A COMPARISON
OF
5R9#{176}
COMPONENT
OF
HUMAN
AND
COWS’
MILK
Conrad P. Straub, Ph.D., and Gopala K. Murthy, Ph.D.
Robert A. Taft Sanitary Engineering Center, The Division of Radiological Health,
((71(1 the Food Chemistry, Milk and Food Research Program, Public Health Service,
U.S. Department of Health, Education, and Welfare, Cincinnati, Ohio
(Submitted NIarch 10; accepted for publication May 19, 1965.)
ADDRESS: (C.P.S. ) Robert A. Taft Sanitary Engineering Center, 4676 Columbia Parkway, Cincinnati.
732
PEDIATRICS, Vol. 36, No. 5, November 1965
I
NFORMATION OIl the concentrations ofspecific radionuclides in htiman milk
as velI as in cows’ milk is needed to under-stand potential exposure to radiation of in-fants consuming these milks. Considerable data are available on radionuclide concen-trations in cows’ milk,’ but similar data for
human milk are meager.25 To obtain data
on radionuclide concentrations in human
milk, samples of human milk were
ob-tamed from Denver, Colorado (July 9, 1959, through February, 1961), and Chicago, liii-nois (December 21, 1959, through August, 1961). The Denver samples represented
pooled htiman milk collected postpartum,
while those from Chicago represented
human milk from individtial donors
con-tributing to a milk bank. For comparison,
samples of cows’ milk corresponding to
that consumed by the donors participating
in the Chicago program were collected
(November, 1960, through August, 1961). In turn, these samples were compared with samples collected monthly from the raw-milk network serving a portion of the Chi-cago milkshed.
Samples were analyzed for calcium,
potassium, strontium-90, and cesium-137,
and the restilts are summarized in Tables I and II. As shown in Table I, the concentra-tions of strontium-90 and calcium in human milk samples from Denver and Chicago are similar, the mean geometric values being 0.62 and 0.56 picocurie of strontium-90 per
liter (pc/i), and 0.24 and 0.25 gm of cal-cium per liter (gm/i), respectively. A corn-parison of the strontium-90 and the calcium
concentrations of cows’ milk with those of
human milk from Chicago indicates that
the concentration of strontium-90 in human milk is smaller by an order of magnitude, and that of calcium by a factor of
approxi-mately 5. There is little difference in the cesium concentrations, but this could be associated with the relatively small envi-ronmental concentrations of cesium.
The measured strontium-90 and calcium concentrations in market milk reported to be consumed by the donors were similar to those found in monthly milk samples col-lected as being representative of a portion of the Chicago raw-milk production area.6 The geometric mean strontium-90 values
were 6.4 pc/I for the market milk constimed
by the donors and 6.6 pc/i for the raw milk
while the corresponding calcium values were 1.12 and 1.13 gm/l.
Radionuclide concentrations reported herein were obtained during the period of
no atmospheric nuclear tests (except for the French test of February, 1960), and
coinci-ded over a period of a few months with the collection of human milk samples from six
Toronto 2 These values were
in-tercompared during a common period (Oc-tober, 1960, through June, 1961) and show (Table III) that the Denver and Toronto values were similar (geometric mean values
equal to 0.259 gm/i and 0.79 pc/I; and
0.252 gm/i and 0.70 pc/l for calcium and
strontium-90, respectively). The values for
milk samples from Chicago for the same
period were somewhat lower, 0.230 gm/i
for calcium and 0.57 pc/i for strontium-90.
The differences were not, however,
be-lieved to be significant.
Lough et al. reported values (see Table
collect-‘#{176}Sr,pc/I Ca, g/l 9#{176}Sr/Ca, pc/gm ‘37Cs, pc/i K, gm/l 16 16 16 14 16 18 18 16 18 10 8 8 6 8 x
0.6 + I .,5.5 1<
O.24±1 *1
1< -52-- I .73
0-6 + I .16
x
0. 56 -i- I ->( 0.)25+1 .6
x .73+ 1.
N 0.31.18 N 6.4 +1 x 1-1#{247}1-o.5 x 6.05+1.15 N 1.4+1 .03
90 Sr, pc/I
Ca, gm/l “'Sr/Ca, pc/gm ‘37Cs, pc/i K, gm/I Cows’ milk-Chicago ‘#{176}Sr,pc/l Ca, gm/I ‘#{176}Sr/Ca, pc/gin ‘3TCs, pc/l K, gm/i 0.65 0.7 3.0 0.636 0.60
0.21()
2.4
0.33
6.6
1.118
6.0
I.43
0.67
U.237
3.1
0.611
0.61
0.’215
0.331
6.5
I .111 6.1
1.42l
0.’2 tol.’2
0.1-26 to 0.358
0.9 to 9.5 ND to 19 0.’271 to 0.777
0.’25 tol.4
0.1’26 to 0.301
1.1 to7.4 Ni) to 10
0.251 to 0.535
4.4 tolO
I .056 to 1 .17’2
4.1 to8.9 5 to25
1.376 to I .464
ARTICLES
TABLE I
733
CHEMICAL AND RADI0Ac’rIvE CONSTITUENTS IN HUMAN AND Cows’ MILK, JULY, 1959, ThROUGh AUGUST, 1961
n* JIQ±Og-x ill - flange
Human milk-Denver
Human milk-Chicago
6 = number of sampies.
x X
Mg Og = geometric mean ± geometric standard deviation.
“.!i = median value. M= arithmetic mean value. ND = not detected.
ed from May through June, 1959;
geomet-nc mean values were computed and found
to be 0.252 gm/i for calcitim, 0.33 pc/i for
trontium-9O, and 1.32 picocuries of
stron-tium-90 and strontium-90/calcium values
values are very similar to other values re-ported in Tables 1 and 3, but the
stron-tium-90 and strontium-90 per calcium values
are lower by a factor of about 2.
A marked difference between the
potas-TABLE II
COMPARISON OF CONSTITUENTS IN Cows’ MILK COLLECTED IN TILE ChIcAGo AREA, NOVEMBER, 1960
THROUGH AUGUST, 1961
n “#{176}Sr,pc/I
1 6
x
6.4±1.
‘, 2t 10 6.6+1.48
6 MiLk consumed by donors.
t Raw milk from portion of milkshed.
Number of samples analyzed.
-N
§Mgtg.
Ca, gm/l 0.59#{247}1.16*
No. of observations 3
90Sr, pc/i No. of observations
‘#{176}Sr/Ca, pc/gin
No. of observations
(‘hicago x 0.’230±1.6 8 x 0.57 +1.48 9 x #{247}I .90 8 x 0.79 #{247}1.83 3 x 3.04 +1.87 3 Toronlo2 x 0.51.Q4 10 N 0.70 #{247}2.0sl 10 2.73 +‘2.04 10
Lough ci (Il.’j
N 5 x 0.33 +1.65 ‘5 x 1.3 #{247}1.59 5 N * Mg+lTg.
t May through June, 1959.
TABLE III
INTERCoapARIsoN OF CALCIUM AND STR0NTIUu-90 CONCENTRATIONS OF HUMAN MILK SAMPLES COLLECTED
FEOM DIFFEHENT (;EOGRAPHIC AIIEAs OCT0BEIL, 1960, THROUGH JUNE, 1961
siufll content of human niilk from Denver
and that fronl Chicago was observed (Table
I). The geometric mean values for the two
areas were O.61.16 (16 values) and O.3
1.18 gm/l (18 values), respectively. This (hiference was believed to reflect the
(lifTer-ence between samples from these two areas.
In 1)enver, the salnples were i)Ooled from
milk collected postpartum from a number of donors and represente(1 colostruin and
tran-sitional fllilk, whereas in Chicago each
sample analyzed came from a sI)ecific (lonor an(I represented nlaturc nulk. The values
we report agree generally with values pub-lisile(1 111 the literature.7 These show
po-tassiiiin levels in colostrum (first to fifth
(lay of lactation) of 0.74 (0.66-0.87) gm/i, in
transitional milk sixth to tenth (lay of
lac-tation) of 0.64 (0.53-0.77) g/liter, an(1 in
mature milk of 0.5,5 (O.27-O.81) gm./l.
Po-tassiuni concentrations in cows’ fllilk
(geo-metric itiean values) were about to 4 times
greater than the concentrations measured in our human milk safllples. Spector7 reports
potassium levels in cows’ milk of 1.38
(0.38-p2.87) gm/I which compare favorably with
OU values of 1.42 (1.38 to 1.46) gm/I.
The concentrations of cesium-137 in the
human milk samples were very small and did
not exceed f20 pc/I, and in most cases were close to the minimum detectable amount for this ra(lionucli(le under the conditions of
nleasurement. Cesium-137 concent rat ions in
cOvs’ milk were also small, 5 to 5 pc/l,
(luring this period.
Information on tile (liscrimination of
strontium-90 in relation to calcium by
mothers consuming cows’ milk was
oh-taine(1 from the Chicago data (Table I).
Based on the assumption that the sole
soul.(e of calcium consumed by tile donors
was cows’ milk (not necessarily a valid
assumption, since the donors may have
re-ceive(l calcium from other sources), the
Observed Ratio* was found to average
(#{241}g7g) 0.39.0 With a range for the
eight values of 0.18 to 0.89. Similarly, the Observed Ratio for the discrifllinlLtiOn of
cesium-137 in relation to potassium was
calculated aIl(I found to be 1.0 and 0.81 for
March and April, 1961 , respectively. These
values have little significance since the
cesium-137 values were very low.
The data reported in this study show that in the metabolism of cows’ milk and
j)r0-(luction of hunian nlilk, the mother
(liscrimi-nates in favor of calcium over strontium
by a factor of approximately .5 which
ac-counts for the lower levels of both
radio-StFOfltiUIfl and stable calcium. Actually, in
terms of the strontium-90 and calcium
con-cent rations, the differences between human and cows’ milk were equivalent to a factor of about 11 and 4.5, respectively. Since
* Observed Ratio,
“#{176}Srh/Cah “7Csh/Kl,
OR. = “#{176}Sr,/Ca, and
ARTICLES 735
stront iuin-90 concentrat ions in hu IIan mi 1k are smaller than those in cows milk by an
order of magnitude, the consumption of
human milk should result in a lower intake of
this radionuclide by infants, which should
reduce potential ra(hation exposu re, tinless
there is a difference in inetabolisni of the
two sources of milk.
REFERENCES
1. Radiological Heaith Data, Monthly Publication, Division of Radiological Health, Public
Health Service, U. S. Department of health,
Education, and Welfare, Washington 25, D.C.
2. Brown, J. R., and Jarvis, A. A. Strontium-90
levels in human milk. A nine-months survey in Toronto. Canad. J. Pub. Health, 52:463,
1961.
3. Lough, S. A., Hamada, G. H., and Comar, C.
L. Secretion of dietary strontium-90 and
calcium in human milk. Proc., Soc. Exp.
Biol. Med., 104:194, 1960.
4. Aarkrog, A. Caesium-137 from fall-out in
hu-man milk. Nature, 197(4868):667, 1963. 5. Jarvis, A. A., Brown, J. R., TiefenLach, B.
Strontium-89 and strontium-90 in breast
milk and in mineral-supplement preparations.
Canad. Med. Ass. J., 88:136, 1963.
6. Campbell, J. E., Murthy, C. K., Lewis, K. H.,
and Straub, C. P. Radionuclides in miTk. In Radioactive Fallout, Soils, Plants, Foods,
Man, E. B. Fowler (Ed). Amsterdam,
Lon-don, New York: Eisevier Publishing Co.,
(1965), pp. 156-179.
7. Spector, W. S. (Ed.), Handbook of Biological
Data, p. 50, Philadelphia: \V. B. Saunders,
Co., 1956.
Acknowledgment
The writers wish to express their appreciation to Drs. L. Gerber and N. C. Telles, who made ar-rangements for the Denver and Chicago samples, respectively; to Messrs. S. Cox and U. Rhea for some of the chemical analyses; and to Mr. B. M.
