Environmental Engineering Reference
In-Depth Information
and 0.5 µg g
1
ww) reported by Thompson (1996) and Eisler
(1987). These observations were consistent with those of pre-
vious studies by Joiris et al. (1997c) of migratory common
guillemots (
Uria aalge
) in the North Sea, and by Borga et al.
(2006) of a suite of Arctic seabirds. The latter studies also
attested to the importance of spatial and temporal variations
on mercury concentrations in those Arctic birds.
Some of the reasons for that variability have been
resolved with complementary measurements of
Consequently, the cycling of mercury in Antarctic marine
food webs is of both basic and applied scientifi c interest.
Most of the data on mercury in Antarctic marine organ-
isms are relatively limited or preliminary (e.g., Ancora et al.,
2002; Bocher et al., 2003; de Moreno et al., 1997; dos Santos
et al., 2006; Honda et al., 2006; McArthur et al. 2003;
Riva et al., 2004), but some studies have begun to address
mercury in Antarctic food webs. Nygård et al. (2001)
investigated metal concentrations in the Antarctic petrel
(
Thalassoica antarctica
), Antarctic krill (
Euphausia superba
)
in petrel stomach contents, and in the petrel's predator, the
South Polar skua (
Catharacta maccormicki
). The average mer-
cury concentration of the krill (40 ng g
1
dw) was compa-
rable to that of copepods (
Calanus hyperboreus
) (20 ng g
1
dw)
from the Beaufort and Chukchi Seas in the Arctic (Stern and
Macdonald, 2005), as well as that of zooplankton elsewhere.
While mercury was biomagnifi ed in that simple food chain,
mercury concentrations in the birds were found to vary sub-
stantially, indicative of variations associated with age, sex,
and diet. This was consistent with the more extensive study
of variations of mercury in feathers of 13 species of seabirds
in the Southern Ocean (Becker et al., 2002), as well as that of
terrestrial and marine birds elsewhere.
Bargagli et al. (1998) conducted a more extensive analysis
of the biomagnifi cation of mercury in an Antarctic marine
coastal food web, extending from phytoplankton to seals
(Table 10.5). They also measured mercury concentrations
in soils at the site (12 ng g
1
dw), which they reported to
be the lowest ever reported for a coastal location. They
attributed the “slightly lower” mercury concentrations in
primary producers and consumers in that food web, as
compared with related species elsewhere, to the low natural
background levels of mercury and minimal contamination
in the Antarctic. However, a comparison with data in Table
10.5 suggests that their results are consistent with mercury
concentrations at those same trophic levels in the Arctic.
Similarly, they noted that mercury concentrations in
piscivorous birds and mammals in the Antarctic food web
were comparable to those observed in similar species in the
northern hemisphere, but attributed that enrichment “to
enhance natural biomagnifi cation processes of Hg in the
pristine Antarctic coastal environment.”
15
N values
to more accurately establish trophic level(s) of organisms in
Arctic food webs (Michener and Schell, 1994). For example,
Atwell et al. (1998) measured both
δ
15
N and mercury in
27 species in an Arctic food web, from invertebrates to
polar bears, and determined that mercury concentrations
were biomagnifi ed in muscle tissue throughout that food
web with one exception—the polar bears. Average mercury
levels in their muscle (0.84
δ
0.17
μ
g g
1
dw) were found
to be lower than those (1.07
g g
1
dw) of their
principal prey, ringed seals. This anomaly was attributed
to the bears preferentially consuming seal blubber, which
is relatively low in mercury compared with other tissues
(Brookens et al., 2008). It has also been noted that polar
bears are able to store unusually high amounts of mercury
in their kidneys (Dietz et al., 1990), which would further
reduce the amount of mercury in their muscle tissue, and
may be related to demethylation of MMHg in the liver, as
observed in other mammals and birds.
Finally, mass balance calculations of mercury fl uxes
through the Arctic Ocean (Outridge et al., 2008) suggest
that the system is near steady state (net annual increase
in mercury of ~0.3%). Sustained reductions in emissions
of industrial mercury would be required to measurably
reduce mercury contamination of marine organisms in the
Arctic. Any such declines are projected to be slower there
than in most other marine ecosystems because of the large
reservoir of mercury in the Arctic relative to inputs, result-
ing in a longer residence time of mercury in the Arctic
Ocean compared with most other oceans (Mason and Sheu,
2002; Outridge et al., 2008; Sunderland and Mason, 2007).
Moreover, dramatic climate change in the Arctic is further
compounding diffi culties with already complicated models
of mercury in the Arctic environment (Macdonald et al.,
2005; Outridge et al., 2008).
0.11
μ
Mercury in Open Oceanic Ecosystems
Mercury in Antarctic Ecosystems
While anthropogenic mercury contamination has occurred
in the Arctic and appears to have occurred in the Antarctic,
the extent of mercury contamination in open oceanic food
webs—where most industrial atmospheric emissions have
been deposited—is unknown. This surprising gap in knowl-
edge was emphasized by Fitzgerald et al. (2007) in their
review on the marine biogeochemical cycling of mercury.
Despite a lack of appreciable data on mercury in open
ocean food webs, there is limited data suggesting that mer-
cury concentrations in biota may vary as a function of
depth in the open ocean. Total mercury concentrations in
There are many similar concerns regarding the biogeo-
chemical cycling, biomagnifi cation, and potential toxic-
ity of mercury in the two polar regions. Mercury deple-
tion events were fi rst reported (Schroeder et al., 1998)
shortly after Arctic springtime; Antarctic AMDE
s were also
detected (Ebinghaus et al., 2002). And while there are no
indigenous peoples in Antarctica who are subject to mer-
cury exposure from the consumption of local species, fi sh
and large marine mammals from the Antarctic, like from
the Arctic, are caught and shipped to markets globally.
