Physical and biological half-life of radiochemically pure 59Fe

Abstract

At delivery commercial 59Fe-preparations contain up to 1% contamination by 60Co, 65Zn, 54Mn, 46Sc, 134Cs, etc., so that the physical half-life of such preparations is not constant and starts to increase permanently after about 100 days. Anion exchange chromatography was used to prepare 59Fe with a radiochemical purity of ≧ 99.999999% as demonstrated by analytical anion exchange chromatography, paper- and thin-layer chromatography, and γ-spectroscopy. The physical half-life of radiochemically pure 59Fe was found to be constant over 500 days with 44.52 ± 0.016 days (λ= 0.015568 ± 0.0000056 [d-1]). The whole-body retention of radiochemically pure 59Fe was measured in man over one year with a 4 π-geometry whole-body radioactivity detector and utilized for the estimation of the effective half-life of 59Fe. The correct physical half-life of radiochemically pure 59Fe was used for the calculation of the biological half-life. Normal male subjects showed an effective half-life of 43.6 ± 0.34 days and a biological half-life of 2136 ± 807 days. This means a whole-body-59Fe-turnover rate of 0.032 ± 0.012%/d equivalent to 1.25 ± 0.46 mg Fe/d (for a whole-body iron pool of 3850 mg in a 70 kg man). Menstruating females were observed to have effective half-lives of 43.1 ± 0.22 days and therefore biological half-lives of 1389 ± 224 days. Their whole-body-59Fe-turnover rate is higher (than in males) with 0.050 ± 0.008%/d. For an optimal whole-body iron pool of 3300 mg (in 60 kg female) this would mean an iron loss of 1.65 ± 0.26 mg/d. Non-menstruating females were quite similar to males. They showed effective and biological 59Fe-half-lives of 43.5 ± 0.48 and 1833 ± 857 days, respectively. Their whole-body-59Fe-turnover rate was calculated to be 0.038 ± 0.018%/d or 1.25 ± 0.59 mg Fe/d (60 kg female with 3300 mg Fe-pool). These experimental data are the first direct and reliable proof for the magnitude of daily iron loss and iron requirements in man.