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

MERCURY 350
2. HEALTH EFFECTS
correlations. Further study is needed on the effects that the exposure level of methylmercury (as well as
other forms of mercury) has on tissue distributions and the correlation to biomarkers of exposure.
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.
Further research on other biomarkers of mercury does not warrant a high priority.
Of particular importance is the collection of pharmacokinetic data showing the relationship between low-
level exposure (acute, intermediate, and chronic) and blood and urine levels throughout the study
.duration. Also tissue levels at necropsy should be taken immediately after cessation of dosing. In animal
studies, a similar group of animals should be followed for urine (and blood, but not as important here)
mercury levels for periods of 30, 60, 90, and 120 days postdosing to examine whole-body excretion, and
necropsy tissue samples should also be taken from several animals at 30, 60, 90, and 120 days postdosing.
Primates would be the best animal model, but rodent models could suffice.
A needed study is a longitudinal epidemiology study that tracked daily individual exposure levels in
chloralkali industry workers, fluorescent lightbulb manufacturers, or other mercury utilizing industries, and
associated these exposure levels with weekly urine and blood samples for a period of 1–2 years.
Neurobehavioral testing (using tests from ATSDR’s recommended test battery for adults) should be used