Bomb ¹⁴C as a biological tracer

Abstract

THE release of ¹⁴C in nuclear explosions, particularly those detonated in 1961–1962, has caused a major disturbance of the steady-state natural distribution of this radioisotope. The resultant pulse of bomb ¹⁴C, detected initially in the atmosphere, has since been used extensively in evaluation of rates of exchange of carbon between major reservoirs of the dynamic cycle — notably atmospheric CO₂ and ocean water bicarbonate^1–7. Within the biosphere, however, investigation of human ¹⁴C levels has been more limited despite the application of bomb ¹⁴C as early as 1959 by Broecker and co-workers⁸ in the determination of residence times of carbon in several tissues. Perhaps the most specific result to emerge from initial research on this topic was the demonstration of almost total inertness of collagen in the adult human skeleton as evidenced by its failure to incorporate significant amounts of artificial ¹⁴C (ref. 9). In other related ¹⁴C measurements^10–13, a non-correspondence between contemporary human and atmospheric ¹⁴C levels was often observed. Nydal and co-workers proposed a combination of three factors to account for such variations¹³ and concluded from a long term analysis of ¹⁴C concentrations in human blood and hair samples that bomb ¹⁴C enters the human body 1.4 years after production in the atmosphere, and remains there with a mean lifetime of 10 years. This article describes the continuation at Glasgow of an intensive investigation of the presence of bomb ¹⁴C in humans, initiated by Harkness and Walton¹². Comparison by these workers of blood plasma protein ¹⁴C data with predicted dietary ¹⁴C levels¹⁴ has confirmed that a finite turnover of carbon in the human body does exist. Here, determination of ¹⁴C activities of atmospheric CO₂, dietary and human tissue samples enables a more detailed evaluation of residence times.