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

designed to recover predominantly atmospheric lead adhering to the plant material, and from the
corresponding residues which primarily represents geogenic lead hosted in the inorganic,
minerotrophic matrix, as well as atmospherically-derived soil dust (Table 3). Leaching of the
peat material was performed with 2N HCl for two hours. The samples were then centrifuged and
the supernatant was carefully pipetted off. The residues were attacked by 8N HBr for 1 day, then
dried and subsequently re-attacked using an HF-HNO 3 mixture for 2 days in Savillex Teflon
beakers. This procedure has been shown to be effective in dissolving both phosphates and
silicates (Frei et al., 1997; Schaller et al., 1998). Lead was processed and separated over 0.5 ml
glass columns charged with a 100 mesh AG-1 x8 anion exchange resin (BIORAD) and purified
in a second clean-up over 200 µl Teflon columns containing the same resin. Liquid aliquots
of both leachates and residues were doped with a 204 Pb spike for isotope dilution concentration
measurements. Lead separates were loaded with a 1M H 3 PO 4 - silica-gel mix and measured
from 20 µm Re-filaments on a VG-54 Sector-IT thermal ionization mass spectrometer at the
Geological Institute, University of Copenhagen. Lead isotopes were analyzed in static multi-
collection mode. Procedural blanks remained below 110 pg Pb: this is insignificant relative to
the amount of Pb contained in the samples. Isotopic fractionation of Pb was monitored by
repeated analyses of the NBS-SRM 981 Pb standard, and the measured data were corrected for
mass bias using the values of Todt (1993).
RESULTS
Mercury concentrations in relation to ash contents and dry bulk density
The large differences in ash contents illustrate the fundamental hydrological
differences between the two peat profiles. In the GL core (Fig. 2a), ash concentrations are in the
range of ca. 10 to 40% whereas the peat samples below 30 cm in the DK core typically contain
ca. 2 % ash (Fig. 2b); these values are typical of minerotrophic and ombrotrophic peats,
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