The entry of strontium-90 into human bone

Abstract

For 6 years human bones, mostly femora, have been analyzed for strontium-90 by radio-chemical methods and for natural strontium spectrographically. The mean concentrations relative to calcium (pc/g Ca and μ g/g Ca) are charted according to age. In each year the peak value for 90 Sr was in juveniles aged 1 to 2 years; it increased progressively in 1956–59 and fell in 1960–61. Values for the newborn which are dependent on maternal plasma and on domicile of mother moved similarly with time. By contrast values for bones of adolescents and adults increased progressively. The concentration was substantially uniform between bones in infants and children. In adults cancellous bones especially vertebrae gave higher concentration than ivory bones. The mean values for stable strontium for the six-year period were ~ 200 μ g/g Ca from birth till 6 months of age; they then rose sharply in the next year and later more slowly to 330 μ g/g Ca in adults. It is deduced (1) that the discrimination between Ca and Sr across the human placenta is nearly twofold, (2) that in the first year of the infant’s life the discriminatory processes especially in absorption observed in the human adult are not fully developed, (3) that by considering the specific activity ( 90 Sr/mg Sr) of bone in children according to cohort, bone turnover must be nearly complete in each of the first few years of life whereas in adolescents accretion of new salt is the preponderant factor, (4) and that in the adult where growth has ceased the relative annual ‘rates of replacement’ of existing mineral by new mineral from diet vary about 2% for ivory bone to 8% for vertebrae.