revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 316
2. HEALTH EFFECTS
Japanese hair mercury levels, the hair levels reported by Nakagawa (1995) of 2–4 ppm for a Japanese
population are 10–20 times higher than levels observed in the Drasch et al. (1997) study (median,
0.247 µg/g in hair; range, 0.43-2.5 µg/g).
Other studies have confirmed a good correlation between hair mercury and brain mercury levels. In a
study on the Seychelles Islands cohort, Cernichiari et al. (1995b) compared maternal hair levels, maternal
blood levels, fetal blood levels, and fetal brain levels. Autopsy brains were obtained from infants dying
from a variety of causes. The concentrations of total mercury in six major regions of the brain were highly
correlated with maternal hair levels. This correlation was confirmed by a sequence of comparisons among
the four measures. Maternal hair correlated to maternal blood (r=0.82) and infant brain level (r=0.6–0.8).
Maternal blood correlated to infant blood (r=0.65); and infant blood correlated to infant brain (r=0.4–0.8).
There are potential confounding factors and other factors to consider when assessing mercury exposure
based upon mercury hair levels. Mercury may be deposited to hair from the air when significant sources
of mercury are present in the air or when certain hair treatments are used (Hac and Krechniak 1993; WHO
1991). Potential sources of external mercury exposure should, therefore, be evaluated as part of an
exposure assessment. Some studies also report a sex related difference in mercury tissue levels. Nielson et
al. (1994) observed a significant sex-related differences in the toxicokinetics of methylmercury in mice
following administration of a single radiolabeled dose. Drasch et al. (1997) reported that mercury levels in
all tissues assayed in their human cadaver study had higher levels compared to male tissues. The
difference was significant for the kidney (median female kidney mercury level=92.0 ng/g,
males=40.8 ng/g; p=0.002). In blood and urine there was a similar trend. In contrast, the authors report
that mercury hair levels in females were significantly lower than in males (median females=205 ng/g,
males 285 ng/g; p=0.02). Nakagawa (1995) also report higher mean mercury hair levels in males
(2.98 µg/g) compared with females (2.02 µg/g) in a Japanese population. Further research is, therefore,
needed to characterize potential sex related difference in the toxicokinetics of mercury under different
exposure scenarios.
Eide and Wesenberg (1993) studied mercury concentrations in various organs and tissues in rats exposed
to mercury vapor for approximately 2 months and proposed that human deciduous teeth may be useful
indicators of chronic mercury exposure, as well as indicators of mercury uptake in organs such as the
kidneys and the brain.