Mercury in the San Francisco Estuary - Reviews of Environmental Contamination and Toxicology - page 38

Table 2 (continued)

Mercury produced Local watersheds upstream

Mining district name (M kg) of estuary

Emerald Lake (1955-1958) 0.09 Redwood Creek

New Almaden (1845-1975) 40 Guadalupe River

New Idria (1858-1972) 17 San Carlos Creek,

San Joaquin River

a USEPA 2007b.
b Sheridan 2006; Wilhelm et al. 2007.
c CARB 2000.
d Nriagu 1987.
e Alpers et al. 2005; Churchill 2000; James 2005.
f CARB 2000; DTSC 2002; Nriagu 1987.
g Nriagu 1987; WHOI 1952.
h D'Itri 1972; Nriagu 1987.
i Cargill et al. 1980; Domagalski et al. 2004; Holmes 1965.

B Forces That Bring Mercury to the Estuary

Mercury contamination from historic mining and industrial sources reaches San
Francisco Estuary via tributaries, wastewater input, and atmospheric deposition. The
magnitude of flux from these various pathways was reviewed by MacLeod et al. (2005)
and is presented in Table 3. Transport of suspended sediment by the Sacramento-San
Joaquin Rivers into the northern reach is the primary input of mercury to the system
(Domagalski 1998, 2001; Roth et al. 2001). This suspended sediment is dispersed
throughout the estuary (Ruhl et al. 2001), but smaller tributaries, such as those draining
the New Almaden Mining District, are important as well (Thomas et al. 2002).
Preliminary data on the mercury isotopic composition of sediments, however, are insuf-
ficient to resolve different sources (Foucher and Hintelmann 2006). Mass balance cal-
culations indicate that inputs of mercury from wastewater discharge are currently
relatively small (Ellgas 2001; Hsu and Sedlak 2003), but may have been higher in the
past before the advent of modern mercury removal technology from waste streams or
when mercury compounds were used as slimicides in wastewater treatment (Nriagu
1987). Atmospheric deposition occurs through wet and dry deposition as a minor part
of total flux to the estuary (Steding and Flegal 2002; Tsai and Hoenicke 2001). Mercury
in precipitation in the region is higher than in adjacent coastal areas, which may repre-
sent scavenging of labile mercury from the atmosphere from local sources (Conaway
et al. 2005; Steding and Flegal 2002). The relative bioavailability of the mercury from
all these previously mentioned sources remains an important unknown.

IV Distribution, Speciation, and Transformation

The legacy of more than 150 years of mercury contamination has been distributed
throughout the San Francisco Estuary, with current estuary surface sediment
mercury concentrations roughly 5-15 times greater than background levels