PUBLIC HEALTH ASSESSMENT

WHITE OAK CREEK RADIONUCLIDE RELEASES
OAK RIDGE RESERVATION (US DOE)
OAK RIDGE, ROANE COUNTY, TENNESSEE

III. EVALUATION OF ENVIRONMENTAL CONTAMINATION AND POTENTIAL EXPOSURE PATHWAYS (cont.)

III.B.2. Past Exposure (1944–1991)

TDOH's Task 4 Study

Wastes from historical X-10 operations were released to White Oak Creek, which travels south along the eastern border of the X-10 site, flows into White Oak Lake, over White Oak Dam, and into the White Oak Creek Embayment before meeting the Clinch River at Clinch River Mile (CRM) 20.8 (see Figure 3 and Figure 4). Radionuclides were released when creek flow eroded the contaminated bottom sediment of White Oak Lake and carried them into the Clinch River. Some of the upstream river sediment containing radionuclides was scoured and the transport of the suspended contaminated sediment contributed to the buildup of radionuclides in sediment further downstream. Prior to the impoundment of Melton Hill Dam in 1963, the particulate in the water column was usually deposited near CRM 14 (close to the mouth of Grassy Creek). This is an area where the river is wider and is influenced by the Watts Bar Reservoir. After 1963, however, the pattern of particulate deposition in sediment changed because of the controlled releases from Melton Hill Dam (Blaylock 2004).

In 1996–1999, TDOH's Task 4 team prepared the Reports of the Oak Ridge Dose Reconstruction, Radionuclide Releases to the Clinch River from White Oak Creek on the Oak Ridge Reservation—An Assessment of Historical Quantities Released, Off-Site Radiation Doses, and Health Risks (referred to as the "Task 4 report") to assess whether individuals visiting or living along the Clinch River area might have come in contact with harmful levels of radioactive materials in the past. Wastes generated at X-10 from 1944 to 1991 (the time frame covered in the Task 4 report) included radionuclides in various chemical forms (solids and liquids). Specifically, the purpose of the Task 4 effort was to:

• Estimate the historical releases of radioactive materials from the X-10 processes to White Oak Creek.
• Review and evaluate the possible exposure pathways for the public who lived downstream from White Oak Creek along the Clinch River and the Tennessee River.
• From these potential exposure pathways, calculate both the radiation doses and risks associated with these exposures. Because historical records were not maintained to today's standards, the Task 4 team performed independent reviews of environmental monitoring reports and existing data on releases and also used mathematical models to estimate the radiation doses and the associated risks (ChemRisk 1999a).

Task 4 Screening Assessment

As an initial evaluation in 1996, the Task 4 team identified 24 radionuclides—americium 241, barium 140, cerium 144, cobalt 60, cesium137, europium 154, hydrogen 3, iodine 131, lanthanum 140, niobium 95, neodymium 147, phosphorus 32, promethium 147, praseodynium 143, plutonium 239/240, ruthenium 106, samarium 151, strontium 89, strontium 90, thorium 232, uranium 235, uranium 238, yttrium 91, and zirconium 95—that were released to the Clinch River via White Oak Creek from 1944 to 1991 (ChemRisk 1999a). The Task 4 team determined that a screening analysis would help focus its efforts on the most important radionuclides and on the ways that people could have been exposed to White Oak Creek radionuclide releases via the Clinch River. The Task 4 team used a risk-based screening process to calculate conservative human health risk estimates for reference individuals and target organs, assuming that exposure occurred between 1944 and 1991 (a period of up to 48 years, except where noted).⁷ These risk estimates represented exposed individuals' increased likelihood of developing cancer–known as "excess lifetime cancer risk estimates." Because of the conservative assumptions used in calculating the estimates, the risk level would likely overestimate the public health hazard for exposed off-site populations. For comparison, the Task 4 team used an upper bound of 1 in 100,000 (1 × 10^-5) as the decision point, or minimal level of concern. This value was one-tenth of the ORHASP-recommended value of 1 in 10,000 (1 × 10^-4); thus, the value used by the Task 4 team was more conservative than the ORHASP-recommended value.

Through this screening process, the Task 4 team eliminated 16 out of 24 radionuclides released to the Clinch River from White Oak Creek because the estimated screening indices were below the minimal level of concern (1 x 10^-5). The eight radionuclides for which additional analysis would be necessary were cobalt 60 (Co 60), strontium 90 (Sr 90), niobium 95 (Nb 95), ruthenium 106 (Ru 106), zirconium 95 (Zr 95), iodine 131 (I 131), cesium 137 (Cs 137), and cerium 144 (Ce 144) (ChemRisk 1999a). Because the screening risk estimates for the swimming and irrigation pathways were below the minimal screening level for all 24 radionuclides, the team was able to eliminate these two exposure pathways (and therefore, consumption of locally grown crops) from further analysis. The team was also able to eliminate external exposure to dredged sediment, which only occurred in the Jones Island study area; the likelihood was low that individuals other than workers would have been exposed. The exposure pathways that required further evaluation were ingestion of fish, surface water, and meat and milk from cattle that grazed near the river, and external radiation from walking on shoreline sediment. Following this screening, the TDOH conducted a supplemental screening that included developing annual release amounts for the eight radionuclides and conducting a more comprehensive analysis of various exposure pathways.

Using its supplemental screening, the Task 4 team determined that four radionuclides (Cs 137, Co 60, Ru 106, and Sr 90) were more likely than the other four (Nb 95, Zr 95, Ce 144, and I 131) to cause adverse health effects to exposed off-site populations (ChemRisk 1999a). For more information on the screening process, see the brief summarizing the Task 4 report in Appendix D. For additional details and calculations used in the screening and supplemental screening processes in the Task 4 report, see Appendices 3A, 3B, and 4A of the document online at http://www2.state.tn.us/health/CEDS/OakRidge/WOak2.pdf .

Estimated Quantities of Radionuclides Released into White Oak Creek

Because accurate environmental monitoring and sampling data were not available, the Task 4 team performed an in-depth evaluation to estimate the amount of radionuclides that flowed from X-10, over White Oak Dam, and to the Clinch River. Through this evaluation, the team derived annual estimates for the eight radionuclides of interest: Co 60, Sr 90, Nb 95, Ru 106, Zr 95, I 131, Cs 137, and Ce 144. In total, about 200,000 curies of radioactive material were released from White Oak Creek into the Clinch River between 1944 and 1991 (ChemRisk 1999a). Using this information, the team then performed mathematical modeling to estimate the annual average concentrations of the eight radionuclides in water and sediment at specified locations downstream of White Oak Creek. To calculate doses for Cs 137, Sr 90, Ru 106, and Co 60, the Task 4 team used—when available—actual measurements from the Clinch River water it collected 1960–1990 at CRM 14.5 (K-25 Grassy Creek) and at 4.5 (Kingston Steam Plant). For the remaining radionuclides and for time periods when data were unavailable, the Task 4 team used modeling to estimate the historical radionuclide concentrations in Clinch River water. Limited available monitoring data were used to calibrate the results of the team's modeling efforts. For more information on the Task 4 team's modeling efforts, please refer to Section 6 of the Task 4 report, which is available at http://www2.state.tn.us/health/CEDS/OakRidge/WOak1.pdf .

Of the radionuclides released to White Oak Creek, the greatest health hazards were believed to be associated with Cs 137. Cs 137 releases along White Oak Creek were highest from 1955 to 1959. The high Cs 137 releases during those years resulted when the creek flow eroded the contaminated bottom sediment of White Oak Lake after the lake was drained in 1955. This was particularly true during the heavy rains in the winter and early spring of 1956. Currently, the elevated levels of Cs 137 are limited to the subsurface sediment buried in the deep channels of the LWBR.

Because of remedial actions and preventive measures at X-10, physical movement of sediments from the area, and radiological decay, the radionuclide releases from White Oak Creek have decreased over time and the concentrations of radionuclides in the water and along the shoreline have decreased as well. For example, Cs 137 in the Clinch River water near CRM 14 and CRM 3 has decreased by about a factor of 100 (see Figure 21). Because Clinch River sediments are not as actively exchanged as the river water itself (i.e., the sediments do not mix as much as the surface water), the Cs 137 in sediment at CRM 14 has decreased as a function of its half-life (see Figure 22) (ChemRisk 1999a).

Figure 21. Comparison of Predicted Annual Average Concentrations of Cs 137 in Water

Figure 22. Annual Average Cs 137 Concentrations in Shoreline Sediment

Task 4 Exposure Pathways Evaluation

For the eight radionuclides (Cs 137, Co 60, Ru 106, Sr 90, Nb 95, Zr 95, Ce 144, and I 131) requiring additional analysis, the Task 4 team conducted an in-depth exposure pathway evaluation of ingestion of fish, surface water, and meat and milk from cattle that grazed near the river, and external radiation from walking on shoreline sediment. Table 9 presents the past exposure pathways, the reference populations, and the radionuclides studied in the pathway exposure evaluation. Individuals were exposed over the entire 48-year study period, except for certain years pertaining to drinking water, external exposures, and meat and milk ingestion (excluded years are noted below in the table). For the fish consumption pathway, the Task 4 team considered three categories of fish consumers to account for differences in the amount of fish that individuals consume (Category I: 1 to 2.5 fish meals/week, Category II: 0.25 to 1.3 fish meals/week, and Category III: 0.04 to 0.33 fish meals/week)⁸ (ChemRisk 1999a).

Table 9. Past Exposure Pathways Evaluated in the Task 4 Report

* Drinking water exposures occurred from 1944 to 1991, except at the city of Kingston (1955–1991) and the Kingston Steam Plant (1954–1989). External exposures occurred from 1944 to 1991, except at Jones Island (1963–1991). Meat and milk ingestion exposures occurred from 1944 to 1991, except at Jones Island (1963–1991).

The Task 4 study covered a broad area along the Clinch River, from the mouth of White Oak Creek to the confluence of the Clinch and Tennessee Rivers. Because exposure situations might vary with the differences in topography and land uses at various sections of the river, the Task 4 team divided the area of study into four segments. Table 10 gives the CRM range, location, and exposure situations evaluated for each segment.

Table 10. Locations and Exposure Scenarios Considered in the Task 4 Study

* The river mile is the distance from the mouth of the river. That is, Clinch River Mile 0 is where the Clinch River empties into the Tennessee River. White Oak Creek enters the Clinch River at Clinch River Mile 20.8.
† The Task 4 report originally included ingesting produce, swimming, irrigating, and contacting dredged sediment (varying by segment) as pathways in its screening analysis. Given the results of its initial screening, however, the Task 4 team eliminated these pathways from further evaluation.

The Grassy Creek area includes portions of the Clinch River from Clinch River Mile (CRM) 17 to CRM 14. The mouth of Grassy Creek empties into the river at CRM 14.5; a tenth of a mile below that (CRM 14.4) is the potable water intake for the K-25 Gaseous Diffusion Plant. Associated with the intake was a combined filtration plant (using sand as the filter) and water storage facility that supplied potable water to the K-25 facility. Any radiological contaminants in the water intake for K-25 originated from the releases from White Oak Creek, approximately 7 miles upstream from the K-25 intake area. ATSDR learned about issues related to the K-25 intake from members of the public at meetings held by the Exposure Evaluation Work Group (EEWG), formerly known as the Public Health Assessment Work Group (PHAWG), as well as from the community concerns database maintained by ATSDR and discussions with DOE. ATSDR also learned from a community member that the K-25 intake was used at the J.A. Jones Construction Camp, which is locally referred to as the Happy Valley Settlement. The Happy Valley Settlement was first occupied in 1943 and 1944, primarily by construction workers, some family members, and a few concessionaires. At its peak in 1945, Happy Valley had more than 8,700 residents, including an estimated 5,600 workers and 3,100 dependents (Keith and Baker 1946; Prince 2003). Most people began leaving the settlement between the spring and fall of 1945, as construction of gaseous diffusion facilities was completed or permanent housing became available. Even so, anecdotal reports by an Oak Ridge community member suggest that the settlement might have been occupied as late as 1948. Because of possible exposure to contaminants in drinking water at Happy Valley, ATSDR conducted a separate evaluation for the Happy Valley community for the years the community was in existence.

Task 4 and ATSDR Estimated Radiation Doses

The Task 4 team derived radiation doses for each pathway of interest to estimate the amount of radiation that a potentially exposed individual might have received.⁹ In deriving the doses, the team used the International Commission on Radiological Protection's (ICRP) critical organ concept of dose limitation. ICRP's method limits dose (and long-term effects) to the critical organ–the organ most sensitive to or receiving the highest radiation dose following an intake of radioactive material. Using this approach, the cumulative dose to an organ from internally-deposited radionuclides is estimated separately from the dose attributed to external exposure (see text box).

The Task 4 team calculated the 95% confidence intervals for the cumulative organ dose equivalents. The 95% confidence interval is defined as the range of values, centered on the estimated mean, within which there is a 95% probability that the true mean will actually fall.¹⁰ The distributions from which the upper and lower confidence limits for each variable are obtained are based on the individual sets of measured data. For internal doses from ingestion, the Task 4 team considered exposure to Cs 137, Sr 90, Co 60, and Ru 106 and estimated dose factors for 22 organs for an adult; the team assessed exposure to I 131 and estimated thyroid doses for a child. The Task 4 team used different methods for estimating dose factors depending on the amount and quality of information available for each radionuclide (ChemRisk 1999a). For external exposures, the team evaluated the following seven radionuclides: Cs 137, Co 60, Ru 106, Zr 95, Nb 95, Sr 90, and Ce 144. The Task 4 team assumed that people were exposed for the entire study period of 48 years (1944 to 1991), except (as noted in Table 10) for a 29-year exposure duration associated with external exposure and ingestion of meat and milk at Jones Island, a 36-year exposure duration for drinking water at the Kingston Steam Plant, and a 37-year exposure duration for drinking water at the city of Kingston.

Using the 50^th percentile value of the uncertainty distribution, ATSDR summarized the Task 4 organ doses for the bone, lower large intestine, red bone marrow, breast, and skin locations. The 50^th percentile (central) values represent the medians of organ doses. ATSDR selected these organs because the contaminants of concern—particularly Sr 90 and Cs 137—tend to concentrate in these organs. ATSDR uses the central values because they provide the most realistic doses for potential past exposures to radionuclides in the Clinch River. Central estimates are used because they describe the risk or dose for a typical, realistic individual. When considering central estimates, half of the potential doses will fall above, and half will fall below the estimate. Therefore, an individual's actual dose would most likely be closer to the central value than to the high or low end of the dose estimate range. Further, 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.

Table 11. Summary of Estimated Organ-Specific Doses and Whole-Body Doses for Each Past Radiation Exposure Pathway and the Estimated Lifetime Organ-Specific Doses and Lifetime Whole-Body Doses From All Past Radiation Exposure Pathways

* Data were derived from ChemRisk 1999a—Tables 13.3, 13.4, 13.5, and 13A.8. The organ-specific radiation doses are the 50th percentile (central estimate) as reported by the Task 4 authors for individuals exposed during the entire study period (48 years), except for specific years that were not included for certain areas (see Table 10).
« To compare the doses in the Task 4 report to the doses in this table, 1,000 mrem is equal to 1 centisievert (cSv). For example, 810 mrem (organ-specific radiation dose to the bone for fish ingestion at Jones Island) divided by 1,000 would equal 0.81 cSv—the same value presented in Table 13.3 of the Task 4 report.
†ATSDR approximated the annual (1-year) whole-body dose for each pathway by applying weighting factors (presented in Table 6) to Task 4's estimated 50th percentile organ-specific doses, adjusting for a 1-year exposure, and summing the adjusted organ doses across each pathway. ATSDR approximated the lifetime (70-year) whole-body dose for each pathway by adjusting the doses for a 70-year exposure and summing the adjusted doses for each pathway.
‡The location represents the locations along the Clinch River of maximum exposure for each exposure pathway.
§ Doses are for females only; doses were too low to be significant in males.
¶ The doses are based on exposure to shoreline sediments.
** As a conservative measure, ATSDR estimated the committed equivalent doses for individuals who could have been exposed via all of the pathways and at all of the locations described above. To approximate a committed equivalent dose to an organ over 70 years, ATSDR summed the organ-specific radiation doses from the Task 4 report—based on up to 48 years of exposure—divided by 48, multiplied by 70 years, and rounded up.
†† ATSDR derived the total annual whole-body dose over a lifetime by summing the annual whole-body doses for each pathway.
‡‡ ATSDR derived the committed effective dose to the whole body by summing the equivalent doses for each organ using ICRP methodology.

ATSDR focused its evaluation on two potential exposure locations—Jones Island and the city of Kingston (see Table 11). ATSDR narrowed its evaluation to these two locations because Jones Island is the closest land mass to the mouth of White Oak Creek and the city of Kingston is the closest large city downstream of the creek before the confluence of the Clinch River and Tennessee River. (For certain pathways, doses at K-25/Grassy Creek are presented as the location of maximum exposure.)

Weighting factors (explained on page 68) are used to convert an organ dose equivalent to a committed effective dose for the whole body that is lower than the organ dose. The committed effective dose is obtained by multiplying the organ dose by the weighting factor. For example, a 5 mrem dose to the thyroid would be multiplied by the weighting factor 0.05 to yield 0.25 mrem whole-body dose. For its evaluation, ATSDR applied weighting factors to the Task 4 organ doses and summed the adjusted organ doses across pathways to derive the annual and whole-body doses for each pathway. Then, ATSDR summed the annual and whole-body dose for each pathway to derive the total annual dose to the whole body and the committed effective dose to the whole body over 70 years. ATSDR also summed the organ doses to derive a committed equivalent dose to an organ over a 70-year (lifetime) exposure. When deriving the committed equivalent dose to an organ, ATSDR adjusted the Task 4 organ doses from a 48-year exposure (except in cases noted in Table 10) to a 70-year exposure so that ATSDR could compare these doses to health guidelines for radiation exposures to the public.

Table 11 presents the organ-specific and whole-body doses for all pathways of interest. As shown in Table 11, the maximum annual whole-body dose from all exposure pathways of interest is 4 mrem. This dose is about 2% of the 360 mrem that the average U.S. citizen receives each year from background radiation (i.e., levels typically found in the environment and in sources from human activities and products). About 300 mrem of background radiation is the amount of radiation to which a member of the general population is exposed from natural sources. These sources include terrestrial radiation from naturally occurring radionuclides in the soil, cosmic radiation originating from space, and naturally occurring radionuclides deposited in the human body. The remaining 60 mrem of background radiation results from sources related to human activities and products, such as medical and dental x-rays (Nuclear Energy Institute 2003). Of the 22 organs evaluated, the Task 4 authors predicted that the bone surface received the highest dose of radiation from any of the exposure pathways. The higher doses to the bone reflect the additional contribution from Sr 90.

After its review of Task 4 organ-specific doses and ATSDR-derived lifetime and whole-body doses, ATSDR determined that exposures to radionuclides by way of fish ingestion, water ingestion, and external radiation were more likely than the other pathways to result in higher radiation exposures in off-site populations. For comparison, doses from ingesting meat and milk were more than 1,000 times less than doses from eating fish (see Table 12). These calculated doses have been screened against the comparison values found in Table 22 of Section IV. Public Health Implications.

Table 12. Ratio of Adult Organ-Specific Radiation Doses Relative to Ingestion of Fish Caught Near Jones Island

*The fish consumption dose used to calculate the ratio was the 50^th percentile dose received by the maximally exposed individuals who consumed fish caught near Jones Island over the 48-year exposure.
† The pathway presented represents the maximally exposed category.
‡ When doses for two areas are given for the same pathway, ATSDR compared the highest dose to fish doses.
§ Doses are for females only; doses were too low to be significant in males.
¶ The doses are based on exposures from walking along the shoreline.

ATSDR discusses the fish ingestion, water ingestion, and external radiation exposure pathways below.

Fish Ingestion

The highest radiation doses were associated with eating fish taken from the Clinch River near Jones Island between 1944 and 1991. Doses were much lower for all other pathways (see Table 11 and Table 12). The Task 4 report's estimated organ doses

• to the bone,
• to the lower large intestine,
• to the red bone marrow,
• to the breast, and
• to the skin

from eating fish were at least 6 times greater than the radiation doses to these same organs from eating meat, drinking water and milk, and external radiation (Table 12). Likewise, ATSDR's derived annual whole-body and committed equivalent doses from eating fish were at least 10 times more than any of the other exposure pathways (Table 11).

The highest organ doses of radiation from fish consumption were estimated for the bone surface (810 mrem for males and 600 mrem for females, central values), and the lowest organ doses were estimated for the skin (310 mrem for males and 230 mrem for females, central values). Despite these differences, the organ doses varied by a factor of only 2 to 3 for males and 3 to 4 for females. This similarity between doses reflects the contribution of Cs 137 to organ doses. Cs 137 distributes rather uniformly throughout the body of the person eating the fish, and therefore, there was little difference among the various organ doses. It should be noted that because different organs are believed to have different sensitivities to radiation-induced cancer, the organ with the highest dose is not necessarily the organ with the highest probability of developing cancer.¹¹

The dose for fish consumption depended on how often people ate fish and the area of the Clinch River where the fish were taken. The highest doses were received by individuals who consumed 1 to 2.5 fish meals per week and caught their fish near Jones Island, close to the mouth of White Oak Creek. The estimated annual whole-body dose of 3.4 mrem from eating frequent meals of fish caught near Jones Island was less than 1% of the average annual background dose of 360 mrem for a U.S. citizen. Doses were much lower for individuals who ate fewer fish or caught their fish further downstream from White Oak Creek and Jones Island. For example, organ-specific and whole-body doses for people who ate fish caught near Kingston were 8 times lower than doses from eating fish caught near Jones Island (see Table 12). People who ate fish caught near Kingston received an estimated annual whole-body dose of 0.4 mrem, which is 900 times less than the average annual background dose of 360 mrem for a U.S. citizen.

Drinking Water Ingestion

In Table 11, ATSDR summarizes radiation doses for drinking water at K-25/Grassy Creek (CRM 17 to 5) and the city of Kingston (CRM 0), located downstream from the mouth of White Oak Creek. These doses are from the Task 4 team's evaluation of drinking filtered, treated Clinch River water. Water from the Clinch River can travel up the Tennessee River when the Clinch River's flow is greater than the Tennessee River's flow. As a result of this backflow, the city of Kingston could receive Clinch River water (ChemRisk 1999a). The Task 4 team estimated 1) the amount of radiological contamination resulting from Clinch River backflow possibly entering the Kingston water intake and 2) the effect of water treatment on the drinking water (ORHASP 1999). The estimated organ-specific and whole-body radiation doses received from drinking water from the Clinch River were much lower than the radiation doses received from eating Clinch River fish. For example, the doses to the bone, lower large intestine, red bone marrow, breast, and skin from drinking Clinch River water were at least 7 times lower than the doses to those same organs from eating Clinch River fish. The highest annual whole-body dose from drinking water of 0.3 mrem was estimated for K-25/Grassy Creek. This annual whole-body dose is more than 1,000 times less than the background dose of 360 mrem that the average U.S. citizen receives each year. Lower doses were associated with drinking water further downstream at the city of Kingston. Organ-specific doses from drinking city of Kingston water were at least 13 times less than the doses estimated for K-25/Grassy Creek drinking water.

In addition to the Task 4 team's analysis of exposure to X-10 contaminants via the K-25 water intake, ATSDR conducted a separate analysis of exposure of residents living in the Happy Valley settlement. In its evaluation, ATSDR derived whole-body doses for hypothetical residents of Happy Valley who drank water from the K-25 intake. Most information about Happy Valley indicates that workers and their families occupied the settlement between late 1943 and 1946. Anecdotal reports suggest, however, that some workers stayed on through 1948. Given the uncertainty about the actual time frame in which Happy Valley was occupied—and the duration of possible exposure—ATSDR overestimated the likely exposure period by conservatively assuming that Happy Valley residents could have been exposed over a 7-year period, from 1944 to 1950. Conservative assumptions such as this create a protective estimate of exposure, which allows ATSDR to evaluate the likelihood, if any, that the K-25 drinking water containing radionuclides could cause harm to Happy Valley residents.

ATSDR did not identify any Clinch River monitoring data for radionuclides covering the period when Happy Valley was used as a housing area. In the absence of historical monitoring data, ATSDR used the 50th percentile of the modeled radioactivity concentrations in the Grassy Creek area of Clinch River as reported in the Task 4 report. ATSDR's highest annual radiological dose estimate at the K-25 water intake was about 14 mrem/year. ATSDR predicted that Happy Valley residents who lived at the settlement from 1944 to 1950 would have received a dose of 98 mrem over the 7-year period. The whole-body dose for drinking water at Happy Valley (from the K-25 intake) was about 2.5 times less than the doses estimated for fish consumption.

External Radiation (Walking on Sediment)

Radionuclides that had accumulated in the sediment deposited along the Clinch River were found in the top layer (averaging about 6 to 7 centimeters [cm], but varying between 2 and 15 cm) of sediment. The Task 4 team derived organ doses for people who might have incurred external exposure to radionuclides while walking on Clinch River shoreline sediment from 1944 to 1991 (except at Jones Island where years of exposure evaluated were 1963 to 1991; see Table 10). When estimating doses from external exposure, the team used dose-rate factors (dose per unit intake) as reported by the ICRP and modified these factors to consider the thickness of the contaminated sediment layer and the width of the Clinch River shoreline. The Task 4 team obtained the external doses by combining the concentrations of radionuclides in sediment with the dose-rate factors and the exposure parameters.

ATSDR focused its evaluation on those exposures occurring near Jones Island and the city of Kingston. Overall, the Task 4 organ doses from walking on sediments were at least 6 times lower than doses received from eating Clinch River fish caught at or near Jones Island. Individuals walking on sediment in the Kingston area were predicted to receive slightly higher doses than individuals at Jones Island. Upstream sediment containing radionuclides was likely dislodged by the water flow and contributed to the buildup of sediment farther downstream. Even so, the maximum annual whole-body dose from external radiation by walking on Kingston sediments (0.2 mrem) is over 1,000 times less than the radiation dose of 360 mrem that the average U.S. citizen receives from background radiation each year (see Table 11).

ATSDR's Review of the Task 4 Dose Reconstruction Report

As part of its involvement at the ORR, ATSDR convened a panel of technical experts to evaluate the study design, the scientific approaches, the methodologies, and the conclusions of the Task 4 report. ATSDR had the report reviewed to determine if it would provide a foundation for follow-up public health actions or studies, particularly ATSDR's congressionally mandated public health assessment of the ORR. The reviewers agreed that the overall design and scientific approach were appropriate. One reviewer commented that the methods and analysis plan "break new and important ground in the use of uncertainty analysis in environmental assessment." The reviewers also commented that the results were generally quite valid and consistent with earlier studies, and were applicable to public health decision-making as long as careful attention was given to the assumptions behind the estimates. Some issues with the team's report raised some concern among the reviewers; in their opinion, however, the report was well written and advanced the science of dose reconstruction.

III.B.3. Current and Future Exposure (Years After 1987)

Lower Watts Bar Reservoir (1988–Present and Future)

Background

The LWBR extends from the convergence of the Clinch River and the Tennessee River (about 22 river miles downstream of White Oak Dam) to the Watts Bar Dam (see Figures 4 and 11). Community members use the reservoir for recreational activities, such as boating and swimming. The LWBR is also a popular recreational fishing spot for area anglers—an estimated 10,000 to 30,000 anglers fish at the Lower Watts Bar Reservoir each year (ORHASP 1999). In addition, Kingston, Rockwood, and Spring City obtain drinking water from surface water bodies flowing into the Watts Bar Reservoir. During rare circumstances, reverse flow conditions could result in ORR contaminants backflowing into these water intakes. Kingston maintains a water intake on Watts Bar Lake, which is upstream from the Clinch River confluence on the Tennessee River at Tennessee River Mile (TRM) 568.4 (Hutson and Morris 1992; G Mize, Tennessee Department of Environment and Conservation, Drinking water program, personal communication re: Kingston public water supply, 2004). Although the intake is slightly upstream, water flow direction in this area is impacted by the Tellico and Fort Loudon Dams and releases through the Watts Bar Dam. Thus, during a rare occurrence where backflow conditions affect these dams, this intake could potentially receive ORR contaminants. Spring City obtains its water from an intake on the Piney River branch of Watts Bar Lake (Hutson and Morris 1992). The city of Rockwood receives its water supply from an intake on the King Creek branch of Watts Bar Lake (Hutson and Morris 1992; TDEC 2001, 2006b). Therefore, ORR contaminants could potentially affect these three intakes, but only during the rare occurrence of reverse flow conditions.

In March 1995, DOE released a proposed plan that called for leaving the contaminated deep sediment in place at the reservoir; deep sediment is generally considered inaccessible to the public, and the LWBR sediment—if left undisturbed—is not expected to pose a concern for public exposure (USDOE 1995a). Because the reservoir was used so widely, some community members expressed concern to ATSDR about possible exposure to contaminants in the water and sediment. The community questioned whether DOE's proposed actions were sufficient to protect people who use the reservoir from exposure to these contaminants. Subsequently, these residents asked ATSDR to evaluate the potential health risks from exposure to the LWBR contamination and provide an independent opinion on whether DOE's selected remedial actions were adequate to protect public health. ATSDR prepared a health consultation in 1996 to respond to community concerns about potential hazards associated with contaminants in the water and deep sediments of the LWBR (ATSDR 1996). See Section II.F.1. in this document and the brief in Appendix D for more details on ATSDR's health consultation.

Since February 1991, the Watts Bar Interagency Agreement has set guidelines related to any dredging in Watts Bar Reservoir and for reviewing potential sediment-disturbing activities in the Clinch River below Melton Hill Dam, including Poplar Creek (Jacobs EM Team 1997b). Under this agreement, the Watts Bar Reservoir Interagency Working Group (WBRIWG) reviews permitting and other activities, either public or private, that could possibly disturb sediment, such as erecting a pier or building a dock (ATSDR 1996; Jacobs EM Team 1997b; USDOE 2003a). The WBRIWG consists of DOE, EPA, USACE, TDEC, and TVA because of their permit authority or their knowledge of the sediment contamination and how that contamination could impact the public if disturbed (Jacobs EM Team 1997b).

Permit coordination under the Watts Bar Interagency Agreement was established to allow TVA, USACE, and TDEC (the agencies with permit authority over actions taken in Watts Bar Reservoir) to discuss proposed sediment-disturbing activities with DOE and EPA before conducting the normal permit review process to determine if there were any DOE contaminants in the sediments. The coordination follows a series of defined processes as outlined in the agreement.

The basic process of obtaining a permit is the same for any organization or individual:

1. An application is completed and submitted to TVA/USACE/TDEC (depending on scope of activity);



2. if the proposed activity would occur within the Watts Bar Reservoir and its tributaries, the application is forwarded to the WBRIWG for review;



3. the WBRIWG reviews available data for the location involved or DOE collects any necessary existing data on sediment contamination;



4. if the location is considered to be uncontaminated or clean enough to pose no significant health risks, then the application is forwarded back to TVA/USACE/TDEC for their standard review process; and



5. if the location is considered to be contaminated and sediments may pose a health risk, DOE works with the applicant to determine how best to conduct the requested activity (assuming TVA/USACE/TDEC permit the action based on their own statutory program of review). The interagency agreement covers any potential sediment-disturbing activity (other than locations predetermined to be free of DOE-related contaminants) (Jacobs EM Team 1997b).

If dredging is necessary in an area with contaminated sediments, DOE will assume the financial and waste management responsibility that is over and above the costs that would normally be incurred. Dredging and subsequent disposal of sediments will take place in accordance with best management practices and in compliance with all state and federal laws regarding downstream impacts and disposal of hazardous or radioactive materials (Jacobs EM Team 1997b).

Environmental Monitoring Data for the Lower Watts Bar Reservoir

To address the community concerns, ATSDR evaluated environmental monitoring data for surface and deep channel sediment, surface water, and local biota collected from the LWBR by DOE and TVA during the 1980s and 1990s (Olsen et al. 1992; USDOE 1994b).¹² In addition to these data, ATSDR evaluated the institutional controls in place to monitor contaminants in the LWBR. These controls, which include measures to keep sediment in place and ongoing water monitoring, have helped to minimize the potential for human exposure to contaminants in sediment and water. Data on radionuclides that were transported downstream from the ORR by the LWBR in sediment, surface water, and fish are discussed below.

Sediment

Radionuclides (Table 13) were detected in the surface and deep subsurface layers of sediment in the LWBR. The surface samples were collected from shallow areas of the reservoir and the subsurface samples were collected from the deep river channels—beneath several meters of water and 40 to 80 centimeters of sediment. Samples collected from the surface layer contained Cs 137, Sr 89/90, and Co 60. Other radionuclides were also detected, but at much lower frequencies and concentrations. The highest concentration of Cs 137 in surface sediment was below 15 pCi/g, the screening value adopted by the Interagency Working Group. This value is also below the soil screening value for Cs 137 used by ATSDR as adopted from NCRP's Report 129 (NCRP 1999).

Table 13. Maximum Radionuclide Concentrations in Lower Watts Bar Reservoir Sediment

Historical documents suggest that 2 to 5 times more strontium than cesium was released to the Clinch River between 1982 and 1992; however, higher concentrations of Cs 137 were detected in the top layers of sediment (Martin Marietta Energy Systems, Inc. 1993). Both cesium and strontium tend to bind to sediment; although, cesium binds more strongly to sediment, while strontium is released from sediment more readily under certain conditions. Cs 137, Co 60, and Sr 90 are the most common radionuclides detected in the subsurface sediment. The depth of the peak concentrations appears to vary with the location in the reservoir, the rate of sediment accumulation, and the type of sediment. In general, radionuclide concentrations were higher in the subsurface sediment than in the surface sediment (see Figure 23), and increased with depth within the subsurface sediment. The highest concentration of Cs 137 (58.35 pCi/g) was found in the deep river channel subsurface sediment at a depth of 15 to 33 inches (Olsen et al. 1992).

Figure 23. Radionuclide Concentrations in Surface Sediment vs. Subsurface Sediment

The vertical distribution of Cs 137 was strongly correlated to mercury (Hg) concentrations, with both exhibiting large subsurface maximum concentrations that coincided with their peak discharge histories. Sr 90 and Co 60 also existed in the subsurface sediment, but they were generally found at concentrations lower than Cs 137. Peak concentrations of Sr 90 and Co 60 do not strongly relate to peak concentrations of Cs 137 and they do not show a similar dramatic change in concentration with depth of sediment. Uranium concentrations were slightly higher than background concentrations for the region.

Surface Water

Some of the radionuclides released to White Oak Creek were suspended in the water. These radionuclides would be expected to decrease in concentration as they mixed with the surface water of the Clinch River before reaching the LWBR. To evaluate surface water sampling data for the reservoir, ATSDR reviewed TVA's 1991 sediment sampling report (TVA 1991) near major water intakes along the Tennessee River system reservoirs of the Watts Bar, Melton Hill, and Norris Dams; the Phase 1 Data Summary Report for the Clinch River Remedial Investigation: Health Risk and Ecological Risk Screening Assessment (Cook et al. 1992); and the ORR 1992 Environmental Report (Martin Marietta Energy Systems, Inc. 1993). Samples were collected from 29 locations at the reservoir and were analyzed for 11 radionuclides. ATSDR also reviewed water samples collected by TVA from the water intakes for the cities of Kingston, Spring City, and Rockwood (TVA 1991). Water sampling data consisted of both grab and composite samples. Composite samples were collected weekly, mixed in one container, and analyzed quarterly. Table 14 summarizes the surface water monitoring data for the Lower Watts Bar Reservoir.

Table 14. Maximum Radionuclide Concentrations in Lower Watts Bar Reservoir Surface Water

Of the seven radionuclides detected, hydrogen 3 (H 3, also known as tritium) reached the highest concentration (853 pCi/L) in the collected surface water samples. According to the Task 4 report, over 90% of the total radioactivity released from White Oak Creek was in the form of H 3. Concentrations of the other radionuclides were less than 1 pCi/L. The likelihood of adverse health effects from H 3 is extremely low; the concentrations were well below the EPA's current maximum contaminant level (MCL) of 20,000 pCi/L of H 3, an amount that would produce a radiation dose of 4 mrem/year if ingested at 2 liters of water per day for a year.

Drinking Water

The cities of Kingston, Spring City, and Rockwood have public drinking water supplies that draw water from the Tennessee River system. EPA's Safe Drinking Water Act (SDWA) requires all public water suppliers in Tennessee to monitor their water to ensure that it meets safe drinking water standards, or MCLs. The public water supplies for Kingston, Spring City, and Rockwood are monitored for substances that include 15 inorganic contaminants, 51 synthetic and volatile organic contaminants, and 4 radionuclides (USEPA 2004a). According to EPA's Safe Drinking Water Information System (SDWIS), the Kingston, Spring City, and Rockwood public water systems meet safe drinking water standards (USEPA 2004b). In 1996, TDEC's DOE Oversight Division started to participate in EPA's Environmental Radiation Ambient Monitoring System. Under this program, TDEC collects water samples from the Tennessee River system around Kingston and Spring City and analyzes them for radiological content. After its review of the public water supply monitoring and ERAMS results, ATSDR concludes that this water is safe for consumption and for other potable uses.

Fish

LWBR sediment and water quality have been affected by radioactive contaminants released from White Oak Creek to the Clinch River and the LWBR. Some of the radiological materials have long half-lives, and thus might remain in the environment for many years after being released. Even though radionuclide levels in surface water or surface sediment of the reservoir might be relatively low, certain contaminants can persist and accumulate in fish tissue. Fish are exposed to contaminants when they eat smaller fish or consume sediment that contains contaminants. Because of this process, larger and older fish can build up high levels of contaminants (TVA 1994).¹³

Limited data describing radionuclide concentrations in fish from the LWBR were available for ATSDR's review in 1995. The available data came from three sites along or downstream of the LWBR: Mid Watts Bar Reservoir (Tennessee River Mile 557.0), the LWBR north of the Watts Bar Dam (Tennessee River Mile 530.5), and the Upper Chickamaugua Reservoir (Tennessee River Mile 518.0 and below Watts Bar Dam). A combined total of 42 fish specimens were collected, coming from three different species—channel catfish, bluegill sunfish, and largemouth bass. All of the fish fillet samples were analyzed for Cs 137 and Co 60. Channel catfish samples with bones were also analyzed for Sr 90, since strontium is a bone-seeking radionuclide. As shown in Table 15, the radionuclides Cs 137, Co 60, and Sr 90 were detected at 0.16 pCi/g, 0.24 pCi/g, and 1.0 pCi/g, respectively.

Table 15. Maximum Radionuclide Concentrations in Lower Watts Bar Reservoir Area Fish

Lower Watts Bar Reservoir Exposure Pathways and Estimated Radiation Doses

In its evaluation of exposures at the LWBR, ATSDR derived whole-body (committed effective) doses for hypothetical people who came in contact with radionuclides while walking on surface and dredged subsurface sediment, swimming or showering in surface water, drinking reservoir water, or consuming fish. When deriving the doses, ATSDR used worst-case exposure scenarios that relied on literature-based conservative (i.e., protective) assumptions for fish ingestion. The worst-case scenarios assumed that the most sensitive population (i.e., young children) was exposed to the highest concentration of radionuclides in sediment, surface water, or fish by the most likely exposure routes—inhalation, ingestion, dermal contact, and external radiation. Using these assumptions when estimating the hypothetical exposure doses likely overestimates the actual magnitude of exposure. These conservative assumptions create a protective estimate of exposure, which allows ATSDR to evaluate the likelihood, if any, that environmental media containing radionuclides could cause harm. ATSDR's estimated doses are summarized in Table 16 and in the discussion that follows.

Table 16. Estimated Whole-Body Doses for Current Lower Watts Bar Reservoir Exposure Pathways

* ATSDR's conservative assumptions used to estimate radiation doses likely created overestimates of the magnitude of the true exposure.
† ATSDR's evaluation of exposure to dredged sediment along LWBR also considered inhalation of, ingestion of, and dermal contact with contaminated dredged sediment.

Fish Ingestion

To determine if the consumption of contaminated fish could be detrimental to human health, ATSDR estimated doses for individuals who eat fish from the LWBR. Because uncertainty exists regarding how often people consume fish from the river and how large a portion might be eaten, ATSDR used worst-case scenarios that assumed an adult and child eat two 8-ounce meals of LWBR fish each week. ATSDR also assumed that the fish consumed contained the highest probable level of each of the primary radionuclides. For example, when evaluating the likelihood of health effects from strontium, ATSDR assumed that the fish fillet meal could include some bone because strontium is a bone-seeking radionuclide. For both an adult and a child, the dose estimated for the primary radionuclides were 6 mrem per year, or less than 420 mrem over 70 years for the committed effective dose. The annual whole-body dose of 6 mrem is more than 60 times less than the background dose of 360 mrem that the average U.S. citizen receives each year.

Water Ingestion

ATSDR examined the possibility that harmful health effects could result from exposure to the radionuclides detected in LWBR surface water. Local residents might be exposed to contaminants in unfiltered surface water through incidental ingestion of water when they use the reservoir for recreational activities, such as swimming. Residents of Kingston, Spring City, or Rockwood supplied with municipal water from the reservoir could potentially contact contaminants when they drink treated water from their taps or use it for other household purposes. That said, however, it is only possible for ORR contaminants to reach these intakes during the rare circumstances of reverse flow conditions resulting in contaminant backflow. Even so, potential exposures to harmful levels of radionuclides in the home from municipal water use are not expected—monitoring data indicate that the drinking water has met safe drinking water standards for radionuclides.

ATSDR evaluated exposure to surface water contaminants for a 10-year-old child who lives near the LWBR. ATSDR focused its evaluation on the child to consider the potential likelihood that this sensitive population might be exposed to surface water contaminants. ATSDR used conservative assumptions to examine how a child could be exposed to contaminants and how much contaminated water that child might ingest each day. In its evaluation, ATSDR assumed that the child drank unfiltered water. ATSDR's estimated dose to a child from drinking unfiltered water obtained from the LWBR is 0.25 mrem per year, or less than 17.5 mrem over 70 years for the committed effective dose. The annual whole-body dose of 0.25 mrem is about 1,440 times less than the background dose of 360 mrem that the average U.S. citizen receives each year.

External Radiation: Contact With Shoreline Sediment or Dredged Sediment

Relatively low levels of radioactive contaminants have been detected in the surface sediment of the LWBR (see Figure 23). People could be exposed to external radiation released from radionuclides in shallow areas of the reservoir or along the shore while swimming, fishing, or boating. The highest concentrations of radioactive contaminants are in subsurface sediment located in the deep river channels and are shielded by several meters of surface water and 15 inches or more of sediment on the river bottom—thus these areas with the highest concentrations are generally inaccessible to the public. In the unlikely event that these subsurface sediments might in the future be dredged from the river channel, ATSDR examined the potential exposure for a hypothetical individual who might come in contact with contaminants when walking on or handling sediment that was dredged from the deep river channel and deposited on the shoreline. ATSDR's committed effective doses to the whole body for individuals hypothetically exposed to external radiation from surface sediment or subsurface sediment were less than 1,050 mrem over 70 years and 1,400 mrem over 70 years, respectively.¹⁴ These committed effective doses were based on annual doses of 15 mrem and 20 mrem for external radiation from surface sediment and subsurface sediment, respectively. These annual whole-body doses are more than 18 times less than the background dose of 360 mrem that the average U.S. citizen receives each year.

External Radiation: Swimming or Showering

Local residents might be exposed to contaminants in surface water through physical contact with water when they use the reservoir for recreational activities, such as swimming and boating. Residents of Kingston, Spring City, and Rockwood who are supplied with municipal water from the reservoir could also contact contaminants when showering or bathing. As previously noted, potential exposures to harmful levels of radionuclides in the home from municipal water use are not expected—monitoring data indicate that the drinking water has met safe drinking water standards for radionuclides.

ATSDR used conservative, worst-case (i.e., protective) assumptions to examine how a 10-year-old child could be exposed to contaminants and how much contaminated water that child might contact each day. In its evaluation, ATSDR assumed that the child showered, or that the child swam in the reservoir, for up to 8 hours a day. In all likelihood, a child would spend far less time in either situation. Still, these assumptions enable ATSDR to calculate a conservative estimate of exposure that it uses to confidently evaluate the likelihood, if any, that contaminants in surface water could cause harm. Potential exposure was also evaluated for a person under similar circumstances who might live near the Watts Bar Lake for a lifetime (70 years). The dose to the whole body from external radiation via bathing or swimming is 0.05 mrem per year, or less than 3.5 mrem over 70 years for the committed effective dose. The annual whole-body dose is more than 7,200 times less than the background dose of 360 mrem that the average U.S. citizen receives each year.

ATSDR combined the annual doses for the surface water exposure pathways (i.e., 0.25 mrem from incidental ingestion and 0.05 mrem from contact via swimming or showering) to obtain the total dose from waterborne radioactive contaminants, which was below 1 mrem over 70 years—less than 1% of the typical background radiation dose that a U.S. citizen receives each year.

Clinch River (1989–Present and Future)

Environmental Data

To evaluate the current exposures and doses related to releases from White Oak Creek, ATSDR obtained data in electronic format from the Oak Ridge Environmental Information System (OREIS), detailed in Section II.F.4 of this document. The data received and analyzed by ATSDR covered the time period 1989–2003. Samples included surface waters collected from the LWBR and sediments from the associated shorelines. ATSDR also evaluated biota data that included fish, geese, and turtle samples. ATSDR analyzed samples for rivers in the watershed that included the Clinch River below Melton Hill Dam and the Tennessee River below the mouth of the Clinch River. For comparison, ATSDR reviewed data collected from background locations (Emory River, streams that feed into the Clinch River, the Clinch River above the Melton Hill Dam, and the Tennessee River upstream of the Clinch River). As stated previously, when contaminant concentrations in White Oak Creek surface water enter the Clinch River, those contaminant concentrations will become diluted. Further dilution will occur when the Clinch River meets the Tennessee River.

For the initial data sorting, ATSDR included the radionuclides associated with the Task 4 report, as well as the radionuclides reported in the OREIS data. The purpose of the data sorting was to collate data by the following parameters: river location, species (for biota), radionuclide, or a combination of one or more of these parameters. As a result of this sorting, ATSDR performed its evaluation on the radionuclides presented in Table 17.

Table 17. Summary of Radionuclides Evaluated for the Clinch River Area

* The half-life is the amount of time required for 50% of the initial amount present to physically decay.
† The mode of decay is the principal method whereby the isotope decays or releases energy. In those instances where a gamma mode is listed, this indicates that the decay product releases a gamma ray (photon) as a method of nuclear rearrangement.
‡ The critical organ, as defined by the International Commission on Radiological Protection, is the organ receiving the highest radiation dose following an intake of radioactive material.
§ The decay product is the first isotope produced during the decay of the parent radioisotope.

Exposure Pathways and Estimated Radiation Doses

ATSDR sorted the environmental monitoring data by pathway: ingestion of biota (fish, geese, and turtle), ingestion of water, and external radiation via walking on shoreline sediment or contacting water while swimming (see Table 18). Exposure scenarios were evaluated by using specific values from the EPA Exposure Factors Handbook, other federal guidance manuals, and/or interviews performed during ATSDR's 1998 exposure investigation that evaluated serum PCB and blood mercury levels in consumers of fish and turtles from the Watts Bar Reservoir. See Section II.F.1. in this public health assessment for additional details and Appendix D for a brief summary of the exposure investigation. In the discussion that follows, ATSDR evaluates these exposure situations and derives estimated radiation doses.

Table 18. Current Exposure Pathways Evaluated for the Clinch River Area

ATSDR reviewed biota (fish, geese, and turtle), surface water, and sediment data for the presence of radionuclides. The samples were collected from the Clinch River below the Melton Hill Dam and from the Tennessee River below its confluence with the Clinch River. For comparison, ATSDR reviewed data collected from background locations (Emory River, streams that feed into the Clinch River, the Clinch River above the Melton Hill Dam, and the Tennessee River upstream of the Clinch River).

For the dose assessment, ATSDR looked at the critical organ and the radiation dose delivered to the whole body. For the time period of the dose assessment (1989 to the present), ATSDR set the age of an adult at 20 years and estimated the dose received until that person was 70 years of age; that is, ATSDR assumed exposure for a 50-year period. For a teenager and child, ATSDR also estimated the dose to age 70, but modified the years of exposure as appropriate for a 15-year-old (55 years) and a 10-year-old (60 years).

Biota Ingestion

ATSDR reviewed biota data for the presence of radionuclides. The biota samples included various species of fish, turtles, and geese that were collected from the Clinch River below the Melton Hill Dam and from the Tennessee River below its confluence with the Clinch River. For comparison, ATSDR reviewed data for background locations.

Fish

In deriving radiation doses from the consumption of fish, ATSDR considered only fillet portions and muscle. ATSDR assumed that a child eating fish from the river consumes 113.4 grams (4 ounces) per week and that an adult consumes 227 grams (8 ounces) per week. Table 19 presents the estimated radiation doses by fish species consumed and the river where the samples were collected for an adult, teenager, and child (until age 70 years).

ATSDR's analysis of fish consumption indicates that the doses to the critical organ and to the whole body are very similar for the 10-year-old, the 15-year-old, and the 20-year-old. Some of the highest doses were associated with eating catfish or largemouth bass caught from the Clinch River below Melton Hill Dam. Even so, to age 70 the highest estimated whole-body dose, or committed effective dose, was 89.3 mrem. The highest committed equivalent dose of 114 mrem to the bone surface was estimated for a 15-year-old, based on a 55-year exposure. Because Sr 90 is a bone seeker and because much bone growth occurs during the teenage years, a 15-year-old could conceivably have a higher dose than either a 20-year-old adult or a 10-year-old child (see Table 19).

At one time, the Clinch River had many species of mussels and dredging for mussels took place in the lower Clinch River on a large scale. But the mussel population declined rapidly after the 1936 impoundment of Norris Dam and the 1963 impoundment of Melton Hill Dam. Many unconfirmed reports suggest that people consumed mussels from the Clinch River (usually on a very limited basis); however, there are no records of mussels being consumed on a regular basis and the Clinch River mussels were generally considered to be a poor source of food. Therefore, the likelihood is low that people consumed mussels from the Clinch River (Blaylock 2004).

Table 19. Estimated Radiation Doses From Current Ingestion of Fish

* The doses are expressed in mrem calculated from age of intake to 70 years. For example, the intake for an adult occurs at age 20 and continues for 50 years.
† Doses are presented for the organ receiving the highest radiation dose and for the whole-body dose (the dose delivered to the entire body).
‡ The doses for sunfish are based on dry weight samples; all other doses are based on wet weight samples.

Turtles and Geese

Canadian geese were introduced into the X-10 area about 20 years ago. Turtles also inhabit the Clinch River environment. Contaminated geese and turtles have been identified in the radioactive ponds at X-10. Geese are grazers that only feed at the ponds in late winter and early spring. For several years, the ORR had a program to control access of waterfowl to radioactive waste ponds, mainly at X-10. These ponds were monitored, and geese that continued to use the ponds were collected. A few geese collected from 3504 waste disposal ponds at X-10 were found to have high concentrations of radionuclides, primarily Cs 137 in their tissues; however, the quantity of geese found with high radionuclide concentrations was extremely small. Further, the possibility of obtaining more than one goose or one turtle with high radioactive concentrations is "highly unlikely" (Blaylock 2004).

For hunters consuming geese, ATSDR assumed that not all portions of the animal would be consumed. Therefore, only the goose liver and the goose muscle were chosen for this analysis. ATSDR selected a consumption value of 500 grams of liver per year (about 1 pound) and 10 kilograms (approximately 22 pounds) of goose muscle per year. For turtle ingestion, only the muscle was analyzed at a consumption value of 100 grams (about 3.5 ounces) per year. For the critical organs, ATSDR used bone surface (Sr 90) and lower large intestine (Cs 137 and Co 60).

Estimated doses for the consumption of geese and turtles are shown in Table 20. As noted in the table, the estimated dose from ingestion of goose muscle and liver was greater than the estimated dose from ingestion of turtle, with most of the dose going to the bone surface. The highest committed effective dose to the whole body was 14 mrem to a 10-year-old child, based on a 60-year exposure for goose consumption. The highest committed equivalent dose was associated with eating geese—230 mrem over a 55-year exposure to the bone surface.

Table 20. Estimated Radiation Doses From Current Ingestion of Geese and Turtles

* For radionuclides with similar critical organs, the doses from each radionuclide were added together. In the case of data reported as strontium 89/90, the doses were calculated as if the reported values were entirely strontium 90. Furthermore, the dose includes the presence of yttrium 90, which is the decay product of strontium 90.
† Doses are presented for the organ receiving the highest radiation dose and the whole-body dose (the dose delivered to the entire body).

Water Ingestion

A person swimming in the river might be exposed to radiation from incidental ingestion of radionuclides in the surface water. To evaluate potential hazards from contact with radionuclides, ATSDR estimated radiation doses for persons swimming in the river. In deriving these doses, ATSDR used exposure values published by the EPA in its Federal Guidance Report 13; these values are conservative and typically overestimate true exposure (USEPA 1999b). ATSDR assumed that a swimmer might incidentally ingest unfiltered surface water at a rate of 0.1 liters per hour (Stenge and Chamberlain 1995). For swimming frequency, ATSDR assumed an exposure of 1 hour per day for 150 days per year (as noted in the EPA Exposure Factors Handbook). Table 21 provides the results of this evaluation.

Table 21. Estimated Radiation Doses From Current Shoreline Recreational Activities for the Clinch River

* Doses are presented for the organ receiving the highest radiation dose and the whole-body dose (the dose delivered to the entire body). For organs receiving the highest dose, ATSDR estimated the committed equivalent dose over 70 years. For doses to the whole body, ATSDR estimated the committed effective dose to age 70. For the radionuclides with similar critical organs, the doses from each isotope were added together. In the case of data reported as strontium 89/90, the doses were calculated as if the reported values were entirely strontium 90.
† Background locations include areas above Melton Hill Dam, above the confluence of the Tennessee River and the Clinch River, Emory River, and streams that feed into the Clinch River. The background dose represents the average radiation dose at these background locations.
‡ The critical organ for incidental ingestion of Clinch River water is the lower large intestinal wall.
§ The dose is too low to be significant.

The analyses indicated that the committed effective dose received by the whole body in the study area of 0.13 mrem is about 3 times higher than the dose for background locations (0.4 mrem). The critical organ for exposure from incidental ingestion of surface water depended on the radionuclide that was ingested. As would be expected, however, the doses to the bone surface of up to 2.8 mrem were higher (by about two orders of magnitude) than those for skin (up to 0.006 mrem).

External Radiation: Contact With Sediment and Surface Water

To evaluate potential hazards from contact with radionuclides in sediment and surface water, ATSDR estimated radiation doses for persons who might walk along the shoreline and swim in the river. In deriving these doses, ATSDR used exposure values published by the EPA in its Federal Guidance Report 13; these values are conservative and typically overestimate true exposure (USEPA 1999b). ATSDR presumed that the average recreational users of the Clinch River would be 20-year-old adults and that they would be exposed to a 2-square-meter area of shoreline for 5 hours per day and for 150 days per year. For swimming frequency, ATSDR assumed an exposure of 1 hour per day for 150 days per year (as noted in the EPA Exposure Factors Handbook). Table 21 provides the results of this evaluation.

The analyses included the doses received by the entire body, as well as the estimated radiation doses to the organs that are receiving the highest radiation doses. (The exposures from the shoreline, both from walking and swimming, basically impacted the skin.) The highest estimated dose to the whole body within the study area of 9.4 mrem is associated with walking on sediment along the Clinch River below Melton Hill Dam. Walking on sediment at this location was also associated with the highest committed equivalent dose of 13 mrem to the bone surface.

The data indicate that the dose from walking along the sediment is higher in the study area along the Clinch River (below Melton Hill Dam) and Lower Watts Bar Reservoir than at the background locations. For example, the resulting committed effective dose to the whole body from walking on the sediment in the study area is over 60 times higher than for background locations. Similarly, the radiation dose to the bone is about eight times higher in the study area than in background locations. As one would expect from the amount of skin exposure, swimming in the Clinch River resulted in the highest doses to the skin out of all pathways evaluated. The estimated dose for swimming at background locations (based on average for all background locations) was, however, actually higher than in the study area.

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