PUBLIC HEALTH ASSESSMENT
US DOE MOUND FACILITY
[a/k/a MOUND PLANT (USDOE)]
MIAMISBURG, MONTGOMERY COUNTY, OHIO
APPENDIX D: TRITIUM IN DRINKING WATER
Background
Hydrogen-3, or tritium, is a radioactive isotope of hydrogen that readily exchanges with hydrogen atoms in water (H2O) and other molecules. ATSDR scientists became interested in investigating tritium in drinking water after noting that tritium in private wells in Bud's Trailer Park in 1975 was reportedly greater than 75,000 picocuries per liter (pCi/L) [1]. There are no data available for the trailer park wells before 1975; however, liquid tritium releases from the Mound Laboratory to the Miami-Erie Canal across the highway from the trailer park were much higher in the 1960s than in 1975 [2]. Because the Miami-Erie Canal is the primary source of tritium in the Buried Valley Aquifer and private wells are within several hundred feet of the canal beds, materials dissolved in the water in the canal can get into private well water [3]. This is particularly true of tritium, which readily dissolves in water and exchanges with hydrogen atoms in water molecules. Because people would have used their wells as a primary household water source, high levels of tritium in the Miami-Erie Canal could have resulted in exposures to tritium at levels of health concern. We have concluded that tritium in private wells was not a health problem. The remainder of this appendix will explain how we reached that conclusion.
* * *
The people we were initially concerned about were those who lived immediately west and southwest of the Mound Laboratory in Bud's Trailer Park and in adjacent properties who used private well water as their primary source of drinking water from 1960 through 1974. We chose these years because they include the years 1967-1974, when greater amounts of tritium were released in water to the Miami-Erie Canal than in 1975, and during all of these years greater concentrations of tritium were measured in water in the Miami-Erie Canal than in 1975.
In the course of our investigation we also became interested in the possibility that high levels of tritium could have infiltrated the water supply for the City of Miamisburg through Miamisburg Well #2 near the foot of the Mound Laboratory drainage ditch. If Well #2 were a sole source of water for Miamisburg, the population of Miamisburg might also have been exposed to levels of tritium at levels of health concern. However, we have not been able to confirm whether Well #2 was ever a source of water for the city, whether it was a sole source of water for the city, when it was in operation, and when its use was discontinued. In any case, our conclusion that tritium was not a health hazard applies to all the receptor populations that we considered, including the city population.
* * *
To study tritium in water near Mound, we first asked what levels of tritium the trailer park residents could have been exposed to in the years before 1975. To answer this, we assumed that there is a relation between the amounts of tritium released to the canal or amounts in the canal and the amount of tritium in the private wells. The dependency of the well tritium concentrations on tritium in the canals can be described mathematically by adopting an appropriate function. The function can be fit to the existing data (after 1974) to characterize how the function behaves (i.e., how changes in the tritium concentrations in the south Miami-Erie Canal affect tritium concentrations in the private wells). By fitting the function to the existing data and characterizing the function, we were able to estimate the tritium concentrations in private wells for the years that we don't have actual measurements in the wells (1960-1974). We present our results below. A more detailed description of our data analysis is at the end of this appendix for interested readers so the present narrative is not interrupted.
The following tables present our starting data and our estimates of well tritium concentrations before 1975. Table I presents the tritium concentrations measured in the canals and wells; these data come from the Department of Energy's annual environmental reports. In Table I, the "Measured Well Concentrations" data are the highest average annual concentrations for off-site wells. These wells were all within Bud's Trailer Park. We did not use data from the Miamisburg Well #2 for these calculations because we are uncertain if or when that well served as a source of drinking water. "Canal Activity" is the total curies of tritium released to the Miami-Erie Canal in a given year, and "Canal Volume" is the volume of water released [4]. The "Calculated Canal Concentration," therefore, is the quotient of these two quantities for a given year. We used these calculated concentrations for the canal tritium concentration for the years we didn't have measured canal tritium concentrations.
In Table II, we present the estimated tritium concentrations in wells based on the derived model (included at the end of this appendix). These tritium concentrations represent our best guess as to the amounts of tritium to which people would have been exposed from water in the private wells. We believe these are the highest levels of tritium that anyone would have been exposed to, off site, from tritium releases from the Mound facility. These concentrations, in picocuries per liter (pCi/L), are the basis for the dose calculations and toxicological analyses that follow.
TABLE I. MEASURED AND CALCULATED TRITIUM ACTIVITIES IN CANAL WATER AND MEASURED TRITIUM ACTIVITIES IN WELL WATER OFF SITE.
| Year | Measured Canal Concentration (pCi/L) |
Canal Activity (pCi) |
Canal Volume (liters) |
Calculated Canal Concentration (pCi/L) |
Assumed Canal Concentration (pCi/L) * |
Measured Well Water Concentration (pCi/L) |
| 1960 | 64,500 | - | - | - | 64,500 | - |
| 1961 | 1,386,000 | - | - | - | 1,386,000 | - |
| 1962 | 60,000 | - | - | - | 60,000 | - |
| 1963 | 306,000 | - | - | - | 306,000 | - |
| 1964 | 784,000 | - | - | - | 784,000 | - |
| 1965 | 311,000 | - | - | - | 311,000 | - |
| 1966 | 253,000 | - | - | - | 253,000 | - |
| 1967 | 150,000 | 1.69e+14 | - | - | 150,000 | - |
| 1968 | 790,000 | 2.02e+14 | - | - | 790,000 | - |
| 1969 | 1,820,000 | 2.33e+15 | - | - | 1,820,000 | - |
| 1970 | 427,000 | 2.50e+14 | - | - | 427,000 | - |
| 1971 | - | 2.67e+14 | 7.29e+08 | 365,844 | 365,844 | - |
| 1972 | - | 6.91e+13 | 5.91e+08 | 116,920 | 116,920 | - |
| 1973 | - | 4.75e+13 | 5.63e+08 | 84,369 | 84,369 | - |
| 1974 | 52,000 | 5.81e+13 | 8.65e+08 | 67,168 | 52,000 | - |
| 1975 | 43,000 | 3.58e+13 | 8.13e+08 | 44,034 | 43,000 | 74,900 |
| 1976 | 41,000 | 2.53e+13 | 6.04e+08 | 41,887 | 41,000 | 59,800 |
| 1977 | 24,000 | 1.57e+13 | 5.82e+08 | 26,976 | 24,000 | 46,700 |
| 1978 | 12,000 | 9.00e+12 | 5.64e+08 | 15,957 | 12,000 | 25,000 |
| 1979 | - | 8.30e+12 | 7.40e+08 | 11,216 | 11,216 | 19,300 |
| 1980 | - | 7.70e+12 | 5.11e+08 | 15,068 | 15,068 | 18,000 |
| 1981 | - | 4.80e+12 | 6.46e+08 | 7,430 | 7,430 | 15,000 |
| 1982 | - | 5.10e+12 | 8.57e+08 | 5,951 | 5,951 | 12,000 |
| 1983 | - | 4.70e+12 | 8.75e+08 | 5,371 | 5,371 | 8,000 |
| 1984 | - | 4.30e+12 | 9.01e+08 | 4,772 | 4,772 | 8,400 |
| 1985 | - | 2.90e+12 | 6.44e+08 | 4,503 | 4,503 | 6,000 |
| 1986 | - | 3.30e+12 | 8.00e+08 | 4,125 | 4,125 | 5,600 |
| 1987 | - | 3.20e+12 | 8.48e+08 | 3,774 | 3,774 | 7,100 |
| 1988 | - | 2.50e+12 | 8.49e+08 | 2,945 | 2,945 | 5,700 |
| 1989 | - | 2.40e+12 | 6.96e+08 | 3,448 | 3,448 | 5,200 |
| 1990 | - | 2.40e+12 | 8.36e+08 | 2,871 | 2,871 | 4,290 |
| 1991 | - | - | - | - | - | 3,590 |
| 1992 | - | - | - | - | - | 3,170 |
| 1993 | - | - | - | - | - | 3,260 |
| 1994 | - | - | - | - | - | 2,560 |
| * The "Assumed Canal Concentration" is the Measured Concentration, if available, otherwise, it is the Calculated Concentration. | ||||||
TABLE II. PREDICTED ANNUAL AVERAGE TRITIUM CONCENTRATIONS
IN OFF-SITE WELLS.
| Year | Predicted Tritium Concentration (pCi/L) | ||
| Best Fit | Minimum | Maximum | |
| 1960 | 51,000 | 45,000 | 57,000 |
| 1961 | 1,100,000 | 1,000,000 | 1,300,000 |
| 1962 | 680,000 | 570,000 | 780,000 |
| 1963 | 540,000 | 450,000 | 620,000 |
| 1964 | 770,000 | 700,000 | 840,000 |
| 1965 | 650,000 | 590,000 | 710,000 |
| 1966 | 490,000 | 440,000 | 540,000 |
| 1967 | 290,000 | 270,000 | 310,000 |
| 1968 | 740,000 | 670,000 | 810,000 |
| 1969 | 1,800,000 | 1,700,000 | 2,000,000 |
| 1970 | 1,300,000 | 1,200,000 | 1,400,000 |
| 1971 | 830,000 | 720,000 | 940,000 |
| 1972 | 340,000 | 310,000 | 370,000 |
| 1973 | 190,000 | 170,000 | 210,000 |
| 1974 | 100,000 | 94,000 | 110,000 |
| 1975 | 73,000 | 68,000 | 78,000 |
| 1976 | 62,000 | 58,000 | 65,000 |
| 1977 | 46,000 | 42,000 | 49,000 |
| 1978 | 28,000 | 26,000 | 30,000 |
| 1979 | 19,000 | 17,000 | 20,000 |
| 1980 | 19,000 | 18,000 | 21,000 |
| 1981 | 15,000 | 14,000 | 16,000 |
| 1982 | 11,000 | 10,000 | 12,000 |
| 1983 | 8,300 | 7,800 | 8,800 |
| 1984 | 7,300 | 6,900 | 7,800 |
| 1985 | 6,700 | 6,300 | 7,100 |
| 1986 | 6,200 | 5,800 | 6,600 |
| 1987 | 5,700 | 5,300 | 6,000 |
| 1988 | 4,800 | 4,500 | 5,100 |
| 1989 | 4,800 | 4,400 | 5,100 |
| 1990 | 4,400 | 4,100 | 4,600 |
Radiation Doses
Once we estimated tritium concentrations in the private wells for the years 1960 through 1974, we used these values along with the measured concentrations (1975 to present) to calculate radiation doses to people who may have used this well water as their sole source of water. (Sole source means drinking the water but also includes other uses, such as bathing, cooking, and washing dishes.) We assumed people were chronically exposed to the different tritium concentrations in different years, and we calculated both annual doses and cumulative doses to persons exposed through 1990 (beginning in any year). We calculated doses for persons whose ages ranged from prenatal to adult; results appear in Tables III, IV, and V.
The International Commission on Radiological Protection metabolic model assumes that 100% of the tritium ingested, inhaled, or absorbed mixes with total body water so that the tritium concentration in sweat, urine, blood, and other body fluids is the same throughout the body [5]. The majority of the tritium stays in the body fluids and is excreted quickly. A small fraction of the tritium is incorporated into other body compounds, i.e., fats, proteins, and carbohydrates, but adds very little to the total dose to the individual. However, for chronic exposures, there is a point of equilibrium at which the concentration of tritium taken into the body is equal to the concentration in the body, which continues as long as the tritiated water continues to be absorbed [6]. In our dose calculations, we assumed the concentration of tritium in the body in any given year is the same as that in the private wells.
Table III shows the annual radiation doses to different aged individuals who used the private wells in and near Bud's Trailer Park as a sole source of water for the years 1960 through 1990. Our highest annual doses occurred in 1969, when Mound Laboratory tritium releases were highest. The highest dose, 292 millirems per year (mrem/yr) would be to a newborn (0 to 1 year old) because the amount of hydrogen in the body relative to the total body weight is highest in a newborn.
Tables IV and V show the radiation doses to females and males who are chronically exposed to tritium in private wells for more than one year. The doses are somewhat different for females and males because, on average, their bodies' hydrogen content is not the same. The years in the left-hand column are the years that exposures began; the age groups are the ages when exposures began. The dose under any age group takes into consideration the person's age over the duration of her or his exposures. Doses are cumulative through 1990; for shorter exposure durations, subtract the dose for the person in the year and the age group exposures end from the dose for the person in the year and age exposures begin.
The highest cumulative dose (1.49 rem) would be for someone who was prenatally exposed in 1960 and chronically exposed (sole source of water) for the next 30 years. Note that this is an average dose of 48 mrem per year.
TABLE III. ANNUAL EFFECTIVE DOSES FROM SOLE USE OF WATER IN OFF-SITE WELLS.
| Year | Tritium Concentration | Fetal Dose (9 mo. +) | Newborn | 1 y old | 5 y old | 10 y old | 15 y old | adult female | adult male |
| Units | µCi/L (kBq/L) |
millirem (or millisievert)
|
|||||||
| 1960 | 0.057 (2.109) | 4 (0.04) | 8 (0.08) | 8 (0.08) | 7 (0.07) | 7 (0.07) | 6 (0.06) | 7 (0.07) | 6 (0.06) |
| 1961 | 1.3 (48.1) | 100 (1.00) | 190 (1.90) | 176 (1.76) | 168 (1.68) | 166 (1.66) | 145 (1.45) | 149 (1.49) | 138 (1.38) |
| 1962 | 0.78 (28.86) | 60 (0.60) | 114 (1.14) | 106 (1.06) | 101 (1.01) | 100 (1.00) | 87 (0.87) | 89 (0.89) | 83 (0.83) |
| 1963 | 0.62 (22.94) | 48 (0.48) | 91 (0.91) | 84 (0.84) | 80 (0.80) | 79 (0.79) | 69 (0.69) | 71 (0.71) | 66 (0.66) |
| 1964 | 0.84 (31.08) | 65 (0.65) | 123 (1.23) | 114 (1.14) | 109 (1.09) | 107 (1.07) | 94 (0.94) | 96 (0.96) | 89 (0.89) |
| 1965 | 0.71 (26.27) | 55 (0.55) | 104 (1.04) | 96 (0.96) | 92 (0.92) | 91 (0.91) | 79 (0.79) | 81 (0.81) | 75 (0.75) |
| 1966 | 0.54 (19.98) | 42 (0.42) | 79 (0.79) | 73 (0.73) | 70 (0.70) | 69 (0.69) | 60 (0.60) | 62 (0.62) | 57 (0.57) |
| 1967 | 0.31 (11.47) | 24 (0.24) | 45 (0.45) | 42 (0.42) | 40 (0.40) | 40 (0.40) | 35 (0.35) | 36 (0.36) | 33 (0.33) |
| 1968 | 0.81 (29.97) | 62 (0.62) | 118 (1.18) | 110 (1.10) | 105 (1.05) | 104 (1.04) | 90 (0.90) | 93 (0.93) | 86 (0.86) |
| 1969 | 2 (74) | 154 (1.54) | 292 (2.92) | 271 (2.71) | 258 (2.58) | 256 (2.56) | 223 (2.23) | 229 (2.29) | 212 (2.12) |
| 1970 | 1.4 (51.8) | 108 (1.08) | 205 (2.05) | 190 (1.90) | 181 (1.81) | 179 (1.79) | 156 (1.56) | 161 (1.61) | 148 (1.48) |
| 1971 | 0.94 (34.78) | 72 (0.72) | 137 (1.37) | 128 (1.28) | 121 (1.21) | 120 (1.20) | 105 (1.05) | 108 (1.08) | 100 (1.00) |
| 1972 | 0.37 (13.69) | 28 (0.28) | 54 (0.54) | 50 (0.50) | 48 (0.48) | 47 (0.47) | 41 (0.41) | 42 (0.42) | 39 (0.39) |
| 1973 | 0.21 (7.77) | 16 (0.16) | 31 (0.31) | 28 (0.28) | 27 (0.27) | 27 (0.27) | 23 (0.23) | 24 (0.24) | 22 (0.22) |
| 1974 | 0.11 (4.07) | 8 (0.08) | 16 (0.16) | 15 (0.15) | 14 (0.14) | 14 (0.14) | 12 (0.12) | 13 (0.13) | 12 (0.12) |
| 1975 | 0.078 (2.886) | 6 (0.06) | 11 (0.11) | 11 (0.11) | 10 (0.10) | 10 (0.10) | 9 (0.09) | 9 (0.09) | 8 (0.08) |
| 1976 | 0.065 (2.405) | 5 (0.05) | 9 (0.09) | 9 (0.09) | 8 (0.08) | 8 (0.08) | 7 (0.07) | 7 (0.07) | 7 (0.07) |
| 1977 | 0.049 (1.813) | 4 (0.04) | 7 (0.07) | 7 (0.07) | 6 (0.06) | 6 (0.06) | 5 (0.05) | 6 (0.06) | 5 (0.05) |
| 1978 | 0.03 (1.11) | 2 (0.02) | 4 (0.04) | 4 (0.04) | 4 (0.04) | 4 (0.04) | 3 (0.03) | 3 (0.03) | 3 (0.03) |
| 1979 | 0.02 (0.74) | 2 (0.02) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 2 (0.02) | 2 (0.02) | 2 (0.02) |
| 1980 | 0.021 (0.777) | 2 (0.02) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 2 (0.02) | 2 (0.02) | 2 (0.02) |
| 1981 | 0.016 (0.592) | 1 (0.01) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) |
| 1982 | 0.012 (0.444) | 1 (0.01) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1983 | 0.009 (0.333) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1984 | 0.008 (0.296) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1985 | 0.007 (0.259) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1986 | 0.007 (0.259) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1987 | 0.006 (0.222) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) |
| 1988 | 0.005 (0.185) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) |
| 1989 | 0.005 (0.185) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) |
| 1990 | 0.005 (0.185) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) |
TABLE IV. CUMULATIVE EFFECTIVE DOSES FOR A FEMALE FROM
SOLE USE OF WATER IN OFF-SITE WELLS FROM 1960 THROUGH 1990.
| Year | Tritium Concentration | Prenatal | 0 to 1 year | 1 to 3 years | 4 to 8 years | 9 to 13 years | 14 to 17 years | 18 years + |
| Units | µCi/L (kBq/L) |
millirem (or millisievert)
|
||||||
| 1960 | 0.057 (2.109) | 1489 (14.89) | 1469 (14.69) | 1460 (14.60) | 1368 (13.68) | 1329 (13.29) | 1293 (12.93) | 1299 (12.99) |
| 1961 | 1.3 (48.1) | 1411 (14.11) | 1485 (14.85) | 1461 (14.61) | 1394 (13.94) | 1333 (13.33) | 1285 (12.85) | 1294 (12.94) |
| 1962 | 0.78 (28.86) | 1269 (12.69) | 1311 (13.11) | 1295 (12.95) | 1249 (12.49) | 1172 (11.72) | 1138 (11.38) | 1144 (11.44) |
| 1963 | 0.62 (22.94) | 1178 (11.78) | 1209 (12.09) | 1197 (11.97) | 1164 (11.64) | 1077 (10.77) | 1048 (10.48) | 1055 (10.55) |
| 1964 | 0.84 (31.08) | 1085 (10.85) | 1130 (11.30) | 1118 (11.18) | 1091 (10.91) | 1000 (10.00) | 978 (9.78) | 984 (9.84) |
| 1965 | 0.71 (26.27) | 991 (9.91) | 1021 (10.21) | 1007 (10.07) | 986 (9.86) | 905 (9.05) | 883 (8.83) | 888 (8.88) |
| 1966 | 0.54 (19.98) | 912 (9.12) | 936 (9.36) | 917 (9.17) | 899 (8.99) | 846 (8.46) | 801 (8.01) | 806 (8.06) |
| 1967 | 0.31 (11.47) | 863 (8.63) | 870 (8.70) | 857 (8.57) | 832 (8.32) | 799 (7.99) | 735 (7.35) | 744 (7.44) |
| 1968 | 0.81 (29.97) | 807 (8.07) | 840 (8.40) | 825 (8.25) | 795 (7.95) | 775 (7.75) | 696 (6.96) | 709 (7.09) |
| 1969 | 2 (74) | 622 (6.22) | 745 (7.45) | 721 (7.21) | 691 (6.91) | 677 (6.77) | 603 (6.03) | 616 (6.16) |
| 1970 | 1.4 (51.8) | 382 (3.82) | 469 (4.69) | 452 (4.52) | 433 (4.33) | 424 (4.24) | 378 (3.78) | 387 (3.87) |
| 1971 | 0.94 (34.78) | 214 (2.14) | 275 (2.75) | 264 (2.64) | 253 (2.53) | 247 (2.47) | 222 (2.22) | 226 (2.26) |
| 1972 | 0.37 (13.69) | 119 (1.19) | 142 (1.42) | 137 (1.37) | 132 (1.32) | 128 (1.28) | 116 (1.16) | 118 (1.18) |
| 1973 | 0.21 (7.77) | 77 (0.77) | 90 (0.90) | 88 (0.88) | 84 (0.84) | 82 (0.82) | 75 (0.75) | 76 (0.76) |
| 1974 | 0.11 (4.07) | 55 (0.55) | 61 (0.61) | 60 (0.60) | 58 (0.58) | 56 (0.56) | 51 (0.51) | 52 (0.52) |
| 1975 | 0.078 (2.886) | 42 (0.42) | 46 (0.46) | 45 (0.45) | 44 (0.44) | 42 (0.42) | 39 (0.39) | 39 (0.39) |
| 1976 | 0.065 (2.405) | 32 (0.32) | 36 (0.36) | 35 (0.35) | 34 (0.34) | 32 (0.32) | 30 (0.30) | 30 (0.30) |
| 1977 | 0.049 (1.813) | 24 (0.24) | 27 (0.27) | 26 (0.26) | 25 (0.25) | 24 (0.24) | 23 (0.23) | 23 (0.23) |
| 1978 | 0.03 (1.11) | 19 (0.19) | 20 (0.20) | 20 (0.20) | 19 (0.19) | 18 (0.18) | 17 (0.17) | 17 (0.17) |
| 1979 | 0.02 (0.74) | 15 (0.15) | 16 (0.16) | 16 (0.16) | 15 (0.15) | 15 (0.15) | 14 (0.14) | 14 (0.14) |
| 1980 | 0.021 (0.777) | 12 (0.12) | 14 (0.14) | 13 (0.13) | 13 (0.13) | 12 (0.12) | 11 (0.11) | 12 (0.12) |
| 1981 | 0.016 (0.592) | 10 (0.10) | 11 (0.11) | 11 (0.11) | 10 (0.10) | 10 (0.10) | 9 (0.09) | 9 (0.09) |
| 1982 | 0.012 (0.444) | 8 (0.08) | 9 (0.09) | 8 (0.08) | 8 (0.08) | 8 (0.08) | 7 (0.07) | 7 (0.07) |
| 1983 | 0.009 (0.333) | 7 (0.07) | 7 (0.07) | 7 (0.07) | 7 (0.07) | 6 (0.06) | 6 (0.06) | 6 (0.06) |
| 1984 | 0.008 (0.296) | 5 (0.05) | 6 (0.06) | 6 (0.06) | 6 (0.06) | 5 (0.05) | 5 (0.05) | 5 (0.05) |
| 1985 | 0.007 (0.259) | 4 (0.04) | 5 (0.05) | 5 (0.05) | 5 (0.05) | 4 (0.04) | 4 (0.04) | 4 (0.04) |
| 1986 | 0.007 (0.259) | 3 (0.03) | 4 (0.04) | 4 (0.04) | 4 (0.04) | 3 (0.03) | 3 (0.03) | 3 (0.03) |
| 1987 | 0.006 (0.222) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 2 (0.02) | 2 (0.02) |
| 1988 | 0.005 (0.185) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) |
| 1989 | 0.005 (0.185) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1990 | 0.005 (0.185) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) |
TABLE V. CUMULATIVE EFFECTIVE DOSES FOR A MALE FROM SOLE
USE OF WATER IN OFF-SITE WELLS FROM 1960 THROUGH 1990.
| Year | Tritium Concentration | Prenatal | 0 to 1 year | 1 to 3 years | 4 to 8 years | 9 to 13 years | 14 to 17 years | 18 years + |
| Units | µCi/L (kBq/L) |
millirem (or millisievert)
|
||||||
| 1960 | 0.057 (2.109) | 1488 (14.88) | 1468 (14.68) | 1458 (14.58) | 1362 (13.62) | 1275 (12.75) | 1213 (12.13) | 1201 (12.01) |
| 1961 | 1.3 (48.1) | 1410 (14.10) | 1484 (14.84) | 1460 (14.60) | 1390 (13.90) | 1286 (12.86) | 1211 (12.11) | 1195 (11.95) |
| 1962 | 0.78 (28.86) | 1268 (12.68) | 1310 (13.10) | 1294 (12.94) | 1246 (12.46) | 1143 (11.43) | 1070 (10.70) | 1058 (10.58) |
| 1963 | 0.62 (22.94) | 1177 (11.77) | 1208 (12.08) | 1196 (11.96) | 1162 (11.62) | 1060 (10.60) | 987 (9.87) | 975 (9.75) |
| 1964 | 0.84 (31.08) | 1085 (10.85) | 1130 (11.30) | 1118 (11.18) | 1089 (10.89) | 991 (9.91) | 921 (9.21) | 909 (9.09) |
| 1965 | 0.71 (26.27) | 990 (9.90) | 1020 (10.20) | 1007 (10.07) | 985 (9.85) | 899 (8.99) | 829 (8.29) | 820 (8.20) |
| 1966 | 0.54 (19.98) | 911 (9.11) | 936 (9.36) | 917 (9.17) | 898 (8.98) | 842 (8.42) | 755 (7.55) | 745 (7.45) |
| 1967 | 0.31 (11.47) | 863 (8.63) | 870 (8.70) | 857 (8.57) | 831 (8.31) | 796 (7.96) | 706 (7.06) | 688 (6.88) |
| 1968 | 0.81 (29.97) | 807 (8.07) | 839 (8.39) | 824 (8.24) | 794 (7.94) | 772 (7.72) | 679 (6.79) | 655 (6.55) |
| 1969 | 2 (74) | 622 (6.22) | 745 (7.45) | 721 (7.21) | 691 (6.91) | 675 (6.75) | 594 (5.94) | 569 (5.69) |
| 1970 | 1.4 (51.8) | 382 (3.82) | 468 (4.68) | 452 (4.52) | 433 (4.33) | 423 (4.23) | 373 (3.73) | 357 (3.57) |
| 1971 | 0.94 (34.78) | 214 (2.14) | 275 (2.75) | 264 (2.64) | 253 (2.53) | 246 (2.46) | 218 (2.18) | 209 (2.09) |
| 1972 | 0.37 (13.69) | 119 (1.19) | 142 (1.42) | 137 (1.37) | 132 (1.32) | 127 (1.27) | 113 (1.13) | 109 (1.09) |
| 1973 | 0.21 (7.77) | 77 (0.77) | 90 (0.90) | 88 (0.88) | 84 (0.84) | 81 (0.81) | 72 (0.72) | 70 (0.70) |
| 1974 | 0.11 (4.07) | 55 (0.55) | 61 (0.61) | 60 (0.60) | 58 (0.58) | 55 (0.55) | 49 (0.49) | 48 (0.48) |
| 1975 | 0.078 (2.886) | 42 (0.42) | 46 (0.46) | 45 (0.45) | 43 (0.43) | 42 (0.42) | 37 (0.37) | 36 (0.36) |
| 1976 | 0.065 (2.405) | 32 (0.32) | 36 (0.36) | 35 (0.35) | 33 (0.33) | 32 (0.32) | 29 (0.29) | 28 (0.28) |
| 1977 | 0.049 (1.813) | 24 (0.24) | 27 (0.27) | 26 (0.26) | 25 (0.25) | 24 (0.24) | 22 (0.22) | 21 (0.21) |
| 1978 | 0.03 (1.11) | 19 (0.19) | 20 (0.20) | 20 (0.20) | 19 (0.19) | 18 (0.18) | 16 (0.16) | 16 (0.16) |
| 1979 | 0.02 (0.74) | 15 (0.15) | 16 (0.16) | 16 (0.16) | 15 (0.15) | 15 (0.15) | 13 (0.13) | 13 (0.13) |
| 1980 | 0.021 (0.777) | 12 (0.12) | 14 (0.14) | 13 (0.13) | 13 (0.13) | 12 (0.12) | 11 (0.11) | 11`(0.11) |
| 1981 | 0.016 (0.592) | 10 (0.10) | 11 (0.11) | 11 (0.11) | 10 (0.10) | 10 (0.10) | 9 (0.09) | 8 (0.08) |
| 1982 | 0.012 (0.444) | 8 (0.08) | 9 (0.09) | 8 (0.08) | 8 (0.08) | 8 (0.08) | 7 (0.07) | 7 (0.07) |
| 1983 | 0.009 (0.333) | 7 (0.07) | 7 (0.07) | 7 (0.07) | 7 (0.07) | 6 (0.06) | 6 (0.06) | 6 (0.06) |
| 1984 | 0.008 (0.296) | 5 (0.05) | 6 (0.06) | 6 (0.06) | 6 (0.06) | 5 (0.05) | 5 (0.05) | 5 (0.05) |
| 1985 | 0.007 (0.259) | 4 (0.04) | 5 (0.05) | 5 (0.05) | 5 (0.05) | 4 (0.04) | 4 (0.04) | 4 (0.04) |
| 1986 | 0.007 (0.259) | 3 (0.03) | 4 (0.04) | 4 (0.04) | 4 (0.04) | 3 (0.03) | 3 (0.03) | 3 (0.03) |
| 1987 | 0.006 (0.222) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 3 (0.03) | 2 (0.02) | 2 (0.02) |
| 1988 | 0.005 (0.185) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) | 2 (0.02) |
| 1989 | 0.005 (0.185) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) | 1 (0.01) |
| 1990 | 0.005 (0.185) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) | <1 (0.01) |
Toxicology of Tritium
The final step in our analysis was to compare our estimated radiation doses with radiation doses that cause adverse health effects. In comparing our results to information in the medical literature, it is important to note that no data exist on the effects on human health from exposures to tritium; therefore, it is necessary to extrapolate from other data. We looked at studies of animals and tissue cultures exposed to tritium, low-energy external gamma radiation, or x-rays. We looked at studies of humans exposed to low-energy external gamma radiation or x-rays.
Radiation effects from tritium in the body are similar to effects from low-energy gamma radiation and x-rays [7]. Therefore, we considered studies of humans exposed to gamma radiation and x-rays for information on cancer and developmental effects (exposures to the fetus in utero) that might also result from tritium exposures. We also reviewed studies of animals and tissue cultures for information on developmental effects, cancer effects, and genetic effects (effects on offspring because of exposures to either parent before pregnancy).
The lowest tritium (or low-level gamma radiation or x-rays) dose capable of causing adverse health effects is 3 rad (0.03 gray [Gy])(1) [8]. This dose (3 rad) resulted in abnormal developmental effects when administered (via x-rays) to mice in utero during the development of the central nervous systems. Our maximum predicted fetal dose from tritium in well water is 154 mrem (1.54 millisievert [mSv]), a dose nearly 20 times lower than 3 rad. Central nervous system development in humans occurs between 8 and 15 weeks of gestation [8]. For the period of gestation from 8 to 15 weeks (not in our tables), our maximum predicted dose is 35 mrem (0.35 mSv), or more than 85 times lower than 3 rad.
The kind and severity of developmental abnormalities appear to be related to the amount of exposure and the stage of fetal development at the time of exposure. In humans, mental retardation, intelligence, and school performance were studied in Hiroshima and Nagasaki atom bomb survivors who were exposed to radiation in utero. Exposure to 70 rads (0.7 Gy) resulted in 25% of the children being severely mentally retarded [9]. The dose-response relationship appears to have a threshold at about 25 rads (0.25 Gy). Intelligence tests administered to prenatally exposed atom bomb survivors at 10 to 11 years of age demonstrated a substantial decrease in test scores for those exposed between 8 and 15 weeks of gestation [9]. These data suggest a linear dose-response curve without a threshold and a decrease in intelligence of approximately 25 points per 100 rads (25 points per 1 Gy). School performance was also investigated, and the data also suggest a linear dose-response curve without a threshold [9]. At our predicted prenatal dose during this period of gestation, the effects on intelligence and school performance would not be measurable. Therefore, we do not expect there would be an increase in developmental effects in people drinking water from private wells near the Mound facility.
Another adverse health effect we considered was cancer. High doses (100 to 300 rad, or 1 to 3 Gy) of x-rays to humans (radiologists) and of tritium to mice have been linked to significantly higher rates of leukemia, but the doses were 67 to 200 times higher than the maximum predicted dose in Tables IV and V [7, 10]. The atomic bomb survivor studies showed the lowest leukemogenic dose was in the range of 20 to 40 rads (0.2 to 0.4 Gy); however, these doses (to people in Hiroshima) included a large neutron component. In Nagasaki, where people were not exposed to the large neutron component, an increased incidence of leukemia was not seen in people who received less than 100 rad (1 Gy) [11]. Studies of children who received x-rays in utero indicate there is a threshold dose for radiogenic leukemia that lies in the range of 10 to 50 rad (0.1 to 0.5 Gy) [11]. By analogy, it appears that the lowest tritium dose associated with cancer effects in humans may be approximately 10 rem (0.1 Sv) received by an unborn child. This dose is approximately 65 times greater than the maximum predicted fetal dose in Table III. Data from a United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report in 1972 suggested that exposure of the fetus in utero to doses on the order of 1 to 4 rad, particularly during the first trimester of pregnancy, will increase the incidence of leukemia, but other data in the same report do not support this contention [10]. These levels are still 6 to 10 times higher than the predicted doses from sole use of the well water; therefore, we do not expect an increase in cancer rates because of exposure to tritium.
The next group of adverse health effects we considered are genetic effects. These are effects passed on to children from abnormal sperm or egg cells in parents. The genetic effects we are concerned about are adverse health effects in children that arise from tritium exposures to parents.
We have not identified human populations that show genetic damage from either external radiation or internally deposited radioactive materials, including tritium, that lead to adverse health effects in offspring [10, 12].
From cellular studies, we know that tritium can be incorporated into DNA and RNA molecules during cell proliferation. Radioactive decay in or near the DNA molecules may cause molecular breaks and rearrangements of the gene code, which could lead to mutagenic effects. For genetic effects (passed on to offspring), damage must occur during the maturation stages of the sperm and oocytes [13]. In the sexually mature male, sperm cells are continuously replenished. The cells go through several stages with different radiosensitivities and potential for cell death. Although we know little about the lowest radiation levels required to produce genetic damage in human sperm cells, we do know that 20 doses of 25 rad (0.25 Gy) produce a more rapid drop in the number of sperm cells and the sperm cell populations require greater recovery time than if they are exposed to a single dose of 500 rad (5 Gy). Also, total doses of 50 to 100 rad (0.5 to 1.0 Gy) administered in increments produce temporary low sperm counts after about 3 months of exposure [10]. These doses are more than 30 times greater than the maximum total dose estimated in Tables IV and V. In females, oocytes are produced in the ovary before birth; therefore, oocytes in the fetus before birth would be the most radiosensitive. When pregnant squirrel monkeys received tritiated water throughout their pregnancy that resulted in mean body water concentrations of tritium ranging from 50 to 3,100 microcuries per liter (µCi/L) (1.85 to 114.7 kilobecquerel per milliliter [kBq/mL]), their newborns showed no discernible effects except that the number of primary oocytes in the female offspring decreased markedly with increasing levels of tritium in the maternal drinking water [14]. However, these tritium concentrations are 25 to 1,550 times higher than the maximum concentration predicted in Table II. Therefore, we do not expect genetic effects in humans who were exposed to tritium from the private wells near the Mound facility.
Another health effect not previously mentioned is the reduction in average life span. The measure of average life span in an irradiated population compared with one that is not irradiated accounts for all radiation injuries that contribute to death. Russian researchers found that when they administered tritiated water to animals in small amounts over a prolonged period with total doses of 24 rad (0.24 Gy), the animals' life spans increased by 12%. At 200 rad (2 Gy) total, the life span of irradiated animals was the same as that for controls that were not irradiated. But increasing the total dose to 1,250 rad (12.5 Gy) and 2,500 rad (25 Gy) reduced the animal's life span by 18% and 33%, respectively. The reduction in life span at the higher doses was the same for rats that were carriers of malignant tumors as for rats that did not have tumors. Therefore, the researchers concluded that there is a common mechanism for natural aging and its acceleration that is independent of the presence of cancer, particularly with high total radiation doses [15]. It appears that animals' life spans were not affected at 200 rad (2 Gy) total; this level is more than 130 times greater than the maximum fetal-plus-30-year dose in Table IV. Therefore, we do not expect that drinking water from the private wells near the Mound facility would decrease anyone's life span.
Conclusions
All of the adverse health effects from exposures to tritium (or low-energy external gamma radiation or x-rays) that we found in the medical literature occurred at levels higher than the exposure levels we estimated for people who used the private wells near the Mound facility for their sole source of water. Therefore, we conclude that tritium in the groundwater from the Mound Laboratory was never a public health hazard.
ESTIMATED TRITIUM CONCENTRATIONS IN PRIVATE WELLS
Since 1975, Mound scientists published tritium concentrations in a few private wells off site in and near Bud's Trailer Park. The private wells were sampled once or twice a month for tritium analyses. Sampling results are available in the Mound annual environmental monitoring reports. From the annual monitoring reports, we listed the highest average annual tritium concentrations in private wells for each year from 1975 through 1994 (in Table I).
Mound personnel have documented total annual releases of tritium to the Miami-Erie Canal since 1967. We do not know the specific dates of the tritium releases. Measurements of tritium in canal water are available in environmental reports from 1960 to 1970 and from 1974 to 1978. The canal water was sampled almost daily in some years and weekly in others. Table I also summarizes these data.
This analysis estimates tritium concentrations in off-site well water (in Bud's Trailer Park) for years in which tritium releases or canal concentrations were recorded, but no well water measurements were made (1960 through 1974). Of particular interest is an estimate of the maximum annual average tritium concentration in well water resulting from releases in 1969, the year with the largest documented annual tritium releases (2,332 curies [Ci]).
Assumptions
This analysis reflects the following assumptions:
(1) No significant hydrogeological changes occurred from 1960 to 1990.
(2) No significant tritium releases occurred before 1960.
(3) No undocumented releases occurred in 1971-1973 or 1979-1990. No documented tritium releases (including air releases) other than those to the Miami-Erie Canal resulted in significant tritium concentrations in well water at Bud's Trailer Park.
(4) Tritium releases were roughly continuous during the course of each year.
(5) The fraction of tritium percolating down through the canal to the aquifer was constant for all releases.
(6) Measured tritium concentrations in well water are accurate.
(7) The relative uncertainty in the measured well water concentrations was roughly constant for all measurements.
(8) The tritium release data are accurate.
We do not believe that the Miami-Erie Canal is the sole source for tritium in the wells, though it is probably the primary source. Other sources of tritium affecting the private wells might include tritium fallout in rain (between 1 and 20 nanocuries per liter in the years 1972-1975 at on-site monitoring stations) and leaks from the waste water pipe (National Pollutant Discharge Elimination System Outfall 001) en route to the river [16]. We observe that the average annual well concentrations of tritium in 1975-1978 most closely resemble the maximum measured concentrations in the south canal, rather than the average. This could be because sampling locations in the canal were further from the outfall of the drainage ditch (and therefore more dilute) than were the private wells from the drainage ditch, or because a source higher in concentration than the canal water is affecting the wells. If we are mistaken in assumption # 3, and a significant fraction of the tritium found in off-site wells is from a source other than the Miami-Erie Canal, then our analysis will have overestimated the well water tritium concentrations in the earlier years.
Definitions
S(t) Measured or calculated tritium concentration in canal water in year "t" (pCi/L)
M(t) Measured tritium concentration in well water in year "t" (pCi/L)
M'(t) Predicted tritium concentration in well water in year "t" (pCi/L)
Analysis and Results
(i) Predictions
A chi-squared minimization technique is used to test predicted concentrations M'(t) against measured concentrations M(t). The "best-fit" prediction is the one in which
is minimized. The uncertainties, s, are unknown, but under the assumption of constant relative uncertainty (s µ M), an alternative minimization can be applied:
In the system analyzed here, the response M need not occur instantaneously following the stimulus S. Rather, the response is a functional of the stimulus:
The response function R(t) completely characterizes the physical system. The data to be fit in this analysis are discrete, so a discrete form of the response function may be used:
To find the best predicted measurements, it is necessary to find the response function that meets the minimization condition (2). From the tabulated data, it is clear that the best-fit response function must decrease rapidly with t, falling by orders of magnitude within a decade. It is reasonable, therefore, to keep only the first few terms of equation (4).
R(0) determines the well water concentration resulting from tritium released to the canal in the same year. R(1) determines the concentration resulting from tritium released the previous year, etc.
Values of K2 were calculated for various values of R(0), R(1), R(2), and R(3). It was found that the best fit had
R(0) = 0.794
R(1) = 0.445
R(2) = 0.192
and
K2 = 0.1718
The best fit values for R(3) and higher terms were zero. A plot of the best fit, along with the measured well water concentrations and measured and calculated canal water concentrations, appears in Figure 1.
ii) Uncertainty Estimates
If the model used to fit the data is a good representation of the system, and the canal water and well water concentrations are accurate, we can determine the best estimates in the uncertainties of the model parameters by finding the values of those parameters at which c2 increases by 1 from the minimum. Without knowledge of the measurement uncertainties, s2, we cannot rigorously determine estimates. We used the following method to approximate these estimates:
First, assume that the calculated "best fit" is indeed a good fit to the data. Further, assume that it is not an abnormally good fit, i.e., c2/n for this fit is not significantly less than 1. Then the relative uncertainty in the measured tritium concentrations in well water must be approximately 12%. An increase of 1 in the unreduced c2 corresponds to an increase of about 0.013 in K2. Since this is a rough approximation only, we will arbitrarily increase this by a factor of 4, so that any fit with K2 < 0.22 will be considered a reasonable fit to the measured data. Note that this approximation is robust against the possibility that the chosen model is a poor fit to the data. In that case, we are overestimating the uncertainty.
Using these estimates, we calculated several additional fits. These were chosen to yield extreme values for the various R(t) just meeting the limit on K2. For each year, we extracted the minimum and maximum of these predictions. For each year, these minimum and maximum predicted tritium concentrations differ from the best-fit concentrations by less than 20%. Best-fit, minimum, and maximum predicted concentrations appear in Table II.
The simplest fit to the data, an arithmetic least-squares fit of M(t) to S(t), is equivalent to a response-function fit with R(1) = R(2) = 0. A similar fit assuming all of the response occurs in the year following the release is equivalent to a response-function fit with R(0) = R(2) = 0. These fits predict high tritium concentrations in the well water. The maximum predicted tritium concentration for the first model is 2.9 million pCi/L in 1969. The maximum for the second model is 2.4 million pCi/L in 1970. However, both of these models are very poor fits to the measured data. Both have K2 = 0.49.
Conclusions
Tritium concentrations in the off-site wells near Bud's Trailer Park ranged from about 100,000 to about 2,000,000 pCi/L in the 1960s. The concentration peaked at about 2,000,000 pCi/L in 1969 or 1970, and fell rapidly thereafter.
FIGURE 1. TRITIUM CONCENTRATIONS IN CANAL AND WELL WATER.
References
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