.

An independent expert panel convened to review ATSDR's site-specific approaches used to evaluate past, current, and future radiation risks to communities surrounding the Oak Ridge Reservation concluded that this combination of approaches (LNT and MOD) is appropriate for ATSDR to use to determine radiation levels at which health effects actually occur. The panel found that ATSDR's use of the MRL of 100 millirem and radiogenic cancer comparison value of 5,000 millirem were appropriate screening values. If extrapolated over 70 years assuming constant exposure, the radiogenic cancer comparison value dose estimate would be about 71 millirem per year—a level the panel determined to be protective of public health in terms of cancer and noncancer risks. The panel also concluded that ATSDR's approach considers evidence for both individual organs and whole-body doses (effective doses), noting that a whole-body dose could not be developed without accounting for doses to single organs. Further, the panel determined that ATSDR's method of distinguishing dose levels from risk levels was acceptable because ATSDR incorporated risk and LNT explicitly and implicitly when calculating doses.

In the words of one peer reviewer regarding ATSDR's radiogenic cancer comparison value, "The general consensus is that the linear non-threshold hypothesis is scientifically reasonable for the purpose of radiation protection. The recent NCRP comprehensive review and UNSCEAR [United Nations Scientific Committee on the Effects of Atomic Radiation] evaluations do not find any alternative model to be better, including one with a threshold. While epidemiology is not capable of detecting risks in the low dose domain, under say 10,000–20,000 millirem, there are cellular experiments and theoretical reasoning that support a linear response."

Discussion of Multiple Radionuclide and Pathway Exposures

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Page 6, Line 7: Are these doses added together for each route of exposure to obtain a cumulative dose for a person that may be exposed by consumption of ALL available aquatic species, PLUS game animals, swimming and sediment contact? Or is the method used something like this: each exposure is "dropped out" of the analysis if he/she doesn't exceed the threshold for that specific route of exposure and environmental media.

This is important, because radiation doses ARE CUMULATIVE and an exposed individual will, in actuality, retain the additional dose from each route of exposure, even though its incremental calculation is "dropped out" for each separate exposure. Then, the sum of all 'sub-dangerous' individual does that he or she would sustain would, actually, exceed the EPA acceptable risk threshold of 1x10^-4 (one extra case of cancer per 10,000 potentially exposed individuals).

(Comment received on the initial release PHA dated December 2003.)

Past exposure pathways (see Table 11) included fish ingestion, drinking water ingestion, meat ingestion, milk ingestion, and external radiation via walking on sediment. For current exposure pathways for the Lower Watts Bar Reservoir, as presented in Table 16, ATSDR evaluated fish ingestion, water ingestion, contact with surface and dredged channel sediment, and swimming in, or showering with, surface water. For current exposure pathways for the Clinch River area, shown in Table 18, ATSDR evaluated ingestion of biota (i.e., fish, geese, and turtles), incidental ingestion of surface water, walking on sediment, and swimming. As explained in the Evaluating Exposures section of the final PHA (Section III.B.2. and III.B.3.), ATSDR calculated estimated annual and lifetime whole-body radiation doses for the Lower Watts Bar Reservoir and the Clinch River by combining the pathways evaluated (also see Table 22 and Table 23 the Public Health Implications section, Section IV.A.).

To explain further, for its evaluation of past exposures, ATSDR applied weighting factors (see Table 6 and page 68 of the final PHA) to Task 4 of the Tennessee Department of Health's Reports of the Oak Ridge Dose Reconstruction (Task 4 report) organ doses and summed the adjusted organ doses across pathways to derive the annual and whole-body doses for each pathway. ATSDR then summed the annual and whole-body dose for each pathway to derive the total annual dose to the whole body and the committed effective dose to the whole body over 70 years. ATSDR also summed the organ doses to derive a committed equivalent dose to an organ over a 70-year (lifetime) exposure.

In its evaluation of current exposures for the Lower Watts Bar Reservoir, ATSDR derived whole-body (committed effective) doses for hypothetical people exposed to radionuclides through contacting surface and dredged sediment, swimming in or showering with surface water, ingesting surface water, or consuming fish. When deriving the doses, ATSDR used worst-case exposure scenarios, assuming that the most sensitive population—that is, young children—were exposed by the most likely exposure routes to the highest concentration of radionuclides in sediment, surface water, or fish: inhalation, dermal contact, and external radiation.

In its evaluation of current exposures for the Clinch River, ATSDR examined incidental surface water ingestion, external radiation via walking on shoreline sediment or contacting water while swimming, and consumption of fish, geese, and turtles. For the dose assessment, ATSDR looked at the critical organ and the radiation dose delivered to the whole body.

ATSDR concluded that past, current, and future exposures to radionuclides released from White Oak Creek to the Clinch River and Lower Watts Bar Reservoir are not a public health hazard for people who use these water bodies. Though people might have or might yet come in contact with X-10 radionuclides that entered the Clinch River or Lower Watts Bar Reservoir via White Oak Creek, ATSDR's evaluation of data for users of these waterways indicates that the levels of radionuclides in biota, sediment, and surface water are—and have been in the past—too low to cause observable health effects.

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Page 84, Table 9. Summary of Estimated Organ-Specific (Equivalent) Radiation Doses For Past Exposure Pathways. ATSDR is supposed to use the standard 'slope factor' approach to ingested radionuclides (discussed previously in these comments), and not the 'millirem' approach. According to standard EPA Risk Assessment Guidelines (RAGs), ingested radionuclides are to be treated the same as all other chemical carcinogens and not to be cranked into the dated approach of simply comparing 'millirems of exposure to a hypothetical annual dose for an 'average' citizen. There is a good reason not to do this. The doses that citizens of Oak Ridge, downwind, downstream, and down-aquifer from DOE ORR are IN ADDITION TO THE AVERAGE CITIZEN'S EXPOSURE. To simply compare these exposed individuals to that for the 'average' exposed individual deceitfully lowballs all radiation exposures these stakeholders are sustaining. Also, all of these radiation doses are CUMULATIVE and in addition to the 'average' dose they are already sustaining. This kind of inconclusive risk analysis is at best deceitful, if not downright malevolent. (Comment received on the initial release PHA dated December 2003.)

Please see the response to comment 44 regarding the policy on ATSDR performing health assessments—not risk assessments.

For past, current, and future exposures to White Oak Creek radionuclide releases, ATSDR estimated maximum whole-body doses over a person's lifetime as well as annual whole-body doses for all radiation exposure pathways. Lifetime doses were compared to ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years, which includes a linear no-threshold factor. In addition, all of ATSDR's dose calculations use the dose coefficients published in EPA's Federal Guidance Report 13, which are actually based on the International Commission of Radiation Protection (ICRP) reports released after ICRP 60 that incorporate linear no-threshold and the dose coefficients.

Estimated annual whole-body doses were compared to the dose of 100 mrem per year recommended for the public by ATSDR, the ICRP, the National Council on Radiation Protection and Measurements (NCRP), and the U.S. Nuclear Regulatory Commission (NRC). This 100 mrem/year recommended dose is based on exposures from all sources of radiation (including future sources), except for medical and background sources considered to be the annual background dose received each year by average U.S. citizens. These recommendations also conservatively assume that there is no threshold dose below which there are no health effects (a linear no-threshold model). The estimated doses presented in the table being referenced by the commenter (Table 11 in the final PHA) are above doses that people normally receive. Thus, these estimated doses are in addition to the average background received by U.S. citizens.

The annual and lifetime doses calculated in this public health assessment include doses from all exposures and pathways combined. For past exposures for the Clinch River, the maximum whole-body dose over a lifetime (estimated committed effective dose of 278 mrem over 70 years) from all evaluated exposure pathways is well below (18 times less than) ATSDR's radiogenic cancer comparison value. Doses below this value are not expected to result in observable health effects. Radiation lifetime doses to critical organs (e.g., bone, lower large intestine, red bone marrow, breast, and skin) are also less than ATSDR's comparison values.

For current exposures for Lower Watts Bar Reservoir, ATSDR estimated committed effective doses (whole-body doses occurring over a lifetime, or 70 years) for exposures to radionuclides by contacting shoreline or dredged sediment, swimming in or showering with surface water, ingesting surface water, or eating fish. ATSDR's committed effective dose to the whole body for all pathways combined is less than 1,900 mrem over 70 years—2.5 times below ATSDR's radiogenic CV of 5,000 mrem over 70 years. The estimated annual whole-body dose is less than 30 mrem, which is below (3 times less than) the dose of 100 mrem per year recommended for the public by ATSDR, ICRP, NCRP, and NRC.

For current exposures for the Clinch River, ATSDR's estimated committed effective dose to the whole body for all pathways combined is less than 240 mrem—more than 20 times below ATSDR's radiogenic CV of 5,000 mrem. The estimated annual whole-body dose is less than 3.4 mrem—about 30 times below ATSDR's screening CV and about 30 times below ICRP's, NCRP's, and NRC's recommended value for the public of 100 mrem/year.

Therefore, ATSDR concludes that past, current, and future uses of these watersheds would not pose a health hazard for people exposed to White Oak Creek radionuclide releases. As demonstrated throughout the PHA and as detailed in this response, estimated exposure doses are below levels at which adverse health effects have been observed, even when taking into account the background radiation dose already received annually by average U.S. citizens.

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Radionuclides are not the only contaminants of concern in White Oak Creek, the Clinch River, or the Lower Watts Bar Reservoir. As noted in Sect. III. A, the ATSDR previously prepared a PHA on uranium releases from the Y-12 Plant and is planning to conduct one on PCB releases from ORNL, the Y-12 Plant, and the K-25 site. There is considerable evidence that risks for some radiogenic cancers (e.g., breast cancers) are additive with those associated with other factors (see, e.g., Annex I in the UNSCEAR 2000 report). Thus, an assessment that evaluates each type of contaminant in isolation, i.e., without considering their combined effects, may significantly underestimate the total risk. This concern should be acknowledged in the revised report.

After completing each individual public health assessment, ATSDR will be evaluating potential health effects from multiple chemical and radiological exposures.