Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
some, but not all, of the Hg became oxidized to mercuric ions. The ions then
became fixed or bound in the skin, some of which then moved upward and was
eventually shed.
Baranowska-Dutkiewicz (1982) exposed the forearms of eight male volunteers to
aqueous mercuric chloride solutions. Aliquots (0.25 ml) of HgCl2 solutions were
applied directly to a 22 cm 2 area of skin and covered with a watch-glass.
Percutaneous absorption of mercury was calculated as the difference between
the amount applied and the amount recovered after the skin and the watch-glass
were washed. In order to examine the effect of concentration on uptake, 3
concentrations (0.01, 0.1, and 0.2 M) were applied for 30 minutes. As
concentration increased, rate of uptake increased. In order to examine the
influence of exposure time on uptake, 0.1 M HgCl2 was applied for 5, 10, 15, 30
and 60 minutes. The authors reported that the average rate of uptake of mercury
decreased from 9.3 µg/cm 2 /min during a 5 minute exposure, to 2.5 µg/cm 2 /min
during a 1 hour exposure. The average percutaneous absorption of mercury was
calculated for exposures of 5, 10, 15, 30, and 60 minutes resulting in 20%, 29%,
37%, 60% and 64% absorption of the applied dose, respectively.
In vivo application of aqueous HgCl2 (0.1% w/v) to normal human skin followed
by biopsy and visualization with electron microscopy found mercury deposits
present intracellulary and extracellularly in the stratum corneum within minutes
after application (Silberberg, 1972). The presence of mercury in the epidermis
was not apparent until 2-4 hrs after application. The finding of immediate
absorption of HgCl2 correlates well with the in vivo findings of Baranowska-
Dutkiewicz (1982), which observed the disappearance of HgCl2 within 5 min after
application to human skin.
An in vivo study in guinea pigs found that dermal absorption of Hg from HgCl2
steadily decreases with increasing dose, suggesting a build up of a secondary
diffusion barrier as a consequence of the electrophilic metal forming irreversible
bonds with proteins of the skin (Friberg et al., 1961). Thereby a depot
accumulates in the stratum corneum retarding further penetration in inverse
proportion to metal concentration. This secondary barrier build-up retarding
absorption was also evident with increasing dermal exposure intervals. HgCl2
applied in vitro on human skin showed greatest percutaneous absorption during
the first 5 hrs (Wahlberg, 1965). With later time periods the absorption rate
decreased. The average absorption rate over the first 24 hrs was only about
one-fourth the rate observed during the first 5 hrs of dermal exposure.
F. 3.7.2 Discussion and Recommendation for an Inorganic Mercury Compound
ABS
More than 98% of mercury in soils is present as nonalkyl Hg(II) compounds and
complexes, with direct deposition a significant component for much of the loading
to terrestrial soils (Davis et al., 1997). In the soil, Hg can occur in three different
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