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PUBLIC HEALTH ASSESSMENT

WELDON SPRING SITE REMEDIAL ACTION PROJECT
(CHEMICAL PLANT, RAFFINATE PITS, QUARRY)
ST. CHARLES, ST. CHARLES COUNTY, MISSOURI


APPENDIX A: CHEMICAL EVALUATION

Agency for Toxic Substances and Disease Registry (ATSDR) scientists consider several factorsin evaluating environmental sampling data and determining the public health significance ofexposure, including the following: (1) concentration of contaminants on and off a site; (2) sampling design, (3) comparison of site-related contaminants concentrations with backgroundconcentrations, ATSDR health-based comparison values for noncarcinogenic and carcinogenicendpoints, other standard health-based doses, and medical and toxicological information; and (4)community health concerns.

Evaluating sampling design includes reviewing approaches used to find contamination. ATSDRconsiders several factors when determining the contaminants to which people might be exposed:spatial distribution of sampling locations, sampling frequency, concentration changes over time,medium-to-medium differences, and correlation between the selected list of analytic parametersand suspected environmental contaminants.

For each medium of concern, health assessors compare site-related data with background data todecide whether the site is the source of contamination. They use state, regional, or nationalbackground data when local data are not available. High levels of chemicals from native mineraldeposits or other natural sources may influence background levels in local soil and watersignificantly. Background levels could be anthropogenic substances in the environment frommanufactured, non-site sources (e.g., gravel for a road or parking lot). If the maximumconcentration of contaminants exceeds background levels, ATSDR scientist will evaluate theseexposures further.

ATSDR scientist perform preliminary screenings of chemical contaminants at potential andcompleted exposure areas by comparing the maximum chemical concentrations in to chemical-and media-specific ATSDR health-based comparison value. ATSDR scientist use the results ofthis conservative preliminary screening to select contaminants for further evaluation. Thecomparison values include Environmental Media Evaluation Guides (EMEGs), Reference Dose-based Media Evaluation Guide (RMEGs), and Cancer Risk Evaluation Guides (CREGs)developed by ATSDR; and Reference Dose (RfD), Maximum Contaminant Levels (MCLs), andMaximum Contaminant Level Goals (MCLGs) developed by the U.S. Environmental ProtectionAgency (EPA).

EMEGs, RMEGs, and CREGs are media-specific comparison values ATSDR developed to assistscientist in selecting environmental contaminants for further evaluation for potential healthimpacts. EMEGs are based on ATSDR minimal risk levels (MRLs) and factor in body weightand ingestion rates. RMEGs are derived from the EPA oral Reference Dose. EMEGs andRMEGs do not consider carcinogenic effects. CREGs are estimated contaminant concentrationsbased on one excess cancer in a million people exposed over a lifetime. CREGs are calculatedfrom EPA's cancer slope factor.

An EPA RfD is an estimate of the daily exposure to a contaminant that is unlikely to causeadverse health effects. EPA's MCLG is a drinking water health goal. These values includemargins of safety and represent levels where no known or anticipated adverse health effectsshould occur. EPA's MCLs represent contaminant concentrations that EPA deems protective ofpublic health (considering the availability and economics of water treatment technology) over alifetime (70 years) at an exposure rate of 2 liters of water per day. While MCLs are regulatoryconcentrations, MCLGs are not.

These comparison values provide estimates of levels believed to be without adverse healtheffects. These comparison values are extremely conservative and protective of public health, inthat these values are based on daily long-term exposure to chemical doses that are unlikely toresult in adverse health effects. The comparison values are usually derived from animal studiesand occupational exposures. The severity of health effects is related not only to the exposure dosebut to the route of exposure (entry into the body) and the amount of chemical the body absorbs.For those reasons, comparison values used in public health assessments are contaminantconcentrations in specific media and for specific exposure routes. There may be severalcomparison values for a specific contaminant. ATSDR generally selects the comparison valuesthat are calculated using the most conservative exposure assumptions to protect the mostsensitive segment of the population.

Evaluators used the following assumptions to calculate comparison values (EMEGs, CREGs, andRMEGs) used in this public health assessment:

Child Body weight = 16 kilograms (kg)
Water ingestion rate = 1 liter(L)/day
Soil ingestion rate = 200 milligrams (mg)/day
Pica soil ingestion rate = 5000 mg/day
Adult Body weight = 70 kg
Water ingestion rate = 2 L/day
Soil ingestion rate = 100 mg/day
Occupational soil ingestion rate = 500 mg/day

Listing of a contaminant in this public health assessment does not mean exposure to thecontaminant will cause adverse health effects. Rather, the listing of a contaminant indicates thatthe concentration of the contaminant exceeded an ATSDR screening comparison value and thatthe contaminant has been evaluated in further detail using realistic site-specific exposurescenarios with standard health-based doses (MRLs, RfD) that are unlikely to cause anappreciable risk to health as well as to other medical and toxicological health guidelines.

APPENDIX B: TOXICOLOGICAL IMPLICATIONS

Uranium

The following is a brief description of the health effects of ingested uranium. Approximately 0.2-5% of ingested uranium transfers to the body; the body excretes the remainder. The major sites ofuranium deposition are bone and kidneys. The health effects of uranium in the bone results fromits radioactive decay. Appendix C, Radiation Evaluation, describes the cumulative health effectsof uranium and the other radionuclides detected in areas at the chemical plant site. The effects ofuranium in the kidneys result primarily from its binding to certain kidney structures (renal tubularcells), causing the tubular cells to die. The death of renal tubular cells can lead to kidney damage.One to three micrograms uranium per gram (µg/g) of renal tissue is the threshold fornephrotoxicity. To protect the public, it is recommended not to exceed a kidney dose of 0.1 µg/g,which corresponds to a total uranium content of 31 µg for 2 kidneys in a standard man (70kilograms, or 154 pounds).

In an actual case for an acute exposure to uranium at a kidney dose of 86.717 mg, initial effectsincluded dizziness, nausea, anorexia, abdominal pain, diarrhea, tenesmus, and pus and blood inthe stool.

Thorium

Studies on thorium workers have shown that breathing thorium dust may cause an increasedchance of developing lung disease and cancer of the lung or pancreas many years after exposure.Changes in the genetic material of body cells have also occurred in workers who breathedthorium dust. Liver diseases and effects on the blood have appeared in people who have receivedthorium injections for special X rays. Many types of cancer have also occurred in these peoplemany years after the thorium injections. Since thorium is radioactive and may be stored in bonefor a long time, bone cancer is also a potential concern for people exposed to thorium. Animalstudies have shown that breathing thorium may cause lung damage. Other animal studies suggestthat drinking massive amounts of thorium can cause death from metal poisoning. The presence oflarge amounts of thorium in the environment could result in exposure to more hazardousradioactive decay products of thorium, such as radium and thorium. Thorium is not known tocause birth defects or infertility.

Nitroaromatics

The understanding of nitroaromatics' effects on humans is based on the evaluation of exposure byway of inhalation of pure product during manufacturing activities. The concentrations in soil areobviously many orders of magnitude smaller that those workers would have encountered in theproduction facilities, and the potential exposures from soil are short-term and infrequent.

The first thorough documentation of the toxic effects of 2,4,6-trinitrotoluene (TNT) occurredduring large-scale production of TNT during World War I. Many workers in munitions factoriesdied of TNT intoxication. With application of hygienic precautions (such as periodic hand-washing, routine changes of protective clothing, and respiratory protection) to prevent inhalationexposure, fatalities decreased. Liver disease and aplastic anemia were the primary resultingcauses of death. Absorption of TNT through the skin or lungs can produce cyanosis (lack ofoxygen-carrying capacity of the blood), severe liver damage, anemia, cataract formation, centralnervous system effects, and kidney damage.

Long-term, low-dose TNT-ingestion studies have been carried out in mice, rats, and dogs.Hematological signs of anemia and liver damage appeared at higher doses in mice and rats over a24- to 26-week period. When dogs were fed TNT over 26 weeks, liver damage appeared at alldosage levels. Increased incidence of urinary bladder papilloma and carcinoma resulted in femalerats. Using this study, EPA classified TNT as a Group C chemical (possible human carcinogen).It should be emphasized, however, that these effects were the result of long-term exposure byingestion, not of such infrequent, incidental exposures that site trespassers would likelyencounter.

There is no information available on the health effects of 1,3,5-trinitrobenezene (TNB). Becauseof its structural similarity to 1,3-dinitrobenzene (DNB), assumptions are that its health effectsmight be similar to those caused by DNB. Data about health effects after exposure to DNB arelimited. Six workers exposed to an unknown concentration of DNB dust developed cyanosis thatbegan within 1 day of exposure and lasted 2 weeks. Health effects also included anemiaaccompanied by palpitations, dizziness, and fatigue. Anemia persisted an average of three days.Follow-up examinations over a 10-year period did not reveal any adverse health effects. Well-documented health effects in animals include toxic effects resulting in death and pathologicaleffects on the liver, spleen, and testes. These effects resulted in weight loss, anemia, anddecreased reproductive capacity. There was some evidence of increased toxicity in older animals.A 16-week study of rats' ingestion of DNB in drinking water detected both splenic and testiculareffects. High uncertainty factors apply because of lack of long-term studies. DNB is considered aClass D chemical (not classified as to human carcinogenicity) because of lack of informationabout its carcinogenicity. Because of the uncertainty of using DNB studies to develop guidelinesfor TNB, additional safety assumptions were included in the calculations. As is the case withTNT, the effects noted are for long-term ingestion, not the infrequent, incidental exposure thattrespassers would experience.

Lead

The effects of lead once it is in the body are the same, regardless of how it enters the body.Exposure to lead is especially dangerous to unborn children, infants, and young children. Forinfants and young children, lead ingestion has been shown to decrease intelligence scores, slowgrowth and cause hearing impairment. Exposure to high lead levels can cause brain and kidneydamage in both children and adults. There has been no demonstration of lead's ability to causecancer in humans. To date, workplace studies do not provide enough information to determineworkers' risk of cancer from lead exposure. However, some research with rats and mice hasshown tumors will develop in subjects fed large doses of lead [30]. The concentrations of lead insome soil samples at the training area are elevated to the point where exposure may reasonablybe considered a hazard.

Polychlorinated Biphenyls

EPA has classified polychlorinated biphenyls (PCBs) as probable human carcinogens. Humanstudies show that acne-like rashes can occur as a result of occupational exposures to PCBs. Otherstudies of occupational exposure suggest that PCBs might cause liver cancer. Reproductive anddevelopmental effects may result from occupational exposure. It must be emphasized that theseeffects are not definitively proven.

Asbestos

The U.S. Department of Health and Human Services has determined that asbestos is a knowncarcinogen. Information on health effects of asbestos in humans comes from studies of workersexposed to high levels of asbestos in the workplace. These worker studies revealed increasedincidence of lung cancer and mesothelioma. These diseases develop over a period of years, andboth are usually fatal. There is also evidence to suggest increased incidence of other cancers (e.g.,cancers of the stomach, intestines, esophagus, pancreas, and kidneys). Members of the public exposed to lower levels of asbestos may be at increased risk for cancer, but the risk is usuallysmall and difficult to verify. Exposure via inhalation also poses the risk of asbestosis, scarring ofthe lungs. This disease causes breathing difficulty and decreases blood flow in the lungs.Asbestosis is a serious illness, in most cases resulting from exposure to high levels of asbestosvia inhalation. There is little evidence that exposure via consumption of asbestos results inadverse health effects.

APPENDIX C: RADIATION

APPENDIX C1: Radiation Overview
APPENDIX C2: Radiation Exposure and Dose Standards
APPENDIX C3: Radiation Doses at the Chemical Plant Site

APPENDIX C1: Radiation Overview

Because radiation has been found at the chemical plant site and adjacent areas and because manypeople are unfamiliar with radiologic terms, a brief overview is presented here. All matter iscomposed of atoms. An atom is the smallest particle of a chemical element that can be dividedand still retain the characteristic properties of the element. The basic components of an atom areprotons, neutrons, and electrons. The quantity of those particles combined with their energy statedetermine the stability or instability of an atom. If an atom is unstable, it can break down into amore stable atom. When that happens, the unstable atom ejects either a particle or a knownamount of energy, and the atom develops greater stability. That process is radioactive decay. Theejected particle or energy is the radiation; the atom that decays is a radionuclide [1].

The ejected particle or energy may be one of three types of radiation: alpha particles, betaparticles, or gamma photons. When radioactive decay occurs, the radiation produced can interactwith nearby objects. During that interaction, energy may be transferred or absorbed from theejected radiation to the object of interaction. Radiation dose, measured in rad or gray, is theamount of energy transferred from the radiation to the object. It is believed that the three types ofradiation affect people with different degrees of severity. The alpha particle has the greatestbiological effect, the beta particle has a mid-range biological effect, and the gamma has the leastbiological effect. Therefore, other units of measure, rem or sievert, express radiation dose topeople and incorporate the biological effectiveness of each radiation type [2].

The penetrating gamma rays and other types of shorter-range radiation particles interact withmaterial and cause ionizations. The number of ionizations that occur in a given volume of airindicate the amount of radiation present in the nearby area. By counting the number ofionizations in a gamma radiation detector, an investigator can determine whether gamma-emitting radionuclides are present [3].

When ionizing radiation travels through the body, it can change the structure of molecules in thebody [2]. The changed molecular structure may have the following results:

  • restorate its original structure,
  • lead to impaired physiological function,
  • lead to a different physiological function, or
  • change the genetic code for future cells, tissues, and organs [4].

Cells that repair their molecular structure behave as normal, unaffected cells in the body [2].Cells that do not repair their molecular structure (e.g., those with damage to the nucleus) canhave an impaired or different function [4]. That is, unrepaired molecules within a cell can lead toabnormal cellular behavior within the body. If the impaired function of a cell is severe enough, itcan lead to the death of that cell (i.e., cellular death) [2, 5, 6].

At moderate to high doses of radiation (acute exposure), a number of biological effects--rangingfrom vomiting and fatigue to changes in the blood and cellular death--are observed [2, 4]. Thehealth effects caused by moderate doses (acute exposures) are generally observed with gammadoses of 25,000 to 50,000 millirads (mrads) [i.e., 25,000 to 50,000 millirem (mrem), which isvery large when compared with the public exposure limit of 100 mrem/year] [2]. At high doses,the number of cell deaths may overwhelm the body, leading to the death of the individual [2].Acute-exposure effects at high doses generally begin to occur at gamma doses of 200,000 mrads(i.e., 200,000 mrem) [2].

The radiation exposures at the chemical plant site and adjacent areas are low-level, chronicexposures. At low doses of radiation (chronic exposure), the body can recover from the death ofcells caused by impaired physiological function, but those cells that are not repaired and survivewith an impaired or different function can be a source of mutations [4]. Cancer is believed to bethe predominant health effect associated with chronic radiation exposures [2, 6]. However,epidemiological methods show increased risks of cancer on the order of 1 in 10 to 1 in 10,000(1/10 to 1/10,000) for 1,000 to 10,000 mrad (i.e., 1,000-10,000 mrem) exposures [7]. Thelowest level of risk that can be attributed to a radiation exposure is 1.40 (i.e., a 40% relativeexcess); therefore, no direct epidemiological method exists to link cancer incidence withradiation exposures less than 10,000 mrem [7]. For the purposes of radiation protection, it isassumed that the incidence of cancer increases linearly as radiation doses increase [2, 7].

APPENDIX C2: Radiation Exposure and Dose Standards

The Agency for Toxic Substances and Disease Registry (ATSDR) has evaluated contaminantsdiscussed in subsequent sections of this appendix to determine whether exposure to them haspublic health significance. To select contaminants for discussion, ATSDR considers severalfactors: contaminant concentrations compared with health-based values, potential pathways ofexposure, and community health concerns.

ATSDR's approach to evaluating radionuclides and other radioactive materials differs from theagency's approach to evaluating nonradioactive hazardous materials. Because of the additiveeffects of radiation on the human body, investigators calculate the dose from radionuclide orradioactive materials for all exposure routes. Once they have determined the doses by variousroutes, they calculate a total dose.

This public health assessment contains discussions of health effects that may result fromexposures to site contaminants. Chemicals released into the environment do not always result inhuman exposure. People can be exposed to a chemical contaminant only if they breathe, ingest,or touch the contaminant. If radioactive materials are present, individuals can experienceexposure by just being near contaminated water, soil, or air (i.e., irradiation by external sources)[2, 8].

Several factors influence exposure: the exposure concentration (how much), the duration ofexposure (how long), the route of exposure (breathing, eating, drinking, skin contact, orproximity to gamma-emitting radionuclides), and the multiplicity of exposure (combination ofcontaminants). Once a person is exposed, individual characteristics--age, sex, nutritional andhealth status, lifestyle, and family traits--influence how the contaminant is absorbed (taken up bythe body); metabolized (broken down by the body); and excreted (eliminated from the body).When the contaminant is a radionuclide, the same factors and individual characteristics apply,along with exposure via external irradiation, in determining the health effects.

ATSDR researched the scientific literature to determine the possible health effects ofradionuclides. For information about radiological hazards, ATSDR reviewed the InternationalCommission on Radiological Protection (ICRP) publications. ICRP's basic responsibility is toprovide guidance in matters of radiation safety by preparing recommendations on the basicprinciples of radiation protection. The recommendations are published in reports and variousjournals (e.g., publications of the ICRP).

For purposes of radiation safety standards, ICRP recognizes three categories of exposure:occupational, public, and medical. For members of the public, ICRP recommends an effective-dose limit of 1 millisievert (mSv) [100 millirem (mrem)] above background in a year [9]. (Thatlimit is for the purposes of radiation protection only. No adverse health effects have been directlyattributed to a radiation exposure at that level.) ICRP does not make recommendations formedical exposures. However, the commission does recommend that people receive onlynecessary exposures and that exposures be limited to the minimum dose necessary for medicalbenefit to the patient.

The current ICRP recommendations specify an annual limit on intake, defined as the amount ofradionuclide that delivers the occupational effective-dose limit from ingestion or inhalationexposures. ICRP staff members use the average career span of an occupationally exposedperson--50 years--to calculate the occupational annual limit of intake. ICRP recommends usingthe average lifetime of an individual (70 years), and the public's effective-dose limit, 1 mSv (100mrem) per year, to determine the public's annual limit of intake by way of ingestion or inhalation.

The probability and severity of health effects increase as exposure to radiation increases,although exposure to background levels of radiation (i.e., those levels naturally occurring in theenvironment) are thought not to produce noticeable health effects in humans [7]. Thus, forradiation protection purposes, the dose resulting from radiation exposures above background iscalculated as an indicator of potential health effects.

In evaluating the data on radioactive contaminants for this public health assessment, ATSDRcould not calculate annual background values in each medium at each exposure point underinvestigation. Thus, to calculate radiation doses from exposure to a contaminated medium,ATSDR used the maximum concentration detected in that medium. The concentrations arevalues transmitted from the Department of Energy or the Department of the Army. In caseswhere needed data were not in the database, ATSDR used maximum concentrations found inpublished documents. One exception was the case of inhaled radionuclides. For inhaledradionuclides, ATSDR modified published dose estimates instead of using measured airconcentrations to calculate inhalation doses.

APPENDIX C3: Radiation Doses at the Chemical Plant Site

Introduction

Radiation dose is usually divided into two categories, internal and external. Internal doses resultfrom exposure to radioactive sources inside the body; external doses result from exposure toradioactive sources outside the body [2].

Whether an exposure contributes to a person's internal or external dose depends primarily on thetype of radiation to which a person is exposed. Most alpha particles cannot travel far and areprevented from entering the body by the body's dead layer of skin. Because the dead layer of theskin--the epidermis--can stop the alphas particles, the particles do not contribute a biologicallysignificant dose. Therefore, exposures to alpha particles originating outside the body would notcontribute to a person's external dose; however, if an alpha particle source is deposited within thebody, it could (depending on its location) contribute to a person's internal dose. Gamma photonscan travel long distances and can easily penetrate and irradiate body tissues; therefore, people canbe exposed to gamma photons through both external or internal sources. Beta particles also maybe responsible for both internal and external doses, but they do not penetrate body tissue as easilyas gamma photons, limiting the dose from external sources. The total dose is the sum of aperson's external and weighted internal doses [2].

For internally deposited radionuclides, the Agency for Toxic Substances and Disease Registry's(ATSDR's) quantitative evaluation of exposures at the chemical plant site and nearby areasconsidered media-specific and activity-specific rates for soil and water ingestion and for fish,wildlife, and vegetable (e.g., corn) consumption. ATSDR staff calculated the radiation doses byfirst estimating a person's annual intake of radioactive material from an exposure scenario. Theythen multiplied the annual intake rate (i.e., exposure) of a particular medium by its maximumconcentrations of radionuclides found in nearby areas. Finally, they compared the estimatedannual intake to the public's annual limit on intake (ALI)1, which infers the annual radiation dose to a hypothetical individual.

For radiation dose resulting from inhalation of radioactive material, ATSDR staff modifiedexisting inhalation dose estimates to correspond to the exposure scenarios in this public healthassessment. They did this because the Department of Energy (DOE) air data transmitted toATSDR were not compatible with the computer formats used by the ATSDR Federal FacilitiesInformation Management System.

For external exposures at the chemical plant site, ATSDR staff assumed the primary externalsource at chemical plant site and associated areas is soil and that the soil is evenly contaminatedthroughout to a depth of 15 centimeters. ATSDR's quantitative evaluation of exposure to adultsconsisted of multiplying the gamma ray exposure factor for each radionuclide found in the soil byits maximum concentration and the time spent in the contaminated area (see exposure scenarios).

Radionuclide Concentrations in Media

The remedial investigation for the Chemical Plant Area indicates that the site is contaminatedwith uranium and possibly thorium. This investigation shows that concentrations of uranium andthorium are higher than expected background in some areas, but that subsequent decay productsin the same areas are not as high, indicating uranium and thorium contamination.

In soils, ATSDR assumed, for the Uranium-238 (U-238) decay series, that U-238 was inradioactive equilibrium with its next three decay products [Thorium-234 (Th-234), Protactinium-234m (Pa-234m), and Uranium-234 (U-234)]; and that the Thorium-230's (Th-230) activity wasfour times as great as the activity of its successive decay products, which were all in radioactiveequilibrium with each other [Radium-226 (Ra-226), Radon-222 (Rn-222), Polonium-218 (Po-218), Lead-214 (Pb-214), Bismuth-214 (Bi-214), Lead-210 (Pb-210), Bismuth-210 (Bi-210),Polonium-210 (Po-210), and Lead-206 (Pb-206)]. One exception to this assumption is at theConservation Areas where ATSDR investigators did not assume the 4:1 ratio because they knewthe actual Th-230 concentration.

For the Uranium-235 (U-235) decay chain, ATSDR assumed that U-235 was in radioactiveequilibrium with its immediate decay product, Thorium-231 (Th-231), and that the subsequentdecay products (of the U-235 contamination) do not have quantities sufficient for assessment.For the Thorium-232 (Th-232) decay chain, ATSDR assumed that all of the decay products werein radioactive equilibrium with Th-232 [note that Polonium-212's (Po-212) concentration is 64%of Th-232's and that Thallium-208's (Tl-208) concentration is 36% of Th-232's because of thenatural branching ratio in the Th-232 decay scheme]. Table C.1 (page C-9) shows the maximumradionuclide soil concentrations at the chemical plant site and nearby areas.

However in water, fish, and wild game, radioactive equilibrium for the decay chains may notexist because there are different water solubilities, hydrological conditions, and bio-availabilityuptake and retention mechanisms. Therefore, in these media, ATSDR evaluated only the dosecontribution from the measured radionuclide and not the contribution from other members of thedecay chain. Table C.2 (page C-10) shows the maximum radionuclide concentrations in water,fish, and wild game at the chemical plant site and nearby areas.

For inhalation, ATSDR did not calculate doses based on concentrations of radionuclides in air,but rather calculated them based on published results of the Weldon Spring Historical DoseEstimate [11].

The time frames of interest for this health assessment include past (1969-1982), present (1983-1995), and future (1996 and beyond) exposures. The historical dose estimates also covered threetime periods: 1957-1966, 1967-1969, and 1969-1982. ATSDR based its inhalation dose on theresults of the 1969-1982 dose estimates. The inhalation doses for that time frame are based onairborne resuspension of radioactive particles and are estimated to be 0.2 millirem per year(mrem/yr) to the maximally exposed individual (here taken as a worker in the County ExtensionCenter exposed for 8 hours per day, 5 days per week, for 50 weeks per year [2,000 hours peryear]).


TABLE C.1.

MAXIMUM REPORTED OR CALCULATED RADIONUCLIDE SOIL CONCENTRATIONS
RadionuclideMaximum Soil Concentration (pCi/g)1, a
Training AreaConservation Areas
U-238229,5303,020
Th-23429,5303,020
Pam-23429,5303,020
U-23429,5303,020
Th-230160.410,100
Ra-226240.1430
Rn-22240.1430
Po-21840.1430
Pb-21440.1430
Bi-21440.1430
Po-21440.1430
Pb-21040.1430
Bi-21040.1430
Po-21040.1430
Th-2322450240
Ra-228450240
Ac-228450240
Th-228450240
Ra-224450240
Pb-212450240
Bi-212450240
U-23521,38849.7
Th-2311,38849.7
a pCi/g = picocurie per gram.
1. To convert pCi/g to becquerel per gram (Bq/g), multiply by 0.037.
2. Values retrieved from the Weldon Spring Site Remedial Action Project database andtransmitted to the Agency for Toxic Substances and Disease Registry or taken from publishedreports. All other values were calculated based on the radionuclide equilibrium assumptionstated in the text for soil. Only one exception exists which is in the case of Thorium-230's soilconcentration at the Conservation Areas. In that case, the concentration was reported in adocument published by the Department of Energy.


TABLE C.2.

MAXIMUM RADIONUCLIDE CONCENTRATIONS IN OTHER MEDIA
RadionuclideQuarry or Raffinate PitsConservation Areas1CropsOff-Site2Private Wells
Surface Water (pCi/L)3, aSurface Water
(pCi/L)3, a
Fish
(pCi/g)3, a
Wild Game (pCi/g)3, bCorn
(pCi/g)3, b
Ground-water (pCi/L)3, a
U-2382580 500.00 0.936 0.00n.a. n.a.
U-2342430 378.00 0.892 0.146n.a. n.a.
Th-230756 8.80 0.03 n.a.1.49 45.1
Ra-226164 6.42 0.15 n.a.0.24 10.3
Pb-2104.1 83.20 n.a. n.a.n.a. n.a.
Po-2101.3 2.30 n.a. n.a.n.a. n.a.
Th-23236.3 2.20 0.00 n.a.0.193 8.5
Ra-22832 15.00 n.a. n.a.0.836 4.0
Th-2283.7 2.20 n.a. n.a.0.221 n.a.
U-235322 38.00 0.035 0.005n.a. n.a.
Ac-2275 12.7 n.a. n.a.n.a. n.a.
a      pCi/L = picocurie per liter.
b      pCilg = picocurie per gram.
1.      Values retrieved from the Weldon Spring Site Remedial Action Project database and transmitted to the Agency for Toxic Substances and Disease Registry (ATSDR).
2.      ATSDR Weldon Spring database does not contain any data appropriate to evaluateexposure to radionuclides through ingestion of water from off-site private wells. However,ATSDR received off-site well monitoring data from Missouri Department of Health(unpublished data), and ATSDR used the maximum radionuclide concentrations from thisdata set to evaluate exposures to radionuclides in off-site wells.
3.      To convert picocurie (pCi) to becquerel (Bq), multiply by 0.037.
n.a.      denotes radionuclide not found in medium.

Exposure Scenarios and Exposure Factors

This section presents ATSDR's method of determining an individual's exposure to radioactivematerials. Exposure to radioactive materials is defined in this section as the total contact one haswith or spends in close proximity to radioactive materials in a year.

For each location where person(s) may have exposure to or were potentially exposed toradioactive materials, ATSDR describes the exposure scenario. The exposure scenario includesthe location, area, or site of the potential exposure; the activity that people engage in that canresult in potential exposure(s); the frequency and duration of the activity, the identification of thecontaminated media and the radioactive contaminants; and activity-based, media-specificexposure rates. ATSDR staff members use this information to calculate an individual's exposureto radioactive materials and the resulting radiation dose.

ATSDR believes exposure to radioactively contaminated material may have occurred in severallocations--Quarry or Raffinate Pits, Weldon Spring Training Area, Conservation Areas, off-siteprivate wells, and Francis Howell High School--and in crops grown nearby. The followingexposure scenarios contain the agency's rationale and calculation of activity-based, media-specific exposure quantities.

Quarry or Raffinate Pits

Swimmers Scenario

At the Quarry or Raffinate Pits, community members identified swimmers in the Quarry orRaffinate Pits as a potentially exposed population. The swimmers might have been exposed tosoil (ATSDR's Federal Facilities Information Management System database contains no valuesfor soil contamination at the Quarry or Raffinate Pits), surface water, and external radiation whileswimming.

Based on anecdotal reports by concerned community members, ATSDR believes that in the past,swimmers swam in the Quarry or Raffinate Pits seven times per year for two hours perswimming event. ATSDR used an incidental water ingestion rate of 25 milliliters (mL) perswimming event (an estimate of 1/3 mouthful of water). ATSDR also determined a dosemodifying factor (i.e., the inhalation scaling factor), which scales the extension center worker'sinhalation dose to appropriate levels to account for possible inhalation exposures to swimmer inthe Quarry or Raffinate Pits. Note: The scaling factor accounts only for the amounts of timepersons spent in the area and does not account for differences in breathing rates.

Surface Water:

    7 swims/year (yr) x 25 mLwater/swim = 175 mLwater/yr or 0.175 Lwater/yr

External irradiation:

    7 swims/yr x 2 hours (hrs)/swim = 14 hrs/yr

Weldon Spring Training Area

U.S. Military Reservist Scenario

At the Training Area, ATSDR identified one potentially exposed population: past U.S. militaryreservists. The U.S. military reservists might have been exposed to soil, air, and externalradiation while performing reserve field training exercises.

ATSDR staff members believe that, in the past, reservists performed field exercises for sevendays per week, 24 hours per day, 2 weeks per year. The reservists probably performed fieldactivities (i.e., in dusty and soil covered areas) with the potential for above average incidental soilingestion rates. Therefore, ATSDR used the incidental soil ingestion rate of 500 milligrams (mg)per day. ATSDR also determined a dose modifying factor (i.e., the inhalation scaling factor),which scales the extension center worker's inhalation dose to appropriate levels to account forpossible inhalation exposures to the reservists. Note: The scaling factor accounts only for theamounts of time persons spent in the area and does not account for differences in breathing rates.

Soil:

    2 weeks/yr x 7 days/week x 500 mgsoil/day = 7,000 mgsoil/yr or 7 gsoil/yr

External irradiation:

    14 days/yr x 24 hrs/days = 336 hrs/yr

Inhalation Scaling Factor:

    (14 hrs/yr) / (2,000 hrs/yr) = 14/2,000

Conservation Areas

At the Conservation Areas, the ATSDR considered the three major activities that occur in theareas and the exposures that are most likely to occur: fishing, hunting, and hiking.

Anglers Scenarios

Anglers at the Conservation Areas might have been exposed to surface water, soil, air, andexternal radiation while fishing. The anglers might also have been exposed by eating their catch.

The ATSDR used the annual fishing rate at the Conservation Areas of 3.5 days per year andbelieves anglers may fish 10 hours per fishing trip. ATSDR also believes the anglers might haveaccidentally ingested 0.1 liters (L) of surface water and incidentally ingested 0.1 grams (g) of soilper fishing trip. ATSDR also assumed anglers caught four fish per fishing trip, consumed all oftheir catch; and the average fish weighs 1 pound (454 grams). ATSDR also determined a dosemodifying factor (i.e., the inhalation scaling factor), which scales the extension center worker'sinhalation dose to appropriate levels to account for possible inhalation exposures to the anglers.Note: The scaling factor accounts only for the amounts of time persons spent in the area and doesnot account for differences in breathing rates.

Surface water:

    3.5 fishing trips/yr x 0.1 Lwater/fishing trip = 0.35 Lwater/yr

Soil:

    3.5 fishing trips/yr x 0.1 gwater/fishing trip = 0.35 gwater/yr

Fish:

    3.5 fishing trips/yr x 4 fish/trip x 100%(consumption) x 454 g/fish = 6,356 gfish/yr

External Irradiation:

    3.5 fishing trips/yr x 10 hrs/fishing trip = 35 hrs/yr

Inhalation Scaling Factor:

    (35 hrs/yr)/(2,000 hrs/yr) = 35/2,000

Hunters Scenarios

Hunters at the Conservation Areas might have been exposed to soil, air, and external radiationwhile hunting. The hunters might also have been exposed by eating their catch.

This exposure scenario assumes that (1) persons hunted 10 times per year for 10 hours per visit,(2) the hunter always catches wild game at a yield of 1.25 catches per visit, (3) the hunter eats alledible portions of the animal he/she catches, and (4) the average weight of the animals caught is28.6 pounds [13 kilograms (kg)]. Hunters might also have incidentally ingested soil at a rate of100 mg per hunting trip. ATSDR also determined a dose modifying factor (i.e., the inhalationscaling factor), which scales the extension center worker's inhalation dose to appropriate levels toaccount for possible inhalation exposures to the hunters. (Note: The scaling factor accounts onlyfor the amounts of time persons spent in the area. It does not account for differences in breathingrates.)

Soil:

    10 hunting trips/yr x 100 mgsoil/hunting trip = 1,000 mgsoil/yr or 1 gsoil/yr

Wild game:

    10 hunting trips/yr x 1.25 game/trip x 13 kg/game x 100%(consumption) = 162.5 kggame/yr

External irradiation:

    10 hunting trips/yr x 10 hrs/hunting trip = 100 hrs/yr

Inhalation Scaling Factor:

    (100 hrs/yr)/(2,000 hrs/yr) = 100/2,000

Hikers Scenarios

Hikers at the Conservation Areas might have been exposed to soil, air, and external radiationwhile hiking.

ATSDR believes hikers visit the site 10 times per year for 4 hours per visit and might haveincidentally ingested soil at a rate of 100 mg per outing. ATSDR also determined a dosemodifying factor (i.e., the inhalation scaling factor), which scales the extension center worker'sinhalation dose to appropriate levels to account for possible inhalation exposures to the hikers.Note: The scaling factor accounts only for the amounts of time persons spent in the area. It doesnot account for possible differences in breathing rates.

Soil:

    10 hikes/yr x 100 mgsoil/hike = 1,000 mgsoil/yr or 1 gsoil/yr

External irradiation:

    10 hikes/yr x 4 hrs/hike = 40 hrs/yr

Inhalation Scaling Factor:

    (40 hrs/yr)/(2,000 hrs/yr) = 40/2,000

Off-Site Private Wells

Off-Site Private Owner Scenario

ATSDR identified an exposed population as those persons who drank water from off-site privatewells and breathed resuspensed air in the past.

ATSDR believes that persons may have consumed well water, via ingestion of drinking water orwater-based foods, at a rate of 2 L per day for 365.25 days per year in the past. ATSDR alsodetermined a dose modifying factor (i.e., the inhalation scaling factor), which scales theextension center worker's inhalation dose to appropriate levels to account for possible inhalationexposures to the off-site private well owners. In this case, ATSDR assumed the well usersbreathed the air 24 hours every day. Note: The scaling factor accounts only for the amounts oftime persons spent in the area and does not account for possible differences in breathing rates.

Groundwater:

    365.25 days/yr x 2 Lwater/day = 730.5 Lwater/yr

Inhalation Scaling Factor:

    (24 hrs/day x 365.25 days/yr) / 2,000 hrs/yr = 8,766/2,000

Francis Howell High School

Student and Staff Scenarios

At the Francis Howell High School, inhalation was the most significant route of exposureidentified by ATSDR staff. Because ATSDR could not fully integrate and use the DOE air datafor the exposure calculation at the high school, ATSDR used dose estimates for the staff andstudents from the Weldon Spring Historical Dose Estimate [11] publication.

ATSDR staff members believe that, in the past, people might have been exposed to radioactiveairborne particles 8 hours per day, 5 days per week, 48 weeks per year (which includes summerschool) [11].

Crops Grown Nearby

Consumers of Corn

Based on concerns from members of the public, ATSDR identified an exposed population asthose persons who consume corn grown near the Weldon Spring Site. The EPA Exposure FactorsHandbook reports that persons may consume corn at a rate of 0.82 pounds per week.

Corn:

    (52 weeks/yr) x (0.82 pounds/week) x (454 g/pound) = 19,359 gcorn/yr

Radiation Dose: Internal and External

Radiation dose is the measure of energy deposited in material from ionizing radiation, and it hasunits of energy per unit mass. Radiation dose is usually divided into two categories, internal andexternal. Internal doses result from exposure to radioactive sources inside the body; externaldoses result from exposure to radioactive sources outside the body.

Internal Radiation Dose

The International Commission on Radiological Protection (ICRP) recommendations specify anAnnual Limit on Intake2 (ALI), defined as the amount of a radionuclide that delivers theoccupational effective-dose limit, 20 millisievert (mSv) [2,000 millirem (mrem)] per year, fromingestion or inhalation exposures. The ALI is calculated using the average career span of anoccupationally exposed person : 50 years. ICRP recommends using the average lifetime of anindividual (70 years) and the public's effective-dose limit, 1 mSv (100 mrem) per year, todetermine the public's annual limit on intake (PALI) by way of ingestion or inhalation.

These calculations are based on remarks contained in ICRP Publication 26, that using anintegration period of 50 years versus 70 years is adequate for members of the public because thecorrection factor could be no more than 70/50 (1.4). Therefore to be conservative on behalf of thepublic's health, ATSDR applied the 1.4 correction factor to fifty-year doses to project seventy-year doses.

The following is the general formula for the ALI:

    ALI = annual effective dose limit (2,000 mrem/yr) / committed effective dose in 50 years

and for exposures to the public:

    PALI = annual effective dose limit (100 mrem/yr) / committed effective dose in 70 years

    PALI = ALI/(20 x 1.4)

The internal radiation dose a person receives is proportional to the amount of radionuclides in theperson's body. By calculating the PALIs, ATSDR determined how much of a particularradionuclide delivers 100 mrem/year to the average person. By manipulating that, ATSDR caninfer doses for the proposed exposure scenarios at the chemical plant site. Estimated internalradiation doses for each radioactive contaminant and its progeny follows.

Intake of Radionuclides

At the chemical plant site, the intake of radionuclides consisted of two routes of exposure (i.e.,entrances into the body); ingestion and inhalation.

To determine the total amount of internal radionuclide intake, ATSDR multiplied the annualingestion or consumption rate by the maximum concentration (or the calculated concentrationbased on equilibrium assumptions) of radionuclides for each medium to establish the amount ofeach radionuclide ingested per year in each medium. After the annual amounts of ingestedradionuclides in each medium were calculated, the amount from each medium for eachradionuclide was added to yield the total annual amount of each radionuclide ingested (presentedin Table C.3, page C-20).

ATSDR health physicists then calculated the PALI for each potentially ingested radionuclide.After determining the annual intake of radionuclides and each PALI, ATSDR health physicistscalculated an internal radiation dose based on each exposure scenario. Table C.4 contains theresults (page C-21).


TABLE C.3.

TOTAL ANNUAL INTERNAL INTAKE OF RADIONUCLIDE THROUGH INGESTION
RadionuclideQuarry or Raffinate PitsTraining AreaConservation AreasOff-site
private wells
Crops
SwimmerU.S.Military ReservistAnglerHunterHikerOwner of wellCorn
U-238177,600260110110n.a.n.a.
Th-234n.a.7,60039110110n.a.n.a.
U-234167,600250990110n.a.n.a.
Th-2304.9401403703701,2001100
Ra-2261.110411616280170
Pb-214n.a.105.61616n.a.n.a.
Bi-214n.a.105.61616n.a.n.a.
Pb-2100.026106.61616n.a.n.a.
Bi-210n.a.105.61616n.a.n.a.
Po-2100.0084105.61616n.a.n.a.
Th-2320.231103.18.88.8230140
Ra-2280.2071103.38.88.8110600
Ac-228n.a.1103.18.88.8n.a.n.a.
Th-2280.0241103.18.88.8n.a.160
Ra-224n.a.1103.18.88.8n.a.n.a.
Pb-212n.a.1103.18.88.8n.a.n.a.
U-2352.136011355.2n.a.n.a.
Th-231n.a.3601.85.25.2n.a.n.a.
Ac-2270.032n.a.0.2n.a.n.a.n.a.n.a.
Bi-212n.a.1103.18.88.8n.a.n.a.
    Above values are in becquerel per year (Bq/yr).
    n.a. denotes intake not applicable because this radionuclide was not measuredin contaminated media nor was its concentration estimated based onequilibrium conditions.


TABLE C.4.

ANNUAL INTERNAL RADIONUCLIDE DOSE THROUGH INGESTION
RadionuclideAnnual Limit on Intake
(Bq)a
Public Annual Limit on Intake
(Bq)a
SwimmerU.S. Military Reservist
(mrem/yr)b
Angler
(mrem/yr)b
Hunter
(mrem/yr)b
Hiker
(mrem/yr)b
Owner of well
(mrem/yr)b
Consumers of Corn
(mrem/yr)b
U-2388 x 10 530,000---25.30.90.40.4n.a.n.a.
Th-2344 x 10 6200,000n.a.3.8---------n.a.n.a.
U-2347 x 10 530,000---25.30.83.30.4n.a.n.a.
Th-2303 x 10 520,000---0.20.71.91.86.15.3
Ra-2269 x 10 44,000---0.31.00.40.47.04.3
Pb-2141 x 10 84,000,000n.a.------------n.a.n.a.
Bi-2142 x 10 88,000,000n.a.------------n.a.n.a.
Pb-2102 x 10 4800---1.30.82.02.0n.a.n.a.
Bi-2101 x 10 7400,000n.a.------------n.a.n.a.
Po-2109 x 10 44,000---0.30.10.40.4n.a.n.a.
Th-2325 x 10 42,000---5.80.20.40.411.56.9
Ra-2287 x 10 43,000---3.90.10.30.33.620
Ac-2284 x 10 72,000,000n.a.------------n.a.n.a.
Th-2283 x 10 520,000---0.6---------n.a.0.8
Ra-2243 x 10 520,000n.a.0.60.1------n.a.n.a.
Pb-2122 x 10 680,000n.a.0.2---------n.a.n.a.
U-2357 x 10 530,000---1.2---------n.a.n.a.
Th-2315 x 10 72,000,000n.a.------------n.a.n.a.
Ac-2279,000400---n.a.---n.a.n.a.n.a.n.a.
Bi-2129 x 10 74,000,000n.a.------------n.a.n.a.
Total---68.84.79.16.128.237.3
    a Bq = becquerel.
    b mrem/yr = millirem per year.
    n.a. denotes internal dose not applicable because this radionuclide was not measured in contaminatedmedia nor was its concentration estimated based on equilibrium conditions.
    --- denotes individual internal doses were not greater than or equal to 0.1 mrem/yr and were consideredinsignificant.

Health physicists used this formula to calculate internal radiation doses:

    [(100 mrem/yr)/PALI] x annual intake of radionuclide = dose.

An example follows for each exposed population for the radionuclide that contributed the largestinternal dose.

Swimmers (Uranium-238)

    (100 mrem/yr)/(30,000 Bq/yr) x 17 becquerel (Bq)/yr = 0.056 mrem/yr 0.0 (< 0.1, insignificant)

Military Reservist Scenario (Uranium-238)

    (100 mrem/yr)/(30,000 Bq/yr) x 7,600 Bq/yr = 25.3 mrem/yr

Angler Scenario (Radium-226)

    (100 mrem/yr)/(4,000 Bq/yr) x 40 Bq/yr = 1.0 mrem/yr

Hunter Scenario (Uranium-234)

    (100 mrem/yr)/(30,000 Bq/yr) x 990 Bq/yr = 3.3 mrem/yr

Hiker Scenario (Thorium-230)

    (100 mrem/yr)/(20,000 Bq/yr) x 370 Bq/yr = 1.8 mrem/yr

Off-Site Private Well Owner Scenario (Thorium-232)

    (100 mrem/yr)/(2,000 Bq/yr) x 230 Bq/yr = 11.5 mrem/yr

Consumers of Corn (Radium-228)

    (100 mrem/yr) / (3,000 Bq/yr) x (600 Bq/yr) = 20 mrem/yr

Inhalation Dose Estimates

For this public health assessment, ATSDR determined an appropriate inhalation scaling factorand multiplied it by the extension center worker's dose. The worker's dose estimates are based onthe ALI method for workers; therefore, ATSDR applied a 1.4 correction factor to account for exposures to members of the public.

ATSDR staff used the following formula to calculate inhalation dose estimates:

    extension workers annual dose x inhalation scaling factor x 1.4 = inhalation dose estimate.

Calculation of the inhalation dose estimates follow. (Note: The on-site inhalation dose from 1957through 1966 was 46 millirem per year (mrem/yr), while the off-site inhalation dose since 1969 is0.2 mrem/yr.)

Swimming Scenario

    46 mrem/yr x 14/2,000 x 1.4 = 0.45 mrem/yr

U.S. Military Reservist Scenario

    0.2 mrem/yr x 336/2,000 x 1.4 = 0.04 mrem/yr

Angler Scenario

    0.2 mrem/yr x 35/2,000 x 1.4 < 0.01 mrem/yr

Hunter Scenario

    0.2 mrem/yr x 100/2,000 x 1.4 = 0.01 mrem/yr

Hiker Scenario

    0.2 mrem/yr x 40/2,000 x 1.4 = 0.01 mrem/yr

Off-Site Private Well Owner Scenario

    0.2 mrem/yr x 8,766/2,000 x 1.4 = 1.23 mrem/yr

Francis Howell High School Staff and Student Scenarios

    0.2 mrem/yr x 1920/2,000 x 1.4 = 0.27 mrem/yr

Table C.5 contains the total internal radiation dose for each potentially exposed population. Health physicists tabulated these values by adding the annual internal radiation dose via ingestion(from Table C.4) and the inhalation dose for each potentially exposed group.


TABLE C.5.

TOTAL INTERNAL RADIATION DOSE
Potentially Exposed PersonAnnual Internal Radiation Dose via Ingestion
(mrem/yr)a
Annual Internal Radiation Dose via Inhalation
(mrem/yr)a
Total Annual Internal Radiation Dose (mrem/yr)a
Swimmer---0.450.4
U.S. MilitaryReservist68.80.0468.8
Angler4.7---4.7
Hunter9.10.019.1
Hiker6.10.016.1
Consumer of PrivateWell Water28.21.2329.4
Francis Howell HighSchool Staff andStudentsn.a.0.270.3
Consumers ofLocally Grown Corn37.3n.a.37.3
a mrem/yr = millirem per year.
n.a. denotes not applicable because ingestion or inhalation of radionuclides is an incompleteexposure pathway.
--- denotes radiation doses are insignificant.

External Radiation Dose

Health physicists also calculated external doses for the populations identified in the exposurescenarios. In these calculations, to permit the use of the dose conversion factors of FederalGuidance Report No. 12, ATSDR staff members assumed the areas were homogeneouslycontaminated with the maximum radionuclide concentration at the surface and up to a depth of15 centimeters. To correct the overestimation of external doses, ATSDR applied a correctionfactor of 10-4 to scale the external dose appropriately. The correction factor takes into account thefact that not all of the property is contaminated. In this case, ATSDR assumed that the ratio ofthe area of radiologically contaminated properties to nonradiologically contaminated properties is1:10,000. Tables C.6 (page C-26) and C.7 (page C-27) contain external radiation dose estimates for each radioactive contaminant and its progeny.



TABLE C.6.

ANNUAL EXPOSURE HOURS PER YEAR (HRS/YR) AND EXTERNAL RADIATION DOSE
RadionuclideExternal
Dose
Conversion Factor
(mrem*m3/Bq s)a
Training AreaConservation Areas
U.S. Military ReservistAnglerHunterHiker
Time Exposed
per Year
(hrs/yr)b
External
Radiation
Dose
(mrem/yr)c
Time Exposed
per
Year
(hrs/yr)b
External
Radiation
Dose
(mrem/yr)c
Time Exposed
per
Year
(hrs/yr)b
External
Radiation
Dose
(mrem/yr)c
Time Exposed
per
Year
(hrs/yr)b
External
Radiation
Dose
(mrem/yr)c
U-2385.52 x 10-173360.00001350.00000011000.0000003400.0000001
Th-2341.29 x 10-143360.002350.000021000.00005400.00002
Pam-2344.20 x 10-143360.008350.000091000.0002400.0001
U-2342.14 x 10-163360.00004350.00000041000.000001400.0000004
Th-2306.39 x 10-163360.000001350.0000051000.00001400.000005
Ra-2261.65 x 10-143360.000005350.0000051000.00001400.000005
Rn-2221.14 x 10-153360.0000003350.00000031000.000001400.0000003
Po-2182.63 x 10-173360.000000007350.0000000081000.00000002400.000000009
Pb-2146.70 x 10-133360.0001350.00021000.0005400.0002
Bi-2144.30 x 10-123360.001350.0011000.002400.001
Po-2142.40 x 10-163360.00000006350.000000071000.0000002400.00000008
Pb-2101.31 x 10-153360.0000003350.00000041000.000001400.0000004
Bi-2101.86 x 10-153360.000001350.0000011000.000003400.000001
Po-2102.45 x 10-173360.000000007350.0000000071000.00000002400.000000007
Th-2322.78 x 10-163360.000001350.000000041000.0000001400.00000004
Ra-2280.003360.00350.001000.00400.00
Ac-2282.76 x 10-123360.008350.00041000.001400.0004
Th-2284.17 x 10-153360.00001350.0000011000.000003400.000001
Ra-2242.62 x 10-143360.00008350.0000051000.00001400.000005
Rn-2201.10 x 10-153360.000004350.00000011000.0000003400.0000001
Po-2164.87 x 10-173360.0000001350.0000000081000.00000002400.000000009
Pb-2123.62 x 10-133360.001350.000061000.0001400.00006
Bi-2125.36 x 10-133360.001350.000091000.0002400.0001
Po-2120.003360.00350.001000.00400.00
Tl-2089.68 x 10-123360.01350.00061000.0001400.0006
U-2353.75 x 10-133360.003350.000041000.0001400.00004
Th-2311.94 x 10-143360.0001350.0000021000.000006400.000002
Total of significantdoses (i.e. 0.01)0.01---------
    a mrem*m3/Bq s = millirem cubic meters per becquerel second.
    b hrs/yr = hours per year.
    c mrem/yr = millirem per year.
    n.a. denotes external dose not applicable (see explanation in text for owner of off-site privatewell external dose calculations).
    --- denotes individual external doses were not greater than 0.01 mrem/yr and were consideredinsignificant. As a result, the sum of the insignificant doses is itself insignificant.


TABLE C.7.

ANNUAL EXPOSURE HOURS PER YEAR (HRS/YR) AND EXTERNAL RADIATION DOSE
RadionuclideExternal Dose Conversion Factor
(mrem*m3/Bq s)a
External Dose Factor for the Skin
(mrem*m3/Bq s)a
Quarry or Raffinate Pits
Swimmers
Time Exposed
per Year
(hrs/yr)b
External
Radiation
Dose
(mrem/yr)c
Radiation Dose to the Skin (mrem/yr)c
U-2387.95 x 10-166.83 x 10-15146.12 x 10-65.26 x 10-5
U-2341.75 x 10-159.55 x 10-15141.27 x 10-56.92 x 10-5
Th-2303.94 x 10-151.01 x 10-14148.89 x 10-62.27 x 10-5
Ra-2266.95 x 10-149.31 x 10-14143.4 x 10-54.6 x 10-5
Rn-2224.16 x 10-154.90 x 10-15144.18 x 10-54.92 x 10-5
Pb-2101.31 x 10-143.00 x 10-14 141.6 x 10-73.67 x 10-7
Po-2109.03 x 10-171.04x 10-16143.5 x 10-104.03 x 10-10
Th-2321.99 x 10-157.65 x 10-15142.17 x 10-78.29 x 10-6
Ra-2280.000.00140.000.00
Th-2282.05 x 10-143.18 x 10-14142.26 x 10-73.51 x 10-7
U-2351.59 x 10-121.89 x 10-12140.00150.0018
Ac-2271.3 x 10-152.23 x 10-15141.94 x 10-83.33 x 10-8
Total of significant doses (i.e. 0.01)------
    a mrem*m3/Bq s = millirem cubic meters per becquerel second.
    b hrs/yr = hours per year.
    c mrem/yr = millirem per year.
    --- denotes external doses were not greater than 0.01 mrem/yr and were consideredinsignificant. As a result, the sum of the insignificant doses is itself insignificant.

Health physicists used the following formula to calculate external radiation doses:

external dose conversion factor x soil (or water) density x exposure time

    x correction factor = dose.

An example follows for each exposed population for the radionuclide which contributed thelargest external dose.

Swimmers Scenario (Uranium-235)

In this case, ATSDR considered two types of external radiation exposures: the radiation dose tothe body and the radiation dose to the skin. ATSDR considered the skin doses because of thedirect contact swimmers could have with radionuclides in the Quarry or Raffinate Pits.

To the body

(1.59 x 10-12 mrem * m3/Bq second) x (1.6 x 106 g/m3) x (Lwater/1000 gwater) x (12 Bq/L) x (14 hrs x 3600 seconds/hr) = 0.0015 mrem/yr

To the skin

(1.89 x 10-12 mrem * m3/Bq second) x (1.6 x 106 g/m3) x (Lwater/1000 gwater) x (12 Bq/L) x (14 hrs x 3600 seconds/hr) = 0.0018 mrem/yr

U.S. Military Reservist Scenario (Thallium-208)

(9.68 x 10-12 mrem * m3/Bq second) x (36%) x (1.6 x 106 g/m3) x (16.65 Bq/gsoil) x (336 hours/yr) x (3600 seconds/hour) x 10-4 = 0.0112 mrem/yr

Angler Scenario (Bismuth-214)

(4.30 x 10-12 mrem * m3/Bq second) x (1.6 x 106 g/m3) x (15.91 Bq/gsoil) x (35 hours/yr) x (3600 seconds/hour) x 10-4 = 0.0013 mrem/yr

Hunter Scenario (Bismuth-214)

(4.30 x 10-12 mrem * m3/Bq second) x (1.6 x 106 g/m3) x (15.91 Bq/gsoil) x (100 hours/yr) x (3600 seconds/hour) x 10-4 = 0.0039 mrem/yr

Hiker Scenario (Bismuth-214)

(4.30 x 10-12 mrem * m3/Bq second) x (1.6 x 106g/m3) x (15.91 Bq/gsoil) x (40 hours/yr) x (3600 seconds/hour) x 10-4 = 0.0016 mrem/yr

Off-Site Private Well Owner Scenario

The external dose calculations were performed for those persons exposed to external radiationemanating from the soil. Because ATSDR has no soil data for the off-site private well locations,no external dose calculations were performed for these locations. In addition, ATSDR does notbelieve external dose emanating from the well water is significant at those locations.

Francis Howell High School Scenario

ATSDR does not believe external dose emanating from the soil is significant at the FrancisHowell High School. Although no external dose calculations were performed explicitly for theschool (because ATSDR has not located any soil data for this area), the external doses in all ofthe cases evaluated thus far have been insignificant.

Table C.8 (page C-31) lists the total radiation dose for each potentially exposed population.Health physicists tabulated the values by adding the total internal radiation dose and the annualexternal radiation dose.



TABLE C.8.

TOTAL ANNUAL RADIATION DOSE
Potentially Exposed PersonTotal Annual Internal Radiation Dose
(mrem/yr)a
Annual External Radiation Dose
(mrem/yr)a
Total Annual Radiation Dose
(mrem/yr)a
Swimmer0.4---0.4
U.S. MilitaryReservist68.80.0168.8
Angler4.7---4.7
Hunter9.1---9.1
Hiker6.1---6.1
Consumer of PrivateWell Water29.4n.a.29.4
Francis Howell HighSchool Staff andStudents0.3n.a.0.3
Consumers ofLocally Grown Corn37.3n.a.37.3
a mrem/yr = millirem per year.
n.a. denotes not applicable because pathway is incomplete.
--- denotes radiation doses are insignificant.

Findings

(1) Because the internal doses of the exposed populations are much greater than the externaldoses, adding the two does not substantially change the total effective doses for thecircumstances described. Thus, external doses are insignificant.

(2) The total effective doses, including background for exposed populations, are less than theICRP's recommended 100 mrem/year [9] for limiting public exposures to radioactive material,and health effects associated with those doses are unlikely.

References

  1. Kaplan I. Nuclear Physics, 2nd Edition. Addison-Wesley Publishing Company, Reading, 1964.
  2. Cember H. Introduction to Health Physics, 2nd Edition. Pergamon Press, New York, 1988.
  3. Knoll G. Radiation Detection and Measurement, 2nd Edition. John Wiley and Sons, Inc., NewYork, 1989.
  4. DeVita V.T., Hellman S., and Rosenberg S.A. Cancer, Principles & Practice of Oncology, 4thEdition. J.B. Lippincott Company, Philadelphia, 1993.

  5. Johns H.E. and Cunnignham J.R. The Physics of Radiology, 4th Edition. Charles Thomas,Springfield, 1983.

  6. National Research Council, 1990, Health Effects of Exposure to Low Levels of IonizingRadiation, BEIR V, Committee on the Biological Effects of Ionizing Radiation, Board ofRadiation Effects Research, Commission on Life Sciences, National Research Council, NationalAcademy Press, Washington D.C.

  7. Mossman K.L. and Mills, W.A. The Biological Basis of Radiation Protection Practice.Williams and Wilkens, Baltimore, 1992.

  8. Eckerman K.F. and Ryman J.C. Federal Guidance Report Number 12: External Exposure toRadionuclides in Air, Water, and Soil. U.S. Environmental Protection Agency, 1993.

  9. The International Commission on Radiological Protection. International Commission onRadiological Protection Publication 60. Pergamon Press, Oxford, 1991.

  10. Missouri Department of Conservation, 1991, Recreational Use of Weldon Spring WildlifeArea, 1989-1990, June 1991.

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