Mercury in the Marine Environment - Mercury in the Environment - page 196

squid, octopus, scallops, and crabs consumed in the United
States range f from only 0.01 to 0.12 µg g 1 wet weight (ww), as
compared with an average concentration of 0.95

enriched in mercury, resulting in anomalously high mercury
levels (e.g., 7 µg g 1 dw) in mussels ( Bathymodiolus azoricus ) and
ascidians ( Polydistoma azorensis ) living in those chemotrophic
systems (Kádár et al., 2007). Several studies have investigated
factors infl uencing the bioavailability, bioaccumulation,
biomagnifi cation, compartmentalization, and toxic effects
of mercury in hydrothermal vent invertebrates (Colaço et al.,
2006; Cunha et al., 2008; Kádár et al., 2005, 2007; Martins
et al., 2001; Ruelas-Inzunza et al., 2005). For example, Kádár
et al. (2005) determined that the bioaccumulation factor for
inorganic Hg(II) in the hydrothermal mussel Bathymodiolus
azoricus was 10 4 , while Colaço et al. (2006) found no clear evi-
dence of mercury biomagnifi cation in seven different species
of invertebrates (worms, mussel, shrimp and crabs) in food
chains of Mid-Atlantic Ridge hydrothermal vent systems. In
a related study, Martins et al. (2006a) found levels of mercury
in fi sh (0.6-1.9 µg g 1 ww) caught at the Mid-Atlantic hydro-
thermal vent fi elds that were relatively high compared with
previously published values for deep-sea fi sh “with identical
diets, but caught in other areas.”

1.3 µg g 1
ww in swordfi sh and shark muscle (US EPA, 1997; US FDA,
2006). The ratio of MMHg to total mercury is also generally
substantially lower in marine invertebrates (<60%) than it
is in edible marine fi sh (60-100%) (Lasora and Allen-Gil,
1995; Andersen and Depledge, 1997). Some exceptions are
marine shrimp, crabs, and lobsters, for which mercury bur-
dens in muscle t issue a re more consistent ly 8 0 -10 0 % M M Hg
(Andersen and Depledge, 1997; Bloom, 1992; Campbell et al.,
2005; Francesconi and Lenanton, 1992; Hammerschmidt
and Fitzgerald, 2006a; Joiris et al., 1997b). A substantial
amount of that mercury in lobsters ( Nephrops norvegicus )
is in the tail, which is the part principally consumed by
humans (Canli and Furness, 1995; Hammerschmidt and
Fitzgerald, 2006a; Perugini et al., 2009).
One reason for interest in mercury concentrations in
marine invertebrates, primarily mussels and oysters, has
been because of their applicability as biomonitors of pol-
lutants in coastal waters. These organisms are used because
they are widespread, numerous, convenient to collect,
sessile, and tend to bioaccumulate pollutants, including
mercury, to levels that are easily measured. Consequently, a
national “mussel watch” program was started in the United
States more than three decades ago (Goldberg et al., 1978),
and comparable programs now exist in most of the world's
coastal waters (Laurier et al., 2007; Nakhlé et al., 2006;
National Oceanographic and Atmospheric Administration
[NOAA], 2007). Cubadda et al. (2006) have reported that
variations of mercury concentrations in mussels ( Mytilus
galloprovincialis ) ranged from 0.02 to 0.07 µg g 1 (ww) and
revealed spatial gradients in anthropogenic pollution in
the Venice Lagoon. The use of mussels as biosentinels is not
as well suited for quantifying differences in mercury pol-
lution across ecosystems or time as for other pollutants if
only total Hg is measured, because there is high variability
in the ratio of MMHg to total Hg in the bivalves used.
Documentation of differences in mercury concentra-
tions and speciation both within and between inver-
tebrate species has catalyzed a number of studies on the
abiotic and biotic factors that account for those differences
(Baeyens et al., 1998; Canli and Furness, 1995; Gagnon and
Fisher, 1997; Mason and Lawrence, 1999). These have gen-
erally shown that MMHg is more readily bioaccumulated
than inorganic Hg(II) in marine invertebrates, ranging
from small deposit-feeding polychaetes ( Nereis succinea and
N. diversicolor ), amphipods ( Leptocheirus plumulosus ), and
mussels ( Mytilus edulis ) to macroinvertebrates, including
scavenging Norway lobsters ( Nephrops norvegicus ). In con-
trast, Laporte et al. (2002) determined that inorganic Hg(II)
and MMHg were accumulated by the blue crab ( Callinectes
sapidus ) at similar rates, albeit by different mechanisms.
Finally, there have been varying accounts of anomalously
high levels of mercury in marine invertebrates at some sub-
marine hydrothermal vent systems. These vents emit fl uids

Mercury in Fish

Interest in mercury levels in fi sh has been catalyzed by con-
cerns of mercury toxicity to humans and other animals,
whose principal source of mercury contamination is from
the consumption of fi sh. Most studies of mercury in marine
fi sh have, therefore, focused on species commonly preyed
upon by marine mammals and birds, or more often, on fi sh
of commercial importance. This anthropocentric orienta-
tion has been of great value in evaluating human exposure
to mercury via fi sh consumption and developing guidelines
for protecting public health (Burger et al., 2005; Mergler et
al., 2007; Mozaffarian and Rimm, 2006; Sunderland, 2007).
However, it may have inadvertently skewed common per-
ceptions of the cycling of mercury in the marine biosphere.
Reviews and public reports on mercury concentrations
in fi sh often focus on those with the highest mercury con-
centrations (e.g., shark and swordfi sh) and those commonly
eaten by affl uent Western and Asian populations (e.g., tuna
and halibut). Although these are appropriate for assisting
people in evaluating the risk of mercury levels in the fi sh
they most often eat, such fi sh do not represent the major-
ity of fi sh in marine ecosystems, nor even the majority of
species harvested by global fi sheries. So while tuna repre-
sents the most important source of mercury to the average
American (Sunderland, 2007), all tuna combined accounts
for less than 5% of the global fi sh catch each year (UN FAO,
2007) and comprise a much smaller percentage of the total
fi sh biomass in the oceans. Table 10.4 provides mercury
concentrations for the 32 leading marine organisms har-
vested globally (by fresh weight), which together account
for over 40% of all fi sh harvested from the oceans. Of these
32, only 4 have mean mercury concentrations in muscle
tissue in excess of 0.2 µg g 1 ww. Many of the ecologically
important smaller fi sh found in Table 10.4, as well as other