Mercury in the Marine Environment - Mercury in the Environment - page 195

of mercury concentrations per mass of phytoplankton, it
is unclear how much of this is intracellular versus simply
sorbed onto the outside of cell surfaces.
Using those normalizations, estimated values of total
mercury concentrations (dry weight) in particles likely to be
phytoplankton in the Arctic Ocean are less than 20 ng g 1
(Atwell et al., 1998; Campbell et al., 2005). These are sub-
stantially lower than mercury levels for similar sized par-
ticles and sestons in estuaries and coastal areas such as
the Seine estuary in France (40-170 ng g 1 ; Laurier et al.,
2003a), Monterey Bay (100-600 ng g -1 ; Martin and Knauer,
1973), San Francisco Bay (500 -3700 ng g 1 , mean

reported in coastal and estuarine waters (Pereira et al.,
2007), but concentrations are generally in the range
0.5-200 ng g 1 (Al-Majed and Preston, 2000; Atwell et al.,
1998; Campbell et al., 2005; Hammerschmidt and Fitzgerald,
2006a; Joiris et al., 1997b; Outridge et al., 2008; Pereira
et al., 2007; Stern and MacDonald, 2005). These mer-
cury concentrations in marine zooplankton are slightly
lower than those for zooplankton from freshwater systems
(10 -500 ng g 1 ; Kainz and Mazumder, 2005; Tremblay et al.,
1995; Watras and Bloom, 1992; Watras et al., 1998). This
disparity presumably refl ects the lower concentrations of
MMHg in microseston of marine environments, but may also
be due to differences in zooplankton community and associ-
ated differences in diet or MMHg assimilation effi ciencies.
The ratio of MMHg to Hg(II) in zooplankton is highly
variable (Al-Majed and Preston, 2000; Campbell et al.,
2005; Francesconi and Lenanton, 1992; Joiris et al., 1997b;
Stern and MacDonald, 2005) and is not consistently as
great as in higher trophic levels. Even when the majority
of the mercury in zooplankton is not MMHg, the %MMHg
is still consistently greater than in phytoplankton from
the same environment because of the higher assimilation
effi ciency of MMHg by zooplankton relative to inorganic
mercury (Lawson and Mason, 1998). Mercury levels tend
to be 2-6 times higher in zooplankton than in phyto-
plankton or microseston, demonstrating bioaccumulation.
In laboratory studies, the assimilation effi ciency by her-
bivorous copepods ( Acartia tonsa, Temora longicornis, and
Centropages sp.) feeding on the diatom Thalassiosira weiss-
fl ogii for MMHg, which was accumulated in the cytoplasm
of the phytoplankton, was fourfold greater than it was for
inorganic Hg(II), which was principally bound to mem-
branes (Mason et al., 1996).
The uptake of Hg(II) and MMHg by zooplankton var-
ies with taxonomic, morphometric, and ontogenic dif-
ferences, but in general zooplankton bioconcentrate
both inorganic Hg(II) and MMHg from the surrounding
medium. However, most accumulated mercury comes from
their food (Mason et al., 1996; Mathews and Fisher, 2008;
Monson and Brezonik, 1999; Pickhardt et al., 2006; Watras
et al., 1998). As a result, zooplankton mercury levels display
spatial and seasonal variability that refl ect differences in
diet, phytoplankton community dynamics, factors affect-
ing phytoplankton uptake of MMHg, and changes in DOM
and suspended particle load (Chen and Folt, 2005; Joiris
et al., 1997b; Laurier et al., 2003a; Lawson and Mason,
1998; Mathews and Fisher, 2008; Monson and Brezonik,
1999; Pereira et al., 2007; Pickhardt et al., 2002; Stern and
MacDonald, 2005).

1200

1000 ng g 1 ; Flegal, 1977), South San Francisco Bay
(80-420 ng g 1 , mean 90 ng g 1 ; Luengen and

Flegal, 2009), or those (60-100 ng g 1 ) estimated for an
estuarine mesocosm experiment (Kim et al., 2004). The
higher concentration of mercury in phytoplankton-sized
particles in coastal waters refl ects the greater mercury con-
tamination here; also, these operationally defi ned size frac-
tions are likely to include a larger percentage of more mer-
cury-contaminated inorganic particles and resuspended
sediment in estuary and coastal environments. These mer-
cury concentrations are well within the range, although
slightly on the lower end, of particulate concentrations
of total mercury on all suspended material in estuary and
coastal waters (Baeyens et al., 1998; Balcom et al., 2008;
Benoit et al., 1998; Choe et al., 2003; Conaway et al., 2003;
Coquery et al., 1997; Laurier et al., 2003a; Leermakers et al.,
1995, 2001; Stordal et al., 1996). Thus, it appears that the
partitioning of total mercury onto phytoplankton is similar
to that for inert particles, as also suggested by laboratory
experiments (Pickhardt and Fisher, 2007).
MMHg concentrations estimated for phytoplankton in
the Seine estuary in France (5

250

3.6 ng g 1 ; Laurier et al.,
2003a) and the San Francisco Bay estuary (0.6-2.2 ng g 1 ;
Luengen and Flegal, 2009) are similar to those measured
by Kim et al. (2004) in an estuarine mesocosm experiment
(1.0 - 6.5 ng g 1 ). These values are noticeably higher than
particulate MMHg concentrations of microseston and sus-
pended particulate matter in these waters and other estuar-
ies and coastal waters (Baeyens et al., 1998, 2003; Balcom
et al., 2008; Benoit et al., 1998; Choe and Gill, 2003;
Conaway et al., 2003; Hammerschmidt and Fitzgerald.,
2006a; Horvat et al., 1999; Leermakers et al., 2001). This
disparity refl ects the preferential bioaccumulation of
MMHg by phytoplankton compared with inorganic Hg(II).

Mercury in Zooplankton

There have been fewer studies of mercury in zooplankton
in saline waters than for zooplankton in freshwaters or
phytoplankton in saline waters. Despite this, the processes
controlling the uptake and trophic transfer of mercury by
zooplankton in freshwater and saline environments are
probably similar. Mercury levels in particles of comparable
size to zooplankton as high as 25 µg g 1 (dw) have been

Mercury in Macroinvertebrates

Analyses of a large number of marine invertebrates have
shown that most contain relatively low concentrations of
mercury and MMHg in contrast to larger, piscivorous fi sh.
Average total mercury concentrations in oysters, clams,