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PUBLIC HEALTH ASSESSMENT

Y-12 Uranium Releases

OAK RIDGE RESERVATION (USDOE)
OAK RIDGE, ANDERSON COUNTY, TENNESSEE


APPENDIX H: RESPONSE TO PUBLIC COMMENTS ON Y-12 URANIUM RELEASES PUBLIC HEALTH ASSESSMENT (Cont.)

 

EPA Comment

ATSDR's Response

ATSDR's Health Guidelines for Radiation Effects

155

ATSDR's health evaluation criteria are less protective than current international, national, and federal radiation protection standards, and the bases for these criteria are inconsistent with widely-accepted radiation protection guidance.

The ATSDR radiogenic cancer comparison value of 5,000 mrem over 70 years is based on peer-reviewed literature and other documents developed to review the health effects of ionizing radiation. ATSDR's radiogenic cancer comparison values are used as a screening tool. If the screening were to indicate that past or current doses exceeded our comparison values, then additional in-depth health evaluation would be conducted to decide whether or not harmful effects might be possible.

The 5,000 mrem is over a lifetime. If one annualizes this value, the dose increases the total average U.S. background dose (including medical sources) (360 mrem/year) by about 20% and would not induce any adverse health effects. As a matter of note, please recognize that as a first approximation, ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years is less than 100 mrem/year (5,000 mrem ÷ 70 years = 71 mrem/year). This value is in line with many of the recommendations of the organizations cited by the commenter.

The first approximation of the 100 mrem/year dose limit recommended by ICRP and NCRP roughly equates into a 7,000 mrem dose over 70 years (100 mrem/year ×70 years). This lifetime dose is higher than ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years. The exposure doses calculated for Scarboro residents (155 mrem over 70 years for past exposures and <1 mrem over 70 years for current exposures) are more than 45 times lower than ICRP and NCRP's guidance. Figure 12 graphically displays NCRP's guidance and NRC's regulations for public exposure (100 mrem/year) in relation to the doses estimated for Scarboro.

The first approximation of EPA's cleanup level into a lifetime dose is roughly 1,050 mrem over 70 years (15 mrem/year ×70 years). The exposure doses calculated for Scarboro residents (155 mrem over 70 years for past exposures and <1 mrem over 70 years for current exposures) are more than 6 times lower than EPA's guidance.

Agency Lifetime
(mrem over 70 years)
Yearly (mrem/year)
ATSDR's radiogenic cancer comparison value 5,000 71
ATSDR's MRL 7,000 100
EPA's cleanup level 1,050 15
ICRP's guidance 7,000 100
NCRP's guidance 7,000 100

ATSDR believes the chronic ionizing radiation MRL of 100 mrem/year is below levels that might cause adverse health effects in people most sensitive to such effects. Further, the ATSDR MRL is the same value that is codified in 10 CFR 20 and other federal regulations.

  • An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure.


  • Most MRLs contain a degree of uncertainty because of the lack of precise toxicological information on the people who might be most sensitive to the effects of hazardous substances.


  • Proposed MRLs undergo a rigorous review process, including: Health Effects/MRL Workgroup reviews within the Division of Toxicology, expert panel peer reviews, and agency-wide MRL Workgroup reviews, with participation from other federal agencies, such as the EPA, and comments from the public.


  • ATSDR derived the chronic-duration, noncancer MRL of 100 mrem/year for ionizing radiation by dividing the average annual effective dose to the U.S. population (360 mrem/year) by three to account for human variability. The annual effective dose of 360 mrem/year has not been associated with adverse health effects in humans or animals.

156

ATSDR defines the MRL as "an estimate of daily human exposure to a substance that is unlikely to result in noncancer effects over a specific duration," which is derived "by dividing the average annual effective dose to the U.S. population (360 mrem/year) by three to account for human variability (i.e., ATSDR applied an uncertainty factor of 3)" (PHA, p. 50 and p. 104). It states that the MRL is "intended to serve only as a screening tool to assist in determining which contaminants should be more closely evaluated further in the public health assessment process," furthering stating that "exposure to estimated doses less than the MRL are not considered to be of health concern and exposure to estimated doses above the MRL does not necessarily mean that adverse health effects will occur". ATSDR bases the MRL, in part, on its conclusion that "the annual effective dose of 360 mrem/year has not been associated with adverse health effects or increases in the incidences of any type of cancers in humans or other animals" (PHA, p. 50).

Minimal risk levels need to be better described and defended, including how they are "unlikely to result in non-cancer effects" versus potential cancer effects. Has the SAB or EPS peer reviewed this approach?

As explained in the Evaluating Exposures section (Section III.A.2.), MRLs are derived when reliable and sufficient data exist to identify the target organ(s) of an effect or the most sensitive health effect(s) for a specific duration for a given route of exposure. An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure. MRLs are based on noncancer health effects only and are not based on a consideration of cancer effects. MRLs, which are intended to serve as screening levels, are substance-specific estimates used by ATSDR health assessors to identify contaminants and exposure pathways at hazardous waste sites that require further in-depth health effects evaluation.

MRLs are derived for hazardous substances using the NOAEL/uncertainty factor approach. They are below levels that might cause adverse health effects in the people most sensitive to such effects. MRLs are generally based on the most sensitive end point considered to be of relevance to humans. Exposure to a level above the MRL does not mean that adverse health effects will occur.

MRLs are intended only to serve as a screening tool to help public health professionals decide where to look more closely. They may also be viewed as a mechanism to identify those hazardous waste sites that are not expected to cause adverse health effects. Most MRLs contain a degree of uncertainty because of the lack of precise toxicological information on the people who might be most sensitive (e.g., infants, the elderly, those who are nutritionally or immunologically compromised) to the effects of hazardous substances. ATSDR uses a conservative (i.e., protective) approach to address this uncertainty, consistent with the public health principle of prevention. Therefore, estimated doses that are less than the MRL are not considered to be of health concern.

Proposed MRLs undergo a rigorous review process, including: Health Effects/MRL Workgroup reviews within the Division of Toxicology, expert panel peer reviews, and agency-wide MRL Workgroup reviews, with participation from other federal agencies, such as the EPA, and comments from the public.

ATSDR derived the chronic-duration, noncancer MRL of 100 mrem/year for ionizing radiation by dividing the average annual effective dose to the U.S. population (360 mrem/year) by three to account for human variability (that is, ATSDR applied an uncertainty factor of 3) (ATSDR 1999b). This annual effective dose to the U.S. population is obtained mainly from naturally occurring radioactive material, medical uses of radiation, and radiation from consumer products (BEIR V 1990 as cited in ATSDR 1999b). The annual effective dose of 360 mrem/year has not been associated with adverse health effects in humans or animals. ATSDR believes the chronic ionizing radiation MRL of 100 mrem/year is below levels that might cause adverse health effects in people most sensitive to such effects. Appendix A of the Toxicological Profile for Ionizing Radiation provides additional details on the derivation of the MRL (http://www.atsdr.cdc.gov/toxprofiles/tp149.html).

157

Since cancer induction is the principal late-term health effect of interest at Scarboro for past and current exposures, ATSDR's "chronic-duration" MRL of 100 mrem/yr for noncancer effects is clearly irrelevant. However, throughout the PHA, ATSDR applies the MRL and the CEDE, indistinguishably, as protective levels at or below which no adverse health effects, whether cancer or noncancer effects, are assumed.

Although cancer is a concern in Scarboro as well as for other areas in and around Oak Ridge, exposure to uranium is also a chemical hazard to the kidneys resulting in renal toxicity. Application of the MRL to screen noncancer health effects resulting both from chemical hazards as well as radiological hazards is an appropriate method.

As stated in the Toxicological Profile for Uranium, "natural and depleted uranium are only weakly radioactive and are not likely to cause cancer from their radiation… However, animal studies in a number of species and using a variety of compounds confirm that uranium is a nephrotoxin and that the most sensitive organ is the kidney…The chance of getting cancer is greater if you are exposed to enriched uranium, because it is more radioactive than natural uranium… Enriched uranium is considered to be more of a radiological than a chemical hazard" (ATSDR 1999a).

Therefore, the use of the radiogenic cancer comparison value for screening cancer over a lifetime is an appropriate method that compliments the use of the MRL for screening noncancer health effects.

158

As used in this context, we believe that the MRL of 100 mrem/yr and the CEDE at 5,000 mrem for 70 years are clearly less protective than the dose and risk limits shown in Table 7. [ATSDR note: Table 7 is provided in the notes section at the end of this table.] The 100 mrem/yr dose limit recommended by ICRP and NCRP for members of the public applies to all man-made radiation sources and exposures, excluding medical and natural background exposures. In contrast, ATSDR applies the 100 mrem/yr MRL to evaluate Scarboro doses from one source, Y-12.

As explained on page D-1, for the evaluation of radiation doses at Oak Ridge, ATSDR used the concept of CEDE. The CEDE is a calculated dose arising from the one-time intake of radiological uranium, with the assumption that the entire dose (a 70-year dose, in this case) is received in the first year following the intake. The value used by ATSDR for the radiogenic cancer comparison value is 5,000 millirem (mrem) over 70 years. ATSDR derived this value after reviewing the peer-reviewed literature and other documents developed to review the health effects of ionizing radiation.

The first approximation of the 100 mrem/year dose limit recommended by ICRP and NCRP roughly equates into a 7,000 mrem dose over 70 years (100 mrem/year ×70 years). This lifetime dose is higher than ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years. The exposure doses calculated for Scarboro residents (155 mrem over 70 years for past exposures and <1 mrem over 70 years for current exposures) are more than 45 times lower than ICRP and NCRP's guidance. Figure 12 of the PHA graphically displays NCRP's guidance along with NRC's regulations in relation to the doses estimated for Scarboro.

159

To evaluate the public health implications of past and current radiological exposures of Scarboro residents to Y-12 uranium releases, ATSDR compares calculated doses with:

  • a "chronic-duration" minimal risk level (MRL) for ionizing radiation of 100 mrem/yr for noncancer effects,
  • a committed effective dose equivalent (CEDE) of 5,000 mrem over 70 years for cancer effects, and
  • an average U.S. background dose of 360 mrem/yr.

ATSDR states that "the CEDE value of 5,000 mrem over 70 years was derived after reviewing the peer-reviewed literature and other documents developed to review the health effects of ionizing radiation," and refers the reader to Appendix D (PHA, p. 49). In Appendix D, ATSDR cites several sources, including the 1994 and 2000 reports of the General Accounting Office (GAO), Report No. 136 of the National Council on Radiation Protection and Measurements (NCRP 2001), ATSDR's 1999 Toxicological Profile for Ionizing Radiation, and the results of three epidemiological studies of radiation workers, as the basis for concluding that:

  • Between 10 rem and 5 rem, the data are not clear as to the health effects. Below 5 rem the effects are not observed, only assumed to occur. Therefore, the risk associated with a dose that approaches background, 0.36 rem/year (360 mrem or 3.6 millisieverts [mSv]) is essentially impossible to measure (PHA, p. D-1, lines 23-26), and
  • ATSDR believes that its reasoning in using a CEDE of 5,000 mrem over 70 years is protective of human health at Oak Ridge (PHA, p. D-5, 11-12).

See the response to comment 156 for a discussion of ATSDR's MRL.

ATSDR publicly discussed the 5,000 mrem radiogenic cancer comparison value in at least four PHAWG meetings and three ORRHES meetings. This comparison value is based on peer-reviewed literature and other documents developed to review the health effects of ionizing radiation.

We believe these statements are correct in general. However, we will modify the text to indicate studies suggest that when one considers radon, evidence suggests that elevated levels of indoor radon have been associated with elevated rates of lung cancer. Even taking into account the radon issues, our screening (when annualized over the 70-year period) is less than 100 mrem/year.

160

To the contrary, we believe that ATSDR's health evaluation criteria are substantially less protective than currently recommended national, international, and federal radiation protection standards (shown in Table 7 [ATSDR note: Table 7 is provided in the notes section at the end of this table.]), and that the bases for ATSDR's heath evaluation criteria are inconsistent with widely-accepted radiation protection guidance. We strongly recommend that ATSDR adopt the available radiation protection standards and guidance or explain how their health evaluation criteria are equally protective.

As explained to the community on multiple occasions, ATSDR's health evaluation criteria were used as a screening tool. If the screening were to indicate that past or current doses exceeded our screening, then additional public health evaluation would have been conducted. The response to comment 54 explains ATSDR's screening process in more detail.

As a matter of note, please recognize that as a first approximation, ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years is less than 100 mrem/year (5,000 mrem ÷ 70 years = 71 mrem/year). This value is in line with many of the recommendations of the organizations cited by the commenter.

Agency Lifetime
(mrem over 70 years)
Yearly (mrem/year)
ATSDR's radiogenic cancer comparison value 5,000 71
ATSDR's MRL 7,000 100
EPA's cleanup level 1,050 15
ICRP's guidance 7,000 100
NCRP's guidance 7,000 100

161

Both the MRL and the CEDE (which equates to ~ 71 mrem/yr) substantially exceed a variety of NRC and EPA annual dose limits by factors of 4 to 10, and both equate to lifetime cancer excess cancer risks that exceed the upper bound of EPA's acceptable risk range.

As noted on Figure 12, EPA's CERCLA cleanup level is 15 mrem/year. This effective dose equivalent corresponds to an individual's excess lifetime cancer risk of approximately 3 x 10-4 (i.e., 3 theoretical excess cases of cancer in 10,000 people). EPA deemed a risk of 3.0 x 10-4 to be essentially equivalent to that of 1.0 x 10-4, which is the presumed safe level considered acceptable and protective under CERCLA (EPA Establishment of Cleanup Levels for CERCLA Sites with Radioactive Contamination 1997).

This cleanup level is used in EPA's risk assessments to determine if levels of chemicals at hazardous waste sites pose an unacceptable risk. As explained in A Citizen's Guide to Risk Assessments and Public Health Assessments at Contaminated Sites (written jointly by ATSDR and EPA Region IV) "conservative safety margins are built into a risk assessment analysis to ensure the protection of the public... 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."

"A risk assessment does not measure the actual health effects that hazardous chemicals at a site have on people. Risk assessments are conducted without determination of actual exposure." A PHA "reviews site-related environmental data and general information about toxic chemicals. Then it compares an estimate of the amount of chemical exposure (i.e., dose) to which people might frequently encounter to the situations that have been associated with disease and injury. However, unlike a risk assessment, a PHA factors in information from the adjacent community about actual or likely exposures and information from the community about their health concerns." Therefore, it is not appropriate to base the decision of public health on risk assessment cleanup criteria. See the response to comment 127 for additional information distinguishing a risk assessment from a health assessment.

It should be noted that the first approximation of EPA's cleanup level into a lifetime dose is roughly 1,050 mrem over 70 years (15 mrem/year ×70 years). The exposure doses calculated for Scarboro residents (155 mrem over 70 years for past exposures and <1 mrem over 70 years for current exposures) are more than 6 times lower than EPA's guidance.

162

By basing the MRL and CEDE on the lack of observable health effects below 5,000 mrem, including the annual background rate, ATSDR leads the reader to conclude incorrectly that there are no effects below this dose (i.e., a dose-response threshold). What the ATSDR does not tell the reader is that this inability to detect excess cancers attributed to low-dose radiation exposures is due to the practical limits of current epidemiological techniques. If excess risk is proportional to the radiation dose, then a population size of about 50,000 people is required to detect a statistically significant excess cancer incidence at 10,000 mrem, or a population size of about 5 million is required to detect a statistically significant excess cancer incidence at 1,000 mrem (E. E. Pochin, Health Phys. 31, 148 (1976) and C. E. Land, Science 209, 1197 (1980).). Even larger populations are necessary to detect changes in cancer rates due to variations in natural background radiation exposures. In other words, extraordinarily large studies are required to quantify the risks of very low doses of radiation.

ATSDR derived the radiogenic cancer comparison value of 5,000 mrem over 70 years after reviewing the peer-reviewed literature and other documents developed to review the health effects of ionizing radiation. ATSDR publicly discussed this issue, among others, in at least four PHAWG meetings and three ORRHES meetings. ATSDR's 5,000 mrem is over a lifetime. If one annualizes this value, the dose increases the total average U.S. background dose (including medical sources) (360 mrem/year) by about 20% and would not induce any adverse health effects.

ATSDR agrees with the commenter's statements with the following caveat:

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.

163

We note that ATSDR's health evaluation criteria exceed the limits of national and international radiation protection advisory organizations, the U.S. Nuclear Regulatory Commission, and EPA. Moreover, the bases for these criteria are inconsistent with widely-accepted radiation protection guidelines and risk estimation methods.

As explained to the community on multiple occasions, ATSDR's health evaluation criteria were used as a screening tool. If the screening were to indicate that past or current doses exceeded our screening, then additional public health evaluation would have been conducted.

As a matter of note, please recognize that as a first approximation, ATSDR's radiogenic cancer comparison value of 5,000 mrem over 70 years is less than 100 mrem/year (5,000 mrem ÷ 70 years = 71 mrem/year). This value is in line with many of the recommendations of the organizations cited by the commenter.

164

At doses below those where significant risks have been demonstrated in human populations (i.e., 5,000 to 10,000 mrem for protracted exposures or 1,000 to 5,000 mrem for acute exposures), epidemiological data alone cannot be used to establish the shape of the dose-response relationship, but must also include radiobiological and biophysical data on the mutagenic, clastogenic (chromosome-damaging), and carcinogenic effects of low dose radiation. Based on an extensive, recent review of the relevant theoretical, experimental and epidemiological data, the NCRP concluded in their 2001 Report No. 136 that "although other dose-response relationships for the mutagenic and carcinogenic effects of low-level radiation cannot be excluded, no alternative dose-response relationship appears to be more plausible than the linear-nonthreshold model on the basis of present scientific knowledge." All international and national radiation protection advisory organizations, and all U.S. federal government agencies, continue to use the LNT model to estimate low dose radiation risks.

ATSDR agrees with this statement. As pointed out in NCRP 136, the issues surrounding the linear non-threshold (LNT) hypothesis are impacted by the end point selected in the experimental design and the system being evaluated (organism, cell, or organ, for example).

Discussion of Multiple Chemical and Pathway Exposures

165

The external pathway for direct gamma radiation should be added here, and mention that dermal has virtually no pathway for radionuclides.

Thank you for the comment. This information has been added to the final PHA.

Quantitative Risk Assessment and Uncertainty/Sensitivity Analyses

166

For past exposures, ATSDR's assertion that estimated doses are overestimated due to "conservative and overly protective assumptions and approaches" is not based on a quantitative sensitivity and uncertainty analysis, and is largely unsubstantiated. ATSDR should conduct a formal uncertainty analysis to determine the distribution of possible doses and risks to Scarboro residents.

Sensitivity and uncertainty analyses should be conducted separately for radiological and chemical assessments. For radiological assessments, age-specific and age-averaged lifetime radiation doses and risks for all exposure pathways combined should be compared with the relevant dose and risk standards provided in Table 7 below (see Comment 7 [ATSDR note: comment 155]). For chemical assessments, age-specific and age-averaged lifetime intakes in mg/kg/d for all exposure pathways combined should be compared with EPA's reference dose (RfD) for uranium and used to calculate a Hazard Index.

This issue of conducting an uncertainty analysis was raised by an ORRHES member at the April 22, 2003 meeting and addressed by ATSDR in a written response provided to ORRHES at the June 2, 2003 meeting. The following provides details from ATSDR's response:

As discussed in the NCRP Commentary 14, A Guide for Uncertainty Analysis in Dose and Risk Assessments Related To Environmental Contamination, issued in 1996, if a conservatively based screening calculation is performed and this screening calculation indicates the risk is "clearly below regulatory or risk levels of concern," and the possible exposure is low, then a quantitative uncertainty analysis may not be necessary. By design, conservative screenings are "highly unlikely to underestimate the true dose or risk."

This issue of uncertainty analyses and sensitivity analysis was evaluated by the Task 6 team, ATSDR's technical reviewers, and ATSDR scientists.

As stated in the title, the Task 6 report was a "Screening Evaluation of Potential Off-Site Exposure," that routinely and appropriately used several layers of conservatism and protective assumptions and approaches in estimating concentrations and doses. Task 6 report states "some level of conservatism was maintained in the uranium concentration estimates used in Level II screening to ensure that hazards to a significant portion of the potentially exposed population were not underestimated" (page ES-9). Also, the Task 6 report states on page 2-13 that a level of conservatism was added by combining the uranium activity amounts for U 234 and U 235 and that this approach is considered reasonable for this screening assessment since the Task 6 estimates do not include a formal uncertainty analysis. On page D-3, the Task 6 authors state "although an uncertainty analysis of the Task 6 air source term was not within the scope of Task 6, experts interviewed during the project consider release estimates for enriched uranium to be suitable for the Task 6 screening assessment and are within an order of magnitude of actual releases" (ChemRisk 1999). The authors also state (on page 5-2) that based on the project team's experience in the Dose Reconstructions Feasibility Study and the Task 6 screening evaluation they identified areas they believe are significant contributors of the overall uncertainty of the results of the Task 6 screening evaluation. The authors state that "these areas should be examined if the evaluation of Oak Ridge uranium releases is to proceed beyond the conservative screening stage and on to nonconservative screening and possibly a stage of refined evaluation that would likely include uncertainty and sensitivity analyses to assist in the decision making process" (ChemRisk 1999).

Also, the internationally recognized expert technical reviewers hired by ATSDR to review the Task 6 report pointed out that the report is somewhat lacking in uncertainty and sensitivity analysis. However, "the estimates made in the report tend to be on the conservative side–one expects, therefore, that (when in error) the report would tend to overestimate the extent to which exposure to uranium is a problem in the Oak Ridge area. Further refinements to the study are likely to reveal that uranium exposures are actually lower than those currently estimated." Also, the technical reviewers stated the report is technically sound and applicable to decision-making (see page G-7 of the PHA).

ATSDR scientists also identified other aspects of the Task 6 report that resulted in several additional layers of conservatism and protective assumptions and approaches (see list of conservative aspects of the screening evaluation on pages 48 and 92 of the PHA). Since the Task 6 screening evaluation of air, soil, and surface water pathways resulted in a total past uranium radiation CEDE (155 mrem over 70 years) well below (32 times less than) the ATSDR radiogenic cancer comparison value (5000 mrem over 70 years), ATSDR does not believe the evaluation of Y-12 uranium releases requires a further nonconservative screening or a refined evaluation with uncertainty and sensitivity analyses.

In addition, the total past uranium radiation CEDE (155 mrem over 70 years) is also less than the average annual background radiation dose received by individuals living in Denver or the radiation dose an individual would receive during a CT scan (1,000 mrem/scan) at a local hospital (see Figure 12). As shown in Table 15, ATSDR also calculated a radiological dose to the lung following the inhalation of uranium. This dose is not considered a dose of public health concern. Even using the conservative overestimated doses, people in the Scarboro community, as well as the Oak Ridge community, were not exposed to levels of uranium that are above levels of health concern.

Additionally, the following is a list of conservative aspect of the screening evaluation that resulted in the overestimated doses.

  1. The Task 6 report noted that the Y-12 uranium releases for some of the years may have been understated due to omission of some unmonitored release estimates. This would cause the empirical c/Q values (used in the air dispersion model) to be overestimated and in turn would cause the air concentrations to be overestimated.


  2. The majority of the total uranium radiation dose is attributed to frequently eating fish from the EFPC and eating vegetables grown in contaminated soil over several years. If a person did not regularly eat fish from the creek or homegrown vegetables over a prolonged period of time (which is very probable), then that person's uranium dose would likely have been substantially lower than the estimated doses reported in this PHA.


  3. According to ATSDR's regression analysis, the method that the Task 6 team used to estimate historical uranium air concentrations overestimated uranium 234/235 concentrations by as much as a factor of 5. Consequently, airborne uranium 234/235 doses based on this method were most likely overestimated.


  4. In evaluating the soil exposure pathway, the Task 6 team used EFPC floodplain soil data to calculate doses instead of Scarboro soil. Actual measured uranium concentrations in Scarboro soil are much lower than the uranium concentrations in the floodplain soil. The estimated doses would be much lower if they were based on actual measured concentrations in Scarboro.

As explained in the ATSDR Public Health Assessment Guidance Manual (http://www.atsdr.cdc.gov/HAC/HAGM/), 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), there are deliberate differences between ATSDR's health assessments and EPA's risk assessments. The two agencies have distinctly different purposes that necessitate different goals for their assessments. A risk assessment is used to support the selection of a remedial measure at a site. An ATSDR health assessment is a mechanism to provide the community with information on the public health implications of a specific site, identifying those populations for which further health actions or studies are needed. See the response to comment 127 for additional information distinguishing a risk assessment from a health assessment.

Data and Modeling

167

ATSDR should provide concise summaries of primary data sources and more detailed discussions of its own assessments and conclusions.

The Task 6 report is discussed throughout the past exposure evaluation. The FAMU (1998) and EPA Region IV (2003) reports are summarized on page 29 of the PHA. A description of OREIS has been added to the final PHA To expand the information presented, ATSDR added summary briefs of the EPA and FAMU reports in Appendix I of the final PHA.

ATSDR provided detailed discussions of our own evaluations throughout the PHA and in the Appendices. For examples, see the uranium enrichment discussion on pages 73–77 and the linear regression analysis in Appendix E.

168

To assess past and current uranium exposures, ATSDR relies on empirical data and analyses provided by other investigators. Throughout the PHA, ATSDR presents these data and analyses in summary form, either as a single data point or as multiple values in data tables, often with only cursory discussions of the original information. Instead of providing detailed discussions, ATSDR frequently refers the reader to the source documents, sometimes citing the relevant sections or appendices, most times not. Such an approach has several drawbacks: it assumes that the reader is already familiar with the original data, or has, or can obtain the specific reference, and has the technical expertise to evaluate the material; it also places the onus on the reader to compare and contrast data sets, assessments, results, and conclusions in the original documents and the PHA; and, overall, it is a laborious, time intensive, and tedious process.

We believe that this approach is largely unnecessary and that most of the associated drawbacks can be avoided, if ATSDR provides more detailed data summaries, discussions, and comparisons, and makes it easier for the reader to obtain key references. We suggest that, at a minimum, ATSDR should provide or refer readers to electronic copies of the following references:

  • Uranium Releases from the Oak Ridge Reservation–A Review of the Quality of Historical Effluent Monitoring Data and a Screening Evaluation of Potential Off-Site Exposures, The Report of Project Task 6, Reports of the Oak Ridge Dose Reconstruction, Vol. 5 (ChemRisk 1999);
  • Release of Contaminants from Oak Ridge Facilities and Risks to Public Health, Final Report of the Oak Ridge Health Agreement Steering Panel (ORHASP 1999);
  • Oak Ridge Dose Reconstruction Project Summary Report, Reports of the Oak Ridge Dose Reconstruction, Vol. 7 (ChemRisk 2000);
  • Final Report on the Background Soil Characterization Project at the Oak Ridge Reservation, Oak Ridge, Tennessee, DOE/OR/01-1175-V1 (DOE 1993);
  • Sampling Approach for Characterization of the Scarboro Community, Oak Ridge, Tennessee (JE/EM-52/RI, 1998);
  • Scarboro Community Environmental Study (FAMU 1998);
  • Scarboro Community Sampling Results: Implications for Task 6 Environmental Projections and Assumptions (Prichard 1998); and
  • September 2001 Sampling Report for the Scarboro Community, Oak Ridge, Tennessee (Draft Report) (EPA 2002).

After receiving comments on the data validation version of the PHA from the ORRHES in March 2003, ATSDR clarified the data sources in the public comment version and during two public presentations to the ORRHES (April 22, 2003) and the DOE Site-specific Advisory Board (SSAB) (May 14, 2003) (two Federal Citizen's Advisory Committees). ATSDR's calculations and exposure parameters were also discussed in detail during the PHAWG and ORRHES meetings.

All the data ATSDR used to evaluated health concerns from Y-12 uranium releases are publicly available:

The sources of data mentioned in comment 168 are available at the DOE Information Center (475 Oak Ridge Turnpike, Oak Ridge TN 37830; phone: 865-241-4780; Web site: http://www.oakridge.doe.gov/info_cntr/index.html Exiting ATSDR Website).

Miscellaneous Comments

169

Thank you for the opportunity to review and provide comments on the subject document.

You are welcome. ATSDR appreciates receiving comments from community members, civic organizations, and other government agencies interested in the public health activities at the ORR.

170

We believe ATSDR should address these issues before the public health assessment process is concluded.

It is ATSDR's policy to address all comments collected during the public comment period. All comments have been addressed in this appendix (see above).

Notes:

The page, figure, and table numbers in the comments are in reference to the public comment release PHA (April 22, 2003). The page, figure, and table numbers in ATSDR's responses are in reference to the final PHA.

The following are comments and tables EPA provided:

For past uranium exposures, we believe that ATSDR has underestimated the radiation dose from the inhalation pathway.


Table 1a presents a summary of the Task 6 and ATSDR pathway-specific radiation doses25 to residents of Scarboro community from past releases of uranium from Y-12.

Table 1a. Pathway-specific Radiation Doses From Past Releases from Y-12
Exposure Pathways Task 6 Level II doses* ATSDR 70-y adjusted doses
U 234/235 (Sv) U 238 (Sv) Total U (mrem) Total U (mrem) Percent of total dose
Air 2.5E-04 4.3E-05 29 40 26%
Surface Water 2.0E-04 1.6E-04 36 49 31%
Soil 2.8E-04 2.1E-04 49 66 43%
All pathways 7.3E-04 4.1E-04 114 155 100%

*Data taken from Tables 4-8 through 4-13 (pp. 4-15 to 4-17) of the Task 6 report (ChemRisk 1999).

To adjust for a 70-y exposure duration, ATSDR multiplied the Task 6 Level II-derived total uranium dose for each pathway (i.e., air, surface water, and soil) by a factor of 1.35 (i.e., 70 y/52 y) and summed these values to arrive at a total effective dose of 155 mrem for all pathways combined. ATSDR made no other modifications to the dose equations or exposure assumptions used by the Task 6 team in their Level II assessment.

As shown in Table 1b below, the total effective dose from the air exposure pathways represents the sum of the uranium doses from six sub-pathways. Of these, the inhalation pathway accounts for 35 mrem, the majority (88%) to the total dose.

Table 1b. Air Exposure Pathway Doses
Air Exposure Pathways Task 6 Level II doses* ATSDR 70-y adjusted doses
U 234/235 (Sv) U 238 (Sv) Total U (mrem) Total U (mrem) Percent of total dose, all air pathways
Inhalation of airborne particulates 2.2E-04 4.0E-05 26 35 88%
Immersion in airborne particulates 7.6E-10 7.7E-14 0.0001 0.0001 >0.01%
Air to livestock, meat ingestion 1.4E-09 2.7E-10 0.0002 0.0002 >0.01%
Air to dairy cows, milk consumption 4.3E-09 8.4E-10 0.001 0.001 >0.01%
Air to vegetables, consumption 2.8E-05 2.1E-06 3 4 10%
Air to pasture to livestock to beef 1.3E-06 1.5E-07 0.1 0.2 0.5%
Air to pasture to dairy cows to milk 3.1E-06 3.6E-07 0.3 0.5 1.2%
Sum of doses from air pathways 2.5E-04 4.3E-05 29 40 100%

*Data taken from Tables 4-8 thru 4-13 (pp. 4-15 to 4-17) of the Task 6 report (ChemRisk 1999).

To calculate the doses for the inhalation pathway for both Level I and Level II screening assessments, the Task 6 team used the following equation (which represents the combination of two equations presented on pages J-4 and 4-9 of ChemRisk 1999):

Dair = Cair * Uair * ft * fs * Binh * EF * ED * CF1 * DCFi

where:

Parameter Definition (units) Task 6 Report Parameter Values
Level I Level II Citation
Dair Committed effective dose from intake of uranium isotopes in air (Sv) (calculated) (calculated) ---
Cair Average concentration of uranium isotopes in air
(pCi m-3)
U 234/235 1.42E-02 1.42E-02 Calculated using data from Table 3-15, p. 3-22.
U 238 3.06E-03 3.06E-03
Uair Average volume of air inhaled per day (m3 d-1) 20 20 Table K-1, p. K-4
ft Fraction of time that a person is exposed (unitless) 0.8 0.4 Table K-1, p. K-4
fs Indoor/outdoor shielding factor (unitless) 0.5 0.3 Table K-1, p. K-4
Binh Bioavailability (inhalation) (unitless) 1 1 Not provided, assumed value
EF Exposure frequency 365 350 Table K-1, p. K-4
ED Exposure duration 52 52 Not provided, assumes value
CF1 Conversion factor (Bq pCi-1) 0.037 0.037 Not provided, assume value
DCFi Dose conversion factor for inhalation of uranium isotopes U 234/235 9.4E-06 9.4E-06 Table 4-5, p.4-9
U 238 8.0E-06 8.0E-06

Substituting the Level II values into the equation above yields the following inhalation doses:

U 234/235
Dair = (1.4E-02) * (20) * (0.4) * (0.3) * (1) * (350) * (52) * (0.037) * (9.4E-06)
Dair= 2.2E-04 Sv (Task 6 value, 52-y)
Dair= 22 mrem (Task 6 value, 52-y)
Dair= 29 mrem (ATSDR value, 70-y)

U 238
Dair = (3.06E-03) * (20) * (0.4) * (0.3) * (1) * (350) * (52) * (0.037) * (8.0E-06)
Dair = 4.0E-05 Sv (Task 6 value, 52-y)
Dair = 4 mrem (Task 6 value, 52-y)
Dair = 5 mrem (ATSDR value, 70-y)

Total U = U-234/235 + U-238
Dair = 2.2E-04 Sv + 4.0E-05 Sv
Dair = 2.6E-04 Sv (Task 6 value, 52-y)
Dair = 26 mrem (Task 6 value, 52-y)
Dair = 35 mrem (ATSDR value, 70-y)

All of the calculated values above match those shown in Table 1b.

After reviewing the default assumptions used in these calculations, we conclude that the Level II parameter values used by the Task 6 team (and by ATSDR) for ft (i.e., the fraction of time that a person is exposed) and ft (i.e., the indoor/outdoor shielding factor) are not appropriate for a "typically" exposed individual. The current ft value of 0.4 equates to an individual being exposed for only 40% of their time each day or 9.6 hr. The current fs value of 0.3 means that the concentration of uranium isotopes in indoor air is only 1/3 of the concentration outdoors, and is based on assumption that the house is made of brick or stone.

For residential exposures, EPA's Exposure Factors Handbook recommends 50th percentile values of 16.4 hr per day indoors and 2 hr per day outdoors (EPA/600/P-95/002Fc, August 1997, p.15-17). Since ft is the sum of the exposures times indoors (ETi) and outdoors (ETo), then ft = ETi + ETo = (16.4/24) + (2/24) = 0.683 + 0.083 = 0.77. For the indoor/outdoor shielding factor, fs, we believe that a value of 0.5 is more reasonable than the current value of 0.3 and is consistent with the value used by the Task 6 team in the Level I assessment for wood houses. It is also consistent with other values reported in the literature 26.

Substituting these values for the current default values and modifying the previous equation to account for ETi and ETo, yields the following revised inhalation doses:

U-234/235
Dair = Cair * Uair * [ETo + (ETi * fs)] * Binh * EF * ED * CF1 * DCFi
Dair = 1.4E-02 * (20) * [0.083 + (0.683 * 0.5)] * (1) * (350) * (52) * (0.037) * (9.4E-06)
Dair = 7.6E-04 Sv (Task 6 value, 52-y)
Dair = 76 mrem (Task 6 value, 52-y)
Dair = 103 mrem (ATSDR value, 70-y)

U-238
Dair = Cair * Uair * [ETo + (ETi * fs)] * Binh * EF * ED * CF1 * DCFi
Dair = 3.06E-03 * (20) * [0.083 + (0.683 * 0.5)] * (1) * (350) * (52) * (0.037) * (8.0E-06)
Dair = 1.4E-04 Sv (Task 6 value, 52-y)
Dair = 14 mrem (Task 6 value, 52-y)
Dair = 19 mrem (ATSDR value, 70-y)

Total U = U-234/235 + U-238
Dair = 9.0E-04 Sv (Task 6 value, 52-y)
Dair = 90 mrem (Task 6 value, 52-y)
Dair = 122 mrem (ATSDR value, 70-y)

Using our suggested values for indoor and outdoor exposure times and shielding, we calculate a committed effective dose of 122 mrem for the inhalation pathway, compared with ATSDR's current value of 35 mrem. As shown in Table 1c, by adding in the doses from the other air pathways and summing the total doses for all exposure pathways, we compute a total effective dose of 242 mrem, compared with ATSDR's current value of 155 mrem.

Table 1c. ATSDR and Revised Pathway-specific Doses for Y-12
Exposure Pathways ATSDR 70-y adjusted doses Revised doses
Total U (mrem) Percent of total dose Total U (mrem) Percent of total dose
Air 40 26% 127 53%
Surface Water 49 31% 49 20%
Soil 66 43% 66 27%
All pathways 155 100% 242 100%


Table 2. Contribution of Fish and Vegetable Consumption to the Total Dose for the Task 6 Level II Assessment*
Exposure pathway Total U dose (Sv) % Contribution to total dose**
Water to fish, consumption 3.3 x 10-4 29%
Air to vegetables, consumption 3.0 x 10-5 3%
Soil to vegetables, consumption 4.0 x 10-4 35%
Total 67%

*Data taken from Tables 4-8 thru 4-13 of the Task 6 report (ChemRisk 1999, pp. 4-15 to 4-17) for the Level II assessment for Scarboro.
**Total effective dose from all pathways and uranium isotopes = 1.2E-03 Sv.


Table 3. Relative Contribution of Fish and Vegetable Consumption to Total Doses for Task 6 Level I and Level II Assessments*
Exposure pathway Level I Level II Dose reduction**
Total U dose (Sv) % of total Total U dose (Sv) % of total
All water pathways 6.3 x 10-4 2% 3.6 x 10-4 31% 2
fish only 3.3 x 10-4 1% 3.3 x 10-4 29% 1
All air pathways 2.0 x 10-3 7% 3.0 x 10-4 26% 6
vegetables only 9.2 x 10-4 3% 3.0 x 10-5 3% 31
All soil pathways 2.4 x 10-2 90% 4.9 x 10-4 43% 49
vegetables only 1.7 x 10-2 66% 4.0 x 10-4 35% 44
  2.7 x 10-2   1.2 x 10-3    

* Data taken from Tables 4-8 thru 4-13 of the Task 6 report (ChemRisk 1999, pp. 4-15 to 4-17) for the Level II assessment for Scarboro.
** Calculated as the ratio of Level I to Level II doses, i.e., Level I dose divided by Level II dose.


Table 4. Comparison of Fish and Vegetables Exposure Parameter Values: Task 6 Level I and Level II Assessments and EPA*
Parameter Level I Level II EPA 1997
mean 95th% recommended
Fish intake rates
Average daily consumption of fish, EFPC (g/d) 4 4

5 - 17

freshwater anglers

13-19

freshwater anglers

20

total fish intake

Average daily consumption of fish, Clinch River/Poplar Creek (g/d) 10 10
Fraction of fish consumed that is contaminated 1
(unitless)
1
(unitless)
Not available Not available Not available
Vegetable intake rates and other parameters
Average daily consumption of vegetables (kg/d wet weight)

0.5

veg. plus some fruit

0.2

veg. only

0.3

veg. only adult, 70 kg

0.2

fruit only adult, 70 kg

0.7

veg. only adult, 70 kg

0.9

fruit only adult, 70 kg

0.3

mean veg. adult, 70 kg

0.2

mean fruit adult, 70 kg

Fraction of vegetables consumed that is contaminated 0.6
(unitless)
0.2
(unitless)
Not available Not available Not available
Fraction of contamination remaining on vegetables after washing 0.7
(unitless)
0.2
(unitless)
Not available Not available Not available

* Data taken from Table K-1, Task 6 report (ChemRisk 1999) and EPA's Exposure Factors Handbook, Volume II, Food Ingestion Factors (EPA/600/P-95/002Fb, August 1997).


Table 5. Comparison of Measured and Task 6 Report Predicted Uranium Air Concentrations at Scarboro for the period 1986-1995*
Year Measured uranium air concentrations at Scarboro (fCi/m3) Task 6 report estimated uranium air concentrations (fCi/m3) Ratio of Task 6 to measured concentrations
U 234/235 U 238 U 234/235 U 238 U 234/235 U 238
1986 0.62 0.08 3.40 0.69 6 9
1987 1.11 0.16 5.70 0.48 5 3
1988 0.60 0.11 2.90 0.47 5 4
1989 0.38 0.05 1.40 0.02 4 .05
1990 0.24 0.03 0.77 0.01 3 0.5
1991 0.17 0.03 0.38 0.06 2 2
1992 0.26 0.03 0.36 0.02 1 1
1993 0.11 0.02 0.29 0.01 3 1
1994 0.05 0.02 0.31 0.08 6 5
1995 0.03 0.01 0.17 0.01 6 1
Based on individual estimates Mean 4 3
Std. dev. 2 3
min. 1 0.5
max. 6 9
Based on combined U 234/235 plus U 238 estimates Mean 3  
Std. dev. 2  
min. 0.5  
max. 9  

*See text for data sources and analytical details.


Table 6. Summary of Recommendations for Improving Historic Dose and Risk Reconstruction Studies for Scarboro Community From Past Y-12 Uranium Releases.
Component Recommendations
Y-12 uranium airborne release estimates
  • Additional searching for and review of effluent monitoring data for Y-12 electromagnetic enrichment operations from 1944 to 1947 and data relating to (unmonitored) depleted uranium operations in the 1950s through 1990s
  • Provide error terms/probability distribution functions (PDFs) and conduct sensitivity and uncertainty analyses
Y-12 uranium surface water release estimates
  • Account for seasonal variability in surface water flow rates and uranium release rates
  • Account for variable levels of uranium enrichment (instead of assuming natural isotopic abundance)
  • Provide error terms/PDFs and conduct sensitivity/uncertainty analyses
Scarboro uranium air concentrations
  • Evaluate the effects of the ridges and valleys that dominate the local terrain surrounding Y-12 and Scarboro and investigate alternative approaches to estimate air concentrations at Scarboro, with an emphasis on using additional monitoring data
  • Use historical data from other air sampling stations in and around Oak Ridge area near Scarboro to validate Scarboro data and assess doses and risks in neighboring communities
  • Revise and validate the empirical c/Q approach, or other approaches, using release and air measurement data, historical wind rose information, and/or measurements of atmospheric dispersion of controlled tracer releases from representative stacks and vents at Y-12.
  • Provide error terms/PDFs and conduct sensitivity/uncertainty analyses
Scarboro uranium soil concentrations
  • Base analyses on measured uranium soil concentrations from core samples (at least 1 meter deep) from selected undisturbed areas in and around Scarboro
  • Validate against estimated uranium soil deposition rates from reconstructed air concentrations or by other means
  • Provide error terms/PDFs and conduct sensitivity/uncertainty analyses
Receptor populations
  • Include other Oak Ridge communities near Y-12 (e.g., Woodland)
  • Identify areas surrounding ORR more likely and more heavily impacted by Y-12 uranium releases than Scarboro
Exposure assessment
  • Include region-specific consumption habits and lifestyles
  • Identify likely exposure scenarios instead of hypothetical upper bound and typical assessments
  • Use dynamic models to account for the temporal distribution and fate of uranium released to the environment
  • Provide error terms/PDFs and conduct sensitivity/uncertainty analyses


Table 7. National, International, and Federal Radiation Protection Guidelines and Standards.
Agency Numerical standard Approximate lifetime excess cancer risk* Description Citation
ICRPNCRP 100 mrem/yr 2 x 10-3 Limit for public exposure from all man-made sources, excluding medical natural background exposures. ICRP Pub. 60 (1991);
NCRP Report 116 (1993)
NRC 25 mrem/yr 5 x 10-4 Radiological criteria for license termination, limit for public exposures. All doses must be kept as low as reasonably achievable (ALARA) 10 CFR 20, Subpart E
EPA 15 mrem/yr 3 x 10-4 Individual protection limit for public exposures to radionuclide releases from the Waste Isolation Pilot Plant (WIPP) and Yucca Mountain. 40 CFR 194.51-194.57
40 CFR 197.20, 197.27
EPA 10 mrem/yr 2 x 10-4 National Emission Standards for Hazardous Air Pollutants (NESHAPs) for airborne emissions from Federal Facilities and licensed NRC facilities. 40 CFR 60, Subparts H and I
EPA 10-6 to 10-4 lifetime cancer risk --- National Oil and Hazardous Substances Pollution Contingency Plan (NCP) cancer risk range for cleanup of CERCLA sites. 40 CFR 300.430
(e)(2)(i)(A)(2)

*Based on EPA's 30-y lifetime exposure duration and cancer mortality coefficient of 5.75 x 10-2 for low-dose, low-LET, uniform whole-body irradiation. See: S. D. Luftig and L. Wienstock, Establishment of Cleanup Levels for CERCLA Sites with Radioactive Contamination, OSWER directive No. 9200.4-18, Aug. 22, 1997. (Available at http://www.epa.gov/superfund/resources/radiation/radarars.htm Exiting ATSDR Website)


Click here to read 4 EPA Correspondence Letters in PDF format (PDF, 591KB)


APPENDIX I: SUMMARY BRIEF

Click here to view Appendix I in PDF format (PDF, 263KB)


APPENDIX J: A CITIZEN'S GUIDE TO RISK ASSESSMENTS AND PUBLIC HEALTH ASSESSMENTS AT CONTAMINATED SITES

Click here to view Appendix J in PDF format (PDF, 816KB)



25 The Task 6 Report and ATSDR incorrectly refer to estimated radiation doses for Scarboro as committed effective dose equivalents or CEDEs. The quantities dose equivalent, committed dose equivalent, and committed effective dose equivalent are based on the dosimetry system, radiation quality factors, and tissue weighting factors formerly recommended by the International Commission on Radiological Protection in Publication 26 (ICRP 1977) and Publication 30 (ICRP 1979, et seq.). For Level I and Level II assessments, the Task 6 team used the adult dose coefficients or dose conversion factors (DCFs) for U 234, U 235, and U 238 taken from Publication 71 (ICRP 1995) for inhalation exposures, from Publication 72 (ICRP 1996) for ingestion exposures, and from Federal Guidance Report No. 12 (EPA 1995) for external exposures (see pp. 4-8 and 4-9 of the Task 6 Report [ChemRisk 1999]). Inhalation and ingestion DCFs are based on ICRP's latest dosimetry system, defined in Publication 60 (1991), for calculating age-dependent doses to members of the public from intakes of radionuclides. This system incorporates revised biokinetic and dosimetric models, radiation weighting factors, and tissue weighting factors. ICRP's current dosimetric quantities are the equivalent dose, committed equivalent dose, and committed effective dose. Calculations using inhalation and ingestion DCFs from ICRP 26/30 vs. ICRP 71/72 result in different radiation dose estimates for internal exposures. Strictly speaking, the radiation doses calculated by the Task 6 team, and used by ATSDR, represent the summation of the committed effective doses from internal exposures and the effective doses from external exposures. The resultant total dose may, perhaps, be best referred to as the total effective dose.
26 For example, see: BIOMASS (The IAEA Programme on Biosphere Modeling and Assessment Methods), 2000. Model Testing Using Chernobyl Fallout Data from the Iput River Catchment Area, Bryansk Region, Russia: Scenario "Iput." BIOMASS Theme 2, Environmental Releases, Dose Reconstruction Working Group. International Atomic Energy Agency, Vienna, BIOMASS/2DR/WD02.

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