Answer to Question #379 Submitted to "Ask the Experts"

Q

What is the biological half-life for ⁵⁴Mn, ⁵⁸Co, and ⁶⁰Co? Thanks.

A

The biological half life for cobalt is complex. Half of the material entering the blood stream is assumed to go directly to excretion, 5% goes to the liver and the remaining 45% goes to other tissues where it assumed to be uniformly distributed. Of the cobalt that goes to any tissue fractions 0.6, 0.2, and 0.2 are assumed to be retained with half-lives of 6, 60, and 800 days respectively. The half life for material in the blood stream is 0.5 days. Manganese: 35% of the material entering the blood stream goes to bone, where it is retained with a half-life of 40 days. Of the remainder, fractions 0.1 and 0.15 go to the liver and are retained with half-lives of 4 and 40 days, respectively, while fractions 0.2 and 0.2 are assumed to become uniformly distributed among other organs and tissues with half-lives of 4 and 40 days, respectively. The biological half-life is independent of the isotope. The effective half-life includes the radioactive decay but this will have little effect on the shorter half-lives given above. Gary Kramer, PhD