Mercury content of hair in different populations relative to fish consumption.

Hair has been used in many studies as a bioindicator of mercury exposure for human populations. At the time of hair formation, mercury from the blood capillaries penetrates into the hair follicles. As hair grows approximately 1 cm each month, mercury exposure over time is recapitulated in hair strands. Mercury levels in hair closest to the scalp reflect the most recent exposure, while those farthest from the scalp are representative of previous blood concentrations. Sequential analyses of hair mercury have been useful for identifying seasonal variations over time in hair mercury content, which may be the result of seasonal differences in bioavailability of fish and differential consumption of piscivorous and herbivorous fish species. Knowledge of the relation between fish-eating practices and hair mercury levels is particularly important for adequate mitigation strategies. Methyl mercury is well absorbed, and because the biological half-life is long, the body burden in humans may reach high levels. People who frequently eat contaminated seafood can acquire mercury concentrations that are potentially dangerous to the fetus in pregnant women. The dose-response relationships have been extensively studied, and the safe levels of exposure have tended to decline. Individual methyl mercury exposure is usually determined by analysis of mercury in blood and hair. The objective of the present review was to examine variations in hair mercury levels from different populations with respect to fish-eating practices.