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

leachable fraction, and 32.1 µg/g Pb in the residual fraction). For comparison with these
concentrations, the “natural background” concentration of Pb in pre-anthropogenic peats in
Switzerland dating from ca. 8,000 to 5,000 14 C yrs BP is approximately 0.2 µg/g Pb, and this
difference indicates in a general way the extent to which the DK core has been contaminated by
industrial Pb. The isotopic composition of Pb in the two fractions, summarized here as the
206 Pb/ 207 Pb ratio (Fig. 6b), is virtually identical and this clearly demonstrates a common origin
of the Pb in both fractions. One possible explanation of the similarity in Pb isotopic composition
in each of the DK peat fractions is that anthropogenic Pb supplied by various industrial
emissions has been scavenged by soil-derived aerosols supplied by crustal weathering, such that
the “soil dust signature” has been overprinted by anthropogenic Pb. A second possible
explanation is that the “residual” fraction obtained by the extraction procedure has included
some of the “leachable” Pb supplied primarily by anthropogenic sources.
Second, the isotopic composition of Pb in the two peat cores is very different, with the
GL samples being far more radiogenic (Fig. 6b). The pattern in 206 Pb/ 207 Pb in the DK core is
remarkably similar to the temporal variation in 206 Pb/ 207 Pb seen in four peat profiles from
Switzerland (Weiss et al., 1999a), as well as the record of 206 Pb/ 207 Pb reported for Sphagnum
moss samples from the University of Geneva herbarium (Weiss et al., 1999b). The ratio
206 Pb/ 207 Pb in the Upper Continental Crust (Kramers and Tolstikhin, 1997) as well as in pre-
anthropogenic (dating from 8,000 to 5,300 14 C yr BP), atmospheric aerosols from Switzerland
(Shotyk et al., 2001), is approximately 1.2. All of the measured values from the DK core are
significantly less radiogenic than this, indicating that anthropogenic Pb has dominated the
atmospheric Pb inputs to the DK bog.
Predominant sources of anthropogenic, atmospheric Pb and As in Denmark
The lithogenic Pb fraction derived from atmospheric soil dust can be estimated as the
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