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

if not predominant source of these contaminants. According to the compilation published by
Farmer et al. (1999), British coal consumption peaked in the early 1950`s. Taken together, it
appears that the changing accumulation rates of anthropogenic Hg, Pb and As revealed by the
DK peat core may reflect to a large extent the history of the British coal industry and the
chronology of the Second Industrial Revolution.
To further evaluate the possible link between these contaminants and British coals, the
ratio 208 Pb/ 206 Pb has been plotted against the 206 Pb/ 207 Pb values (Fig. 7). Clearly, the DK peat
samples are much closer in isotopic composition to the values for British coals (Farmer et al.,
1999) than they are to the values for U.K. gasoline leads (Monna et al., 1997). Thus, the Pb
isotope data, combined with the chronology of the enrichments in Hg, Pb and As concentrations,
suggest that coal burning was the main source of these contaminants to the DK peat profile.
In samples above ca. 20 cm in the DK profile, there is a sharp shift (after AD 1959)
toward much less radiogenic values 206 Pb/ 207 Pb (Fig. 6c) which reflects the growing importance
of leaded gasoline contributions; the ores used to synthesize alkyllead compounds for gasoline
such as Pb from the Broken Hills mine of Australia, have had 206 Pb/ 207 Pb values as low as 1.04.
The most recent sample in the profile (AD 1999) shows significantly more radiogenic values,
compared to the 1970`s, clearly reflecting the reduction in gasoline Pb concentrations, and the
eventual phasing-out of leaded gasoline in Europe; this change is also seen in four peat profiles
from Switzerland (Weiss et al., 1999a, Shotyk et al., 2003), 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). It is important to emphasise that the decline in anthropogenic Pb concentrations
(starting in 1954) which is shown in Figure 6c pre-dates by approximately 25 years the minimum
in 206 Pb/ 207 Pb; the minimum in this Pb isotope ratio corresponds to the maximum impact in
gasoline Pb emissions (Shotyk et al., 2002a). As noted earlier, this decline in 206 Pb/ 207 Pb was
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