Environmental Engineering Reference
In-Depth Information
order of decades—a result that is supported by long-term
monitoring of temporal changes of mercury concentra-
tions in surface sediments in the Bay (Conaway et al.,
2007).
(Martins et al., 2006b). The lack of change in mer-
cury concentrations in lanternfi sh is in contrast to the
Sunderland and Mason model (2007), which suggests
a ~38% anthropogenic enrichment of total mercury in
waters to a depth of 1500 m in that region over such a
period, but is more consistent with the other models,
which suggest a smaller change in mercury concentra-
tions in subthermocline-mesopelagic waters over that
time (0.1-0.2% per year over the past 150 years; Table
10.6). Such differences in modeled increases in oceanic
Hg concentrations and measured Hg concentrations in
biota over time is, in part, due to the global models of
mercury cycling created to date only including total
mercury, whereas most of the mercury bioaccumulated
by marine organisms is MMHg. Because of the complex
nature of MMHg production and bioaccumulation, tem-
poral and spatial trends in total Hg fl uxes in many cases
do not directly parallel MMHg production and uptake
into the food web.
The use of bird feathers appears to have emerged as a
more sound approach for monitoring changes in mercury
exposure over time (Fitzgerald et al., 2007). Feathers are
typically cleaned for surfi cial contamination (including
mercury used as a preservative) and then analyzed solely
for MMHg, which comprises the majority of mercury in
feathers (Monteiro and Furness, 1997; Thompson et al.,
1998). Furness and Camphuysen (1997) summarized the
applicability of using bird feathers as biomonitors of mer-
cury contamination in the marine environment. Since
then, feathers from museum collections have been used to
chronicle increases in mercury contamination of marine
seabirds over the past 150 years, as well as to trace spa-
tial variations of this contamination (Ancora et al. 2002;
Burger and Gochfeld, 1995; Monteiro and Furness, 1997;
Thompson et al., 1992, 1998).
A study of mercury in bird feathers by Dietz et al.
(2006a) documented signifi cant (
p
Measuring Changes in Biota
Are measured and modeled mercury changes in abiotic
compartments of the ocean refl ected in changes in biota
in marine ecosystems? This is an important question, but
diffi cult to answer because most studies have not focused
on measuring how mercury concentrations in fi sh or other
populations change with geographic location and time.
Nonetheless, a few approaches have been taken to detect
temporal changes and human infl uence on mercury in
biota, including the use of museum archive samples and
long-term monitoring datasets. The use of stable mercury
isotopes in “fi ngerprinting” human infl uence on mercury
concentrations represents an emerging tool for such stud-
ies, and it is discussed in other chapters.
Museum collections have been used in studies of environ-
mental mercury contamination of fi sh and birds (Martins
et al., 2006b; Monteiro and Furness, 1997; Thompson et al.,
1992, 1993, 1998). The veracity of these data, however, has
been questioned because collection and storage techniques
gave little foresight to future mercury analysis (Fitzgerald
et al., 2007). As a result, the limitations associated with the
use of historic material to document temporal changes in
mercury concentrations in biota require consideration
(Martins et al., 2006b; Renaud et al., 1995). Potential prob-
lems include: (1) sample contamination or loss of mercury
via volatilization after sample collection, (2) changes in Hg
speciation (e.g., MMHg demethylation) during storage or
preparation, (3) limited information on the health, sex,
developmental state, and age of the organisms, and (4) tem-
poral changes in trophic structure and size of prey that
would affect the amount and speciation of mercury con-
sumed during different periods.
Kraepiel et al. (2003) compared mercury concentra-
tions in yellowfin tuna (
Thunnus albacares
) collected
near Hawaii in 1971 and 1998. They concluded that
there was no apparent temporal increase in mercury lev-
els in the tuna from the region, and that their results
would be inconsistent (with 95% confidence) with any
increase of more than 6% (i.e., 0.2% per year). Using this
value as a constraint, Kraepiel et al. (2003) developed a
multispecies box model to describe the distribution of
mercury in the ocean, concluding that MMHg formed
in the deep sea was a potential source of mercury to yel-
lowfin tuna.
An examination of mercury content in the mesopelagic
glacier lanternfish (
Benthosema glaciale
) from the Atlantic
(39°N, 70°W) showed no long-term change for 1936-1993,
although there was apparently an increase in mercury
contamination in the Atlantic Ocean during World War II
0.05) temporal
increases in mercury concentrations in three species of
west Greenland birds of prey from 1851-2003, and
attributed that increase to anthropogenic contamina-
tion. Similarly, a study of museum bird specimens col-
lected from the North Atlantic (primarily the Azores
archipelago) by Thompson et al. (1998) showed mean
increases of 65-100% from pre-1931 to post-1979 in
three seabirds feeding predominantly in the epipelagic
zone. This translates to an increase in mercury in those
birds of 0.7-1.4% yr
1
, which is in agreement with the
predictions of the MFM model (Mason et al., 1994) for
past increases in surface waters, but smaller than the
12% yr
1
estimated for that time period by the Selin et al.
(2008) model. The other four models summarized in
Table 10.6 estimate that total Hg concentrations in sur-
face waters increased during the past at a rate of
0.6%
yr
1
when averaged over the past 150 years, but some
estimate current increases in Hg concentrations in surface
