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

MERCURY 465
5. POTENTIAL FOR HUMAN EXPOSURE
waste sites may be exposed to mercury through several exposure pathways, including inhalation, dermal, and
oral exposures. For example, numerous studies have reported increased levels of mercury in air, water, soil,
plants, and fish in areas surrounding industrial facilities involved in production or use of mercury (Harnly et
al. 1997; Lodenius and Tulisalo 1984; Shaw et al. 1986; Yamaguchi et al. 1971). Significant concentrations
of mercury have been detected in sewer overflows and urban runoff (Murphy and Carleo 1977). Thus,
general population exposure to mercury may be higher in both industrial and urban areas. Mercury has been
detected in various environmental media (air, surface water, groundwater, soil, sediment, and fish and
wildlife samples) collected at some of the 714 NPL sites where it has been detected in some environmental
media (HazDat 1998). Populations living near hazardous waste sites may be at risk for exposure to high
levels of mercury as a result of mercury contamination of surface waters, groundwater, soils, or fish.
However, the available data are insufficient to allow for the characterization of the sizes of these populations
or the intake levels of mercury to which they are exposed. In 1996, however, De Rosa et al. (1996) reported
than in terms of populations at risk, an estimated 41 million people in the United States live within a 4-mile
radius of at least one of the 1,134 NPL sites, and 3,300 people live within a 1-mile radius of an NPL site.
These authors also reported that metallic mercury was ranked third on the top 10 priority list of hazardous
substances found at these NPL sites.
Adults may receive higher mercury exposures from dermal contact if they work with mercury-contaminated
soils. Mercury has been detected in soil and sediment at 350 and 208 sites, respectively, of the 714
NPL sites where it has been detected in some environmental media (HazDat 1998). No experimental
information on dermal exposure related to the bioavailability of mercury or mercury compounds sorbed to
soils was found. However, Hursh et al. (1989) conducted a study to determine the role of dermal exposure in
the uptake of mercury vapor from air. These authors estimated that during an 8-hour day, a person would
absorb through the skin only 2.6% of the mercury vapor retained by the lungs exposed to the same
atmosphere. These authors also noted that half of the dermal uptake is lost through normal shedding of the
stratum corneum. Therefore, dermal uptake of mercury adsorbed to soil is likely to be minor compared to
other exposure pathways. Recent information from Harnly et al. (1997) showed that urine mercury levels in
a Native American population living near an inactive mercury mine in Clear Lake, California were
comparable to background levels, indicating that soil and dust exposures were not substantially elevated in
the resident population near the inactive site. However, the mean blood methylmercury level in residents of
this same community that consumed fish from Clear Lake was 15.6±8.8 µg/L (ppb), which was more than 7
times higher than the mean blood level in individuals that did not consume fish from the lake (2 ppb).