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

further improve our knowledge of pre-industrial and post-industrial Hg accumulation rates.
Temporal changes in the isotopic composition of Pb in Greenland
As noted earlier, Pb concentrations are far lower in the GL core compared to DK. The
Pb EF calculated using the Pb and Ti concentrations failed to reveal a significant enrichment of
Pb in the surface layers of the GL core (Fig. 5a). However, in the surface and near-surface peat
layers at GL, the Pb is much less radiogenic in both the leachable and residual fractions (Fig. 6b),
compared to deeper, older peat layers. Given that this zone dates from the past century, the shift
in Pb isotope ratios probably reflects the input of anthropogenic Pb with lower 206 Pb/ 207 Pb ratios.
Anthropogenic, atmospheric Pb in Greenland has previously been shown to be derived primarily
by gasoline lead used in North America (Rosman et al., 1998). Alklyllead compounds in N.
America were synthesized primarily using lead ores of the Mississipi Valley type deposits which
are much more radiogenic ( 206 Pb/ 207 Pb ca. 1.2) compared to the ores used for gasoline lead in
Europe. However, even these, relatively radiogenic leads are considerably less radiogenic than
the rocks and minerals of Greenland ( 206 Pb/ 207 Pb up to 1.3 in Fig. 6b). Thus, addition to the
surface peat layer at GL of Pb derived from N. American gasoline lead, could easily have caused
the significant decrease in 206 Pb/ 207 Pb revealed by the peat core. The shift in 206 Pb/ 207 Pb to less
radiogenic values in samples above ca. 20 cm in the GL core (Fig. 6b), therefore, most likely
reflects the addition of Pb derived from the combustion of leaded gasoline in N. America. Thus,
while total Pb concentrations and their ratio to Ti failed to indicate an anthropogenic impact, the
Pb isotope data clearly does. Additional work is required with respect to leaching techniques
such as those now being used to fractionate Pb in soils (Harlavan and Erel, 2002; Emmanuel and
Erel, 2002), with the goal of improving the recovery of the atmospheric Pb component which has
been supplied by anthropogenic emissions.
The Pb concentrations in the leachable fraction generally exceed those of the residual
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