This work has been carried out in order to clarify the distribution of metal elements in human hair, using atomic absorption spectroscopy and transmission electron microscopy. The transmission electron micrograph of the cross section of human hair without staining metal showed that the melanin granule and inter and beneath cuticular area was darkened as black shadow. Moreover, ICP analysis showed that some metals existed more abundantly in refined melanin granule than in whole hair. The metal content of black hair was two times higher than that of white one. For the hair samples treated with alkaline hydrogen peroxide solutions (pH; 9, 10, 11), the reducing agents of permanent wave lotions (acidic, neutral, alkaline) and concentrated formic acid, the remaining metal quantities were measured. The metal quantities eluted by the above solutions were also measured. The quantities of metals extracted by several bleaching solutions were small. This means that even in bleaching hair sample, the metals are still strictly combined to the melanin granule. In the case of treating with reducing wave lotions, the dependency of the ratio of extraction of metal to the pH of the solutions was slightly smaller than that of bleaching solutions. Treating with formic acid, Ca and Mg were completely extracted. From these results, it has been suggested that some metals exist more abundantly in melanin granule and the intercellular area than internal area of cortex cell.
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Watanabe et al. (1994) studied this question.