Permanent waving does not change mercury concentration in the proximal segment of hair close to scalp

Mercury in hair is a generally accepted biomarker of methylmercury exposure, and permanent waving has been reported to affect the mercury concentration in hair. We conducted an experimental-field study to examine the changes in the mercury concentration in hair induced by treatments such as permanent waving, straightening and coloring. Hair samples were collected from 19 female subjects enrolled before and after hair treatment by a beautician during each visit to a beauty saloon. A total of 38 pair samples were cut in 1-cm segments from the proximal end up to 10 cm, and then as 2-cm segments up to the distal end thereafter. Each segment was analyzed for total mercury concentration by cold-vapor atomic absorption spectrometry. Permanent waving decreased mercury concentration for most of the segments except for the proximal two segments and the 8-9 cm segment from the proximal end. Nevertheless the average mercury concentration of 3-cm segments from the proximal end showed no significant decrease by permanent waving. Since females usually have hair longer than 3 cm, hair samples subjected to permanent waving may give lower mercury exposure estimates when the full-length hair strands are analyzed. However, analyzing the proximal 3-cm segment of hair samples does not give lower mercury exposure estimates. Assuming that hair samples are collected from puerperal women around the time of delivery, the 3-cm segments represent fetal exposure to methylmercury during the third trimester when fetuses are most vulnerable to methylmercury exposure. Therefore, mercury concentrations in the proximal segment of maternal hair collected in the right time can be a good biomarker of fetal methylmercury exposure.