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A five-compartment model for carbon cycling in the world's terrestrial ecosystems, which includes a concise treatment of the releases of carbon and shifts in carbon storage due to forest clearing, is presented. The dynamics of the less abundant isotopes, 13 C and 14 C, are included in the model to allow interpretation of available isotopic time series. The sensitivity of the net carbon flux between the terrestrial component of the model and the atmosphere to I 0% variability in terrestrial rate coefficients and growth parameters is examined; for the particular case considered here, the variability in model response is "'='I 0%. Response of the model agrees reasonably well with observations of historical changes in the specific activity of 14 C in the atmosphere. The model-calculated Suess effect in 1952 is 2%, and the time constant of the exponential decrease in atmospheric 14 C following the weapons test ban is 14 yr. By adjusting the releases of carbon due to forest clearing, a fit of model response to 13 C/ 12 C tree-ring time series is derived. The resulting forest-clearing carbon release function rises to 2.5 Pglyr by 1910 and remains constant to the present. Due to establishment of ground vegetation following clearing, the net carbon flux from the terrestrial biotic system to the atmosphere is less than the release due to clearing in some instances. To accomodate this net input to the atmosphere in addition to that due to fossil fuel combustion, the pre-industrial C0 2 concentration must be assumed to have been lower than is implied by extrapolating the modem instrument records backward in time.

The Feed Materials Production Center, northwest of Cincinnati, processed uranium concentrates and uranium compounds recycled from other stages of nuclear weapons production, as well as some uranium ore and thorium. Particulate releases were primarily uranium (natural, depleted, and slightly enriched. In addition, two large silos containing radium-bearing residues were emission sources of radon and its decay products. The Fernald Dosimetry Reconstruction Project was undertaken to help the Centers for Disease Control and Prevention to evaluate the impact of the Feed Materials Production Center on the public from radionuclides released to the environment from 1951 through 1988. At this point in the study, the project has estimated the quantities of radioactive materials released to air, surface water, and in groundwater; developed the methodology to describe the environmental transport of the materials; developed mathematical models to calculate the resulting radiation doses; and evaluated environmental monitoring data to verify that the estimates of releases and transport are reasonable. Thorough review of historical records and extensive interaction with former and current employees and residents have been the foundation for reconstructing routine operations, documenting accidents, and evaluating unmonitored emission sources. The largest releases of uranium to air and water occurred in the 1950's and 1960's. Radon releases from the silos remained elevated through most of the 1970's. The quantity of uranium released to surface water was much less than that released to air. Best estimates of releases are reported as median values, with associated uncertainties calculated as an integral part of the estimates. Screening calculations showed that atmospheric pathways dominate the total dose from Feed Materials Production Center releases. Accordingly, the local meteorology, effluent particle size and chemical form, and wet and dry deposition, were particularly important in this study. The final goal of the project is the calculation of radiation doses to people living in the study domain, which is represented by a circle with radius of 10 km centered on the Feed Materials Production Center production area.

A hazard index methodology called CUMEX has been developed for limiting human exposure to environmental pollutants. Hazard index is defined as Q/Q. where Q is exposure or dose to total-body, organ or tissue from all environmental pathways and Q. is a limit which should not be exceeded because of health risk to humans. Mathematical formulations for hazard indices ire developed for each sampling medium corresponding to each effluent type. These hazard indices are accumulated into composite indices such that total human intake or dose would not exceed the health risk limit. Mathematical formulation for composite hazard indices or CUMEX indices for multiple pollutants are presented. An example CUMEX application to cadmium release from a smelter complex in East Helena, Montana demonstrates details of tne methodology for a single pollutant where human intake occurs through inhalation and ingestion. v TABLE OF CONTENTS PAGE LIST OF TABLES ix LIST OF FIGURES xi LIST OF APPENDICES xiii CONCLUSION APPENDIX t. MODIFICATIONS OF TERMOO APPENDIX II. CADMIUM REVIEW REFERENCES 59 vili LIST OF TABLES TABLE PAGE 3.4.1 Average cadmium concentrations 3.4.2 The average daily intake of cadmium as a function of diet for the U.S. and the study site in Helena, Montana .... 20 4.1.1.1 Source data for East Helena smelter area 22 4.1.2.1 Deposition of cadmium around Helena smelter area 24 4.1.2.2 Air concentrations of cadmium around Helena smelter area 25 4.1.2.3 Deposition of cadmium around Helena smelter area 39 4.1.3.1 Cadmium concentrations in area around East Helena .... 31 4.2.2.1 Equilibrium cadmium concentrations in various compartments 33 4.2.2.2 Equilibrium intakes by reference man S3 ix LIST OF FIGURES FIGURE PAGt 2.2.1 Block diagram of the terrestrial food pathways 4.1.2.1 Average deposition of cadmium (5i_) around East Helena smelter (mg/m 2 /month) 4.1.2.2 Average air concentration of cadmium (5") around East

The Feed Materials Production Center (FMPC) at Fernald, Ohio produced uranium metal products for use in Department of Energy defense programs. Radium-contaminated waste material was stored on-site in two K-65 silos on the west side of the facility and provided a source of 222 Ra. The initial objective of this study was to estimate radon exposures to employees at FMPC working from 1952 to 1988. A modified Gaussian plume model was used to estimate exposures to workers. In an effort to validate these model-based estimates, we used 138 CR-39 film assays from window glass sampled in buildings throughout the site. Results from the CR-39 assays indicated a second substantial source of radon, the smaller Q-11 silos located in the production area. A response-surface regression analysis using a cubic spline model was fit to the CR-39 data to estimate 210 Po surface activity levels at geographic coordinates throughout the facility. Knowledge of the age of the glass, the amount of contaminated waste in the Q-11 silos, and 210 Po decay rates were used to estimate annual exposures to radon decay products (WLM: working level months). Estimated WLM levels associated with the Q-11 source term indicated that employees working in the vicinity during the period when they were filled with radium-contaminated waste (1952)(1953)(1954)(1955)(1956)(1957)(1958) received substantially higher radon exposures than those from the K-65 source during this period. Results of the two models, corresponding to the K-65 and Q-11 sources, were combined to estimate WLM levels by year for each of the 7143 Fernald workers during the period 1952-1988. Estimated cumulative exposures to individual workers ranged from o0.5 to 751 WLM. Estimated radon exposures from this newly discovered source have important implications for future epidemiologic studies of lung cancer in workers at the Fernald facility.