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

MERCURY 458
5. POTENTIAL FOR HUMAN EXPOSURE
concentrations in breast milk from women in the Faroe Islands, a population that consumes large quantities
of fish and marine mammal tissue, were 2.45 and 8.7 ppb, respectively (Grandjean et al. 1995a). Breast milk
mercury concentrations reported by these authors were significantly associated with mercury concentrations
in cord blood and with the frequency of pilot whale dinners during pregnancy. These are relatively low
values in contrast to the values reported in Minamata, Japan, for women who ate
contaminated seafood in the Minamata episode, which resulted in total mercury concentrations in breast milk
of 63 ppb (Fujita and Takabatake 1977), and in Iraq, where consumption of homemade bread prepared from
methylmercury-contaminated wheat occurred, resulted in breast milk concentrations of up to 200 ppb (about
60%) methylmercury (Amin-Zaki et al. 1976; Bakir et al. 1973).
Children can be exposed to mercury by many of the same pathways as adults as discussed in
Sections 5.4.4., 5.5, and 5.7. Children can receive mercury exposures from oral or dermal contact with
mercury-contaminated soils and sediments or mercury-contaminated objects. Exposure analysis of
individuals living near an abandoned mercury-contaminated industrial site suggested that children were
exposed primarily via soil ingestion (Nublein et al. 1995). Little experimental information on the
bioavailability of mercury via oral or dermal exposure was found relative to mercury or mercury compounds
sorbed to contaminated soils and sediments (De Rosa et al. 1996). Paustenbach et al. (1997) noted that, due
to the presence of mercury at a number of major contaminated sites in the United States, the bioavailability
of inorganic mercury following ingestion has emerged as an important public health issue. Although precise
estimates are not available, in vivo and in vitro estimates of the bioavailability of different inorganic
mercury species in different matrices suggest that the bioavailability of these mercury species in soil is likely
to be significantly less (on the order of 3 to 10 fold), than the bioavailability of mercuric chloride, the
mercury species used to derive the toxicity criteria for inorganic mercury (Paustenbach et al. 1997). These
authors suggest that site specific estimates of bioavailability be conducted of various mercury compounds
because bioavailability can vary significantly with soil type, soil aging, the presence of co-contaminants and
other factors. Canady et al. (1997) concluded that the “100% bioavailability assumption” for mercurycontaminated
soils is excessively conservative. These authors note that various mercury compounds have
distinctly different bioavailability. For example, mercuric chloride has been reported to be approximately
20–25% bioavailable in adult animals (Nielsen and Andersen 1990; Schoof and Nielsen 1997).
Methylmercury is thought to be nearly completely absorbed (Aberg et al. 1969; Miettinen et al. 1971; Rice
1989a, 1989b). Mercuric nitrate was reported to be only 15% bioavailable in humans (Rahola et al. 1973)
and elemental mercury is thought to be very poorly absorbed, although experimental evidence is lacking for
the latter. Recently, Barnett et al. (1997) reported that analysis of mercury contaminated soil from the flood