Strontium-89 and Strontium-90 Levels in Breast Milk and in Mineral-Supplement Preparations

Strontium-90, strontium-89 and S.U. values were determined in human milk before and after the resumption of atmospheric nuclear testings in 1961, and the levels were compared to cows'' milk values reported during the same time. S.U.⁹⁰ levels in human milk were approximately one-fifth of those found in cows'' milk. Assuming an average dietary intake of 11-13 S.U.⁹⁰ during the period tested, the mean strontium/calcium ratio of 1.78 found in human milk represents an Observed Ratio milk-diet of approximately 0.14-0.16. Although strontium-89 was present in cows'' milk already in September 1961, it did not appear in human milk until November 1961. It seems, therefore, that there was a two-month lag period between the appearance of fresh fallout in cows'' milk and human milk. Calcium-supplement mineral preparations used by pregnant and lactating women were tested to find their strontium-89, strontium-90 and S.U. levels, because strontium isotopes, if present in these products, will be transferred to the fetus and to breast-fed infants. The compounds tested had S.U.⁹⁰ levels of 0.13-2.62; in none of the preparations was Sr⁸⁹ present.