Environmental Engineering Reference
In-Depth Information
the top of their food web, while concentrations in other
seabirds are relatively low (Campbell et al., 2005; Jarman
et al., 1996). This variability was illustrated in a study by
Borga et al. (2006), who found that average total mercury
levels in the muscle tissue of seven species of Arctic sea-
birds ranged from 0.05
including the endangered California clapper rail (
Rallus
longirostris obsoletus
), are believed to reduce their reproduc-
tive success (Schwarzbach et al., 2006).
Mercury in Marine Ecosystems
μ
g g
1
(ww) in the black guillemot
g g
1
(ww) in the glaucous-winged
gull (
Larus hyperboreus
). Higher concentrations have been
reported for other species of marine birds (Eagles-Smith
et al., 2009a, 2009b; Ruelas-Inzunza et al., 2009).
B e c a u s e of f t h e h i g h l e v e l s of f m e r c u r y i in s of m e m a r i in e b i r d s ,
there are concerns that mercury may pose a health threat
both to the birds (Scheuhammer et al., 2007) and humans
that consume the birds and their eggs. For example, Burger
et al. (2007) found that 95% of the pigeon guillemot (
Cepphus
columba
) muscles sampled in the Aleutians had Hg concen-
trations greater than 0.3
(
Cepphus grylle
) to 0.8
μ
Mercury in Arctic Marine Ecosystems
There is great interest in mercury contamination in Arctic
marine ecosystems because of concerns that: (1) the Arctic
may serve as a global “sink” for global industrial mercury
emissions due to springtime atmospheric mercury depletion
events (AMDEs) that are unique to polar regions (Schroeder
et al., 1998), (2) some native Arctic people are exposed to
unusually high amounts of mercury through their con-
sumption of marine mammals, birds, and fi sh with unusu-
ally high levels of mercury (Burger and Gochfeld, 2007;
Burger et al., 2007; Johansen et al., 2007), and (3) high lev-
els of mercury are potentially toxic to the marine organ-
isms themselves (Burger and Gochfeld, 2007; Lockhart
et al., 2005; Sonne et al., 2007). These concerns have been
amplifi ed by measurements of relatively low mercury con-
centrations in numerous preindustrial archived Arctic
marine organisms, including beluga whales, ringed seals,
polar bears, and a variety of seabirds, as well as humans,
as compared with those found in contemporary organ-
isms in the Arctic. Mercury levels in these contemporary
organisms are reportedly as much as an order of magnitude
greater than their prehistoric baseline levels (Outridge et al.,
2005; Dietz et al., 2006a, 2006b).
There are several reviews of mercury in Arctic marine
food webs. These include general summaries of mercury
concentrations in different trophic levels (Campbell et al.,
2005; Dehn et al., 2006; Outridge et al., 2008; Riget and
Dietz, 2000; Riget et al., 2007b), as well as more specifi c
studies that address the role of trophic level or feeding
ecology on mercury concentrations in a single species or
group of species (Borga et al., 2006; Joiris et al., 1997a,
1997b; Lockhart et al., 2005; Outridge et al., 2005; Riget
et al., 2005; Wagemann and Kozlowska, 2005). While all
of the preceding studies have focused on organisms at or
near the top of Arctic marine food webs, a few studies have
focused on mercury concentrations in primary consumers
(e.g., zooplankton and shrimp) in the Arctic (e.g., Joiris
et al., 1997b; Stern and Macdonald, 2005).
Results from those studies attest to the complexity of
tracing mercury in Arctic marine food webs. For example,
Burger and Gochfeld (2007) tentatively attributed dif-
ferences in mercury concentrations in various species of
marine birds in the Arctic to differences in their diets, while
acknowledging that the diets of birds within the same spe-
cies can be highly variable. They also noted that mercury
concentrations in the eggs of common eiders (
Somateria
mollissima
) and glaucous-winged gulls (
Laurus glaucescens
),
which averaged 0.43
μ
g g
1
and 43% were greater than
0.5
g g
1
, and therefore they represented a potential health
risk to indigenous peoples of the Aleutians. In a follow-up
study, Burger and Gochfeld (2007) found that 100% of
glaucous-winged gull (
Larus glaucescens
) eggs in that region
were above 0.3
μ
μ
g g
1
, 62% were above 0.5
μ
g g
1
, and 8%
were above 1.0
g g
1
. Nearly all of the mercury in bird
eggs is MMHg, which is easily transferred from mother to
egg (Heinz and Hoffman, 2004; Scheuhammer et al., 2001).
In fact, deposition of mercury into eggs is an important
elimination route in birds for MMHg, as is incorporation
of MMHg into growing feathers (Braune and Gaskin, 1987;
Monteiro and Furness, 2001).
The elevated mercury levels in marine birds are of concern
because, as in eggs and feathers, most of the mercury in sea-
bird muscle is MMHg. For example, Joiris et al. (1997c) deter-
mined that mercury in muscle tissues of fi ve seabird species
ranged from 0.8 to 4.1
μ
g g
1
(dw), and the correspond-
ing MMHg concentrations ranged from 0.7 to 4.1
μ
g g
1
(dw), with MMHg accounting for 85-100% of the mercury
measured in those samples. In contrast, they found that
MMHg constituted a relatively low percentage of the total
mercury burden in two other species of seabirds: 63% in
black scoters (
Melanitta nigra
) and 39% in black-legged kitti-
wakes (
Rissa tridactyla
). These anomalously low values may
have refl ected the poor health of the birds that were col-
lected after they had been beached.
Variations in mercury concentrations in various tissues
from various water birds in the San Francisco Estuary were
associated with differences in foraging areas, time spent
in the estuary, and the onset of breeding (Ackerman et al.,
2007; Eagles-Smith et al., 2009a). Some of the highest mer-
cury concentrations in the bird species studied were found
in colonies that fed in the southern reach of the estuary,
where mercury concentrations in sediments and surface
waters were anomalously high because of contamination
from historic mercury mining (Conaway et al., 2004). This
is consistent with observations that mercury levels increase
in birds that migrate there from less-contaminated areas.
Moreover, mercury levels in some birds in this estuary,
μ
0.97 µg g
1
(ww)
respectively, were above the levels of sublethal toxicity (0.2
0.22 and 0.68
