Anal. Chem. 1980, 52, 777-779
777
Determination of Uranium Isotopes in Human Bone Ash Isabel M. Fisenne," Pamela M. Perry, and George A. Welford Environmental Measurements Laboratory, U.S. Department of Energy, 376 Hudson Street, New York, N. Y. 100 14
T h e mass of uranium in air, vegetation, soil, water, tissue, and excreta has been measured primarily by fluorimetry (1-5) and more recently by neutron activation analysis (6-12). Both methods are capable of detecting extremely small masses of uranium. The lower limit of detection a t the 95% confidence level for uranium is 1 ng by fluorimetry (13). T h e sensitivity of neutron activation analysis is estimated t o be 0.05 ng (10, 14). These measurement techniques directly quantitate the 238Umass and provide no information on the 234U/238U and 235U/238U activity ratios in the sample. Analytical methods are available for the determination of the isotopic uranium concentration in soil, sediments and bioassay samples by alpha spectrometry (13, 15-17). There are no reported determinations of the isotopic uranium concentration in human bone. Welford et al. (18) determined the median mass concentration of uranium in 63 vertebrae samples obtained in New York City t o be 2.7 x g U/g of ash. Hamilton (6) reported a mean value, based on t h e measurement of 12 vertebrae samples, of 1.7 X g U/g of ash for the U.K. T h e former determinations were performed by fluorimetry while the latter were obtained by neutron activation analysis. Both investigators have reported a daily dietary intake of approximately 1 Mg U per day ( 3 , 6). Although the difference in the estimates of the uranium mass concentration in human bone between the U.S. and the U.K. might be due t o geographical differences, a high yield analytical method was developed to separate uranium from large quantities of bone ash for measurement by a third technique, alpha spectrometry, in order to establish t h e magnitude of the uranium concentrations in U.S. bone.
Table I. The Half-Lives and &-Energiesof the Principal Members of the Uranium and Thorium Series and Three Tracer Nuclides ( 19 ) nuclide
energies, MeV
uranium series 4.47 x 109 y 2.45 x 105 y '"Th 9.03 x 1 0 4 y 226Ra 1.60 x 103 3.82 d 222Ra 3.05 m 2'8Po 2 1 4 P ~ 1 6 4 ps 210Po 138.4 d 23Su
234U
4.196 (77%), 4.149 (23%) 4.777 (72%), 4.724 (28%) 4.688 (76%), 4.621 (23%) 4.785 (94.5%), 4.602 (5.6%) 5.490 (100%) 6.003 ( 1 0 0 % ) 7.687 (100%) 5.305 (100%)
thorium series 232Th 1.41 X 10" y 228Th 1.913 y 224% 3.67 d '*'Rn 55.6s 216Po 0.145 s Zl2BiQ 60.6 m 2'2Po
0.296 ps
tracer nuclides 232U 71.79 y 233U 1.59 X l o 5 y
2 0 e P ~ 2.898 y "'Th 7.34 X l o 3 y
EXPERIMENTAL Reagents a n d Apparatus. A 30% Alamine-336 v/v with toluene is shaken twice with an equal volume of 6 M HC1 for 5 min. Dilute acids, 6 M and 0.1 M HC1,O.l M NaOH, 0.3 M H2S0, are prepared from analytical grade acids and deionized water. The 232Usolution may be purchased from the Amersham Corp., Arlington Height, Ill. The 2TJ/232U activity ratio is 2 X lo*% and the 234U/232U activity is 2 X for the tracer solution. A mercury cathode electrolysis unit (Eberbach Corp., Ann Arbor, Mich.) and triply distilled mercury are used for the removal of iron. Phenolphthalein and thymol blue indicators, a 100-pL pipet, electrodeposition cells, platinum and nickel disks, a platinum electrode, a motorized stirrer, and a 1.5-A power supply are used in the procedure. Sample Preparation. Transfer 50 g of ground bone ash to a 400-mL beaker and add 0.5-1 dpm 232Utracer solution. Add 100 mL of HCl and gently heat on a hot plate for 10 min with occasional stirring. Add 70 mL of water and stir to obtain a clear solution. The resultant solution should be >5.8 M HC1. The acid normality of the solution may be checked by pipetting 100 pL of the sample in 25 mL of water and titrating the solution with 0.1 M NaOH to the phenophthalein end point. The sample may be diluted or HC1 added, as appropriate, after the measurement of the initial sample volume ( 1 2 ) . Procedure. Transfer the sample with washings to a 500-mL separatory funnel containing 50 mL of pre-washed 30% Alamine-336 and shake for 5 min. Allow the phases to separate and draw the aqueous phase into a second 500-mL separatory funnel containing an additional 50 mL of pre-washed Alamine-336. Shake the separatory funnel for 5 min, allow phase separation, draw off and discard the aqueous phase. (Since uranium and iron are extracted in the organic phase, the efficiency of the extraction process may be gauged visually by the removal of the yellow
half-life
a
4.011 ( 7 7 % ) , 3.957 5.423 ( 7 3 % ) ,5.341 5.686 (96%), 5.449 6.288 (100%) 6.779 (100%) 6.090 ( 2 7 % ) , 6.050 5.769 ( 1 . 7 % ) 8.784 (100%)
(23%) (27%) (5%) (70%),
5.320 (68.7%), 5.264 (31.2%) 4.824 (84.4%), 4.783 (13.2%), others 5.116 (100%) 5.051 (5.2%), 4.968 (6.4%), 4.901 (10.8%),4.845 (56.2%), 4.816 (8.4%), others
36% a-emission, intensity normalized t o 100 a-decays.
Table 11. Decontamination of Uranium from Polonium and Thorium experiment nuclide 1
2=u Po 232u u)8
2
208Po
3
233u
4
2 3 3 u
5
210Po Z3*U 229Th
2'0Po
6 229
a
Th
added 10.5 10.0 10.4 10.6 11.6 8.1 10.0 7.6 11.1 12.0 10.8 13.3
dPm found 8.9 I0.2a 0.10 I 0.02 9.0 * 0.2 0.11 2 0.03 9.4 2 0.2 0.02 t 0.02 8.9 t 0.1 0.02 ? 0.02 9.3 ? 0.3 0.14 * 0.03 9 . 1 * 0.2 0.09 i 0.02
found, % 84.8
I
1.9
1.0 r 0.2
86.5 * 1.0 f 81.0 f 0.3 i 89.0 * 0.3 * 83.8 ? 1.2 * 84.3 2 0.7 t
1.9 0.3 1.7
0.3 1.0 0.3 2.7 0.3 1.9 0.2
1 Poisson standard deviation
coloration from the aqueous phase.) Combine the Alamine-336 phases and wash four times for 5 min each with 100 mL of 6 M HCl. Discard the washings. Strip the uranium and iron from the Alamine-336 by shaking three times for 5 min with 100-mL portions of 0.1 M HC1. Combine the strip solutions in a 400-mL beaker and discard the Alamine-336. Add 1 mL of H2S04to the strip solution and evaporate to sulfur trioxide fumes. Remove any organic material present by the dropwise addition of "OB. The solution is evaporated to dryness and the residue is dissolved in a few drops of HC1.
This article not subject to U.S. Copyright. Published 1980 by the American Chemical Society
778
ANALYTICAL CHEMISTRY, VOL 5 2 , NO 4, APRIL 1980
______ _____ _ _ _ _ _ _ _ _ _ _ . Table 111. Uranium Activity in Composited Human Bone Ash Samples
composite year
amount of ash, g
1965 1967 1969(A) 1969(B)
50. 50.
50. 50.
*"U
-.
234u
0.0007
95. 100. 98.
0.0010 0.0005 0.0008
100. -
Y a 1 Poisson
dpm per g of bone ash
.-
yield, %
2 3 6 u
0.0003a 0.0003
t
0.0002 0.0002 0.0002
1.4 = 1.7 0.7 i 1.6 _c
L
0.0001
1.1 0.4
0.0005 t 0.0001 0.0006
t
0.0003
0.0007 0.0005
c).O008 - 0.0002
0.0006
t
- 0.0002
+
3
0.7 0.8
0.4 1.0
+
standard deviation.
To remove iron, add '75 mL of 0.3 M H,SO, to the sample. stir. and cool to room temperature. Add 20 mI, of mercury to the beaker and electrolyze the solution at 5 A for 1 h. Remove and rinse the electrodes with water. Filter the solution by gravity through a 12.5 cm Whatman =42 paper inro a 250-mL beaker. Wash the filter and mercury with water. (Reserve the mercury in a closed glass container for redistillation.) Discard the filter paper. Evaporate the iron-free uranium solution to H2S04fumes and remove any organic material with a few drops of HN03. The uranium solution is prepared for electrodeposition by the method developed by Talvitie (17). Cool the solution to room temperature and add 0.5 mL of H,SO, and 3 mL of H,O. CS'arm to dissolve any residue and cool to room temperature. Add 2 drops of thymol blue indicator solution. Neutralize to the salmon-pink end point (pH 2) with ",OH. If the end point is ovprstepped to the yellow color, add 1:9 H2S0, dropwise to reach the pink end point. Transfer the solution to the plating cell. Wash the beaker with a total of 6 mL of 1:99 H,SO,, adding the washings to the Place the cell. Reneutralize the solution to pH 2 with ",OH. cell in an ice water bath and electroplate with a rotating anode for 2 h at 1.2 A. Quench the electrolyte with 10 mL of 1.5 M ",OH. Continue the electrolysis for 1 min. Pour off the solution into a beaker and rinse the disk three times with 1:99 ",OH. Disassemble the cell, remove the platinum disk and wash the disk with 95% EtOH. Dry and flame the disk to a red glow over a Meker burner. Determine the isotopic uranium content of the sample by solid state alpha spectrometry.
R E S U L T S AND DISCUSSION T h e members of the uranium and thorium series are the principal a-emitting nuc!ides present, in human bone. A series of experiments were performed to demonstrate the decontamination of 238U and a34LJ from other c1 emitters. T h e CY energies and half-lives of the naturally occurring nuclides and three tracer nuclides are listed in Table I ( 2 9 ) . T h e cu-spectrometry systems used for the measurements were calibrated a t 10 keV per channel and covered an energy range of 2.5 to 12.5 MeV. Under these conditions, any ctemitting nuclide present on the electrodeposited sample disk would be detected during the measurement period. For the chemical methodology described. the only nuclide likely to interfere with the tu-spectrometric determination of the uranium concentration in bone ash is "OPo with an (Y energy within 15 keV of the principle N energy of the 232U tracer. Significant quantities of ""Po are not to be expected in dry ashed bone (>SO0 "C) because of the well-known volatility of this nuclide (20). T o verify the removal of 21"Poin the separation procedure, two experiments were performed in duplicate. Mixtures of approximately equal activities of (a) 232Uand eonPoand (b) 233Uand 'loPo were prepared in 6 M HCI and analyzed as described previously. Although the (Y energies of the '"Th and *%Upair and the 23% and ' T h pair are easily identifiable and accountable, a mixture of ' q h and 232Uwas also prepared as test solutions. T h e results of these six test preparations are listed in Table 11. Only 1% of the '08Po was carried through the procedure while 86 f 1 % of the "*U and 85 f 6% of the 2'i3Uwere recovered. As pointed out by Beasley (16),the actinides extract most efficiently from heavily salted
solutions so that the uranium tracer yields for these pure solutions were obtained with less than ideal conditions. In the extraction of 50 g of bone ash, nearly 20 g of calcium are present and provide the salt conditions for optional extraction. T h e Alamine-336 extraction procedure was then applied to the determination of the isotopic uranium concentration in human hone. The uranium was extracted from 50-g aliquots of composited vertebrae ash, electrodeposited on platinum disks, and measured by solid state alpha spectrometry. T o provide quality control for these analyses, one bone ash sample was analyzed in duplicate and four reagent blanks were also processed for uranium. The reagent blanks were of considerable importance since the lower limit of detection of the alpha spectrometry measurement is dependent on the standard deviations of background and blank for the particular energy region of interest (13, 22). For the Alamine-336 extraction procedure, the lower limit of detection a t the 95% confidence level was 0.005 dpm *%Uper sample and 0.012 dpm aa4Uper sample for a 5000-min counting period with detector efficiencies of 25%. The net measured uranium activities from the four vertebrae samples were in all cases greater than the lower limit of detection by a t least a factor of 2. It must be noted that the bone ash for these demonstration samples was obtained from three United States cities and was not systematically cornposited on an equal weight per subsample basis. These samples should be indicative of the order of the magnitude of the uranium concentration in human bone ash for t.he U.S. population. T h e analytical results obtained for the human vertebrae composite samples are presented in Table 111. The mean 238U activity of 6 X 10 l o dpm/g of bone ash may be converted t o a mass per gram basis using the 238Uhalf-life of 4.468 X lo9 y (19). This value is 8 X lo-'' g 238U/gof human vertebrae ash, within a factor of 3 of the median uranium bone ash value reported by Welford e t al. for New York City (18) and more than a factor of 20 lower than that reported by Hamilton for the United Kingdom (6). Edgington (22) reported a single value of 4 x IO-' g '38U/g of human femur ash, in agreement with the current estimate for the US.population. In addition, the isotopic uranium concentration determinations allow us to calculate the 23U/238Uin human bone ash. From Table XI, it can he seen that the activity ratio for these isotopes is unity within the error of the ratio. This indicates no preferential deposition of either uranium isotope in human bone.
CONCLUSION A method has been developed for separation of uranium from 50 g of human bone ash. T h e Alamine-336 extraction scheme, coupled with alpha spectrometry measurement, provides a reliable high yield method for the determination of the isotopic uranium concentration in this matrix.
LITERATURE CITED (1)
Price, G.
R . ; Ferretti, R . J.: Schwartz, S . Anal. Chem. 1953, 25,
322-331. (2) Hoffman, J. U . S . A t . Energy Comm. Rep. 1943, AEC-b-2663. (3) Welford, G . A,: Baird. R . Health Phys. 1967, 13, 1321-1324.
Anal. C h e m . 1980, 52, 779-780 (4) Quigley. J. A.; Heatherton, R. C.: Ziegler J. F., U . S . At. Energy Comm. Rep. 1958, HASL-58, 33-40. (5) Boirie, C.; Bosc. D.; Hugot. G.; Platzer, R. Acta Chim. Hung. 1962, 3 3 , 281-287. (6) Hamilton, E. I. Health Phys. 1972, 22, 149-153. (7) Donoghue, J. K.; Dyson, E. D.; Hislop, J. S.; Leach, A. M.; Spoos, N. L. Br. J . Ind. Med. 1972, 29, 81-89. (8) Dyer, F.F.; Emery, J. F.; Leddicotte. G. W. U . S . At. Energy Comm. Rep. 1962, ORNL-3342. (9) Gale, N. H. "Radioactive Dating and Methods of Low-Level Counting", IAEA; Vienna, 1967; pp 431-452. (10) Nozaki, T.: Ichikawa, M.; Sasuge, T.; Inarida, M. J . Radioanal. Chem. 1970, 6 , 33-40. (11) Gladney, E. S.: Rook, H. L. Anal. Chem. 1975, 47, 1554-1555. (12) Gladney, E. S.; Hensiey, W. K.: Minor, M. M. Anal. Chem. 1978, 5 0 , 652-653. (13) Harley, J. H., Ed. "EML Procedures Manual", U.S.Dept. Energy Rep. 1976, HASL -300.
779
(14) Decat, D.; Van Zanten, 6.; Leliart, G. Anal. Chem. 1963, 35, 845-847. (15) Sill. C. W.; Puphal, K . W.; Hindrnan, F. D. Anal. Chem. 1974, 46, 1725-1 737. (16) Beasley, T. M. Health Phys. 1965, 74, 1059-1065. (17) Veselsky, J. C . ; Kirl, P. C.; Sezginer, N. J , Radioanal. Chem. 1974, 21, 97-106. (18) Welford, G. A.; Baird, R.; Fisenne, I. M. Proc. 70th Midyear Top. Symp. Health Phys. SOC. 1976, 239-244. (19) Lederer, C. M.; Shirley, V. S. "Table of Isotopes". 7th ed.; John Wiley and Sons: New York, 1978. (20) Cleary, J. J.; Hamilton, E. I. Analyst (London) 1968, 9 3 , 235-236. (21) Currie, L. A. Anal. Chem. 1968, 4 0 , 586-593. (22) Edgington, D. N. Int. J . Appl. Radiat. hot. 1967, r8, 11-18.
RECEIVED for review September 13. 1979. Accepted January 15, 1980.
Determination of Dissolved Kepone by Direct Addition of XAD-2 Resin to Water Richard L. Harris," Robert J. Huggett, and Harold D. Sone Virginia Institute of Marine Science a n d School of Marine Science, College of William a n d Mary, Gloucester Point, Virginia 23062
Kepone (decachlorooctahydro-1,3,4-metheno-2H-cyclobuta[c,d]pentalen-2-one), a chlorinated hydrocarbon pesticide,
The filters were then Soxhlet extracted with 1:l. (v/v) diethyl ether/petroleum ether ( 4 ) . No Kepone was detected (lo L) of water, yet retain the use of the highly sorptive polymer resins to collect nanogram quantities of organics, an analytical procedure was developed to quantify parts-per-trillion concentrations of Kepone by the addition of XAD-2 resin directly t o water. To alleviate the problem of reduced XAD extraction efficiency from accumulation of suspended solid in the resin ( I I ) , water samples were vacuum filtered through a manifold filtration setup containing 0.8-pm Millipore filters. This filtration was necessary prior t o XAD column elution to remove suspended solids and to quantify only "dissolved" Kepone, which is defined here as Kepone in water samples with no particles > O B pm. T o determine if Kepone could be adsorbing onto the Millipore filter, 20 L of distilled water containing 25 n g / L dissolved Kepone was passed through 0.8-pm Millipore filters. 0003-2700/80/0352-0779$01 0010
EXPERIMENTAL Apparatus. Analysis of the extracts for Kepone was carried out using a Tracor Model 222 gas chromatograph with an electron capture detector. The gas chromatographic conditions were: detector-electron capture (63Ni)350 "C, injector 220 "C, column 210 "C, carrier gas 95% argon/5% methane, flow: 80 mL/min. The column was 6 f t X 2 mm i.d. glass, 1.5% OV-l7/1.95% QF-1 on 100/120 Chromosorb W HP. Reagents. All solvents were chromatography grade, distilled-in-glass (Burdick and Jackson Laboratories). The 86.6% pure Kepone reference standard (Environmental Protection Agency, Research Triangle Park. N.C.) was used as supplied and stored in a desiccator. The XAD-2 polymer resin (Rohm and Haas) was purified by a 24-h Soxhlet extraction with methanol ( 8 ) ,and stored in methanol. Florisil (Floridin Co.) was kept in an oven at 135 O C . Procedure. At least 20 I, of York River water (19% salinity, pH 7.8) was prefiltered through 0.8-pm Millipore filters and collected in a polyethylene carboy. The carboy was placed on a magnetic stirrer, Kepone dissolved in acetone was added, and the water stirred for several minutes. Sixty grams of precleaned XAD-2 resin was added and the water and resin were stirred for at least 8 h. The water was then vacuum filtered through a Buchner funnel containing Whatman z1 filter paper (18.5 cm). The collected XAD-2 resin was placed in a 500-mL glass beaker on a magnetic stirrer, and stirred for 10 h with 200 mL 1:3 (v/v) toluene/ethyl acetate mixture. After vacuum filtering the resin-organic mixture and collecting the resin on Whatman ;1 filter paper (9.0 cm), the resin was again extracted with 200 mL of 1:3 (v/v) toluene/ethyl acetate for 10 h. Each extract was then placed C
1980 American Chemical Society
