Accumulation of inorganic mercury in hair of rats exposed to methylmercury or mercuric chloride.

The concentration of methylmercury (MeHg) in human hair is an excellent marker for its exposure, since a portion of MeHg is taken up from the blood circulation to the hair protein in a dose-dependent manner. However, a small portion of the mercury in human hair is found in the inorganic form, though the mechanism of its occurrence is not well established. Here, we examined the hair uptake of inorganic mercury in the rat. Male Wistar rats were exposed to MeHg (1 microg Hg/ml) or HgCl(2) (20 microg Hg/ml) for 84 days through drinking water. The hair, grown from 49 to 84 days, was collected from the MeHg-exposed rats, and the hair samples showed 54.5 microg/g hair of the total mercury concentration, 6.1% of which was in the inorganic form. The inorganic mercury in the plasma (0.022 microg/ml), which would probably be formed from MeHg in rat tissues, accounted for as high as 29% of the total mercury (0.076 microg/ml). The hair uptake rate of inorganic mercury estimated from the hair/plasma ratio was about 1/6 lower than that of MeHg. On the other hand, the total hair mercury level in the HgCl(2)-exposed group at the same time point was 2.86 microg/g, with the inorganic portion being as high as 62%. These findings suggest that the inorganic mercury is also taken up by rat hair from the blood circulation, as is the MeHg, irrespective of the consequences of the biotransformation of MeHg or exposure to inorganic mercury itself. Accordingly, a selective quantification of inorganic mercury in human hair may be useful in detecting inorganic mercury exposure.