Correlation of lead-210 with strontium-90 in human bones.

Abstract

THE radioactive gas radon-222, produced by the decay of radium-226, diffuses from the ground and is transported by atmospheric turbulence far from its origin through the troposphere and into the stratosphere1. The radioactive decay of radon-222 and its short-lived descendants produces measurable quantities of lead-210 in the atmosphere1–3. Lead atoms so formed become attached to dust particles and eventually return to the Earth's surface, principally in rainfall1,4,5. Hill's4 report of a correlation coefficient of 0.87 between the quantity of rainfall and the concentration of lead-210 in grass clearly indicates a linear relationship. Holtzman6 reported a relationship between the concentration of lead-210 in the human skeleton and in the atmosphere. Whether the lead-210 enters the body principally through precipitation on foodstuffs that are later eaten5 or through direct inhalation, or by both means7, is at present uncertain. It is therefore feasible to view the occurrence of lead-210 as a “natural fall-out” product, similar, in this respect, to fission product fall-out, artificially produced from a nuclear detonation. In fact, very strong similarities between lead-210 and fission product activities have been reported with respect to their behaviour in the atmosphere1, to their rate and mode of deposition1,5, and to their concentration in grasses4. The similarities between lead-210 and fission product activities do not imply any relationship in their production. The formation of lead-210 in nuclear weapons explosions is improbable, and if any were so formed it would be negligible in comparison with the amount formed by natural processes8. The observed similarities between lead-210 and fall-out are caused by their similar behaviour in the atmosphere.