The effects of dyes and bleaches on the sorption and desorption of trace elements in human hair

Trace element concentrations and isotope ratios of hair reflect the blood levels at the time of hair formation, but can be affected by external factors such as dyeing, bleaching, and bathing. To investigate the effect of dyeing, bleaching, and bathing on hair, hair was immersed in tap water, and changes in trace element concentrations and the Sr isotope ratio were observed over time. During soaking, alkaline earth metals (Ca, Mg, and Sr) from tap water were gradually absorbed into the hair over time. After about one day, the adsorption capacity of hair reached a maximum and the reverse reaction started to occur. In contrast, alkaline metals (Na and K) behaved in reverse. In dyed and bleached hair, Na was significantly desorbed from the hair and gradually migrated to the water over time. The adsorption and desorption of trace elements were minimal in untreated original hair, but much higher in dyed and bleached hair. Thus, dyeing and bleaching appear to damage the hair surface structure and greatly promote the exchange of trace elements. The rapid exchange of trace elements, including Sr, between hair and tap water observed in this study indicates that hair samples can be easily contaminated during bathing.