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Comparison of the Removal of Radiostrontium from In Vivo- and In Vitro-Labeled Milk by Ion Exchange Resins

Dairy Products Laboratory, Eastern Utilization Research and Development Division, USDA, Washington, D. C.

ABSTRACT

Studies were made to determine differences in the amount of radiostrontium removed by ion exchange resins from milk labeled in vivo and in vitro with Sr⁸⁵ or Sr⁸⁹, or both. The distribution of Sr⁸⁵ and calcium between phases of centrifugally fractionated milk was also studied. The milks were adjusted to pH levels as low as 5.2 with citric acid before passing through ion exchange columns, and before centrifuging.

The amount of strontium removed varied from about 95% at pH 5.25 to 45% at pH 6.65 for in vitro-labeled milk. The amounts for in vitro-labeled milk were only slightly higher at low pH, but ranged from 79 to 50% at pH 6.65, for equilibration times of 30 min and 120 hr, respectively, before resin contact.

Portions of milk labeled in vivo with Sr85 were centrifuged at 105,000 x G for 90 min. The amounts of strontium in the serum were 86, 46, and 19%, respectively, for pH levels of 5.2, 5.8, and 6.6. Corresponding calcium levels were 84, 59, and 33%. Practically all of the remainder was in the sediment. Less than 1% was recovered in the fat layer.

¹ Public Health Service, Department of Health. Education and Welfare, Washington, D. C.