Natural Radioactivity and 137Csin Alaskan Caribou and Reindeer Samples Richard L. Blanchard and Jasper W. Kearne!
U. S. Department of Health, Education, and Welfare, Public Health Service, National Center for Radiological Health, Radiation Bio-effects Program, Cincinnati, Ohio 45226
The concentrations of zl@Po,zl@Pb,226Ra,and 137Cs were determined in bone, muscle, and rumen content of caribou and reindeer from Alaska. The ?loPoand l37C.s concentrations in the muscle varied with the season, reaching a maximum in spring and a minimum in the fall. A similar variation in the 210Poand 137Cs concentrations was observed in the rumen content. The relationships of 21@Po and l3jCs between muscle and rumen content are examined. The ?loPoto 210Pbratio in muscle also varied during the year reaching a maximum in the spring. The zloPbcontent of the bone did not appear to vary with the season; however, a n increase occurred with increasing latitude and age. Except for animals one year or less in age, the 210Poto zloPbactivity ratio was near unity. The specific activities of zz6Rain bone and muscle were small in comparison with the concentrations of ?l@Pb, zlOPo,and l3Q.
A
rctic ecosystems have received increased attention during recent years because of their capacity to transmit significant amounts of radionuclides to human populations. Studies conducted during the last 5 to 6 years have revealed unusually high levels of the fission products, 9@Sr and 137Cs, in Swedish and Finnish Laplanders (Liden, 1961 ; Miettinen and Hasanen, 1967), and in Alaskan Eskimos (Schulert, 1962; Watson, Hanson, et al., 1964; Hanson, 1966; Hanson and Palmer, 1964, 1965). More recently, high concentrations of 21@Pband zlOPohave also been observed in Arctic Eskimos (Hill, 1965, 1966), reindeer and caribou (Hill, 1965; Beasley and Palmer, 1966; Holtzman, 1963a), and in other biological materials from the Arctic (Hill, 1965; Beasley and Palmer, 1966; Holtzman, 1966). [Concentration in this paper will refer to specific radioactivity, picocuries (pCi.) per gram or per kilogram, unless otherwise stated.] The source of the 210Pbis undoubtedly from the decay of atmospheric 222Rn(Hill, 1960; Blanchard, 1966; Holtzman, 1965). Lead atoms so formed eventually return to the earth's surface primarily in rainfall and are continually accumulated by lichens during their long life span. During the winter months, lichens become the prime diet of caribou and some reindeer, which in turn constitute a substantial portion of the diet of many Laplanders and Alaskan natives. Cesium-137, produced in the atmosphere by nuclear detonations, returns to the earth's surface and is accumulated by lichens similar t o
[email protected], in the Arctic ecosystem conditions exist in which both artificial and natural radionuclides are of considerable interest. 932 Environmental Science and Technology
The purpose of this study was to investigate in detail the intermediate link in this food chain, lichen-caribou(reindeer)man, and to estimate, since no specific data are available, the dietary intake of zl@Pb,210Po,and l3?Cs.
Analytical Procedures Determination of ?loPo and *lOPb.The procedure employed for the determination of ?LoPowas similar to that described by Minto (1950) and Black (1961). Samples were dissolved in hot concentrated H N 0 3 and fumed in 7 2 z HCIOl until the solution became clear. The solution was then neutralized with 18N NaOH, diluted to 100 ml. with distilled water in a 150-ml. beaker, and made 0.5N in HCI. Two-hundred milligrams of ascorbic acid were added, and the solution was heated t o 85" C. beneath a watch glass. The sample was then placed in a constant-temperature bath at 85" C. and a 1.5inch silver disk (coated on one side with polyethylene to allow deposition to occur on only one side) was suspended in the solution on a platinum wire for 4 hours. During the electrochemical deposition, the solution was stirred at 400 r.p.m. with a glass stirring rod, and the sides of the beaker were washed with distilled water every hour. After deposition, the silver disks were rinsed with distilled water and allowed to dry at room temperature. The alpha activity of the 21aPo deposited on the disk was measured in a low-background (0.2 to 0.8 c.p.h.) ZnS (Ag) scintillation counter. To measure the amount of ?lOPbin the sample, the solution from which the ?1@Po had been plated was stored from 4 to 6 months. The solution was then returned to a 150-ml. beaker, 200 mg. of ascorbic acid were added, and the zlOPoformed in the decay of the *'OPb present was deposited on a second silver disk by the above procedure. The amount of ?loPo obtained on the second deposition was a measure of the ?l0Pb in the sample. After the 210Pb was determined, the 210Po concentrations were corrected for decay and ingrowth to the time of collection. The recovery of the 21@Po on the silver disks was monitored by spiking every tenth sample with a National Bureau of Standards standard R a D E F solution. Recoveries varied from 88 to 101 % with an average of 94 =t4 2 . To obtain a more reproducible basis for reporting bone weights, the bone samples were fat-extracted with anhydrous benzene. Less than 0.1 % of the ?loPoand zl@Pb was lost from the bone samples during the benzene extraction. Determination of 137Cs. The concentration of 137Cs was determined by gamma spectroscopy as described by Hagee, Karches, er al. (1960). Solutions of digested sample material used for the z10Po-210Pb analyses were diluted to 100 ml. in a
plastic container and analyzed for 100 minutes on a 4- X 4inch NaI(T1) crystal coupled through a preamplifier to a 400 channel model ST-400 Victoreen pulse-height analyzer. The 137Cs gamma activity was obtained by summing the 0.662 m.e.v. peak and subtracting background and the 4OK compton contribution. The counting efficiency of the 0.662 m.e.v. gamma-ray for the 100 ml. sample was determined to be 8.3 & 0.1 %. Determination of 226Ra. The 226Racontent was measured by the radon emanation method (Lucas, 1961; Blanchard, 1964). In each case, the 226Racontent was measured in the same sample used for the 210Poand zloPb analyses. Results
Samples of caribou and reindeer bone, muscle, and rumen content were collected from herds in 15 Alaskan locations, ranging from the peninsula to north of the Arctic Circle and from the sea coast to near the Canadian border. The samples, collected by the Alaskan Department of Fish and G a m e and the U. S. Bureau of Indian Affairs, were preserved in Dry Ice during shipment. Table I lists the sites from which caribou and reindeer were sampled. These sampling locations are shown in Figure 1; the numbers correspond to the figure designation in Table I. The number of animals taken, the location, and the dates on which the animals were sacrificed are given in Table I. One bone and one muscle sample were collected from each animal, and the rumen contents were composited into one sample. In the last column is listed the range in age of the animals sampled. Caribou (Rang$& tarandus stonei) were sampled from all sites except at Nunivak Island, Teller, Shishmaref, and Nome from which reindeer (Rangifer tarandus granti) were taken.
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The mean zlOPoand 210Pbconcentrations in the Alaskan caribou and reindeer bone, muscle, and rumen content samples are given in Table 11. The errors shown represent one standard error of the mean. The bone samples analyzed were the midshafts of the femur, and the results are based upon defatted weights. The average weight ratio, defatted weight to fresh bone, was 0.66, with an average deviation of 0.05. The results of the meat samples, obtained from the hock, are based on fresh weights. Owing to the obvious effect which age had upon the bone and muscle results for samples NI-4, the results are given separately for the two age groups, 1 year and 1/3 year. The results for the rumen content are given as the mean of three analyses of the composite sample. The rumen samples were dried overnight at 96" C. prior to digestion. The mean l37Cs concentrations of the caribou and reindeer meat and rumen content samples are given in Table 111. The errors shown are for one standard error of the mean. Again the results for the rumen content are given as the mean of three analyses of the composite sample. The results for the muscle samples refer to wet weight and the results for the rumen content refer to dry weight. Owing to the small concentration of 226Rain these caribou and reindeer samples, especially in the muscle, the samples which had been previously analyzed for ?loPo, ?I0Pb, and I3;Cs were combined according to the time of slaughter and location, and analyzed as one sample each of muscle and bone. Since each meat sample consisted of 20 grams and each bone sample 3 grams, the analysis of the sum will reflect an average value. The results of the ?26Raanalyses are listed in Table IV. The errors shown are for a two standard deviation counting error ( 2 ~ )Not . all samples were included in the ??'jRaanalysis because of the small concentration in the meat and, hence, the smaller importance attached to it relative t o 210Po,'?l0Pb,or l3;Cs from the standpoint of radiation exposure through ingestion. I n some cases, the ?2FRain the muscle could not be detected at the 95 confidence level, and the concentration in those cases can be given only as being 5 0 . 2 2 pCi. per kg. Discirssion
PACIFIC OCEAN
-
0
5 0 100
100
300
MILES
Figure 1. Locations in hleska from which reindeer and caribou samples were obtained
The concentration of ?loPo and eloPbin bone is of interest because the skeleton acts as a n internal reservoir for these nuclides. The concentrations found in the caribou and reindeer bone samples are considerably greater than those observed in beef femurs from the central United States. The concentrations of ?loPbfound in two beef femurs were 261 = 7 and 307 i 12 pCi. per kg. These values are similar to those reported by Holtzman (1963b) and Lucas and Di Ferrante (1966), and they are at least an order of magnitude less than that found in the caribou and reindeer bone. Except for the young animals, NI-4, the 210Poto 210Pbactivity ratio in the bone is similar to that reported for human bone (Holtzman, 1963b), varying from 0.59 to 1.0 with an average of 0.78 i 0.03. This ratio is about 30z higher than one reported by KaLiranen and Miettinen (1967) for the shinbone of six reindeer from Finland. Because the effective half-life of ?lOPb in bone is long compared with the 138-day physical half-life of ?loPo, one explanation for the lack of equilibrium between 210Pband 210Poin bone is the partial removal of 210Poafter it is formed by the decay of ?loPb. A higher or lower ratio may be due to the type of bone analyzed. Since a greater Volume 1, Number 11, November 1967 933
Table I. Alaskan Caribou-Reindeer Sample Collection Data Figure Designation
1 1
1 2 2 2 2 2 3 4 5
6 7 7 8 9 10 11 11 12 13 14 15
Site
Sample No.
Date Collected
No. of Animals
Anaktuvuk Pass Anaktuvuk Pass Anaktuvuk Pass Nunivak Island Nunivak Island Nunivak Island Nunivak Island Nunivak Island Butte Lake Soule Lake Cinder River Pilot Point Ugashik Lake Ugashik Lake Tyone Lake Monsoon Lake King Salmon Teller Teller Copper Glacier Shishmaref Black Mountains Nome
AP-1 AP-2 AP-3 NI-1F NI-IA NI-2 NI-3 NI-4 BL-1 SL-1 CR-1 PP-1 UL-1 UL-2 TL-1 ML-1 KS-1 T-1 T-2 CG-1 s-1 BM-1 NO-1
9120165 11/16/65 3115/66 10115/65 10115/65 1/10/66 4/1/66 8/24/66 7/27/65 7/28/65 8/26/65 9/29/65 9/29/65 3/31/66 9/29/65 9/25/65 1/10/65 1/30/65 6/16/66 12/4/65 1130165 3/23/66 6/13/66
5
Age Range, Y r .
2-3 2-3 1-6 2 years plotted against the ratio of the average *lOPbbone concentration of animals < 2 years to the average *loPbbone concentration of animals > 2 years. A linear correlation between age and the concentration of *lOPbin bone is clearly visible, and the linear correlation coefficient was calculated from these data to be 0.87 (P = 0.001). Except for the very young animals, NI-1F and N1-4, age did not appear to have any effect on the concentration of *'OPo in muscle. The concentration of *loPoin the muscle of fawns sampled on Nunivak Island was about Ijrg as great as that found in the muscle of adult reindeer collected at the same time. This may be due to a smaller intake per day and to less ? l o P oavailable in the skeletal reservoir for redistribution. Note the low ?l@Pb and 210Poconcentrations in the bone of the young reindeer of NI-4. Lower concentrations might also be expected for fawns that are being suckled or were recently weaned. 936 Environmental Science and Technology
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Concentration of 210Poin muscle VS. rumen content
A large variation of 210Poin muscle with season, however, is quite evident. The results obtained for the Nunivak Island samples are listed in Table V according to the season of the year in which they were collected. The concentration of 210Po in the meat increased by a factor of 4 from fall to earl) spring. This seasonal variation in muscle content of 210Po is very similar to that reported for 13jCs(Hanson and Palmer, 1965; Liden and Gustafsson, 1967; Lindell and Magi, 1967). The low 210Pocontent of muscle collected in August is undoubtedly biased t o some degree by the young age of these animals. Surprisingly, as the loPo content increased markedly with the winter months, the *lOPbcontent remained nearly constant, producing a large increase in the 210Poto *lOPbratio in the muscle. This variation in the 210Poto *lOPbratio with season was generally observed in muscle samples from all collection sites. The 210Po activity associated with the Nunivak Island muscle samples exceeds those observed in muscle samples from the mainland. The l3;Cs muscle content of the Nunivak samples were also high with respect to mainland samples, and relatively high levels of 9% have also been reported for the Nunivak Island reindeer (Watson, Hanson, et al., 1964). These reindeer are from a managed herd on the island, and the high radionuclide levels may be a consequence of different food habits or greater precipitation (Watson, Hanson, etal., 1964). There is also a definite increase in the concentration of *lOPband 210Poin the rumen content during the winter months followed by a decrease during the summer months, similar to that observed for 210Poin the muscle. This seasonal cycle observed for ?loPo in muscle and rumen content indicates
1
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3
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Figure 4. Concentration of ZlOPo os. concentration of 137Cs in rumen content
that the biological half-time for zlOPoin muscle is short and directly related to the rate of intake. The relationship of the concentration of 210Poin muscle t o that in the rumen content is shown in Figure 3. An increase in the concentration of zlOPoin the rumen content is generally reflected by a n increase in the muscle. A linear correlation coefficient of 0.85 ( P = 0.001) was calculated for this relationship. This correlation is good when considering biological differences, size of sample analyzed, and the fact that the concentration in the meat reflects the intake over a number of days while the concentration in the rumen content reflects only that which was ingested less than 10 dabs before slaughter (Dukes, 1955). The ?loPoto z l a P bactivity ratio in the rumen content, similar to lichen, is near unity (Kauranen and Miettinen, 1967; Blanchard, 1967a); however, the *loPb and zlOPoconcentrations in the rumen content during the winter months appear to exceed that normally reported present in lichens. Concentrations of 210Poand ?I0Pb in Alaskan lichens have been reported to range from about 8 to 20 pCi. per gram dry weight (Holtzman, 1963a; Blanchard, 1967a). This same apparent discrepancy has been observed for l37Cs, and Hanson, Watson, et al. suggested that this may be due to animals eating lichens other than those normally sampled (1967). Holtzman (1963a) reported 61 pCi. per gram in a n Alaskan lichen sample which would indicate that lichens are available which contain larger quantities of 210Poand 210Pb than normally observed. Even though the initial sources of l37Cs and zlOPodiffer, some correlation may exist between the two nuclides in rumen content and caribou muscle since their mode of de-
Table V. z10Pb-210Po Content of Reindeer Muscle and Rumen Content from Nunivak Island Rumen Content, Muscle, pCi.jKg. pCi./Gram z1op0 21OpI) ZlOPo/ 2lOpo 2IOPb 21opo/ Season 2 10pb'
21opb'
Fall (Oct.) Winter(Jan.) Spring (Apr.) Summer (Aug.)
135 257 507 58
7.5 10 7.1 15
18 28 73 3
... 16.7 25 8 4 5
... 20.6 28.7 5.2
... 0.81 0.90 0.87
position is assumed t o be the same and since both tend to concentrate in lichen. The relationships between zlOPoand 137Csin the rumen content and in muscle samples are shown in Figures 4 and 5 , respectively, The linear correlation coefficients calculated for these two nuclides in rumen content and muscle are 0.78 (P = 0.005) and 0.69 (P = 0.01), respectively. The reason that a better correlation is not realized is probably the result of their two different initial sources, 2 2 2 R nemanation from the ground and 1 3 T s from nuclear detonations. Although Jaworowski (1966) recently reported that approximately one-half of the Arctic, ?loPbmay have been produced by nuclear detonations in the Arctic the absence of a n increased l0Pb atmospheric content following Arctic nuclear detonations (Patterson and Lockhart, 1964), as well as observations by other investigators (Hill, 1965; Holtzman, 1963a; Blanchard, 1966), discounts nuclear detonations as a significant source of environmental *lOPband, consequently, zloPo. Volume 1, Number 11, November 1967 937
. .
.1
e
The average concentration of 226Rafound in the caribou and reindeer bone, 265 =t 118 (S.D.) pCi. per kg. defatted weight, is in the range but lower than that found by Di Ferrante (1964) for bovine bones from animals of a comparable age. This may be due to the relatively lower concentration of 226Rareported to be present in lichens relative to other types of vegetation (Holtzman, 1966). This is demonstrated in reindeer bone from the Nunivak Island herd, NI-2 and NI-3, and the Teller herd, T-1. These animals feed on sedges and grasses other than lichen t o a larger extent than d o the caribou (Chandler and Snavely, 1966). I n each case, where both 226Raand 210Pbbone data are available, the zloPbconcentration is considerably greater than the concentration of 226Ra.The average 226Rato zloPbactivity ratio in bone was calculated to be 0.053 & 0.021 (S.D.), which indicates that very little of the zloPb present in the bone is produced by the decay of the 226Raparent in the bone. Consequently, nearly all of the zloPb observed in the bone is the result of the direct ingestion of 210Pb. The concentrations of 226Rain the muscle were, in all cases, much smaller than for zloPo. The somewhat higher concentration of 226Raobserved in the muscle samples of reindeer from Nunivak Island, samples NI-2 and NI-3, may, as in the case for the bone, be a consequence of their diet. Assuming the 226Raconcentrations of samples AP-1 and UL-2 to be 0.22 pCi. per kg., the average activity ratio, 226Rato 210Po,is only about 4 X 10-3. Consequently, the internal radiation dose from 226Ra,received by Alaskan natives consuming caribou meat, is insignificant when compared with the dose contributed by 210Poand l3'Cs. The segment of the Alaskan population that utilizes caribou or reindeer as food will obviously have much higher body burdens of these radionuclides than populations that do not include these meats in their diets. For example, the natives at Anaktuvuk Pass slaughter caribou for food twice a year, in fall and spring, coinciding with the migration of the Arctic herd through the Pass (Hanson and Palmer, 1964). This meat is then stored and consumed throughout the year. If it is assumed that the adult Eskimo consumes 0.8 kg. of meat per day (Hanson and Palmer, 1965), and taking the average zloPo, 210Pb,and 137Csconcentrations in the fall and spring dressed meat to be 233 and 13.9 pCi. per kg., and 14.9 nCi. per kg., respectively, the adult Eskimo at Anaktuvuk Pass will ingest on the average approximately 200 pCi. of 210Po, 11 pCi. of 210Pb,and 12 nCi. of 13Tseach day. I n comparison, zloPb ingested by adults in the conterminous United States is estimated t o be about 2 pCi. per day (Holtzman, 1963b), with somewhat less than this amount of 210Po.The 13jCsintake has been reported to be about 60 pCi. per day for 9- to 12year-old children in mid-1966 (Radiol. Health Data Rep., 1967a). Considering dietary consumption, the intakes for 938 Environmental Science and Technology
.
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Figure 5. Concentration of 310Pocs. concentration of I3;Cs in caribou and reindeer muscle
adults would probably not exceed this amount by more than 20% (Radiol. Health Data Rep., 1967b). Reindeer from the Seward Peninsula area are consumed locally, while reindeer meat from the government-owned herd on Nunivak Island is shipped to the lower Kuskokwim River Basin, Anchorage, Fairbanks, Juneau, and Seattle, (Chandler and Snavely, 1966). Although the meat from the Nunivak Island herd reflects the highest levels of 210Poand 13iCs observed in the herds studied, the fact that reindeer are usually slaughtered in the fall minimizes the zlOPoand T s intake by individuals consuming the meat from Nunivak Island. Therefore, meat shipped from the Nunivak Island herd would probably more closely reflect the 135 pCi. per kg. 210Polevel than the higher concentrations present in the winter killed meat. In addition, because the 210Po in the meat is not supported by 21aPb,storage of the meat prior to consumption will tend to reduce the amount of 210Poingested. Very few 210Pband 210Pomeasurements on Eskimos have been reported. Hill (1965) has measured the 210Pbin a rib bone from a 42-year-old resident of Igloolick, N. W. Territory, Canada, and found the concentration to be 15 times greater than that observed by Holtzman (1963b) in autopsy specimens from individuals residing in Illinois. Hill (1966) has also measured zlOPoin human placentas and found concentrations 80 times greater in caribou- and reindeer-eating residents of northern Canada than in residents of the United Kingdom. I n addition, Beasley and Palmer (1966) report 210Pourine levels from residents at Anaktuvuk Pass 230 times higher than those observed by Sultzer and Hursh (1954) from individuals exposed only to normal environmental levels of 210Pband 210Po. It is very difficult to calculate even an approximate body
burden of *loPoone might expect as a result of eating caribou or reindeer meat. The exponential model of nuclide metabolism used to calculate the body burden from intake, as well as the necessary biological data for 21nPopresented by the ICRP Committee I1 Report (1960), may be in substantial error (Holtzman, 1966; Blanchard, 1967b). Beasley and Palmer (1966) estimated the dose of 210Porelative to l3?Cs by assuming the maximum permissible concentration of 21nPo and ‘;j7Csare the same in meat as in water. They calculated an MPC 1 3 T s per MPC 210Poof 30, meaning that ?loPo present in the same concentration as 13Cs would provide 30 times the radiation dose. Applying this factor to the average concentration of 210Po and l3iCs in Anaktuvuk Pass caribou killed in the spring and fall, the dose contributed by ?loPo 0 253 X 30 = 0.51. That is, an relative to ’;j7Cswould be 14.9 Eskimo who has the maximum body burden of l3Ts would be overexposed by about 5 0 z . Since it is known that some Eskimos have body burdens of approaching the maximum which has been recommended by the I C R P for a general population (Palmer, Hanson, et a/., 1965), it is possible that some Alaskan populations may be overexposed due to the combined dose of 13Csand 210Po. AcX no w/e(/gnient
The authors are grateful t o Ewald Pyzel, Southwestern Radiological Health Laboratory, USPHS, who supplied the caribou and reindeer samples, and of this laboratory, Alex Martin and James Moore who provided the 13Cs and 22fiRa analyses, and Bernd Kahn for his many helpful suggestions. L.iteruture Cited
Beasley, T. M., Palmer, H. E., Science 152, 1062 (1966). Black, S. C., Health Phj)s. 7, 87-91 (1961). Blanchard, R . L., “Environmental Health Series,” U. S. Public Health Service 999-RH-9 (1964). Blanchard, R. L., Nature 211, 995-6 (1966). Blanchard, R. L., Radioecological Concentration Processes; Proc. Intern, Symp., Stockholm, April 25-29, 1966, B. Aberg and F. P. Hungate, Eds., pp. 281-96, Pergamon Press, N . Y., 1967a. Blanchard, R. L., Health P h ~ ~13, s . 625-32 (1967b). Chandler, R . P., Snavely, D. R., Radio/. Health Datu Rep. 7, 675-89 (1966). Di Ferrante, E. R., Health Phys. 10, 259-64 (1964). Dukes, H. H.. “The Phvsiologv of Domestic Animals.” pp. 365-6, Comstock Pul&she;*Assoc., Ithaca, N. Y., 1955. Hagee, G. R., Karches, G. J., Goldin, A. S., Talanta 5, 36 (1960). Hanson, W. C., Palmer, H. E., Trans. N . Am. Wildlife Conf. 29, 215-25 (1964). Hanson, W. C., Palmer, H . E., Heulth Phys. 11, 1401-06 (1965).
Hanson, W. C . , Science 153, 525 (1966). Hanson, W. C., Watson, D . G., Perkins, R. W., RudioecoIogicul Concentration Processes; Proc. Intern. Symp., Stockholm, April 25-29, 1966, B. Aberg and F. P. Hungate, Eds., pp. 233-45, Pergamon Press, N. Y., 1967. Hill, C. R., Nnrrrve 187, 211-12 (1960). Hill, C. R., Nuture 208, 423-8 (1965). Hill, C. R.,Science 152, 1261 (1966). Holtzman, R.B., ANL-6769, 59-65 (1963a). Holtzman. R . B.. Health Ph13s. 9. 385-400 (1963b). Holtzman; R. B:, First IRPA Congress, Rome, ’Italy, Sept. 5-10 (1966). Holtzman, R’. B., Health PIIJS.11, 477-80 (1965). I.C.R.P. Committee I1 on Permissible Dose for Internal Radiation (1959), Heulth P17j.s. 3, 219-20 (1960). Jaworowski, Z., Nuture 212, 886-9 (1966). Kauranen, P., Miettinen, J. K., Rudioecologicul Concentration Processes; Proc. Intern. SJ,nip., Stockholm, April 25-29, 1966, B. Aberg and F. P. Hungate, Eds., pp. 275-80, Pergamon Press, N. Y . , 1967. Liden, K.. Acru Rudiol. 56, 237 (1961). Liden, K.: Gustafsson, M., Rudioecologicul Concentration Processes; Proc. Intern. S~,nip.,Stockholm, April 25-29, 1966, B. Aberg and F. P. Hungate, Eds., pp. 193-208, Pergamon Press, N. Y . ,1967. Lindell, B., Magi, A., Rudiioecologicul Concentrution Processes; Proc. Intern. S p p . , Stockholm, April 25-29, 1966, B. Aberg and F. P. Hungate, Eds., pp. 217-19, Pergamon Press, N. Y . ,1967. Lucas, H. F., ANL-6297, 55 (1961). Lucas, H. F., Di Ferrante, E. R., Rudiol. Res. 27, 718-26 (19 66). Miettinen, J. K . , Hasanen, E., Rudioecologicul Concentrution Processes; Proc. Intern. S ~ w p . Stockholm, , April 25-29, 1966, B. Aberg and F. P. Hungate, Eds., Pergamon Press, N. Y., 1967. Minto, W. L., “Biological Studies with Polonium, Radium, and Plutonium,” p. 15, R . M . Fink, Ed., McGraw-Hill, New York, 1950. Nelson, N. S., Rust, J. H., A.E.C. Document No. COO-1148-4 (1966). Neuman, W. F., Neuman, M. W., “The Chemical Dynamics of Bone Mineral,” University of Chicago Press, Chicago, Ill., 1958. Patterson, R . L., Lockhart: L. B., “The Natural Radiation Environment,” pp. 383-92, J. A. S. Adams, Ed., University of Chicago Press, Chicago, Ill., 1964. Palmer, H. E., Hanson, W. C., Griffin, B. I.. Brabq, L. A , , Science 147,620 (1965). Rudiol. Heulth Datu Rep. 8, 15-18, No. 1 (1967a). Rudiol. Heulth Data Rep. 8, 271-5, No. 5 (1967b). Schulert, A. R., Science 136, 146-8 (1962). Sultzer, M., Hursh, J. B., Arch. Ind. Hj3g. Occupcitiontil Med. 9,89 (1954). Wasserman, R . H., Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva, P/816 (1958). Watson, D. G., Hanson, W. C., Davis, J. .I.,Science 144, 1005-09 (1964). Receiced J;)r recien. June 26, 1967. Accepted October 26, 1967, Volume 1, Number 11, November 1967 939
