Appendix D Food Codes for NHANES - OEHHA

Scientific Review Panel Draft February, 2012
valence states, namely as Hg 0 , Hg2 2+ and Hg 2+ (Andersson, 1979). Hg 2+ forms
various complexes with OH - and Cl - ions, with the dominating mercuric
complexes being HgCl2, Hg(OH)2 and HgOHCl. Only a small fraction of
mercuric Hg species occurs free in solution; the major fraction is either bound to
or in the soil material. Hg 2+ and gaseous Hg 0 forms are preferably bound to
organic matter in acidic soils, whereas in neutral and slightly alkaline soils,
mineral components are active as well. Mercury exhibits a very high affinity for
sulfide in reducing environments, forming relatively insoluble HgS (Davis et al.,
1997).
Human skin both in vivo and in vitro has been shown to have a large capacity to
accumulate metallic mercury vapor or mercury salts (as HgCl2) applied in
aqueous solution directly to skin. When freshly mixed with soil, Hg salts appear
to have a greater ability for absorption into skin than other metal salts of concern
in this section (i.e., Ni, Pb, Cd, etc.). However, similar to other metals, aging of
Hg salt in soil significantly reduces the fractional absorption of Hg into skin.
Therefore, a fractional absorption of 3% for HgCl2 aged in soil prior to testing was
chosen as the basis of the ABS to account for the aging affects in soil.
The Hg ABS is based on the in vitro study in pigs by Skowronski et al. (2000), in
which HgCl2 aged in soil for three months resulted in a considerable reduction of
fractional absorption compared to HgCl2 freshly mixed with soil. Limitations of
this study include use of skin from a non-primate species, less than 24-hr
exposure, and likely exceedance of soil monolayer coverage during the
exposure. However, the human in vitro studies shown in Table F-2 also have
their limitations for estimating fractional absorption, including exceedance of soil
monolayer coverage (Sartorelli et al., 2003), or use of soil fractions that do not
include soil particles less than 90 to 180 µm, which most commonly adhere to
skin (Wester et al., 1995; Moody et al., 2009b).
Given the limitations, it is still unlikely that the ABS will underestimate fractional
absorption. While both the human and animal in vitro studies show a large
capacity for dermal absorption of Hg salt, very little reaches the diffusion cells
(see Table F-2). Other studies reviewed here indicate that some of the Hg ++ ions
in mercuric salts tend to bind tightly to cellular proteins in all strata of skin,
including stratum corneum, which may then impede further diffusion of mercury
(Friberg et al., 1961; Silberberg, 1972; Hostynek, 2003). Mercury bound in
stratum corneum would likely be removed via desquamation of skin. Hursh et al.
(1989) have shown that a considerable portion of absorbed Hg in skin will
eventually be lost (up to 50%) due to desquamation.
Nevertheless, the development of a Hg ABS would benefit from human in vitro
studies with Hg salts aged in soil, and continued monitoring after 24-hr dermal
exposure to better estimate the amount of Hg that reaches the circulation (i.e.,
reaches the diffusion cells) and how much is likely to be lost due to
desquamation. Because the ABS is based on Hg aged in soil, the ABS may
F-40