Precaution in the Use of Iodine-125 as a Radioactive Tracer

Journal/Book: Reprinted from Science February 21 1964 Vol. 143 No. 3608 pages 799-800. 1964;

Abstract: Y. S. BAKHLE WM. H. PRUSOFF J. F. MCCREA Departments of Pharmacology and Microbiology Yale University New Haven Connecticut Abstract. The absorption of the low-energy radiation from iodine-125 under certain circumstances may be a serious disadvantage in its use as a radioisotopic tracer. The advantages of iodine-125 over iodine-131 as a radioactive tracer isotope of iodine have been reviewed recently by Daniel et al. (1). A limitation in the use of I125 has been observed however in that a high proportion of the gamma radiation derived from this isotope is absorbed by solutions of certain electrolytes for example cesium chloride and potassium iodide. Although this absorptive effect could have been predicted from theoretical considerations and is obvious to the physical scientist other biologists may overlook this point as we did in changing from the use of I131 to I125. During a study of the possible incorporation of 5-iodo-2'-deoxyuridine-I125 into viral DNA (2) it was observed that an aqueous of radioactive DNA labeled with 5-iododeoxyuridylic acid-I125 appeared to "lose" as much as 80 percent of its radioactivity as measured by a gamma-scintillation counter... schö

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