PUBLIC HEALTH ASSESSMENT

ATSDR's Health Guidelines for Radiation Effects

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Similar concerns appear when we look at individual organ or tissue doses, where, in some cases, the upper credibility limit of the cumulative doses exceed the ATSDR's radiogenic cancer "Comparison Value" of 5000 mrem over 70 years. For example, the upper credibility limits of cumulative doses to bone surfaces for individuals of either sex who were Category I consumers of fish caught near Jones Island exceeded 7000 mrem over 48 years. The upper credibility limit of cumulative dose to the lower large intestine for males who were Category I consumers of fish caught near Jones Island was 5200 mrem over 48 years. Upper credibility limits of cumulative doses to red bone marrow for individuals of either sex who were Category I consumers of fish caught near Jones Island were 4800 mrem over 48 years, and the upper credibility limit of the cumulative dose to the lower large intestine for females who were Category I consumers of fish caught near Jones Island was 4500 mrem over 48 years. Addition of doses received via other pathways could increase each of these doses by another 10–20%, and adjusting for a 70-year exposure results in an increase of 46% (see Table 11 on page 84). Thus, the upper credibility limits for the cumulative doses for all of the organs or tissues cited above would exceed the ATSDR's 5000-mrem criterion when extended over 70 years.

For whole body exposures, the excess risk of cancer incidence associated with the 5000 mrem CV exceeds several chances in one thousand. Consideration of the uncertainty in radiogenic cancer risk, as obtained using the NIH update of the 1985 Radioepidemiological Tables (Land et al., 2003) combined with information on the baseline incidence of cancer from the NCI SEER registry (1973-2002), would show that a cumulative whole body dose of 5000 mrem could approach or exceed an excess lifetime risk of cancer incidence of one chance in 100 depending on the individual's gender and age during the years of highest exposure.

At the dose levels equal to ATSDR's radiogenic cancer CVs, the relative risk of radiogenic cancer could be sufficiently high to warrant compensation and medical care for those who were exposed before the age of twenty and have been diagnosed with cancer a few decades later. [This statement applies only if the same relative risks used for compensating sick DOE workers for Cold War era exposures to radiation were to be extended to the general public. The National Research Council/National Academies of Sciences (2005) has recently recommended that Congress consider such an extension.] For example, the relative risk would be in the compensable range for a person exposed at age 10 and diagnosed with acute lymphocytic leukemia at age 20, when the whole body dose is 5,000 mrem.

In his opinion, implying that there is no public health concern below 5,000 mrem over 70 years is wrong.

ATSDR staff health physicists appear to be relying on the advice of others within the Health Physics community who erroneously claim that there is no evidence for increased cancer risk below an effective whole body dose of 10 rem and who urge that risk not be quantified at effective whole body doses below 5 rem in one year or 10 rem lifetime.

The possible extent of dose underestimation is large enough that, under some circumstances, both the ATSDR MRL of 100 mrem for exposure in a single year and cancer Comparison Values for the whole body and the lower large intestine (5000 mrem) could have been exceeded.

The assertion that there is still significant public health concern for adverse health effects below a lifetime whole body dose of 5000 mrem needs its basis stated explicitly. A report entitled, "Bridging Radiation Policy and Science", from an international conference held in December 1999, (see the citation for Mossman et al. 2000, listed at the top of p.155 of the draft White Oak Creek PHA) states that the lowest dose at which a statistically significant radiation risk has been shown is about 10,000 mrem.

The lowest dose from whole body irradiation at which a statistically significant relative risk has been established is less than 10 mGy (less than one rad). This does not mean, however, that health effects from doses below 10 mGy are not to be observed or expected to occur. See recent publications and presentations by Dr. David Brenner from Cornell University. He and Mossman debated each other last summer on this very topic. Mossman lost resoundly.

ATSDR uses the central values—not the upper-bound value of the dose estimates. These provide the most realistic doses for potential exposures to radionuclides in the Clinch River and the Lower Watts Bar Reservoir. Because the 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 used the 50^th percentile (central) value from the Task 4 of the Tennessee Department of Health's Reports of the Oak Ridge Dose Reconstruction (Task 4 report). The values calculated by ATSDR are in line and agree with the Task 4 values, even though the methods of analyses were different (see the response to comment 12 for more information on how these different methods were used to develop the same basic conclusions). Central estimates 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. When using the central estimates, all estimated doses in this public health assessment were below levels shown to cause observable and tolerable effects. In fact, ATSDR's calculated whole-body dose for past exposures via all pathways was 278 millirem over 70 years—more than 17 times less than ATSDR's radiogenic cancer comparison value of 5,000 millirem over 70 years.

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 could be based entirely on risk assessments. The ATSDR Cancer Policy Framework, adopted in 1993, addresses many factors to 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 prevention of exposure. "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 in 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 44 for additional information distinguishing a risk assessment from a health assessment.

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 National Council on Radiation Protection and Measurements (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 developing 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 in collaboration 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 site-specific approaches that ATSDR used to evaluate past, current, and future radiation risks to communities surrounding the Oak Ridge Reservation. The panel concluded that this combination of approaches (LNT and MOD) is appropriate for ATSDR 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."

Thank your for your comment.

An extended abstract for the referenced debate and follow-up lecture between Drs. David Brenner and Kenneth Mossman titled Do Radiation Doses Below 1 cGy Increase Cancer Risks? is available at http://dceg.cancer.gov/pdfs/travis1636952005.pdf . ATSDR contacted Dr. Mossman who, contrary to this commenters opinion, stated that the claim that he lost "resoundly" was not shared by everyone attending the American Statistical Association Conference on Radiation and Health meeting (June 2004), including representatives from EPA. As Dr. Mossman stated to ATSDR, "I don't argue that the risk is zero; my view is that the risk is too small to measure reliably."

According to the abstract, Dr. Mossman finds that "Direct measurement of risks at very small radiation doses is difficult because of limitations of epidemiological studies to detect risk. Accordingly, risks are estimated by extrapolating from direct observations made at high doses to the low-dose region using predictive theories such as the linear, no-threshold theory. However, estimates are highly uncertain because the required dose extrapolation is very large."

"Estimating low-dose risks using very large dose extrapolations strains the credibility of risk assessment. Accordingly, numbers of cancer deaths due to low levels of radiation exposure must be considered speculative; risk estimates at low doses have great uncertainties because they are derived theoretically."

"The possibility that there may be no health risks from radiation doses comparable to natural background radiation levels cannot be ruled out; at low doses and dose rates, the lower limit of the range of statistical uncertainty includes zero."

Therefore, Dr. Mossmans position on this matter is not in line with the commenters implication that "health effects from doses below 10mGy are not to be observed or expected to occur". Given the abstract and Dr. Mossmans statement to ATSDR above, his position is that "if risks exist below 1 cGy, they are too small to measure reliably."

Also, please refer to the summary of the debate, which states that "the lowest radiation dose associated with statistically significant increased risk remains controversial. Epidemiological studies are not powerful enough to detect risks at doses approximating 1 cGy in the general population because the necessary large populations are not available although unequivocal evidence of risk is unavailable at very low doses, this does not mean that increased risks do or do not exist. That said, however, if a risk below 1 cGy is present, it is very small for any given individual the controversial issue being the risk to a large population potentially exposed to these small risks."

Furthermore, another radiation expert conveyed to ATSDR that much difficulty is involved in understanding the concept of extrapolated risk "such as 5 extra cancer deaths over a lifetime per 100 million persons exposed to 1 µSv (0.1 mrem)." For example, this expert stated, "It would take more than the worlds population of 5 billion persons to be exposed to one gamma ray for even a single excess cancer death to occur. The probability of the event is of the order of one in a million billion, i.e., less than one in a trillion. This probability might be placed in context with the fact that each hour over 200 million gamma rays pass through our bodies as the result of exposure from naturally occurring radiation in the soil, building materials, food commodities, and from cosmic rays."

Therefore, ATSDR as well as other experts in the field of radiation epidemiology and radiation health believe that it is inappropriate, misleading, and not good science to apply a tiny dose far below the level for which health effects have been observed to a large population and compute or assign predicted numbers of excess cancers that "could" occur over decades.

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Page 8, lines 20–21: The implication that a dose of 390,000 to 620,000 mrem is associated with measurable bone cancer in radium dial workers is incorrect. The analysis by Thomas (1995) (see discussion in Annex G of the UNSCEAR 2000 report) indicated that this dose range represented a threshold for tumor induction, i.e., at or below which no tumors were observed. He further proposed a rounded value of 10 Gy (1,000,000 mrem) as a "practical threshold" below which there should be little cause for concern. [Although the ATSDR cites the report by Rowland (1994) as the source of its information, the follow-up analysis by Thomas postdates that of Rowland, and was cited by UNSCEAR.]

The ATSDR's use of epidemiologically derived "Comparison Values" is reportedly not consistent with its practice in other PHAs. One such "value," a dose range of 390,000 to 620,000 mrem cited for red bone marrow, is not technically justifiable.

Most concerning to me is the cancer comparison value that ATSDR has given for bone and red bone marrow of 390,000 to 600,000 mrem (3.9 to 6.0 Gy). This cancer comparison dose value is inconsistent with the scientific literature of epidemiological studies of human populations (workers including members of the public) exposed to ionizing radiation.

For radiogenic leukemia, the ATSDR cancer comparison value of 390,000 mrem to 600,000 mrem to the red bone marrow (equivalent to organ doses of 390 rem to 600 rem) is neither protective of public health nor is it commensurate with a value below which the risk of cancer can be considered to be negligible.

The cancer CV for radiogenic leukemias of 390,000 to 620,000 mrem to the bone marrow is far above the lower limits of statistical significance of an observed relative risk in human cohorts. A more thorough review of the literature would show that statistically significant relative risks of leukemia have been reported in public and worker cohorts exposed to radiation at doses ranging from below 1,000 mrem to 40,000 mrem, which is a factor of about 10 to 400 below that given by ATSDR as a cancer CV for the red bone marrow. In his opinion, it was misleading the public by promulgating these numbers and implying that there is no public health concern below them. In his opinion, these numbers were not scientifically defensible or commensurate with standard practice in radiation health assessment.

A critic of the document has noted that "ATSDR uses a 'cancer comparison value' of 390,000 mrem for the irradiation of the red bone marrow. This rather high dose level is based on the limits of epidemiological detection in the cohort of radium dial painters. The implication is that doses at or below 390 rem to the red bone marrow are of no concern for public health. Such a conclusion is ... not consistent with mainstream science, nor is it consistent with how ATSDR evaluates minimum risk levels for other known human carcinogens." Please address this criticism and explain why this dose level was used.

Page 115: The ATSDR report states: "Doses on the order of 25,000 mrem are believed to affect the formation of blood cells and may induce leukemia." ATSDR also states on page 115 that leukemia in A-bomb survivors was observed for doses as low as 50,000 mrem. However, they use a dose limit for bone of 390,000 to 620,000 mrem as obtained from the radium dial workers. The difference between the lowest doses producing a statistically significant relative risk from the A-bomb Survivors and those from the radium dial workers is only due to the difference in exposure rate (acute vs. chronic exposure). The radium dial painters were adults at the time of exposure, and the study included a smaller number of people than the A-bomb survivors. Thus, we do not believe that the CVs derived from the radium dial workers are realistic, or representative for the population exposed downstream of White Oak Creek.

P. 111. The comparison values listed on p. 111 for bone surface and red bone marrow look quite high. All the comparison values listed on p. 111, except the one for a whole body dose, are apparently single organ doses. These can and should be checked for reasonableness and consistency by using the weighting factors listed on p .66 to calculate the corresponding effective whole body doses, which should all be less than 5000 mrem. The comparison values for bone surface and red bone marrow fail this test. Therefore, these values need more scrutiny.

ATSDR has changed from its past proclamation that a cancer CV is legitimate at 5,000 mrem over 70 years to using a CV of 390,000-620,000 mrem for red bone marrow based on apparent limits of epidemiologic detection in radium dial painters. In his opinion, it is well known that the radium dial painters consisted of a statistically low power cohort, and a statistically significant dose response is unlikely with low power epidemiologic studies.

The ATSDR has produced lifetime cumulative doses, defined as cancer Comparison Values (CVs) that are inappropriate for the evaluation of the health risk to individuals who may have been exposed to past, present, and future releases of radioactive substances from White Oak Creek. These cancer CVs for radiation exposure, which range from 5,000 mrem to 620,000 mrem, are associated with high relative and absolute risks of excess cancer incidence. With the exception of the CV used for the red bone marrow, they are approximately equal to the lowest published dose at which a statistically significant relative risk has been reported from epidemiological investigations in human cohorts. They are not, however, dose levels below which no health effects have been observed or expected to occur.

He referred to Table 2 [of the summary document], reading that the implication was that the dose for red bone marrow is "less than 1,100 mrem". If reviewing the dose estimates, the confidence intervals would overlap and exceed 5,000 mrem. He expressed his belief that only the 50^th percentile of the uncertainty analysis is being used and the remaining probability distribution is being ignored. In his opinion, this was censoring important information and was not representative of the less than value. It implies that a radiation dose to the red bone marrow of "less than 1,100 mrem" is of no concern for public health, yet the uncertainty analysis produced by our dose reconstruction indicates the potential for red bone marrow doses to have been much higher than this value.

Although the epidemiological study of radium dial painters which was used to generate the Comparison Value for red bone marrow did not indicate an excess of leukemias attributable to radiation exposure, it is inapplicable to the exposures that resulted from the past releases from White Oak Creek and the contamination of the Clinch River and Lower Watts Bar Reservoir. Exposures resulted largely from whole body exposure to Cs-137 gamma radiation, with an additional contribution from Sr-90 beta particles. The statistical power to detect leukemias in the radium dial painters was relatively low, and there are serious unanswered technical questions about the relative biological effectiveness of exposures from radium because of non-uniform irradiation of the bone marrow and a potential protective effect of irradiated marrow (Spiers and Vaughan 1989; Stebbings 1998).

Studies of the Japanese atomic bomb survivors and a variety of other groups who were exposed to external irradiation or to a mixture of external and internal radiation (e.g., the Techa River population) have shown that there are significant excess relative risks of leukemia at doses of 1 Sv (100,000 mrem) or less (Little et al. 1999; UNSCEAR 2000). The leukemia risks (either incidence or mortality) in the A-bomb survivors were significantly elevated at all doses >400 mSv (400,000 mrem, UNSCEAR 2000). Estimated risks for leukemia induction based on the international study of combined cohorts of radiation workers do not suggest that current estimates of leukemia risks at low levels of exposure based on the A-bomb survivor data are appreciably in error (Cardis et al. 2001). Another set of information on leukemia risks at low doses is that resulting from exposures to children and young adults in Utah who were aged 019 years when exposed to fallout from the Nevada Test Site (Stevens et al.1990; UNSCEAR 1994). Significant excess risks (defined on the basis of 95% confidence levels) were observed in the groups who received 6.030 mGy (600 to 30,000 mrem) to the bone marrow.

As discussed in the public health assessment, ATSDR's use of the cancer comparison value for bone surface and red bone marrow is based on reviews of radium dial painters. The values used are derived from analyses of radium dial painter remains (autopsy), tissue analysis, direct measurements of absorbed dose, and observations. The doses we cite are typically considered a threshold dose for the appearance of bone sarcomas associated with alpha particles. Therefore, we believe their use is appropriate. ATSDR has also consulted with the former director of the United States Uranium and Transuranium Registry who agreed with the agency's use of these numbers.

Our selection of the dose was derived from several sources that evaluated the radiation dose to humans involved in the radium dial painting during the early part of the 20^th century. One advantage of these studies was the ability to measure the amount of radium in the bone—the major organ where the radium was stored. Moreover, one could determine the radiation dose to the skeleton and a correlation of the dose to clinically observed skeletal damage. At the time the radium studies ended in 1993, about 1,000 of the estimated 2,400 dial painters were still alive.

The radium dial studies have shown that following the ingestion of less than 100 microcuries of radium, the probability of developing a bone sarcoma is very low. The reports also state, "no symptoms from internal radium have been recognized at levels lower than those associated with radium-induced malignancy." Even at intakes of about 1,000 times greater than background, there does not appear to be any or little evidence of damage to the skeleton. Based on Federal Guidance Report 13, the ingestion of 100 microcuries of Ra-226 imparts a dose to the red bone marrow of 1,500 rem for a 15-year-old and 320 rem for an adult. The dose to the bone surface is 35,000 rem and 4,610 rem for a 15-year-old and an adult, respectively. This is in line with the ATSDR comparison value used in this public health assessment.

The Biological Effects of Ionizing Radiation (BEIR) V study evaluated various studies of x-rays or gamma radiation to the bone. In one study the BEIR V committee stated that no bone sarcomas were found when the dose to bone was less than 30 Gray (Gy, or 3,000 rads) over a 3-week period. Nonetheless, other studies were either inconclusive or showed large uncertainties. Thus, the BEIR V committee stated that studies of alpha emitters such as radium intake studies should be used to evaluate the induction of radiation-induced bone cancer. From a risk perspective, BEIR V stated that the risk of bone sarcoma per person was on the order of 1.4 × 10^-6 per rad with the peak occurrence at 8 years following exposure.

We agree that studies are available showing damage at doses lower than these. We are, however, applying our screening value as a long-term screen. Many of the studies you may be referring to involve acute or short-term exposures. There is much disagreement in the scientific community as to the methods used to adjust long-term exposures to short-term exposures. Also, as a reminder, the studies mentioned by the commenter are retrospective, whole-body exposures based on cohort or case-controlled studies with poor dosimetry. By contrast, the radium dial studies are based on analyses of radium dial painter remains (autopsy), tissue analysis, direct measurements of absorbed dose, and observations, and these studies are not affected by weighting factors (rad versus rem).

There are subtle differences between 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 International Commission on Radiological Protection (ICRP) publications. It is of interest to note that 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 man 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, 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 the agency evaluates chemicals.

It is true there is a major difference in the values cited in the case of acute versus chronic exposure. What is not clearly evident is that the critical organs for each exposure scenario are different: bone marrow (acute) and bone surface (chronic). The atomic bomb survivor studies only a few years following the exposure identified leukemia as the major cancer observed. Also, the atomic bomb survivor cancer rates have been used to estimate both acute and chronic cancer risks associated with radiation exposure. Use of the comparison value for bone cancer is appropriate as the values used for bone surface and red bone marrow doses are based on autopsy and actual bone uptake, measurements, and observations.

As mentioned, the values used for bone surface and red bone marrow doses are based on autopsy and actual bone uptake, measurements, and observations. Therefore, we believe their use is appropriate. In the public health assessment, the use of weighting factors as described by the International Commission on Radiological Protection (ICRP) is to ensure equal detriment to all organs of exposure; that is, when evaluating future exposures, weighting factors are a type of risk analysis and probability exercise. The dose coefficients, tissue weighting factors, and radiation weighting factors are based on statistical estimates of the energy absorbed, risks of cancer or other deleterious effects, and the relative harm or damage caused by a specific type of radiation—alpha, beta, or gamma. These units are combined to give an estimate of the dose coefficient. When insufficient information is given, these values are used to project or predict a radiation dose. In the case of the dose comparison value used by ATSDR for the dose to the bone, however, we relied on human data as discussed in the next paragraph.

For the evaluation of bone sarcoma, ATSDR used data derived from human observation of the radium dial painters via autopsy, bone analyses, and other direct observation studies. The doses we cite are typically considered a threshold dose for the appearance of bone sarcomas associated with alpha particles. Furthermore, the commenters statement that ATSDR has changed from its past proclamation that a cancer CV is legitimate at 5,000 mrem over 70 years to using a CV of 390,000-620,000 mrem for red bone marrow is incorrect and indicates a misunderstanding of ATSDRs radiogenic cancer comparison value. Our radiogenic cancer comparison value of 5,000 millirem over 70 years is used for comparing estimated whole-body, lifetime committed effective doses, whereas the CV of 390,000-620,000 millirem in this public health assessment compares estimated committed equivalent doses over a lifetime for both bone and red bone marrow.

As noted, the radium dial painters are actual measured doses as seen in the expression of their doses (rads). ATSDR has also consulted with the former director of the United States Uranium and Transuranium Registry who agreed with ATSDRs use of these numbers.

ATSDR uses the central values—not the upper-bound value of the dose estimates—because these provide the most realistic doses for potential exposures to radionuclides in the Clinch River and the Lower Watts Bar Reservoir. The 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. Thus ATSDR used the 50^th percentile (central) value from the Task 4 of the Tennessee Department of Healths Reports of the Oak Ridge Dose Reconstruction (Task 4 report). The values calculated by ATSDR are in line and agree with the Task 4 values, even though the methods of analyses were different (see the response to comment 12 for more information on how these different methods were used to develop the same basic conclusions). 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 individuals 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, ATSDRs 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. When using the central estimates, all estimated doses in this public health assessment were below levels shown to cause observable and tolerable effects.

We agree that the bone marrow alpha particle dose should not be used to estimate leukemia, and we did not use this as a comparison value. For annual whole-body doses, we used the annual screening dose limit of 100 millirem per year recommended for the public by the International Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), and the U.S. Nuclear Regulatory Commission (NRC), as well as ATSDRs minimal risk level (MRL). ATSDR compared lifetime doses to the agencys 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. Because the screening indicated that past or current doses did not exceed our comparison values, further in-depth health evaluation was determined unnecessary.

As noted, the radium dial painter values are actual measured doses as seen in the expression of their doses (rads). The values cited in this comment are not absorbed doses, but are calculated estimated doses expressed as effective doses since the unit Sievert is given. If these were measured doses the units would have been Grays. ATSDR has also consulted with the former director of the United States Uranium and Transuranium Registry who agreed with the agencys use of these numbers.

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In my comments submitted on the ATSDR PHA on Radionuclides Released from White Oak Creek to Clinch River, I have remarked that the cancer Comparison Values for radiation that have been produced by ATSDR for PHAs at Oak Ridge are inconsistent with ATSDR practices for other known human carcinogens provided.

These are presented in the ATSDR PHA Guidance Manual and ATSDR Cancer Policy Framework that clearly document the policy of ATSDR regarding other carcinogens.

The opinion that there is no need for communication of risk to the public at levels below the ATSDR cancer comparison values is certainly a topic that should be subjected to community debate. However, the conclusion that radiogenic cancer risk is inherently negligible at doses below the ATSDR cancer comparison values is inconsistent with mainstream science in radiation protection, radiation epidemiology, and radiation biology, and it is inconsistent with the manner in which ATSDR evaluates the risk to public health from exposures to other toxic substances.

The issue regarding ATSDR's review of dose levels defining statistically significant relative risks for radiogenic cancers and the use of these dose levels as "cancer comparison values," is extremely important. This is coupled with the concern that ATSDR has adopted an administrative policy to not acknowledge nor discuss the range of risks of past exposures below these dose levels. These concerns are not new. They have been raised by many others in the past.

Not only are the cancer comparison values (in the PHA) incorrect, but the dose levels are high. It's misleading to the public to imply that there is no concern for public health.

In his opinion, the CVs being used were not only conceptually incorrect, but the numbers were above dose levels where there has been statistically significant confirmation of radiogenic cancer in populations. He expressed his belief that statistical limits of epidemiologic detection should not be used as limits of concern. In his opinion, this violated the standard practice of radiation health assessment and environmental risk assessment, and inaccurately implied that there was no concern at levels below these cancer CVs.

In his opinion, these CVs were in violation of any scientific knowledge of interaction of radiation and the ability of radiation to cause cancer in human and animal populations. He expressed his belief that this work was misleading, technically deficient, and inappropriate.

I believe the values proposed as "cancer comparison values" are not consistent with proper evaluation of radiogenic cancer risk in exposed populations. I know of no other known human carcinogen for which ATSDR has chosen a dose level approximately equal to a lowest observed adverse health effect level (or lower limit of epidemiological detection) as a surrogate for a limit of public health concern. The use of the lowest observable adverse effects level as an equivalent for a safe or negligible level of exposure is in fact inconsistent with ATSDR policy and practices used for all potentially toxic substances including those attributable to non-cancer health endpoints and those that cause cancer.

For other toxic substances, ATSDR applies a considerable margin of safety to the lowest observed adverse effects level before designating an exposure or dose level as being commensurate with a minimal public health risk. For radiation, however, ATSDR designates dose levels that are considered to be at or just below the limits of statistical significance in epidemiological studies as "cancer comparison values," and implies that there is no concern for public health at doses below these levels.

I do not object to the reporting of radiation dose levels that are equivalent to epidemiological limits of statistical detection in specific exposed cohorts. This is appropriate information to convey to the general public, as long as the attendant risk of exposure to doses below these levels are also communicated. It's a totally different matter, however, to assert that such dose levels are equivalent to safe or negligible risk levels, and to ignore or censor information about the potential for risk at lower dose levels.

For instance, in my recent reading of the ATSDR PHA for radiation released from X-10 to the Clinch River, I have discovered that ATSDR has issued "cancer comparison values" of 5000 mrem to the whole body and lower large intestine, 9,000 mrem for the skin, 10,000 mrem for the breast, and 390,000 to 620,000 mrem to the bone surface and red bone marrow.

These values are not appropriate for use as safe or negligible risk levels for exposures in human populations to ionizing radiation. This is most certainly the case for radiogenic leukemia, which is manifested through irradiation of the red bone marrow. The fact that such high dose cancer comparison values have been officially released for public communication by ATSDR is a matter that I find most troubling, both personally and professionally.

When I evaluate the relative risk associated with this dose comparison value, I find the risk of radiogenic cancer to be extremely high. Yet, ATSDR is implying that doses at or below this level are inconsequential.

In Section III. H. of ATSDR's Cancer Policy Framework, the agency recognizes that, at present, no single generally applicable procedure for exposure assessment is available. Therefore exposures to carcinogens must be assessed on a case-by-case or context-specific basis. While the need for, and reliance on, models and default assumptions is acknowledged, ATSDR strongly encourages the use of applicable empirical data (including ranges) in exposure assessment. Also, in Section IV. A, subsections 1 and 2, the position of ATSDR is interpreted as being related to chemical carcinogens and is not related to radiological contamination. Following the ATSDR Cancer Framework Policy, ATSDR does not perform risk assessments. The agency, however, does recognize the importance of the U.S. Environmental Protection Agency's (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 and to help 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 see the response to comment 44 regarding the intentional differences between a public health assessment and a risk assessment and review the framework policy that can be found at http://www.atsdr.cdc.gov/cancer.html.

In this public health assessment ATSDR compares annual whole-body doses to the 100 mrem/year dose limit of the International Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), and the U.S. Nuclear Regulatory Commission (NRC), as well as ATSDR's minimal risk level (MRL). ATSDR compares lifetime whole-body 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 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 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, scientific literature associated with radiological doses and dose estimates, particularly those related to adverse health effects, is reviewed. 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."

Also, in this public health assessment ATSDR uses different comparison values depending on the organs and tissues being evaluated. While the cancer comparison value of 5,000 mrem over 70 years is used to compare effective whole-body doses over a lifetime and the 100 mrem/year is used to compare annual whole-body doses, these organ comparison values (discussed in detail below) were used to screen committed equivalent doses to organs over a lifetime.

A comparison value of 390,000–620,000 millirem was used to compare estimated committed equivalent doses over a lifetime for bone surface and red bone marrow. ATSDR's use of the cancer comparison value for bone surface and red bone marrow, as discussed in the public health assessment, is based on reviews of radium dial painters. The values used are based on analyses of radium dial painter remains (autopsy), tissue analysis, and direct measurements of absorbed dose, and observations. The doses we cite are typically considered a threshold dose for the appearance of bone sarcomas associated with alpha particles. Therefore, we believe their use is appropriate. ATSDR has also consulted with the former director of the United States Uranium and Transuranium Registry who agreed with the agency's use of these numbers.

Our selection of the dose was derived from several sources that evaluated the radiation dose to humans involved in the radium dial painting during the early part of the 20^th century. One advantage of these studies was the ability to measure the amount of radium in the bone—the major organ where the radium was stored. Moreover, one could determine the radiation dose to the skeleton and a correlation of the dose to clinically observed damage to the skeleton. At the time the radium studies ended in 1993, about 1,000 of the estimated 2,400 dial painters were still alive.

The radium dial studies have shown that following the ingestion of less than 100 microcuries of radium, the probability of developing a bone sarcoma is very low. The reports also state that "no symptoms from internal radium have been recognized at levels lower than those associated with radium-induced malignancy." Even at intakes of about 1,000 times greater than background, there appears to be little or no evidence of damage to the skeleton. Based on Federal Guidance Report 13, the ingestion of 100 microcuries of Ra-226 imparts a dose to the red bone marrow of 1,500 rem for a 15-year-old and 320 rem for an adult. The dose to the bone surface is 35,000 rem and 4,610 rem for a 15-year-old and an adult, respectively. This is in-line with the ATSDR cancer comparison value being used in this public health assessment.

The Biological Effects of Ionizing Radiation (BEIR) V study evaluated various studies of x-rays or gamma radiation to the bone. In one study, the BEIR V committee stated that no bone sarcomas were found when the dose to bone was less than 30 Gy (3,000 rads) over a 3-week period. Nonetheless, other studies were either inconclusive or showed large uncertainties. Thus, BEIR V stated that studies of alpha emitters such as radium intake studies should be used to evaluate the induction of radiation-induced bone cancer. From a risk perspective, BEIR V stated that the risk of bone sarcoma per person was on the order of 1.4 × 10^-6 per rad, with the peak occurrence at 8 years following exposure.

For evaluating estimated committed, equivalent, lifetime doses to the breast, ATSDR used a comparison value of 10,000 mrem over a lifetime. This value (reported in Schull's 1995 Effects of Atomic Radiation: A Half-Century of Studies from Hiroshima and Nagasaki) is based on an investigation focusing on a sample of women from the Life Span Study—a Radiation Effects Research Foundation program investigating the long-term effects of atomic bomb radiation on cancer incidence and causes of death. On the basis of an investigation focusing on women in the Life Span Study, women who were irradiated before 20 years of age experienced the highest rates of radiation-related breast cancer when receiving a dose of at least 0.10 Gy (10 rad or 10,000 mrem) of radiation.

To evaluate estimated committed equivalent lifetime doses to the skin, ATSDR used a comparison value of 9,000 mrem over a lifetime. This value is based on the BEIR V report (titled Biological Effects of Ionizing Radiation) that evaluated potentially the most extensive study of radiation-induced skin cancer. In 1990, the National Research Council reviewed and evaluated the findings presented in BEIR V on the relationship between skin cancer and radiation and presented its findings in a 1990 report titled Health Effects of Exposure to Low Levels of Ionizing Radiation.

The study involved investigating 2,226 individuals who had received radiation to the scalp for the treatment of ringworm during childhood. On average, these persons were studied for over 25 years. Basal cell carcinomas of the skin appeared in 41 of the 2,226 exposed individuals. These carcinomas began to appear after about 20 years of exposure. Instead of concentrating in the most heavily irradiated areas of the scalp, most of the tumors tended to appear at the margins of the scalp and in nearby areas of skin that had not been covered by clothing or hair. An excess of skin cancers was identified on the neck and cheek even though doses to the cheeks were approximately only 12 rad (12 rem or 12,000 mrem) and doses to the neck were only 9 rad (9 rem or 9,000 mrem).

In the ICRP's Publication 59 (1991), the agency stated, "Although it has traditionally been thought that there was little if any risk of skin cancer below 10 Gy [1,000 rad or 1,000,000 mrem], there are now several sets of data indicating excess skin cancer following doses of a few grays [a few hundred rad], with one study suggesting risk below 1 Gy [100 rad or 100,000 mrem]. The evidence does not indicate that the risk per unit dose is greater at higher doses than at lower [doses]."

Therefore, the value of 9,000 mrem used as a comparison value for committed equivalent lifetime doses to the skin is based on absorbed dose and direct observation of individuals who received radiation of the scalp. This is the lowest reported dose where adverse effects have been observed following irradiation of the skin and significantly below dose levels reported by the ICRP as having resulted in health effects.

For evaluating estimated committed equivalent lifetime doses to the lower large intestine, ATSDR used the radiogenic cancer comparison value of 5,000 mrem over a lifetime in the PHA. ATSDR could not locate a reliable comparison value to estimate a dose to the lower large intestine so ATSDR used the whole-body CV of 5,000 millirem over 70 years. We believe this is appropriate for the following reason. In general, the faster a cell system divides, the more sensitive that system is to the effects of radiation. The intestinal tract cell lining divides rapidly; the blood cells, especially the red blood cells, divide fastest (estimated production of RBC is 2.5 million per second). Following an acute radiation exposure to humans resulting in a dose of about 100 rads, the gastrointestinal tract begins to show damage. The dose of 100 rads agrees with the single dose to mouse intestinal cells of 130 rads. In humans, however, the Centers for Disease Control and Prevention (CDC) reports that symptoms may not appear until a dose of 600 rads has been received. The full expression of damage may require up to 1000 rads. And the dose of 600 rads is about 120 times higher than the estimated ATSDR CV for the large intestine. Therefore we believe the use of 5,000 millirem over 70 years is justified.

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The NAS/NRC has recently recommended the use of the NIH-Interactive Radioepidemiological Program (IREP) program for estimating the attributable risk (or assigned share) for individuals diagnosed with disease who were exposed in the past to radioactivity released from the testing of nuclear weapons who should be evaluated for medical screening and compensation. Until such time as the publication of BEIR VII is released to the public, I believe the NIH-IREP program is the most thorough quantitative evaluation of the uncertainty in radiogenic cancer risk currently available.

In current radiation compensation programs administered by the Department of Veterans Affairs and the Dept. of Labor, the value of the Probability of Causation/Assigned Share (PC/AS) used for the adjudication of claims is the upper 99th percentile of the probability distribution of PC.

If a DOE worker had cancer, it would be compensable at these dose levels. He knew this because his company developed the probability of causation and radio-epidemiological tables being used for adjudicating claims by the Department of Labor and the Department of Veteran Affairs. He expressed his belief that these were high doses, which were not commensurate with levels below which there should be no health concern. To clarify a statement that exposure rates in this document are at a level that would be compensable under the Energy Employees Occupational Illness Compensation Program Act (EEOICPA) without any other exposures, he answered that the cancer CVs would be compensable, and the upper bounds of exposure that exceeded the 5,000 mrem whole-body dose for some cancers and some age groups would be compensable. The current rules extend only to workers, not to the general public. He expressed his belief that this was particularly true considering the red bone marrow cancer CV (390,000–620,000 mrem), which in his opinion, was high and not appropriate to use.

He expressed surprise that this had passed through the extensive review process, and questioned whether ORRHES might not have the necessary technical expertise to review these documents.

In 1985, a working group for the National Institutes of Health (NIH) initially created the radioepidemiological tables the commenter references. The tables, updated in 2003, are used by the Department of Veterans Affairs as a reference for estimating the probability of causation for workers with cancer who had been exposed to ionizing radiation. The Department of Labor uses a version of the Interactive Radioepidemiological Program (IREP), referred to as the National Institute for Occupational Safety and Health (NIOSH)-IREP, to address workers under the Energy Employees' Occupational Illness Compensation Program Act (EEOICPA). The NIOSH-IREP, most recently updated in 2006, was created to evaluate the probability of causation associated with radiation and risks specific to energy employees for the purpose of adjudicating claims.

Please note that these radioepidemiological tables are only used for litigation purposes and for the adjudication of claims for workers. This means that worker exposures are evaluated from a legal perspective—this is not a health-based assessment. As mentioned on several occasions, ATSDR's congressional mandate does not allow an evaluation of worker exposures. Therefore, this public health assessment evaluates off-site exposures to White Oak Creek radionuclide releases for downstream residents and others who use or live along the Clinch River and the Lower Watts Bar Reservoir only. It does not evaluate any exposures potentially occurring onsite at the reservation, including exposures to workers and other individuals who may contact contaminants while at the ORR. ATSDR does not prepare any public health assessments to evaluate on-site worker exposures. Other agencies are responsible for evaluating worker exposures that occur on site.

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 health physicists conduct a health effects evaluation by carefully examining site-specific exposure conditions about actual or likely exposures; conducting a critical review of available radiological, medical, and epidemiologic information to ascertain the substance-specific toxicity characteristics (levels of significant human exposure); and comparing an estimate of the amount of radiological 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 weigh the scientific evidence and keep site-specific doses in perspective when deciding whether harmful effects might be possible in the exposed population. The output is a qualitative description of whether doses are of sufficient nature and magnitude to trigger a public health action to limit, eliminate, or study further any potentially harmful exposures. The PHA presents conclusions about the actual existence and level of the health threat (if any) posed by a site.

The White Oak Creek Radionuclide Releases PHA underwent several phases of review before its final release, including an internal ATSDR review, a data validation review by other agencies (i.e., DOE, EPA, and TDEC), an Oak Ridge Reservation Health Effects Subcommittee (ORRHES) review, an independent external peer review, and a public comment review. During the agency's internal review process, individuals within the agency who have the proper background (e.g., toxicology and health physics) carefully reviewed the document for technical content and other aspects. After receiving comments from other agencies during the data validation review, ATSDR made changes to the document as appropriate. ORRHES members consisted of individuals with different expertise, backgrounds, interests, and geographic areas from communities surrounding the Oak Ridge Reservation. ORRHES included among its members technical experts in toxicology, health physics, medicine, geology, and other disciplines. ORRHES members carefully reviewed this PHA, discussed suggested editorial and technical changes among themselves, then submitted recommendations to ATSDR for changing the document. Through its external peer review process, ATSDR's Office of Science had three scientific experts review this public health assessment (see Appendix H for the peer reviewer comments and ATSDR's responses). The agency's peer review process allows an external and thorough evaluation of this PHA by experts in the field that this assessment covers: health physics. During the external review process, individuals not employed by ATSDR or the CDC independently reviewed this document and provided their unbiased, scientific opinions. Also, several times at public meetings, including work group and ORRHES meetings, ATSDR presented the data and information used in this public health assessment. In addition, during the public comment period, any member of the public can provide comments to ATSDR. These public comments, such as those presented within this appendix, are addressed for each public health assessment.

ATSDR uses a multi-disciplinary approach for reviewing public health assessments; experts in toxicology, medicine, health physics, and other disciplines review our work. All peer reviewers approved of this assessment and found no major flaws that would invalidate ATSDR's conclusions and recommendations. In the words of one peer reviewer: "You [ATSDR] have done a good job under very difficult circumstances with a lot of unwanted publicity and carping. The science under the report is very good and the report is well written in a very good manner that is suitable for both an informed and interested public and the scientific community."

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P. 111. The footnotes on pages 111, line 4-5 and 112, line 5-6 as well as the definition in the glossary on page A-7 are expressed as a double negative "unlikely and non-cancerous." Is there a more positive way to define MRL that will facilitate understanding? Perhaps, give an example in the glossary or context of the report that demonstrates what is meant by non-cancerous effects and how they are taken into consideration. Also, it may be helpful to refer the reader to the ATSDR web site to read the document on MRLs (http://www.atsdr.cdc.gov/mrls.html). [In that document it says "An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse non cancer health effects over a specified duration of exposure."] Is the MRL more conservative (protective) than CVs that take into consideration cancer effects alone? What really distinguishes the MRL from the CVs from other sources?

Thank you for your comment. The definitions were changed in the footnotes for Tables 22 and 23, and in the glossary in Appendix A. "Unlikely" was changed to "likely to be without" as suggested. The term "noncancerous" is a standard term used by ATSDR and other agencies, and was retained throughout the document.

Also, "noncancerous effects" was added to the glossary in Appendix A of the final PHA with the following definition: "Health effects or health endpoints other than cancer, such as cardiovascular disease or genetic effects, that result from exposure to a particular hazardous substance. ATSDR derives health guidelines for noncancerous effects, called minimal risk levels (MRLs), and compares exposure doses to these MRLs. Doses below MRLs are unlikely to cause noncancerous health effects; those above MRLs are evaluated further." Also, the Web site link was added to the footnotes of Tables 22 and 23 for readers who would like to see more information on MRLs.

MRLs for radiation are estimates of daily human exposure to an amount of radiation that is likely to be without appreciable risk of adverse noncancer health effects. MRLs are screening tools used by public health professionals to determine which exposure situations require further evaluation. The chronic MRL for ionizing radiation is 100 mrem/year. This is consistent with the dose limits recommended for the public by the International Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), and the U.S. Nuclear Regulatory Commission (NRC). Although the MRL is for noncancerous health effects, when deriving the MRL no studies were identified that did not result in cancer as the specific end point.

In this public health assessment, ATSDR compares annual doses to the 100 -mrem/year dose limit of the ICRP, NCRP, and NRC, as well as ATSDR's 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 these 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, 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. 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: when calculating doses, ATSDR explicitly and implicitly incorporated risk and LNT.

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. Interestingly, in its 1989 NCRP Report 96 (titled: Comparative Carcinogenicity of Ionizing Radiation and Chemicals), the NCRP stated that less than 30 chemicals were known to be cancer inducing in man 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 there is 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 a similar manner to which it evaluates chemicals.

More information about the ATSDR evaluation process can be found in ATSDR's Public Health Assessment Guidance Manual at http://www.atsdr.cdc.gov/HAC/PHAManual/toc.html or by contacting ATSDR at 1-888-42-ATSDR. An interactive program that provides an overview of the 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.

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A rationale for the nature and level of the ATSDR dose criteria for public health purposes and especially how the resulting doses vary from the more conservative levels used by the Environmental Protection Agency and other environmental agencies to meet their regulatory responsibilities should be explained. The differences from the liberal National Institute for Occupational Safety and Health work place levels should also be explained. This addition should also attempt to make clear the various connotations of the terms, "zero" and "none" as applied to risk analysis and public exposures.

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. Since ATSDR does not use risk to develop public health conclusions, such an appendix is not normally included in ATSDR's public health assessments. Please note that ATSDR does not base its public health conclusions on these risk numbers—they are presented in this PHA to provide detailed information on risk for the community. In addition, text was added to Section III. Evaluation of Environmental Contamination and Potential Exposure Pathways to explain the difference between dose and risk. Note further, however, that ATSDR does not discuss the National Institute for Occupational Safety and Health (NIOSH) work place levels. This public health assessment does not deal with worker exposures; it solely evaluates exposures for off-site communities.

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The use of natural background radiation in some comparisons can also be misleading, because the risks from some components of background (e.g., radon) are not negligible. Indoor exposure to the decay products of radon are now known to be the second leading cause of lung cancer (Field 2001, 2003).

ATSDR agrees that radon should not be included in background unless directly comparing to radon levels. As the commenter points out, radon progeny contribute to lung dose and should not be mixed with whole-body dose. The natural range of background, not including radon, ranges from 80 mrem/year to 26,000 mrem/year (1). The nominal background dose from naturally occurring radiation in the contiguous United States is 100 mrem/year not including radon, but can range from 80 to about 1,000 mrem/year (2). No data suggest that radiation doses from background, excluding radon, have any deleterious effects. In fact, recent studies from the high background region in Ramsar, Iran, have shown protective effects up to doses of 10,000 mrem/year (3,4,5,6). The ATSDR MRL of 100 mrem/year is 0.38% of the range of natural background, not including radon.

In addition, the Iowa Radon Study [Field RW, et al. (7)], referenced by the commenter, suffers from the following problems:

1. The total difference in lung cancer cases can be accounted for by natural variation among the cases (n=413). The natural variation in the number of cases is 20.3, while the 33% of cases exposed above 4 pCi/L and 28% of controls corresponds to 5% of 413 cases, or 20.6.



2. The study controls have an 11% higher rate of post-secondary education than the cases. Highest educational level has been strongly correlated to greater longevity and overall health. It does not appear that the odds ratios were corrected for educational level.



3. Due to the etiology of lung cancer, the mean life expectancy after diagnosis is around 5 years. Therefore, it is unreasonable to exclude cases that died during the 5-year study, but it may be reasonable to exclude only those cases for which the families disposed of the radon measuring devices before a radon measurement could be made.



4. If statistical significance can only be achieved by omitting cases that died during the study period, this might "imply" a protective effect from radon exposure.



5. A possible smoking and radon-exposure synergistic effect for developing lung cancer may not be accounted for in the analysis. Many of the uranium miner studies did not clearly identify the smoking status of those with lung cancer. The uranium miner studies appear only to show a relationship between radon exposure and cancer among the smokers and miners of unknown smoking status.



6. The cases had an ever-smoked rate of 86% versus a rate of 32% ever-smoked among the controls. The smoking correction is not defined, and the much higher rate of smoking among the cases is going to make the corrected odds ratio extremely sensitive to the smoking correction.



7. The intervals of cumulative radon exposure are made at strange, noninteger values and are not evenly spaced. No cases or controls were exposed to zero pCi/L of radon. There was a threshold of exposures. What was that value?



8. When confidence intervals are graphed for the odds ratios versus exposure categories, no clear dose response appears. A line requires at least two significant points to test for linearity, and the origin does not count.

Overall, this study does not appear to demonstrate any statistically significant association or dose response between residential radon and lung cancer.

(1) Ghiassi-nejad M, Mortazavi SM, Cameron JR, Niroomand-rad A, and Karam PA. 2002. Very high background radiation areas of Ramsar, Iran: preliminary biological studies. Health Phys 82(1):87–93; January.

(2) Eisenbud M and Gesell T. 1997. Environmental radioactivity from natural, industrial, and military sources. Fourth edition. Pp. 198–200. San Diego, CA: Academic Press.

(3) Masoomi JR, Mohammadi Sh, Amini M, and Ghiassi–Nejad M. 2006. High background radiation areas of Ramsar in Iran: evaluation of DNA damage by alkaline single cell gel electrophoresis (SCGE). J Environ Radioact 86(2):176–86.

(4) Ghiassi-Nejad M, Zakeri F, Assaei RG, and Kariminia A. 2004. Long–term immune and cytogenetic effects of high level natural radiation on Ramsar inhabitants in Iran. J Environ Radioact 74(1-3):107–16.

(5) Ghiassi-Nejad M, Beitollahi MM, Asefi M, and Reza-Nejad F. 2003. Exposure to (226)Ra from consumption of vegetables in the high level natural radiation area of Ramsar-Iran. J Environ Radioact 66(3):215–25.

(6) Saadat M. 2003. No change in sex ratio in Ramsar (north of Iran) with high background of radiation. Occup Environ Med 60(2):146–7; February.

(7) Field RW, Steck DJ, Smith BJ et al. 2000. Residential radon gas exposure and lung cancer: The Iowa Radon Lung Cancer Study. Am J Epidemiol 151:1091–102.

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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 the U.S. Environmental Protection Agency (EPA) uses 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 prevention of exposure.

The general consensus is that the linear nonthreshold hypothesis is scientifically reasonable for the purpose of radiation protection. The recent National Council on Radiation Protection and Measurement's (NCRP) comprehensive review (Report No. 136 titled Evaluation of the Linear-Nonthreshold Dose-Response Model for Ionizing Radiation) and the United Nations Scientific Committee on the Effects of Atomic Radiation's (UNSCEAR) evaluations did not find any alternative model to be better, including one with a threshold. The NCRP Report No. 136 also states that some adaptive responses may come into play at low doses, and these responses may result in the variations seen at low dose response levels. Further, the NCRP concluded "there is no conclusive evidence on which to reject the assumption of a linear-nonthreshold dose-response relationship for many of the risks attributable to low-level ionizing radiation although additional data are needed. However, while many, but not all, scientific data support this assumption, the probability of effects at low doses such as are received from natural background is so small that it may never be possible to prove or disprove the validity of the linear-nonthreshold assumption." Therefore, ATSDR does not deny the presence or absence of a linear response and the presence of risk at low levels. We evaluate public health implications based on the observations of adverse health impacts at low doses.

35

The comparison of ATSDR dose estimates between past, present, and future exposures makes no sense. ATSDR states that the maximum cumulative dose from past releases was 278 mrem to the whole body, but that for present releases (1988 to the present time) the doses would be "less than 1,900 mrem for Lower Watts Bar Reservoir and 235 mrem for the Clinch River." This is absurd. There is no conceivable way that the doses from past releases are equal to or less than the doses from present releases. It appears as if two completely different methods of exposure analysis have been applied, one for past releases and another for present releases, with two completely different sets of assumptions.

However, a comparison between the ATSDR estimates of present and future doses with those from the past indicate that widely different methods and assumptions have been used, giving the misleading impression that present and future exposures are of the same magnitude or larger than past exposures. This is clearly not the case.

ATSDR's evaluation of past exposures in this public health assessment is based on doses presented in Task 4 of the Tennessee Department of Health's Reports of the Oak Ridge Dose Reconstruction (Task 4 report). The Task 4 report only evaluated the area along the Clinch River from the mouth of White Oak Creek to the confluence of the Clinch and Tennessee Rivers. The Task 4 team's analysis did not, however, include evaluating exposures to the Lower Watts Bar Reservoir. In evaluating current and future exposures for the Lower Watts Bar Reservoir in this public health assessment, ATSDR based its analysis on our 1996 health consultation, which calculated doses by incorporating conservative exposure assumptions using worst-case scenarios.

Table 22 in the final PHA presents the committed effective dose to the whole-body of 278 mrem for past radiation exposure associated with the area along the Clinch River, based on data presented in the Task 4 report. Table 23 presents the committed effective dose to the whole-body of less than 236 mrem for current and future exposures to the Clinch River, based on ATSDR's individual evaluation, which is indeed lower than the whole-body dose for past exposure to the Clinch River of 278 mrem. The dose referred to in this comment of "less than 1,900 mrem" refers to the estimated whole-body dose for exposure to the Lower Watts Bar Reservoir, which was based on the findings of ATSDR's 1996 Lower Watts Bar Reservoir Health Consultation. Thus, because the Lower Watts Bar Reservoir was not evaluated by the Task 4 team in its evaluation of past exposures to X-10 releases to the Clinch River via White Oak Creek, this dose cannot be compared to the past exposure dose.

Miscellaneous Radiation Comments

36

Pp. 68 and 70. If the effective rate of decrease of radiation in the body is the sum of the rates of decrease due to radioactive decay and biological elimination, then the reciprocal of the effective half-life should be the sum of the reciprocals of the physical and biological half-lives. The numbers for Sr-90 on p. 68, and in Table 7, don't quite satisfy this relationship, as well as the numbers for Sr-90 on p. 68 not quite agreeing with those in Table 7. The numbers on p. 68 need to agree with those in Table 7, and all the numbers need to satisfy their correct relationship.

Your comment is noted. ATSDR compared the reciprocal of the effective half-life for the radionuclides presented in Table 7 with the sum of the reciprocals of their physical and biological half-lives, and they match. The correct definition of effective half-life is the sum of the radioactive decay constant and the biological decay constant. The decay constant is defined as ln2/half-life, where ln is the natural log. The radioactive decay constant and the biological decay constant have to be in the same units, as they are in Table 7 and in the discussion on pages 71 and 73 of the final PHA.

37

P. 69. Table 7. Compare years rather than days for Strontium 90 to correspond with the discussion on page 68 in which years are used.

ATSDR presented the data in days because the original reference material expressed the biological half-lives in terms of days. Therefore, changes were made in the final PHA to present half-lives in terms of days throughout the discussion on pages 71 and 73 and in the text in Table 7.

38

Please adopt a consistent set of radiation units.

These changes have been made in the final PHA.

39

Present-day radiation dose limits by national regulatory authorities and national and international advisory committees on radiation protection have been misrepresented. The ATSDR PHA and its accompanying summary document state that the public dose limit of the ICRP, NCRP, and NRC of 100 mrem/y is equivalent to saying that 7000 mrem over a 70-year lifetime is an acceptable cumulative dose. This is not true. These dose limits apply to a single year of exposure from multiple sources of operations (releases). Furthermore, the public dose constraint for releases from a single source is 25 mrem/y. In addition, there is the overarching provision that actual doses to real persons be restricted to levels that are as low as is reasonably achievable. The NCRP negligible dose level is 1 mrem/y.

Federal radiation protection standards and ICRP and NCRP recommendations for the limitation of public exposures to ionizing radiation have been improperly cited by ATSDR. These are maximum annual dose limits that apply to the total dose received from multiple sources of exposure. ATSDR misinterprets these annual limits as annual averages that apply over a 70 year lifetime for limitation of public exposures originating from a single operation or source.

No section of this PHA extrapolates the 100 mrem/year dose limit to 7,000 mrem over a 70-year lifetime. Instead, in this PHA ATSDR compares estimated annual doses to the 100 mrem/year dose limit of the International Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), and the U.S. Nuclear Regulatory Commission (NRC), as well as ATSDR's minimal risk level (MRL). ATSDR compares estimated 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 are used as screening tools during the public health assessment process. If the screening indicates that past or current doses exceed our comparison values, then we would conduct further in-depth health evaluation.

Even though this was not explicitly stated in the document as implied by the commenter, ATSDR believes that the first approximation of the 100 mrem/year recommended dose limit 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.

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 of 71 mrem/year is less than 100 mrem/year as recommended for the public by the ICRP, NCRP, and NRC. ATSDR publicly discussed this issue in at least four Exposure Evaluation Work Group (EEWG) meetings, formerly known as Public Health Assessment Work Group (PHAWG), and three Oak Ridge Reservation Health Effects Subcommittee (ORRHES) meetings.

The Ionizing Radiation Toxicological Profile states: "the annual dose of 3.6 mSv [360 mrem] per year has not been associated with adverse health effects or increases in the incidences of any type of cancers in humans or other animals" (ATSDR 1999b). The past annual doses for the Clinch River, as well as the current radiation doses for the Lower Watts Bar Reservoir and the Clinch River, for all pathways combined were below ATSDR's comparison values and below the 100 mrem/year dose limit for the public as recommended by the ICRP, NCRP, and NRC.

40

Delete all wording indicating that exposure to radionuclides originating in White Oak Creek, the Clinch River, or the Lower Watts Bar Reservoir in the past, present, or future have not caused any "harmful health effects" (e.g., as on page 4),

"are not expected to cause any harmful effects" (e.g., as on page 6), or

"pose no threat to public health" (as on page 8) (emphasis added).

On the basis of current knowledge, no dose of radiation, including that resulting from exposures to natural background (which includes radon, for which significant health effects have been documented, e.g., even in some residential exposure settings), can be assumed to be completely without risk. All national and international organizations responsible for setting radiation standards and estimating risks posed by radiation exposure recognize that, despite uncertainties in risks at low doses and dose rates, "no alternate dose-response relationship appears to be more plausible than the linear-non-threshold model on the basis of present scientific knowledge" (NCRP 2001). The current wording reflects adversely on the credibility of the ATSDR and the dose levels chosen to represent radiogenic cancer CVs for radiation.

Regarding the findings that it was safe to use the shoreline and waterways for recreation, food, and drinking water, he said that's just not right.

The complete wording as presented in the PHA for the sections referenced by the commenter are presented below:

Page 4: "ATSDR's evaluation showed that the estimated external and internal radiation doses were not expected to cause harmful health effects. Therefore, ATSDR concluded that past off-site exposure to those radionuclides traveling from X-10 to the Clinch River via White Oak Creek was not a public health hazard."

Page 7: "ATSDR's review of environmental data collected in and around the Clinch River and LWBR areas shows that the following practices

• annual environmental monitoring,
• institutional controls intended to prevent disruption of sediment,
• on-site engineering controls to prevent off-site contaminant releases, and
• DOE continuing its expected appropriate and comprehensive system of monitoring (e.g., of remedial activities and contaminant levels in media), maintenance, and institutional and engineering controls,

have limited exposure to the current levels of radionuclides in surface water, sediment, fish, and game to the point that radionuclides are not expected to cause any current or future harmful health effects. Given this evaluation, ATSDR concludes that current and future off-site exposure to radionuclides in the Clinch River and the LWBR via White Oak Creek is not a public health hazard."

Page 10: "ATSDR considers that current exposures to detected levels of radionuclides in sediment, surface water, fish, geese, and turtles of the Clinch River pose no threat to public health."

Having thoroughly evaluated past public health activities and available current environmental information, 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 effects 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.

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 Health's Reports of the Oak Ridge Dose Reconstruction (Task 4 report) (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.

On page 15-4 of the Task 4 report, the authors' state: "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 [centisievert]) 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 ORHASP's 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, "Although the White Oak Creek releases caused increases in radiation dose, the calculated exposures were small, and less than one excess cancer is expected." In addition, on page 38 of the ORHASP report regarding the number of health effects that would be expected from exposure to X-10 radionuclide releases via White Oak Creek, the panel estimates "less than one excess cancer case from 50 years of contaminated fish consumption" would result.

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 was not expected to cause adverse health effects.