# Trace Element Concentrations in Bearded Seals (Erignathus barbatus) Near Red Dog Mine Compared to Other Locations in Alaska

Authors: Lori Quakenbush; John J. Citta
Journal: Journal of Marine Biology
 (2009)

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## Abstract

To determine if bearded seals (Erignathus barbatus) harvested near a zinc and lead mine (Red Dog, Alaska , USA) by subsistence hunters from Kivalina, Alaska, were as safe to eat as bearded seals from other locations in Alaska, we compared 19 trace element concentrations in liver tissue. Liver concentrations from nine bearded seals harvested near the Red Dog Mine (RDM) port site were compared with 15 bearded seals from two reference sites (Hooper Bay and Little Diomede, Alaska, USA). Concentrations did not differ by gender, but we found statistically significant trends in concentrations of cadmium, mercury, manganese, selenium, and vanadium with age. Arsenic and copper were the only elements found to be more concentrated in the liver of bearded seals harvested near RDM than in the other locations. The predominant form of arsenic in marine mammals is known to be a nontoxic organic form, not the toxic inorganic form, and copper is an essential element. Although elevated near RDM, neither element was found at concentrations that presented health risks. We found no evidence that bearded seals harvested near RDM were less safe to eat or that trace element concentrations were greater than those found in bearded seals harvested elsewhere in Alaska or Canada.


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## Body

## 1. Introduction

Kivalina, Alaska, USA is a village of approximately
375 people located 129 km from the city of Kotzebue in northwestern Alaska on
the coast of the Chukchi Sea (Figure1). The population is 97% Inupiat Eskimo who
obtain much of their food from local marine and terrestrial resources. Concerns
regarding food safety have arisen due to studies that have shown contaminants
are found in the Arctic, great distances from where they are produced and used (see
review in Bard [1]) and there has been an increase in local industrial
activity related to mineral and petroleum extraction.
One potential source of local contamination is the Red Dog Mine, an open-pit
zinc and lead mine located approximately 80 km northeast of Kivalina. The mine
is operated by Teck Cominco and has been in operation since 1989.  Ore is transferred from the mine to a nearby
processing facility, where it is crushed and concentrated.  The ore is then trucked to the port site, approximately 29 km southeast of
Kivalina, where it is stored until it can be loaded on barges and transferred
to cargo ships.  Dust from ore removal
and transportation has been identified as a source of heavy metal contamination
[2, 3]. Based upon these findings,
numerous assessments have quantified the risks of contamination for people using local
resources for food (e.g., [4–8]).
Although studies of marine sediments identified elevated concentrations
of barium, cadmium, chromium, copper, silver, strontium, and zinc near Red
Dog Mine port site, no contaminants exceeded the screening standards
used to assess human health (see description of screening standards [7]).  For this reason, contaminant concentrations
in marine mammals near the Red Dog Mine port site have
not been assessed.Figure 1
Harvest locations for bearded seals sampled for trace element concentrations.However, marine mammals, especially bearded seals (Erignathus
barbatus), are
an important local subsistence resource (Alaska Department of Fish and Game
(ADF&G), Alaska, USA unpublished data, available at http://www.subsistence.adfg.state.ak.us/CSIS/,
[9]). During public meetings with Teck Cominco, area residents expressed
concern that mine-related contaminants may make bearded seals unsafe to eat [10, 11].
Bearded seals near Kivalina are known
to eat invertebrates (crabs, shrimp, and clams) and fish (cod and sculpins) [12]
that feed on or near the bottom and therefore may
ingest contaminants from their food sources and directly from marine sediments
while foraging.  In response to this concern, ADF&G
agreed to work with local subsistence hunters and Teck Cominco to determine
trace element (including heavy metal) concentrations in tissues from bearded seals.The purpose of
this study was to determine if bearded seals harvested in the vicinity of the
mine were as safe to eat as bearded seals from other locations in Alaska. We compared trace
element concentrations in bearded seals harvested by Kivalina hunters near the
Red Dog Mine (RDM) port site with bearded seals harvested where no mining was occurring.
We did not attempt to determine if mine-related activities were contaminating
seals. Because there was no systematic monitoring program in place for
contaminants in this area, we used a retrospective approach and compared the
bearded seals harvested by Kivalina hunters near the RDM in 2005 with bearded
seals harvested near Little Diomede and Hooper
Bay, Alaska, in 2003–2005, where no
mining was occurring.


## 2. Methods

Bearded seal teeth and liver tissue were contributed by
hunters from Kivalina, Alaska (see Figure1) in June 2005 and from Little
Diomede and Hooper Bay in 2003, 2004, and 2005.
Liver was chosen for sampling because many elements bioaccumulate in
liver tissue and data from liver tissue is available from other studies for
comparison. Although muscle and blubber are the tissues most consumed by
people, neither are good tissues for evaluating and comparing trace elements. Although
sampling other tissues or substances, such as stomach contents or blood,
may be better for determining levels of contaminants directly available in the
local environment, our focus was whether bearded seals harvested near RDM were
less safe to consume than bearded seals harvested from other areas.


### 2.1. Trace Element Analyses

Liver tissues were frozen in Ziploc bags and transported to
ADF&G in Fairbanks.  Tissues were then subsampled under clean
conditions using titanium knives on a Teflon covered surface [13]. Clean
samples were placed in I-Chem glass jars and stored at −55°C.  Samples were analyzed by LET Laboratories in
Columbia, Missouri, USA.
The laboratory quantified the concentration (μg/g or ppm dry
weight) of aluminum (Al), arsenic (As), boron (B), barium (Ba), beryllium (Be),
cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), magnesium
(Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), selenium (Se),
strontium (Sr), vanadium (V), and zinc (Zn).
Silver (Ag) was not included because it would have required
contracting another laboratory at additional cost and although Ag has been
found at relatively high concentrations in beluga whales in Alaska [14], there
are no studies regarding its toxicity. With no way to evaluate the results, we
did not feel the additional cost was warranted.Liver samples were
first homogenized with a meat grinder. An aliquot of approximately 100 g was
weighed and freeze-dried and then further homogenized using a blender prior to
extraction. Percent moisture was calculated by comparing the weight of the wet
sample with the weight of the dry samples before a 0.5 g sample was extracted and
digested in a microwave wet ash procedure using H2O2 and
HCl. Percent moisture was used to convert dry weight to wet weight and all results
are presented in μg/g wet
weight. Microwave digestion was used for all elements except As and Se.Samples analyzed
for As and Se were digested using magnesium dry ash digestion methods. This
method uses methanol, HNO3, HCl, and heat for digestion. After
digestion, As and Se were analyzed using hydride generation AA.  Pb was
analyzed using graphite
furnace AA.  For total
mercury, a 10 mL aliquot
was removed immediately after dilution, HCl
was added, and concentrations were determined using cold vapor AA.  All other elements were analyzed using ICP on
a Perkin Elmer 4300 DV.Quality assurance included the analysis of
procedural blanks, duplicate samples, and spiked samples run with each group of
10 samples.  Instruments were also calibrated
after every 10 samples. If quality
standards were not met samples were rerun.
Standard reference materials (SRM) provided by the National Institute of
Standards and Technology (NIST 1566b, oyster tissue) and the National Research
Council, Canada (NRCC DOLT-3, dogfish liver) were used. The data were accepted if the SRM reported
value was within 2 standard deviations of the certified mean of the SRM.  LET Laboratories participates in annual interlaboratory trials to
maintain quality assurance and comparability with other participating laboratories.


### 2.2. Aging

Lower jaws were submerged in hot water for 30 minutes and a
canine tooth was extracted and placed in a paper envelope. Teeth were sent
to Matson’s Laboratory in Milltown, MT, USA for slide preparation. Teeth were sectioned (14μm),
placed on glass slides, and stained with Giemsa histological stain. Age was
determined by counting growth layer groups that are generally accepted to represent
one per year [15], although validation studies are lacking.  Bearded seal teeth show excessive wear at
early ages and lower canines have been reported to be missing frequently [16], which
can make accurate aging problematic [17]. Lower canines were present in our
specimens and Matson’s Laboratory provided ages accompanied by a certainty code
that described the potential error associated with the ages. The error
associated with aging ranged from 0 to 4 years, with a mean of 2 years.


### 2.3. Statistical Analyses

To compare RDM to sites without possible mine
contamination, we pooled samples from Little Diomede and Hooper Bay
and treated them as a reference group. For concentrations below the detection
limit, we followed the standard practice of assigning one half the detection
limit for calculating statistics such as means (e.g., [6]); however, no
statistical analyses were conducted when >50% of samples had concentrations
below the detection limit.Our data presented
two obstacles for analysis. First, our sample sizes were small, making the
assumptions required by parametric tests difficult to assess. Second, because
concentrations of some elements are known to covary with age [17–19]
and/or gender [19], we were concerned that sites may have sample compositions
with different age or sex ratios, thereby confounding differences in element
concentrations. For example, if the RDM sample was composed of older seals, we
may incorrectly conclude that there was greater contamination there for a
contaminant that bioaccumulates with age. To assess if element concentrations
differed by gender or location, we used nonparametric Mann-Whitney U statistics
(see [20], page 146).  Exact P-values were
calculated using PROC NPAR1WAY in SAS 9.1 [21]. To assess gender effects, we
used 2-sided tests. Because we wanted to know if seals harvested near RDM had
higher element concentrations, we used 1-sided tests when comparing locations.
To control for age effects, we used parametric tests using age as a covariate.
Because tests of normality are known to have low power [20], we primarily
relied on nonparametric procedures and only applied the parametric test to
control for age when the element was identified as covarying with age. For
parametric comparisons, we first log transformed element concentrations and
then fit a linear model with age treated as a
continuous covariate. The model was specified as ln(yi)=β0+β1xi1+β2xi2+ε1, where y is concentration (μg/g) for seal i, x1 is a dummy variable (0,1) that adjusts the mean for site (RDM or reference), x2  is seal age
(years), and ε is
residual error.  This
is analogous to an ANCOVA model, where site is a categorical variable and age
is a continuous covariate. We fit age effects with a simple linear model, as we
did not have enough samples to reliably estimate separate slope parameters for
RDM and reference sites or to identify nonlinear relationships between element
concentrations and age. Although we know that the bioaccumulation of
contaminants is likely nonlinear and probably differs by sampling locations,
modeling age as a linear covariate still eliminated much of the variance among
seals of different ages. We investigated fitting curvilinear models to the data
and found that such models sometimes identified patterns that were clearly
spurious. Choosing to model age effects as linear is a major improvement
over assuming the same age distributions exist between the RDM sample and the
control sample and therefore provides the best balance between over and under
parameterizing the models we used. For elements without a significant age effect (i.e., if the
slope was not significantly different from 0 at P≤.05), we relied upon Mann-Whitney U
statistics.


## 2.1. Trace Element Analyses

Liver tissues were frozen in Ziploc bags and transported to
ADF&G in Fairbanks.  Tissues were then subsampled under clean
conditions using titanium knives on a Teflon covered surface [13]. Clean
samples were placed in I-Chem glass jars and stored at −55°C.  Samples were analyzed by LET Laboratories in
Columbia, Missouri, USA.
The laboratory quantified the concentration (μg/g or ppm dry
weight) of aluminum (Al), arsenic (As), boron (B), barium (Ba), beryllium (Be),
cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), magnesium
(Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), selenium (Se),
strontium (Sr), vanadium (V), and zinc (Zn).
Silver (Ag) was not included because it would have required
contracting another laboratory at additional cost and although Ag has been
found at relatively high concentrations in beluga whales in Alaska [14], there
are no studies regarding its toxicity. With no way to evaluate the results, we
did not feel the additional cost was warranted.Liver samples were
first homogenized with a meat grinder. An aliquot of approximately 100 g was
weighed and freeze-dried and then further homogenized using a blender prior to
extraction. Percent moisture was calculated by comparing the weight of the wet
sample with the weight of the dry samples before a 0.5 g sample was extracted and
digested in a microwave wet ash procedure using H2O2 and
HCl. Percent moisture was used to convert dry weight to wet weight and all results
are presented in μg/g wet
weight. Microwave digestion was used for all elements except As and Se.Samples analyzed
for As and Se were digested using magnesium dry ash digestion methods. This
method uses methanol, HNO3, HCl, and heat for digestion. After
digestion, As and Se were analyzed using hydride generation AA.  Pb was
analyzed using graphite
furnace AA.  For total
mercury, a 10 mL aliquot
was removed immediately after dilution, HCl
was added, and concentrations were determined using cold vapor AA.  All other elements were analyzed using ICP on
a Perkin Elmer 4300 DV.Quality assurance included the analysis of
procedural blanks, duplicate samples, and spiked samples run with each group of
10 samples.  Instruments were also calibrated
after every 10 samples. If quality
standards were not met samples were rerun.
Standard reference materials (SRM) provided by the National Institute of
Standards and Technology (NIST 1566b, oyster tissue) and the National Research
Council, Canada (NRCC DOLT-3, dogfish liver) were used. The data were accepted if the SRM reported
value was within 2 standard deviations of the certified mean of the SRM.  LET Laboratories participates in annual interlaboratory trials to
maintain quality assurance and comparability with other participating laboratories.


## 2.2. Aging

Lower jaws were submerged in hot water for 30 minutes and a
canine tooth was extracted and placed in a paper envelope. Teeth were sent
to Matson’s Laboratory in Milltown, MT, USA for slide preparation. Teeth were sectioned (14μm),
placed on glass slides, and stained with Giemsa histological stain. Age was
determined by counting growth layer groups that are generally accepted to represent
one per year [15], although validation studies are lacking.  Bearded seal teeth show excessive wear at
early ages and lower canines have been reported to be missing frequently [16], which
can make accurate aging problematic [17]. Lower canines were present in our
specimens and Matson’s Laboratory provided ages accompanied by a certainty code
that described the potential error associated with the ages. The error
associated with aging ranged from 0 to 4 years, with a mean of 2 years.


## 2.3. Statistical Analyses

To compare RDM to sites without possible mine
contamination, we pooled samples from Little Diomede and Hooper Bay
and treated them as a reference group. For concentrations below the detection
limit, we followed the standard practice of assigning one half the detection
limit for calculating statistics such as means (e.g., [6]); however, no
statistical analyses were conducted when >50% of samples had concentrations
below the detection limit.Our data presented
two obstacles for analysis. First, our sample sizes were small, making the
assumptions required by parametric tests difficult to assess. Second, because
concentrations of some elements are known to covary with age [17–19]
and/or gender [19], we were concerned that sites may have sample compositions
with different age or sex ratios, thereby confounding differences in element
concentrations. For example, if the RDM sample was composed of older seals, we
may incorrectly conclude that there was greater contamination there for a
contaminant that bioaccumulates with age. To assess if element concentrations
differed by gender or location, we used nonparametric Mann-Whitney U statistics
(see [20], page 146).  Exact P-values were
calculated using PROC NPAR1WAY in SAS 9.1 [21]. To assess gender effects, we
used 2-sided tests. Because we wanted to know if seals harvested near RDM had
higher element concentrations, we used 1-sided tests when comparing locations.
To control for age effects, we used parametric tests using age as a covariate.
Because tests of normality are known to have low power [20], we primarily
relied on nonparametric procedures and only applied the parametric test to
control for age when the element was identified as covarying with age. For
parametric comparisons, we first log transformed element concentrations and
then fit a linear model with age treated as a
continuous covariate. The model was specified as ln(yi)=β0+β1xi1+β2xi2+ε1, where y is concentration (μg/g) for seal i, x1 is a dummy variable (0,1) that adjusts the mean for site (RDM or reference), x2  is seal age
(years), and ε is
residual error.  This
is analogous to an ANCOVA model, where site is a categorical variable and age
is a continuous covariate. We fit age effects with a simple linear model, as we
did not have enough samples to reliably estimate separate slope parameters for
RDM and reference sites or to identify nonlinear relationships between element
concentrations and age. Although we know that the bioaccumulation of
contaminants is likely nonlinear and probably differs by sampling locations,
modeling age as a linear covariate still eliminated much of the variance among
seals of different ages. We investigated fitting curvilinear models to the data
and found that such models sometimes identified patterns that were clearly
spurious. Choosing to model age effects as linear is a major improvement
over assuming the same age distributions exist between the RDM sample and the
control sample and therefore provides the best balance between over and under
parameterizing the models we used. For elements without a significant age effect (i.e., if the
slope was not significantly different from 0 at P≤.05), we relied upon Mann-Whitney U
statistics.


## 3. Results

We obtained liver samples from 24
bearded seals, nine from RDM, and 15 from reference sites (nine from Little
Diomede and six from Hooper Bay). Five seals from RDM and 12 from reference
sites were aged. Seals ranged from <1
to 23 years old; seals sampled near RDM averaged 11.2 years of age and
seals sampled at reference sites averaged 7.1 years of age. Of 19 elements
analyzed, eight (Al, B, Ba, Be, Cr, Mo, Ni, Pb) were detected in fewer than 50%
of samples, from both RDM and reference sites and eight others (Cu, Fe, Hg, Mg,
Mn, Se, Sr, Zn) were detected in all
samples from all sites (Tables1 and 2). Of the elements detected,
nonparametric Mann-Whitney tests identified no differences in element
concentrations by gender at the P = .05
level.  As, Cu, Hg, and Se were
identified as having significantly higher concentrations near RDM (Table 2).  Both Hg and Se varied significantly with age;
however, once age effects were controlled for, concentrations were not
significantly different between locations. Cu and As did not vary significantly
with age; therefore, it appears that higher concentrations of Cu and As occurred
in liver tissues collected near RDM.Table 1
Trace element concentrations (μg/g wet weight) in bearded seal liver
samples from nine seals harvested near the Red Dog Mine port site (RDM) and 15
seals harvested near reference sites. Concentrations are summarized as arithmetic
and geometric means, arithmetic standard deviations, and ranges. Detection
limits are presented in Table  2. Elements in which concentrations were found to
be significantly different between sites are in bold.
ElementSiteArithmetic
meanGeometric meanArithmetic   SDRange(μg/g wet  weight)(μg/g wet weight)AlRDM1.101.030.460.84–1.91reference0.610.500.450.29–1.72AsRDM0.580.520.280.22–1.15reference0.410.310.320.04–1.13BRDM0.280.280.010.27–0.3reference0.360.340.170.28–0.89BaRDM0.090.080.070.07–0.29reference0.030.030.000.03–0.03BeRDM0.010.010.000.01–0.01reference0.010.010.000.01–0.02CdRDM5.244.252.990.97–10.59reference7.120.9411.160.01–39.93CrRDM0.070.070.000.07–0.07reference0.130.070.190.01–0.77CuRDM40.7138.7213.8019.84–70.74reference24.6521.8212.127.8–42.78FeRDM598.40589.44108.23421.5–781.44reference620.09575.16238.49272.91–1078.68HgRDM3.233.081.051.92–5.22reference3.931.257.280.13–28.31MgRDM185.36184.8015.58168.02–216.75reference183.76182.6220.09127.88–218.73MnRDM5.095.020.843.52–6.29reference4.514.361.252.67–6.78MoRDM0.350.330.130.27–0.58reference0.340.330.100.28–0.61NiRDM0.080.080.020.07–0.14reference0.070.060.020.03–0.08PbRDM0.030.030.000.03–0.03reference0.040.040.020.03–0.09SeRDM4.794.681.103.4–6.5reference4.353.194.581.29–18.48SrRDM0.210.180.140.12–0.57reference0.280.210.340.09–1.47VRDM0.700.410.880.07–2.9reference0.290.180.300.07–1.01ZnRDM62.4562.265.0954.91–68.85reference62.8559.1923.0730.83–115.19Table 2
Statistical comparisons of trace element
concentrations in bearded seal liver tissue between Red Dog Mine port site (RDM)
and reference sites. No statistical tests were conducted when trace elements
were detected in less than 50% of samples. ANCOVA was used to control for
possible age effects when the nonparametric Mann-Whitney test identified
differences in trace metals concentrations between RDM and reference samples. Trace
elements detected in more than 50% of samples that Mann-Whitney tests
identified as statistically different between RDM and reference sites are in
bold.
Minimum detection limitProportion of samples above detection limitElement(μg/g wet weight)RDM (n  =  9)Reference sites (n = 15)Above threshold for statistical analyses?Mann-WhitneyPSignificant age effect?ANCOVAPAl1.780.220.33NoAs0.191.000.96Yes.03No—B0.620.000.08NoBa0.150.110.04NoBe0.030.000.00NoCd0.031.000.88Yes.24Yes.53Cr0.160.000.13NoCu0.091.001.00Yes<.01No—Fe0.891.001.00Yes.5No—Hg0.31.001.00Yes.04Yes.54Mg1.391.001.00Yes.43No—Mn0.161.001.00Yes.1Yes.28Mo0.620.220.17NoNi0.160.110.04NoPb0.090.000.04NoSe1.191.001.00Yes.01Yes.59Sr0.061.001.00Yes.46NoV0.160.890.63Yes.06Yes.06Zn0.161.001.00Yes.28No


## 4. Discussion

Mining-related contamination has been found in marine
mammal tissues. Lead and zinc mines in Arctic regions have contaminated local
marine environments in both West Greenland [22, 23] and Baffin Island, Canada [24].
In both cases, elevated levels of elements were found in marine sediments and
invertebrates near port sites or near tailings dumps, relative to pre-mining
conditions and/or reference sites. On Baffin Island, Wagemann [18] followed up the
work of Fallis [24] and found elevated levels of lead in liver and muscle
tissue and elevated selenium in muscle tissue in ringed seals (Phoca hispida)
collected near the Nanisivik Mine port site compared with a reference site.  Prior to Wagemann’s [18] study, Fallis [24] reported
that the mine concentrates were likely entering the marine environment via
runoff, wind, and spills when loading the concentrate onto ships at the port
site. These pathways are similar to that described for the entry of mine
concentrate into the marine environment near RDM [7]. Lead and zinc
concentrates from RDM are known to have concentrations of Al, Ba, Cd, Cu, Pb,
and Zn in excess of 1000 ppm [7, Table 2-1]. Although mines occur in areas
that have naturally high concentrations of elements, studies have concluded
that excavating and transporting the ore have elevated element concentrations near RDM
facilities relative to local reference samples (e.g., [2, 3]).  Hence, local
concerns regarding food safety are justified.Although such
concerns are justified, it is unclear whether
high contaminant concentrations would be transferred to bearded seals even if
they were present because they may not spend much time feeding there. For
example, ringed seals that were believed to feed near the Nanisivik Mine on
Baffin Island, Canada were found to have elevated levels of Mg, Pb, and Cd [18].
On the contrary, short-finned pilot whales (Globicephala macrohynchus) and pygmy sperm whales (Kogia breviceps) that stranded on the
coast of New Caledonia, where local sediments and food webs were known to be contaminated
with high levels of Co, Cr, Fe, and Ni, did not show elevated concentrations of
mine-related elements, probably because the whales were not regularly feeding
in inshore waters [25].We do not know how much time bearded seals
spend feeding near RDM, but available information indicates that bearded
seals may be highly mobile. During the fall seasons of 2004–2006, 26 bearded
seal pups were captured and fitted with satellite transmitters near Kotzebue [26].
After tagging, the pups left Kotzebue Sound by the end of October or early
November, with several moving
300–400 km in the
first few weeks. None lingered near Kivalina or RDM, although several transited
through this area. Extrapolations and assumptions based on Kotzebue tag data,
however, should be made with caution because it is unknown how pup movement
patterns compare to adult movement patterns. Also, these pups were tagged at
the end of the open-water season as they were beginning to leave the area and
we do not know how movement patterns may change by season. Regardless, a better
understanding of the movement patterns of seals near RDM would help us
understand the potential for exposure to mine-related elements and would also
help us interpret observed element concentrations.We found little evidence that the concentrations of
trace elements were elevated in the liver tissue of bearded seals sampled near RDM
compared to our reference sites. Concentrations of Cd, Pb, and Zn in liver
tissue from RDM were not statistically greater than what was observed at reference
sites (Table2). In fact, Pb was below detection limits in all of the RDM samples.  After accounting
for how elements accumulate with age, only As and Cu were more concentrated in
seal liver near RDM than in the other locations we sampled (Tables 1 and 2).Arsenic is found widely in marine and freshwater
environments and has both natural (volcanic) and anthropogenic (industrial and
agricultural) sources [27]. Higher concentrations of As near RDM are probably
not related to mining activities. Although studies have found high levels of As
in stream sediments [28] and caribou tissues [8, 29], the concentration of As
in ore from RDM has been shown to be no higher than that observed within local
soil samples [7].  Hence, higher
concentrations of As may occur naturally within the RDM region.Concentration of As does not increase with trophic level
and lower level consumers have the highest concentrations, suggesting that As
does not biomagnify [30]. In general, species feeding on cephalopods and
crustaceans tend to have higher concentrations [30]. As such, we might expect
bearded seals to have higher concentrations. In agreement with Kubota et al. [30],
we found that As concentrations were not influenced by age or gender. Although
many forms of As occur, including the highly toxic inorganic form, the
predominant form found in marine mammals is the relatively nontoxic organic
form called arsenobetaine [31–33].
Kunito et al. [33] found that arsenobetaine composed between 68 and 98% of extractable
arsenic in four species of marine mammals, including bearded seals (68%). As
such, the health risks of As may be low even with high concentrations of total
As in tissue [33]. Little is known about concentrations that are problematic
for seals or their predators; however, a review of contaminants in marine
mammals that included the levels reported here did not recognize any studies
that reported toxic levels of As [34]. Domestic livestock show toxicity at levels
of 14-15 μg/g wet weight [35]. Levels of As below
0.8 μg/g wet weight are considered to be very
low by Alaska Department
of Health and Social Services, Alaska, USA  [36].Most trace elements are found in the highest concentrations
in organ tissues; however, organic As has been found at higher levels in seal
blubber [32]. Mean blubber concentrations (range 0.60–1.76 μg/g wet
weight) were 2.4 times higher than liver concentrations (range 0.19–0.74 μg/g wet
weight) in 18-ringed seals from Canada [32].
Hence, levels of As in bearded seal blubber might be much higher than
what we observed in liver tissue. There are no comparable studies for bearded
seal blubber; however, Becker et al. [13] examined the concentration of As in
liver tissues from bearded seals from Norton Sound.
Concentrations of As we observed from RDM (arithmetic mean = 0.58 μg/g) are similar
to what Becker et al. [13] observed (range = 0.161–0.577; n = 3). The
amount of organic versus inorganic As is unknown for both our study and Becker
et al. [13].We also found elevated concentrations of Cu in seal liver
near RDM compared to reference sites (Tables1 and 2). Cu is known to be more
concentrated in soil and marine sediments near the RDM port site [7] and the
concentration of Cu from RDM (arithmetic mean = 40.71 μg/g wet weight)
was higher than that for liver tissue from Barrow (arithmetic mean = 22.69 μg/g wet weight,
Table 3). We do not think that
this is a cause for concern, as Cu is an essential element required for
the formation of red blood cells, cell metabolism, neurological function, and
the detoxification of free radicals [37]. Cu
poisoning in humans generally occurs at concentrations from 1–40 mg/g, which is
approximately 100 times greater than what we observed in this study (see review in
[38]).Table 3
Comparisons of element concentrations in
liver of bearded seals between this and other studies. Concentration units areμg/g wet weight and are summarized as the
arithmetic mean and standard deviation for comparison with other studies. Mackey
et al. [14] and Becker et al. [13] used the same samples from the Alaska Marine
Mammal Tissue Archival Project. We present the results of Mackey et al. [14]
except when Becker et al. [13] provide data on different elements.
ElementLocationYearLiver mean (SD)nMean age (yrs)Referenceμg/g wet weightAsNome, Alaska1989–19930.161–0.577(1)3—[13]This study: reference sites2003–20050.41 (0.32)157.1This study: RDM20050.58 (0.29)911.2CdNome, Alaska1989–19930.99–2.00(1)3—[14]Pt. Barrow, Alaska1998–20018.66 (7.03)38—[19]This study: reference sites2003–20057.12 (11.16)157.1This study: RDM20055.24 (3.00)911.2CuNome, Alaska1989–19936.82–34.44(1)3—[13]Pt. Barrow, Alaska1998–200122.69 (7.99)38—[19]This study: reference sites2003–200524.65 (12.12)157.1This study: RDM200540.71 (13.80)911.2HgHolman, western Canada1973143.00 (170.00)68.5[39, 40]Belcher island, eastern Canada197426.18 (26.13)564.9[40]Alaska—1.91 (1.20)4—[41]Nome, Alaska1989–19931.4–9.4(1)3—[14]Pt. Barrow, Alaska1998–20013.84 (3.55)34—[19]This study: reference sites2003–20053.93 (7.28)157.1This study: RDM20053.23 (1.05)911.2PbNome, Alaska1989–19930.031—[13]This study: reference sites2003–20050.04 (0.02)157.1This study: RDM20050.03 (—)(2)911.2SeHolman, western Canada197334.42 (33.23)68.5[39, 40]Belcher Island,
eastern Canada197420.83 (13.47)104.9[40]Nome, Alaska1989–19930.43–5.3(1)3—[14]Pt. Barrow, Alaska1998–20015.27 (3.51)38—[19]This study: reference sites2003–20054.35 (4.58)157.1This study: RDM20054.79 (1.10)911.2VNorton Sound, Alaska1989–19930.15–1.04(1)3—[14]This study: reference sites2003–20050.29 (0.30)157.1This study: RDM20050.71 (0.88)911.2ZnNome, Alaska1989–199332.60–103.70(1)3—[13]Pt. Barrow, Alaska1998–200157.48 (10.37)38—[19]This study: reference sites2003–200562.85 (23.07)157.1This study: RDM200562.45 (5.09)911.2(1)Range provided instead
of a mean and standard deviation.(2)All samples below the
detection limit.Of the elements that did not differ in concentration
between RDM and reference sites (Cd, Hg, Se, Zn, and V), Hg and Se
concentrations are comparable to concentrations found in similar tissues from
other locations in Alaska and are lower than concentrations found in Arctic
Canada (Table3). Concentrations of Zn, Cd, and V could not be compared to
those in Canada, as no data are available for comparison; however,
concentrations at both RDM and reference sites are similar to those observed in
other locations in Alaska (Table 3).The overall variability in concentrations of trace elements
was generally higher in the reference sample than the RDM sample. Of the
elements suitable for statistical tests (i.e., the element was detected in >50% of the samples), the standard deviation of element concentration was higher
in the reference sample than the RDM sample in 9 of 10 cases (Table1). The
difference in variability was due to fewer low concentrations in the RDM sample
(compare ranges in Table 1). In all cases, the minimum concentration observed
within the reference sites was lower than that observed within the RDM sample. The
larger range of variability within reference samples might be due to a larger
proportion of younger seals compared to the RDM sample; the average age within
the reference sample was 7.1 years, compared to 11.1 within the RDM sample.
This underscores the need to statistically control for age effects where
possible.Most studies
indicate that the concentration of some elements change with animal age (e.g.,
see reviews in [18, 42]). However, we found no studies on bearded seals that
controlled for age effects when making statistical comparisons between sampling
locations. Had we simply interpreted mean concentrations without controlling
for unequal age distributions, we would have erroneously concluded that higher
concentrations of both Hg and Se occur in bearded seals near RDM. For many
studies, animals must be harvested to sample tissues and harvest-based sampling designs are likely not random. Statistical
methods that adjust for differences in age or gender are especially important
in such instances.In conclusion, we
examined the concentrations of 19 trace elements in the liver tissues of
bearded seals harvested near RDM and reference sites. Only As and Cu were found
to be elevated near RDM. However, neither of these elements is known to be
toxic in the chemical form or at the concentrations found. In addition, the
concentrations of As and Cu found near RDM although significantly higher than
our reference samples, they were not higher than concentrations found elsewhere
in Alaska or Canada. Because we found that concentrations of trace elements in
bearded seal liver near RDM were not higher than elsewhere, we conclude that
muscle tissue, which is more commonly eaten but has much lower concentrations,
would also not be higher. Therefore, we found no evidence that bearded seals
harvested by hunters near RDM were less safe to eat or that trace element
concentrations were greater than those found in bearded seals harvested
elsewhere in Alaska or Canada.



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