Analysis of 14C and 13C in teeth provides precise birth dating and clues to geographical origin

摘要

The identification of human bodies in situations when there are no clues as to the person’s identity from circumstantial data, poses a difficult problem to investigators. The determination of age and sex of the body can be crucial in order to limit the search to individuals that are a possible match. We analyzed the proportion of bomb pulse derived carbon-14 (¹⁴C) incorporated in the enamel of teeth from individuals from different geographical locations. The ‘bomb pulse’ refers to a significant increase in ¹⁴C levels in the atmosphere caused by above ground test detonations of nuclear weapons during the cold war (1955-1963). By comparing ¹⁴C levels in enamel with ¹⁴C atmospheric levels systematically recorded over time, high precision birth dating of modern biological material is possible. Above ground nuclear bomb testing was largely restricted to a couple of locations in the northern hemisphere, producing differences in atmospheric ¹⁴C levels at various geographical regions, particularly in the early phase. Therefore, we examined the precision of ¹⁴C birth dating of enamel as a function of time of formation and geographical location. We also investigated the use of the stable isotope ¹³C as an indicator of geographical origin of an individual. Dental enamel was isolated from 95 teeth extracted from 84 individuals to study the precision of the ¹⁴C method along the bomb spike. For teeth formed before 1955 (N = 17), all but one tooth showed negative Δ¹⁴C values. Analysis of enamel from teeth formed during the rising part of the bomb-spike (1955-1963, N = 12) and after the peak (>1963, N = 66) resulted in an average absolute date of birth estimation error of 1.9 ±1.4 and 1.3 ± 1.0 years, respectively. Geographical location of an individual had no adverse effect on the precision of year of birth estimation using radiocarbon dating. In 46 teeth, measurement of ¹³C was also performed. Scandinavian teeth showed a substantially greater depression in average δ¹³C (−14.8) than teeth from subjects raised in Japan (−13.5), Middle East and North Africa (−12.7) and South America (−10.9). In summary, isotopic analysis of carbon in enamel from a single tooth can give a good estimate of the year of birth of an individual and also provide information about the geographical origin of the individual. This strategy can assist police and forensic authorities when attempting to solve unidentified homicide cases and may facilitate the identification work associated with mass disasters.