Mercury in the San Francisco Estuary - Reviews of Environmental Contamination and Toxicology - page 35

habitats around the estuary showed relatively low mercury concentrations (<1 g

g −1 dry weight tissue) in salt marsh harvest mice ( Reithrodontomys raviventris ),
house mice ( Mus musculus ), and deer mice ( Peromyscus maniculatus ), although
concentrations did reach 4

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g g −1 in house mice at one site; these burdens had no
observable effect on health of the mice (Clark et al. 1992). An investigation of
mercury and MMHg in blood, hair, and liver of harbor seals ( Phoca vitulina
richardii ) from central and northern California, including sites in the San Francisco
Estuary area, showed concentrations that were considered toxic in other mammals
(Brookens et al. 2007). However, the study did not have sufficient statistical power
to resolve effects of sampling location on mercury concentrations (i.e., if seals from
the estuary had higher concentrations than seals in adjacent coastal areas).

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III Sources and History

The elevated concentrations of mercury in fish and birds in San Francisco Estuary
are attributed to the widespread and persistent mercury contamination in the region
(Greenfield et al. 2005; Schwarzbach et al. 2006). This contamination comes from
both natural sources and anthropogenic activities, with origins ranging from local,
to regional, to global scales. In this section, we review these sources and the trans-
port of mercury to the estuary through water, sediment, and the atmosphere.

A Sources and Reservoir Size

Mineral Resources and Extraction

The estuary lies in the heart of the highly mineralized circum-Pacific mercury belt.
The regional geology has been described in several sources, most notably the work
of Bailey and Everhart (1964) and, more recently, Rytuba (2003). Within the
California Coast Range part of this belt, major deposits are typically associated
with serpentinites emplaced along fault zones and altered to an assemblage of sili-
cate and carbonate minerals by carbon dioxide-rich hydrothermal fluids (Rytuba
2003). Background concentrations in the region are in the range of 10-100 g g −1

(Conaway et al. 2004; Domagalski 2001; Hornberger et al. 1999; Kerin 2002;
Thomas et al. 2002). Emissions of mercury vapor from natural background and
mineralized areas in the region may contribute a sizeable amount of mercury to the
atmosphere (Coolbaugh et al. 2002; Engle et al. 2006).
There are several large economic mercury deposits in the region, with locations
and mining activities described in detail by Holmes (1965) and summarized by
Cargill et al. (1980) and Rytuba (2000). The New Almaden mercury mining dis-
trict, North America's largest, is situated 30 km south of the estuary and drains

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