Mercury in the San Francisco Estuary - Reviews of Environmental Contamination and Toxicology - page 29

of kilograms of mercury were used. It is also a heavily urbanized area that once fea-
tured chloralkali facilities and numerous shipyards potentially contaminated with
mercury-based paints. In addition, it is a drainage area for rich agricultural regions
that may have seen substantial environmental applications of mercury insecticides
and fungicides. In this review, we present a survey of literature on mercury contami-
nation and biogeochemistry focusing on San Francisco Estuary. Our intent is to
stimulate scientific questions addressing mercury contamination in this and other
estuarine systems, as well as to describe the restoration and management efforts that
accompany mercury-contaminated sites.

B Overview of the Problem

Before presenting work specific to mercury contamination in San Francisco Estuary,
an overview of the environmental mercury problem and mercury chemistry is appro-
priate. There are many valuable reviews on this wider topic, with focuses on toxico-
logical (Clarkson and Magos 2006), biogeochemical (Benoit et al. 2003; Fitzgerald
and Lamborg 2003; Fitzgerald et al. 2007; Ravichandran 2004; Ullrich et al. 2001),
ecological (Wiener et al. 2003), and microbiological aspects (Barkay et al. 2003).
Mercury is an environmental and human health concern largely because of the
formation of methylmercury, particularly monomethylmercury (MMHg), which is
bioaccumulated and biomagnified to toxic concentrations in higher trophic level
organisms, including birds (Schwarzbach et al. 2006) and mammals (Wiener et al.
2003). It is a neurotoxin for humans, and effects have been noted in populations
consuming fish (Clarkson and Magos 2006). In estuarine systems, sediments are a
primary area of MMHg production (Mason et al. 2006). Sulfate-reducing bacteria
are thought to be the principal methylators of mercury in anoxic estuarine sediment
(Compeau and Bartha 1985), although iron-reducing bacteria have recently also
begun receiving scrutiny (Kerin et al. 2006). The production of MMHg is, therefore,
controlled by factors influencing the distribution of mercury between abiotic and
biotic compartments, such as sulfur chemistry and organic matter, and by factors that
control microbial activity, such as temperature and the availability of suitable
organic matter for cellular respiration (Gilmour and Henry 1991; Hammerschmidt
and Fitzgerald 2004; Heyes et al. 2006; King et al. 2001). Methylmercury produced
in sediment that is exported to the water column can be bioaccumulated by phyto-
plankton or other organisms (Pickhardt and Fisher 2007) and biomagnified to higher
trophic levels (Lawson and Mason 1998).

C Environmental Setting of San Francisco Estuary

An understanding of the setting of San Francisco Estuary is essential as a backdrop
for this review. The monograph San Francisco Bay: The Urbanized Estuary is an older,
but excellent description (Conomos 1979), as is the more recent San Francisco