[H-TT35_1PM1] Developments and applications of AMS techniques for earth and human environmental research

[HTT35-P11_PG] Accurate age estimation using ¹⁴C in human teeth enamel.

3-min talk in an oral session

*Keisuke KUNITA¹, Toshio NAKAMURA² (1.Graduate School of Environmental Studies, Nagoya University, 2.Center for Chronological Reserch, Nagoya University)

Keywords:human tooth, enamel, ¹⁴C, forensic science, nuclear bomb testing, age estimation

Radiocarbon (¹⁴C) concentration in the atmosphere showed a stable value until 1955. However, as a result of the nuclear bomb testing, modern ¹⁴C concentration in the atmosphere dramatically increased during late 1950s and early 1960s. These bomb-produced ¹⁴C is then oxidized to form CO₂, and incorporated into plants by photosynthesis. Then, by eating plants or animals fed by these plants, the ¹⁴C concentration in human body reflects the ¹⁴C value of atmospheric CO₂ at a certain time. Recent studies insisted that these ¹⁴C can play important role for forensic analysis, especially age estimation using ¹⁴C in human teeth enamel. Teeth enamel is such a harder part of the human body that they are hardly destroyed by a natural process. And, the most important is, there is no turnover of enamel after its formation has completed. Although there are previous works which estimate the birth year of individuals by using ¹⁴C concentration in enamel, their samples are teeth from Swedish, Scottish and American people, and study areas are mainly at high latitudes of the northern hemisphere. The precision of age estimation using teeth enamel is determined by enamel formation time of teeth and atmospheric ¹⁴C concentration in a certain area at a certain year. It is known that teeth formation time of Japanese is different from that of Caucasian. It has been found that ¹⁴C concentration in the atmosphere indicates 5 different zones according to different peak ¹⁴C concentration of the nuclear bomb testing. These zones are named NH zone1, NH zone2, NH zone3, SH zone3 and SH zone1-2 from north to south. The boundary between NH zone1 and NH zone2 is Ferrel cell - Hadley cell boundary. It is nearly located at 35 ^oN. So it means that previous works mainly focused on NH zone1 samples, not NH zone2 samples. One of NH zone2 samples, teeth enamels of Japanese have not studied sufficiently. The aim of this study is to clarify whether age estimation using teeth enamels of Japanese can determine the precise year of birth of individuals and to discuss the mechanism of carbon fixation of enamels or other parts of the teeth. 7 of 44 collected tooth samples have been analyzed. They are 5 third molars and 2 second molars. The year of birth of each individual is 1943, 1946, 1951, 1951, 1951 for third molars, and 1933 and 1959 for second molars. In order to get the estimated year of birth, a model age for enamel completion of Japanese was subtracted from the year given by the ¹⁴C analysis of samples. The result shows that age estimation using teeth of Japanese gives precise age determination. Needless to say, taking account of the degree of individual variation and possibility of differences in local environment or in diet is important, however, this result seems to be uninfluenced by those effects. Larger number of, more and more various parts of teeth (for example, first molars, anteriors, such as early-completed teeth.) have to be analyzed. To determine whether an individual is born before or after the peak of atmospheric ¹⁴C concentration (in 1964, in NH zone2), root of teeth have to be analyzed. Since root completion age is some years after enamel completion age, it can be easily found that the sample age is whether rising or falling part of the atmospheric ¹⁴C curve. We now are preparing for analysis of ¹⁴C of root dentine collagen and root inorganic matter. Their results will give more compelling data, now discover what is waiting for you!!