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Rubidium-87 Concentration in Market Milk
Rubidium-87 Concentration in Market Milk G. K. MURTHY Milk and Food Research, National Center for Urban and Industrial Health U. S. Public Health Service Cincinnati, Ohio Abstract
Market milk samples collected on a quarterly basis from various cities in the United States were analyzed for rubidium (Rb) content by atomic absorption spectrophotometry. The 8~Rb concentrations were computed from the specific activity data. The average =Rb of milk varied from 14.2 to 84.8 p C i / k g of sample. Statistical analysis of the data showed that the ~Rb concentration in milk from various cities was significantly different at a = 0.01. I n addition, samples from cities in the Southeast showed significant differences from one sampling period to another. In general, the ~Rb concentration in milk from inland states was less than that of milk from cities of coastal states and those lying i n the Missouri and Mississippi Valley. Rubidium-87 (~Rb) is a naturally occurring radioactive element. The presence of Rb in milk has been demonstrated, and a review of early work has indicated that it exists in fairly constant amounts (1.5 to 3 ppm) in cows' milk (1, 8). In a previous paper, Murthy and Campbell (4) reported values for ~TRb of powdered milk samples produced from 1923 to 1936 and from 1946 to 1960. The yearly average ~Rb concentration varied between 10.9 to 24.9 pCi per 100 g of powder. Most of these samples were produced at Washington State University, Pullman (4). Rubidium-S7 is a beta-emitting radionuclide ~ith a half-life of 4.7 × 10 ~° yr. Its abundance in the naturally occurring element is 27.85%, the specific activity being 2.5 × 10 -8 Ci/gram of element (7). This report presents data of ~TRb concentrations computed from Rb content of market milk samples reported in a previous p a p e r (5). Experimental Procedure
The technique of m i l k collection and procedures for analyses of milk for Rb content have been described previously (5). Samples from the Northeast (Winchester, Massachusetts) and Southwest (Las Vegas, Nevada) Radiological Received for publication December 14, 1966.
Health Laboratories were received during the months of May, August, and November, 1965, and February, 1966 (Area 2) ; whereas, samples from the Southeast (Montgomery, Alabama) Laboratory were received during January, April, June, July, and October, 1965, and January, 1966 (Area 1). Results and Discussion
Direct detel~nination of ~Rb by radiochemical procedures was not made, since separation of Rb from the chemically interfering substances is elaborate and time-cor~suming. I n addition, atomic absorption spectrophotomet~:/ for determination of Rb was rapid, sensitive, and accurate. Analyses of eight replicate samples of the same milk showed recovery and reproducibility data of 98.7 ~ 2.8% and 0.620 ~__ 0.023 ppm, which were considered very satisfactory. Ranges in the above values represent standard deviations between replicate samples. F o r statistical analysis, the analytical data in Table 1 have been divided into two geographical areas based on sampling schedule. Detailed discussion of results in Table 1 was not considered, because they were similar to those presented earlier (5). Average ~Rb concentration in milk varied between 14.2 to 84.8 p C i / k g of sample. Analysis of variance of the data indicated that the ~TRb concentration of milk from different cities was significantly different at a = 0.01. Only in Area 1 (southeastern United States) was there a significant difference from one sampling period to another. Mean values of S~Rb for the various cities in each area were separated by Duncan's test (3). Despite the fact that the average values between cities was large in the extremes, one cannot identify welldefined groups. F o u r and five arbitrary groups for Areas 1 and 2 are shown in Table 1. I n general, the ~TRb concentrations of milk are smaller for cities of inland states and larger for cities of the coastal states and those in the Mississippi and Missouri Valley. One plausible explanation for this may be related to the meteorological and climatological factors prevailing in each area. The chemical and metabolic behavior of Rb in the environment is closely related to that of potassium. The amount of Rb available to cows through plant foods would be a function of soil 818
SCRb IN MILK TABLE 1 Rubidinm-87 concentration in market milk
Group
Sampling station
~TRb (pC~/l~g) Range
Average
Area i La. : New Orleans 74.5-88.3 Ga. : Atlanta 56.3-94.0 Ala.: Montgomery 40.5-90.8 Miss. : Jackson 65.2-80.0
84.8 78.0 72.5 67.8
2
N.C.: Charlotte Ark.: Little Rock Va. : Norfolk
45.8-82.5 49.8-69.0 41.2-63.0
63.2 (6) 60.8 (6) 51.8 (7)
3
P.R.: San J u a n Tenn.: Chattanooga Tenn. : Memphis C.Z.: Cristobal S.C. : Charleston Texas: Dallas Texas: Austin Md.: Baltimore
47.8-53.0 44.2-56.8 42.5-57.5 39.8-52.5 44.8-53.2 37.8-50.5 33.0-45.8 30.5-45.5
49.5 49.5 49.2 48.8 46.8 43.5 38.5 39.5
(5) (6) (6) (5) (7) (6) (6) (4)
4
Fla. : Tampa Ky.: Louisville W.Va.: Charleston Okla.: Oklahoma City
26.2-42.2 25.0-49.0 22.5-37.8 19.0-32.2
34.8 30.2 27.0 26.8
(6) (6) (6) (6)
1
Area 2 N.H.: M ~ c h e s t e r 68.5-75.0 Calif.: Sacramento 51.5-73.0 Calif.: San Francisco 42.2-73.8 Mass. : Boston 52.8-64.2
71.0 62.5 61.5 56.5
(4) (4) (4) (4)
2
R.L : Providence Iowa: DesMoines Del.: Wilmington Ill. : Chicago Wis.: Milwaukee Oreg. : Portland Conn.: H a r t f o r d N.Y.: Buffalo N.Y. : New York Mich.: Grand Rapids Ohio: Cleveland Mo. : Kansas City N.Y.: Syracuse Mo.: St. :Louis 1)a.: P i t t s b u r g h
44.8-51.5 42.8-58.2 42.8-51.2 43.0-51.5 41.5-50.2 37.0-51.8 42.8-48.2 42.5-45.8 39.5-46.8 41.8-45.0 39.2-48.0 35.8-51.0 37.2-44.2 30.2-45.8 32.2-45.8
48.5 48.5 48.5 48.2 47.0 46.5 44.8 44.0 42.2 43.2 42.2 42.2 42.0 40.5 40.5
(4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4)
3
N.J.: Trenton Vt.: Burlington Mich.: Detroit Ind.: Indianapolis Wash.: Seattle Pa. : Philadelphia Ohio: Cincinnati
31.5-44.0 33.8-40.2 39.2-39.5 30.2-40.2 29.0-36.0 25.8-37.8 27.5-34.8
38.2 36.0 35.8 33.8 32.5 32.0 31.0
(4) (4) (4) (4) (4) (4) (4)
4
Kansas: Wichita Idaho: Idaho Falls Wash.: Spokane U t a h : Salt La~e City
23.8-33.0 20.0-32.2 18.5-28.8 19.8-27.0
29.0 27.5 25.5 23.8
(4) (4) (4) (4)
1
(6) (5) (6) (6)
819 Mont.: Helena N.Mex.: Albuquerque Wyo. : Laramie N.Dak. : M i n o t Ariz.: Phoenix Colo. : Denver S.Dak. : Rapid City
]~igures in parentheses sa~mples analyzed.
14.0-31.8 17.8-24.0 16.1-27.0 14.8-28.5 15.2-19.0 16.2-18.0 13.0-15.5 refer
22.5 21.0 20.5 18.8 17.2 16.5 14.2
(4) (4) (4) (4) (4) (4) (4)
to number
of
condition, t h e p o t a s s i u m c o n t e n t o f soil, u p t a k e b y p l a n t s f r o m soil, etc. T h e a m o u n t excreted into milk would d e p e n d u p o n the m e t a b o l i s m of R b in the cow. The l i t e r a t u r e indicates the p o t a s s i u m c o n t e n t i n t h e t o p food of soil i n t h e U n i t e d S t a t e s v a r i e s f r o m less t h a n 0.3 to 2.5% ( 2 ) . Coastal p l a i n soils a l o n g the A t l a n t i c Coast a r e in the lowest r a n g e , whereas soils f r o m the G r e a t P l a i n s , R o c k y M o u n t a i n s a n d Pacific Coast regions n o r m a l l y h a v e a b o u t 1.5 to 2.5% (2, 6). W h e n t h e p o t a s s i u m c o n t e n t of soil is h i g h t h e r e is a g r e a t e r d i s c r i m i n a t i o n a g a i n s t u p t a k e of R b b y plants. These findings c o r r o b o r a t e the observed v a r i a t i o n s in the STRb c o n c e n t r a t i o n in milk. References
(1) Archibald, J. G. 1958. Trace Elements in Milk: A Review. P a r t II. Dairy Sci. Abstr., 20: 801. (2) Clark, K. G., Anderson, M. S., and Shaw, B. T. 1944. The Potash Problem in the United States. p. 93. Agr. Research Admin., USDA, Beltsville, Md. (3) Duncan, D. B. 1965. Multiple Range a~ld Multiple F Tests. Biometrics, 11: 1. (4) Murthy, G. K., and Campbell, J. E. 1964. Profile of Long-Lived Radionuclides in Milk, 1923 to 1936, 1946 to 1960. U. S. Dept. of Health, Education, and Welfare. Public Health Serv. Publ. 999-F-2. (5) Murthy, G. K., Rhea, U., and Peeler, J. T. 1967. Rubidium and Lead Content of Market Milk. J. Dairy SCi., 50: 651. (6) Reitemeier, R. F. 1957. Soil Potassium Fertility. Soil. A. Sleffernd, ed. USDA. U. S. Govt. P r i n t i n g Press Office. p. 101. (7) Stokley, 5. (Rev. by D. T. Goldman a::d J. R. Stehu.) 1962. Chart of the Nuclides. 6th ed. Knolls U. S. Atomic Lab. ; General Electric Co., Schenectady, New York. (8) Underwood, E. J. 1958. Trace Elements in Animals. Trace Elements. p. 37. Academic Press, New York.
J. DArav SCIENCE VOL. 50, NO. 6
Market milk samples collected on a quarterly basis from various cities in the United States were analyzed for rubidium (Rb) content by atomic absorption spectrophotometry. The 8~Rb concentrations were computed from the specific activity data. The average =Rb of milk varied from 14.2 to 84.8 p C i / k g of sample. Statistical analysis of the data showed that the ~Rb concentration in milk from various cities was significantly different at a = 0.01. I n addition, samples from cities in the Southeast showed significant differences from one sampling period to another. In general, the ~Rb concentration in milk from inland states was less than that of milk from cities of coastal states and those lying i n the Missouri and Mississippi Valley. Rubidium-87 (~Rb) is a naturally occurring radioactive element. The presence of Rb in milk has been demonstrated, and a review of early work has indicated that it exists in fairly constant amounts (1.5 to 3 ppm) in cows' milk (1, 8). In a previous paper, Murthy and Campbell (4) reported values for ~TRb of powdered milk samples produced from 1923 to 1936 and from 1946 to 1960. The yearly average ~Rb concentration varied between 10.9 to 24.9 pCi per 100 g of powder. Most of these samples were produced at Washington State University, Pullman (4). Rubidium-S7 is a beta-emitting radionuclide ~ith a half-life of 4.7 × 10 ~° yr. Its abundance in the naturally occurring element is 27.85%, the specific activity being 2.5 × 10 -8 Ci/gram of element (7). This report presents data of ~TRb concentrations computed from Rb content of market milk samples reported in a previous p a p e r (5). Experimental Procedure
The technique of m i l k collection and procedures for analyses of milk for Rb content have been described previously (5). Samples from the Northeast (Winchester, Massachusetts) and Southwest (Las Vegas, Nevada) Radiological Received for publication December 14, 1966.
Health Laboratories were received during the months of May, August, and November, 1965, and February, 1966 (Area 2) ; whereas, samples from the Southeast (Montgomery, Alabama) Laboratory were received during January, April, June, July, and October, 1965, and January, 1966 (Area 1). Results and Discussion
Direct detel~nination of ~Rb by radiochemical procedures was not made, since separation of Rb from the chemically interfering substances is elaborate and time-cor~suming. I n addition, atomic absorption spectrophotomet~:/ for determination of Rb was rapid, sensitive, and accurate. Analyses of eight replicate samples of the same milk showed recovery and reproducibility data of 98.7 ~ 2.8% and 0.620 ~__ 0.023 ppm, which were considered very satisfactory. Ranges in the above values represent standard deviations between replicate samples. F o r statistical analysis, the analytical data in Table 1 have been divided into two geographical areas based on sampling schedule. Detailed discussion of results in Table 1 was not considered, because they were similar to those presented earlier (5). Average ~Rb concentration in milk varied between 14.2 to 84.8 p C i / k g of sample. Analysis of variance of the data indicated that the ~TRb concentration of milk from different cities was significantly different at a = 0.01. Only in Area 1 (southeastern United States) was there a significant difference from one sampling period to another. Mean values of S~Rb for the various cities in each area were separated by Duncan's test (3). Despite the fact that the average values between cities was large in the extremes, one cannot identify welldefined groups. F o u r and five arbitrary groups for Areas 1 and 2 are shown in Table 1. I n general, the ~TRb concentrations of milk are smaller for cities of inland states and larger for cities of the coastal states and those in the Mississippi and Missouri Valley. One plausible explanation for this may be related to the meteorological and climatological factors prevailing in each area. The chemical and metabolic behavior of Rb in the environment is closely related to that of potassium. The amount of Rb available to cows through plant foods would be a function of soil 818
SCRb IN MILK TABLE 1 Rubidinm-87 concentration in market milk
Group
Sampling station
~TRb (pC~/l~g) Range
Average
Area i La. : New Orleans 74.5-88.3 Ga. : Atlanta 56.3-94.0 Ala.: Montgomery 40.5-90.8 Miss. : Jackson 65.2-80.0
84.8 78.0 72.5 67.8
2
N.C.: Charlotte Ark.: Little Rock Va. : Norfolk
45.8-82.5 49.8-69.0 41.2-63.0
63.2 (6) 60.8 (6) 51.8 (7)
3
P.R.: San J u a n Tenn.: Chattanooga Tenn. : Memphis C.Z.: Cristobal S.C. : Charleston Texas: Dallas Texas: Austin Md.: Baltimore
47.8-53.0 44.2-56.8 42.5-57.5 39.8-52.5 44.8-53.2 37.8-50.5 33.0-45.8 30.5-45.5
49.5 49.5 49.2 48.8 46.8 43.5 38.5 39.5
(5) (6) (6) (5) (7) (6) (6) (4)
4
Fla. : Tampa Ky.: Louisville W.Va.: Charleston Okla.: Oklahoma City
26.2-42.2 25.0-49.0 22.5-37.8 19.0-32.2
34.8 30.2 27.0 26.8
(6) (6) (6) (6)
1
Area 2 N.H.: M ~ c h e s t e r 68.5-75.0 Calif.: Sacramento 51.5-73.0 Calif.: San Francisco 42.2-73.8 Mass. : Boston 52.8-64.2
71.0 62.5 61.5 56.5
(4) (4) (4) (4)
2
R.L : Providence Iowa: DesMoines Del.: Wilmington Ill. : Chicago Wis.: Milwaukee Oreg. : Portland Conn.: H a r t f o r d N.Y.: Buffalo N.Y. : New York Mich.: Grand Rapids Ohio: Cleveland Mo. : Kansas City N.Y.: Syracuse Mo.: St. :Louis 1)a.: P i t t s b u r g h
44.8-51.5 42.8-58.2 42.8-51.2 43.0-51.5 41.5-50.2 37.0-51.8 42.8-48.2 42.5-45.8 39.5-46.8 41.8-45.0 39.2-48.0 35.8-51.0 37.2-44.2 30.2-45.8 32.2-45.8
48.5 48.5 48.5 48.2 47.0 46.5 44.8 44.0 42.2 43.2 42.2 42.2 42.0 40.5 40.5
(4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4) (4)
3
N.J.: Trenton Vt.: Burlington Mich.: Detroit Ind.: Indianapolis Wash.: Seattle Pa. : Philadelphia Ohio: Cincinnati
31.5-44.0 33.8-40.2 39.2-39.5 30.2-40.2 29.0-36.0 25.8-37.8 27.5-34.8
38.2 36.0 35.8 33.8 32.5 32.0 31.0
(4) (4) (4) (4) (4) (4) (4)
4
Kansas: Wichita Idaho: Idaho Falls Wash.: Spokane U t a h : Salt La~e City
23.8-33.0 20.0-32.2 18.5-28.8 19.8-27.0
29.0 27.5 25.5 23.8
(4) (4) (4) (4)
1
(6) (5) (6) (6)
819 Mont.: Helena N.Mex.: Albuquerque Wyo. : Laramie N.Dak. : M i n o t Ariz.: Phoenix Colo. : Denver S.Dak. : Rapid City
]~igures in parentheses sa~mples analyzed.
14.0-31.8 17.8-24.0 16.1-27.0 14.8-28.5 15.2-19.0 16.2-18.0 13.0-15.5 refer
22.5 21.0 20.5 18.8 17.2 16.5 14.2
(4) (4) (4) (4) (4) (4) (4)
to number
of
condition, t h e p o t a s s i u m c o n t e n t o f soil, u p t a k e b y p l a n t s f r o m soil, etc. T h e a m o u n t excreted into milk would d e p e n d u p o n the m e t a b o l i s m of R b in the cow. The l i t e r a t u r e indicates the p o t a s s i u m c o n t e n t i n t h e t o p food of soil i n t h e U n i t e d S t a t e s v a r i e s f r o m less t h a n 0.3 to 2.5% ( 2 ) . Coastal p l a i n soils a l o n g the A t l a n t i c Coast a r e in the lowest r a n g e , whereas soils f r o m the G r e a t P l a i n s , R o c k y M o u n t a i n s a n d Pacific Coast regions n o r m a l l y h a v e a b o u t 1.5 to 2.5% (2, 6). W h e n t h e p o t a s s i u m c o n t e n t of soil is h i g h t h e r e is a g r e a t e r d i s c r i m i n a t i o n a g a i n s t u p t a k e of R b b y plants. These findings c o r r o b o r a t e the observed v a r i a t i o n s in the STRb c o n c e n t r a t i o n in milk. References
(1) Archibald, J. G. 1958. Trace Elements in Milk: A Review. P a r t II. Dairy Sci. Abstr., 20: 801. (2) Clark, K. G., Anderson, M. S., and Shaw, B. T. 1944. The Potash Problem in the United States. p. 93. Agr. Research Admin., USDA, Beltsville, Md. (3) Duncan, D. B. 1965. Multiple Range a~ld Multiple F Tests. Biometrics, 11: 1. (4) Murthy, G. K., and Campbell, J. E. 1964. Profile of Long-Lived Radionuclides in Milk, 1923 to 1936, 1946 to 1960. U. S. Dept. of Health, Education, and Welfare. Public Health Serv. Publ. 999-F-2. (5) Murthy, G. K., Rhea, U., and Peeler, J. T. 1967. Rubidium and Lead Content of Market Milk. J. Dairy SCi., 50: 651. (6) Reitemeier, R. F. 1957. Soil Potassium Fertility. Soil. A. Sleffernd, ed. USDA. U. S. Govt. P r i n t i n g Press Office. p. 101. (7) Stokley, 5. (Rev. by D. T. Goldman a::d J. R. Stehu.) 1962. Chart of the Nuclides. 6th ed. Knolls U. S. Atomic Lab. ; General Electric Co., Schenectady, New York. (8) Underwood, E. J. 1958. Trace Elements in Animals. Trace Elements. p. 37. Academic Press, New York.
J. DArav SCIENCE VOL. 50, NO. 6