FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

138 F. Roos-Barraclough et al. / The Science of the Total Environment 292 (2002) 129–139
species or between mosses growing within different
microclimates on the surface of a bog could
be inconsistent (Norton et al., 1997).Mercury
concentrations within one small horizontal section
of peat may be uneven.Several subsamples should
be taken from each peat slice in order to obtain a
representative Hg concentration for the whole
slice.Because large fluctuations in bulk density
values can occur throughout a peat core, bulk
density should be determined in each slice to allow
Hg flux rates to be calculated accurately.
Finally, mixing together the moss component of
the subsamples increases the homogeneity of the
material to be analysed.Here, grinding in a coffee
mill resulted in a slight loss of Hg.However,
simple hand mixing of the dried samples held in
a plastic bag resulted in low standard deviation of
duplicate pairs.
5. Conclusions
The following protocol is proposed for the
determination of mercury concentrations in solid
peat samples:
Cores should be transported frozen from the
field to the laboratory, if possible, to avoid unnecessary
compaction and losses of water or Hg.The
peat should be kept in clean (wrapped airtight in
plastic), cool conditions until analysis.The edge
of the core should be removed prior to analysis in
case of contamination (by smearing) during core
collection.Several subsamples should be analysed
from each peat slice in order to obtain a representative
value.These subsamples can be air-dried at
room temperature in a clean environment, such as
a Class 100 laminar flow cabinet, without significant
loss of mercury.During this period, the
cabinet should be darkened to avoid light-enhanced
evasion of mercury from the samples (Gustin and
Maxey, 1998).Dried subsamples can be homogenised
by crushing air-dried plugs of peat together
into a powder and mixing; this can be done by
hand, with the samples in a sealed plastic bag.
One or more subsamples from each slice should
be used for bulk density determination, which is
required to allow mercury deposition fluxes to be
calculated.Bulk density can be determined from
the dry weight of a peat subsample of known
volume.Air drying this subsample with the subsamples
to be used for mercury analysis (of the
same shape and volume) before drying it in a
drying oven to constant weight allows the water
content of the air-dry samples to be accurately
estimated; this information can be used to correct
the masses of the samples analysed for Hg to their
true dry weights.
Suggested times for a Leco AMA 254 air-dry
peat analysis program are: 30 s (drying), 125 s
(decomposition) and 45 s (waiting for emission
of waste gases before Hg content determination by
AAS).
Acknowledgments
Financial support for this work, including graduate
student assistantships to F.R. and N.G., was
provided by the Swiss National Science Foundation
(grants 21-55669.98 and 21-061688.00) to
W.S. Peat core collection in the High Arctic of
Canada was made possible by a research grant to
W.S., Heinfried Scholer ¨ (University of Heidelberg)
and Stephen Norton (University of Maine) by the
International Arctic Research Centre, Fairbanks,
Alaska.Many thanks to Drs W.O.Van der Knaap,
E.Feldmeyer, A.Gruenig and A.Holzer for plant
identification and B.Eilrich for considerable field
assistance.
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