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Chemosphere 65 (2006) 1909–1914
www.elsevier.com/locate/chemosphere
Review
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An exploratory study of total mercury levels in archaeological
caribou hair from northwest alaska
Department of Anthropology, 310 Eielson, P.O. Box 757720, University of Alaska Fairbanks, Fairbanks, AK 99775-7720, United States
b
Department of Chemistry and Biochemistry, 362 Natural Science Facility, P.O. 756170, University of Alaska Fairbanks, Fairbanks,
AK 99775-6170, United States
c
Northern Land Use Research Inc., 600 University Avenue, Suite 6, Fairbanks, AK 99708, United States
d
State of Alaska Public Health Lab, 4500 Boniface Parkway, Anchorage, AK 99507, United States
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S. Craig Gerlach a, Lawrence K. Duffy b,*, Maribeth S. Murray a, Peter M. Bowers c,
Rachel Adams b, David A. Verbrugge d
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Received 23 March 2006; received in revised form 17 May 2006; accepted 31 May 2006
Available online 31 July 2006
Abstract
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Over the past ten years, total mercury (THg) levels have been surveyed in Alaskan wildlife and fish as part of the Arctic Monitoring
and Assessment (AMAP). Beyond these studies there is little historical data on THg levels in important subsistence species for people in
Alaska. A survey of THg in caribou hair from archaeological deposits would provide data to develop temporal trends for this region of
the Arctic. Caribou hair from a Western Thule settlement beneath the Alaska native village of Deering (ca. AD 1150) show variability in
hair THg values, with a mean level (86 ng/g) which is in the range that is observed in modern Rangifer sp. (caribou and reindeer). Hair
from House 1 had a THg mean level of 99.6 ng/g and hair from House 2 had a THg mean of 64.2 ng/g. This is the earliest reported record
of mercury in caribou associated with human subsistence activities in the western North American Arctic, and is a first step toward compilation of a needed database through which to measure and evaluate exposure to mercury by people who rely heavily on caribou as a
food source. We hypothesize that similarity in mercury values in archaeological samples of caribou and in contemporary samples would
give an additional perspective on human exposure to mercury through caribou harvest and consumption today. Since this hypothesis will
be more useful if evaluated at a regional rather than global scale, further studies will be needed at different archaeological sites across
Alaska to determine the generality of this observation in relation to geographic scale.
2006 Elsevier Ltd. All rights reserved.
Contents
3.
*
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1. Sample descriptions and context. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2. Sample preparation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3. Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Keywords: Alaska; Caribou; Rangifer; Hair; Mercury; Deering; Archaeofauna; Beringia
Corresponding author. Tel.: 907 474 6751; fax: 907 474 7453.
E-mail address: ff[email protected] (L.K. Duffy).
0045-6535/$ - see front matter 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2006.05.060
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S. Craig Gerlach et al. / Chemosphere 65 (2006) 1909–1914
Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1912
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1913
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1913
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Among a host of potential individual and systemic variables, both ecosystem and community health are linked to
small and large-scale industrial developments, commercial
enterprises, and anthropogenic pollutant outputs (AMAP,
2003; Van Oostdam et al., 2005). The bioaccumulation of
metals as contaminants, especially mercury (Hg), continues
to be a global concern, but one with regional ramifications.
Hg exposure risk over time and space is a significant environmental health issue in Alaska today (Rothschild and
Duffy, 2002; Jewett et al., 2003; Dehn et al., 2006). Mercury
poisoning may cause paresthesia and tunnel vision, and
have other adverse effects on health as well as a negative
influence on fetal growth, development and survival
(Grandjean et al., 1997; Grandjean et al., 2004).
Data on total Hg (THg) in ancient biological samples is
useful for identifying temporal patterns in concentrations
and variations in THg input sources, and for modeling
the possible effects of anthropogenic sources (Outridge
et al., 2005; Braune et al., 2005). Past studies of Hg accumulation in arctic food chains and temporal trends in
heavy metal accumulation are focused mostly on aquatic
and marine biota (Outridge et al., 2000; Beckmen et al.,
2002; Outridge et al., 2002; Braune et al., 2005; Campbell
et al., 2005), while information on contaminants levels in
terrestrial wildlife species in circumpolar regions is less
abundant (Elkin and Bethke, 1995; Aastrup et al., 2000;
Larter and Nagy, 2000; Duffy et al., 2001; Robillard
et al., 2002; Duffy et al., 2005). Some data on temporal
trends of Hg in wildlife of the north exist (Outridge
et al., 2002; Gamberg et al., 2005) but more studies are
needed to understand long term patterns of accumulation.
The transport of Hg from plant and seed biomass to larger terrestrial herbivores is low when compared with conversions in marine systems (Froslie et al., 1984; Gamberg
et al., 2005), although high consumption rates of grasses
and lichens among arctic herbivores may intensify Hg
uptake (Larter and Nagy, 2000). Among the many mammal and bird species of potential concern for human health
issues, Rangifer sp. (caribou and reindeer) are particularly
important because they served and continue to serve as a
food staple in circumpolar regions. Caribou and reindeer
are associated with the taiga and tundra biomes where they
are known to favor low-growing species such as sedges and
cotton grasses which are a major component in the summer
diet, and lichens which are more important in the winter
diet of caribou (Aastrup et al., 2000; Robillard et al., 2001).
Hg reaches caribou and reindeer via the food chain
(Gamberg and Braune, 1999). Their food sources, especially lichens, are hypothesized to have become increasingly
contaminated as new Hg is input to the Arctic from global
industrialization. Hg that is absorbed by plants and
ingested by caribou accumulates in tissue and organs
(Gamberg et al., 2005), resulting in biomagnification, a trophic process in which retained substances become more
concentrated with each increase in food chain trophic levels
(AMAP, 2003). It is not known if Hg levels in Alaskan caribou are increasing compared to levels in the past as there
are few temporal studies of Hg levels in Alaska. For Canada, Outridge et al., 2002; Outridge et al., 2005 reported
that in both Odobenus rosmarus (walrus) and Delphinapterus leucas (beluga whales), concentrations of mercury and
some other metals in teeth are now similar to or higher
than concentrations in historical specimens, suggesting that
the current levels in marine mammals in some arctic
regions result from increased output from industrial
sources.
In terrestrial settings, the concentration of mercury in
caribou hair offers a means of measuring variation in Hg
bioaccumulation (Duffy et al., 2001; Duffy et al., 2005),
and in selected samples the MeHg levels in reindeer hair
is approximately 79% of THg (range 58%–97%), (Duffy
et al., 2005). In the present study, we report the levels of
THg in almost a thousand year old caribou hair samples
from northwestern Alaska.
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1. Introduction
2. Materials and methods
2.1. Sample descriptions and context
The 37 samples of prehistoric caribou hair used in this
study were recovered from two discrete archaeological
house deposits located in Deering, Alaska (Fig. 1). Deering
is located on the northern Seward Peninsula, within an area
of discontinuous permafrost, with mean annual temperatures between 4C and 8 C, and mean annual precipitation of 130–150 mm. Vegetation is described as shrub
tundra, with the spruce tree line about 75 km to the east
(Hulten, 1968; Matthews, 1974). The modern village of
Deering is built upon a gravel and sand spit that has been
aggrading for over two thousand years. The 2 km long spit
has a maximum height of 4.3 m ASL and has formed via a
combination of eastward longshore sediment flow derived
from bluff erosion, replenished periodically by storm
surges. It forms a barrier that tends to impound sediments
from the northward flowing Inmachuk River and it’s tributary, Smith Creek. Surficial sediments comprise a series of
gravel and sand beds, capped in places by sand dunes
(Bowers et al., 1999; Bowers, 2006).
Bedrock in the region consists of Paleozoic metalimestone and schistose pelitic rocks. Thick deposits of Quater-
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S. Craig Gerlach et al. / Chemosphere 65 (2006) 1909–1914
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Fig. 1. Locations noted in the text.
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nary age alluvium fill the Inmachuk River valley, while at
Cape Deceit, located about 4 km to the west, primary or
reworked loess is present, in places capped by thick sedge
or moss turf (Matthews, 1974). The area was not glaciated
during the Wisconsin glaciation, although outwash and
loess may have provided a source for some of the sediments
which were later reworked to form the Deering spit (Mason
et al., 1997).
Located near the headwaters of the Inmachuk river,
about 32 km from the study area, are gold placer deposits
within the Fairhaven Mining District. Gold was discovered
there in 1900, with sporadic mining activity lasting until
1963. Bedrock in the headwaters area consists of Paleozoic
schist and crystalline limestone, with Holocene gravel and
basaltic lava flows located to the south in the Imuruk Lake
area. Significant amounts of zinc, molybdenum, chromium,
gold and silver have been reported 40 km south of the
study area in the Inmachuk River mining area; however,
no detectable levels of mercury are reported in these geochemical soil and stream sediment samples.
Age estimates of the Deering archaeological deposits
(House 1 and House 2) from which the caribou fur samples
were collected are provided by radiometric dating of adjacent wood and charcoal samples. In House 1, hair from fur
samples was collected from the surface of the floorboards,
and from midden fill immediately above the floorboards.
In House 2, hair samples were also collected from the floorboards and associated midden fill directly above these. No
individual age or gender information was available for the
archaeofauna assemblage associated with the houses.
2.2. Sample preparation methods
All hair samples were washed, dried, and homogenized
at the University of Alaska Fairbanks (UAF). First, they
were swirled vigorously in 1% solution of an all-purpose
cleaner (409 detergent). The samples were disrupted with
Dounze homogenizer, thrust five times in the 1% 409 detergent solution, and then rinsed three times in RO water. The
samples were dried in an oven overnight and cut with clean
scissors into segments of 1 cm or less. The 37 samples were
weighed, packaged, and sent to the State Public Health Lab
in Anchorage, Alaska to be analyzed for mercury content.
The State Public Health Lab used the following standard methodology for analyzing hair for mercury content.
Total mercury was determined using the Direct Mercury
Analyzer, DMA-80 (Milestone Inc.). The DMA-80 analyzer combines thermal decomposition sample preparation
and atomic absorption detection. The sample is dried (10 s
at 300 C) and then thermally decomposed (180 s at
850 C) within the first furnace stage. Decomposition products are carried by flowing oxygen into the catalytic furnace
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S. Craig Gerlach et al. / Chemosphere 65 (2006) 1909–1914
stage, trapping halogens and nitrogen/sulpher oxides.
Remaining decomposition products are carried to the gold
amalgamator stage, which selectively traps mercury. The
instrument is purged (60 s) with oxygen to remove any
remaining decomposition products. After the drying/
decomposition cycle is complete (250 s total), Hg is
released by rapidly heating the amalgamator (900 C for
12 s). Flowing oxygen carries the mercury vapor through
two absorbance cells positioned in the light path of a single
wavelength atomic absorption spectrophotometer. Absorbance peak height is recorded at 253.7 nm. Total analysis
cycle time is 360 s. A seven (7) point calibration curve
covering the range of concentrations was prepared; the
DMA-80 automatically calculates a second order calibration curve. Instrument calibration is confirmed daily by
acceptable analysis of TORT-2 (10 mg), Hair-086 (15 mg)
and Soil-2709 (20 mg). Based on ongoing blank analysis
(n = 30), the absolute instrument detection limit (IDL) is
0.06 ng of THg (Mean + 3 · SD). The method detection
limit (MDL) is 5 ng/g and the method quantitation limit
(MQL) is 15 ng/g.
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Age estimates of the Deering archaeological deposits
from which the caribou hair samples were collected are provided by radiometric dating and dendrochronology of adjacent wood and charcoal samples. House 1 (KTZ-300)
samples are dated by two C-14 dates; the most reliable is
from charcoal found beneath the main room floorboards:
870 ± 40 C-14 yrs BP (Beta-138568). Charcoal from the
base of the entrance tunnel dates to 920 ± 40 C-14 yrs BP
(Beta-138565). One tree ring date of AD 1203 was obtained
from structural wood from House 1 timbers. House 2
(KTZ-301) is dated by one sample of wood from a subfloor
cache wall to 790 ± 40 C-14 yrs BP (Beta-189091). House 1
thus appears to predate House 2 by about one century. The
combined one sigma calibrated C-14 range for the two
houses is AD 1035-1270 (Bowers, 2006).
NLUR-4204
NLUR-4203
NLUR-4194.1
NLUR-4194.2
NLUR-4194.3
NLUR-4218
NLUR-4219
NLUR-4198
NLUR-4209
NLUR-4221
NLUR-4211
NLUR-4193
NLUR-4217
NLUR-4220
NLUR-4207
NLUR-4208
NLUR-4199
NLUR-4216
NLUR-4215
NLUR-4202
NLUR-4200
NLUR-4201
97.0
64.0
210.6
143.6
277.0
52.8
136.6
109.3
79.1
69.2
37.4
121.8
83.8
43.2
33.7
106.9
65.4
32.9
21.5
112.4
206.8
86.3
N = 22
Mean THg = 99.6
UIC-336
UIC-QOPXJ
UIC-2545
UIC-1096
UIC-673
UIC-OUR8
UIC-58
UIC-970
UIC-607
UIC-608
UIC-1116
UIC-NCFTF
UIC-570
UIC-1231
UIC-327
38.7
92.2
18.2
173.0
40.6
170.6
30.3
32.9
62.3
61.1
61.0
80.0
33.0
41.1
28.3
N = 15
Mean THg = 64.2
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House 2
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3. Results
Total Hg (ng/g)
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Summary House 1
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DMA-80 analyzer calibration was prepared and verified
using Certified Reference Materials (CRM): (1) TORT-2,
Lobster Hepatopancreas for trace metals, from the
National Research Council Canada Standard Reference
Material, which has a certified Hg concentration of
270 ± 60 ng/g; (2) Soil-2709, Standard Reference Material
2709, San Joaquin soil, from the National Institute of Standards and Technology, which has a certified Hg concentration of 1400 ± 80 ng/g; and (3) Hair-086, Reference
Material IAEA-086, methylmercury, total mercury and
other trace elements in human hair, from the International
Atomic Energy Agency, which has a certified Hg concentration of 573 ± 39 ng/g. CRM moisture content was determined to be 14%, yielding wet weight Hg concentration of
493 ± 34 ng/g.
Sample No.
House 1
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2.3. Quality control
Table 1
Individual Hg levels (ng/g) of archaeological caribou fur from Deering,
Alaska
Summary House 2
Mercury was detected in all archaeological samples analyzed, with the data on total Hg for the archaeological caribou hair samples summarized in Table 1. Archaeologically
recovered hair show a wide range for THg, displaying THg
values from 18.2 ng/g to 277 ng/g. The 22 samples from
House 1, circa AD 1035–1220, have a mean THg of
99.6 ng/g with a range of 21.55–277 ng/g. Samples from
House 2, circa AD 1220–1270, have a mean THg of 64.2
with a range of 18.2–170.6 ng/g for 15 samples. The overall
mean of all samples is 86 ng/g.
4. Discussion
In Alaska, mean values of mercury in various lichens,
mosses, and blueberries range from 2 to 50 ng/g (Ford
S. Craig Gerlach et al. / Chemosphere 65 (2006) 1909–1914
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hair from fur, has given us a starting point during the
Medieval Warm Period (MWP) (between 800 and 1300
AD) from which to work toward assembling a database
that trends into the present. The history of the Arctic,
where there are few prey species-caribou, seals, whales
and fish – reflects human resilence in the face of past climate and other changes. As the arctic people and ecosystems confront the possibility of accelerated warming,
surpassing that of the MWP, we need to consider how such
conditions may be reflected in regional variation in contaminant input and we might predict fewer impacts in the
Alaskan Arctic as compared to the eastern Canadian Arctic with its input of contaminants from the industrial east
coast.
A common working assumption is that arctic biota are
accumulating the highest levels of toxic metals in history,
and that most exposure is related to industrial development
and global transport from lower latitudes. This assumption
is based on data from contemporary marine mammal and
fish studies in the North Atlantic/Eastern Canadian Arctic
regions, with only limited observational and retrospective
data related to mercury accumulation in the western Arctic
and Bering Sea coastal regions. Our data on Rangifer tarandus (caribou) hair from two northwestern Alaskan
coastal archaeological deposits suggest that the historical
picture may be more complex, at least with respect to terrestrial ecosystems. This biocomplexity warrants further
retrospective studies looking at contaminants in other
Alaskan historical ecosystems.
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et al., 1995), although higher values are reported elsewhere
(Nimis et al., 2002; Bennett and Benson, 2005). For caribou, the amount of lichen in the annual diet may explain
the variation in mercury values for these samples. Lichens
are long-lived and readily accumulate atmospheric contaminants in a non-selective manner (Hanson, 1967; Holleman
et al., 1971; Crete et al., 1992; Thomas et al., 1992; Elkin
and Bethke, 1995). Caribou that feed substantially on
lichens, or in areas that are possibly rich in natural mercury, would accumulate higher levels of mercury. In the
Deering region possible sources of mercury in the prehistoric context include that found in soils, streams, tephras,
and lava flows. Wilcox (1959) reported only a trace of
Hg detectable in samples of various Alaskan soils affected
by recent volcanic ashfalls, and no discernible Hg has thus
far been identified in the local soil and stream geochemistry. It is also unlikely that mineral licks are a source of
Hg, since Hg has not been reported for salt licks in Alaska
or the US (Jones and Hanson, 1985). There are no known
tephras in the Deering archaeological sediments, so tephra
does not appear to be a source of Hg in these samples.
There is the possibility that the lava flows associated with
Imuruk Lake, 40 km south of Deering, are Hg rich, but
as with many areas in the Arctic the geology and archaeology are incompletely explored. Lastly, the THg levels in the
hair samples are unlikely to be caused by diagenesis
because they are similar in range to modern caribou hair
THg levels (Duffy et al., 2001).
All our archaeological samples display Hg levels that are
well below different thresholds for biological effects (Gamberg et al., 2005), and show no community health issue with
Hg from caribou for the ancient inhabitants of the archaeological community of Deering, northwest Alaska. Hg may
be monitored through a combination of modern Rangifer
sp. ‘‘control’’ cases, archaeological samples, and ethnobotanical data. This exploratory research suggests that
hypotheses about bioaccumulation must be evaluated on
a regional rather a circumpolar or global scale. Our data
also highlight the value of archaeological samples for establishing baseline information on non-anthropogenic Hg
accumulation, and as we expand our database, we expect
that uncertainty about Hg bioaccumulation will decrease.
Table 1 suggests that current exposure levels of Hg on the
Seward Peninsula (Duffy et al., 2005) may be similar to
those of nearly a thousand years ago. While we do not have
THg data from modern caribou immediately near Deering,
reindeer from elsewhere on the Seward Peninsula where
Deering is located have similar THg levels (Duffy et al.,
2005). A limitation of these ancient hair samples is the lack
of age and gender information for individuals which sometimes can influence Hg bioaccumulation. The mean value
should be interpreted with this uncertainty in mind.
Importantly however, we need to consider how current
conditions might change under scenarios of climate warming and increased development which could accelerate Hg
inputs and, in turn, Hg bioaccumulation at the regional
level. Our data for archaeofauna, as exemplified by ancient
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Acknowledgements
Research was supported as part of the Sustainability
and Stewardship Alaska (NSF GEO-0331261) project
and Subsistence, Mercury, Ecosystem Change Project
(NSF OCE 0525275) with a grant from the National Science Foundation. We appreciate the help of the people of
Deering, staff from the Departments of Anthropology
and Chemistry and Biochemistry at the University of Alaska Fairbanks and personnel from Northern Land Use research, Inc. Lawrence K. Duffy was supported by NIH
grant U54 NS41069. Rachel Adams was supported by
ASHSSS. Archaeological excavations in Deering were
funded by a contract between Deering and Northern Land
Use Research, Inc. with funding provided under the
requirements of the National Historic Preservation Act
by the ADEC Village Safe Water Program.
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