60
Peter Stille and Graham Shields
consider that the lead concentrations in cereal crops and beer are very low, around
0.04 his 0.08 ppm. Tap water also lies on the mixing line but below that value
which is characteristic for natural lead from the area around Munich and in the
drainage area for the Munich water. This allows us to surmise that a part of the
lead in tap water comes from anthropogenic sources. As the lead concentrations in
tap water are extremely low, around 0.002 ppm, even the tiniest traces of
anthropogenic lead are likely to have an influence and cause a shift in the lead
isotopic composition.
Lead in the sewage from a sewage works in Munich (#1) shows a completely
different isotopic composition than tap water (#6). Astoundingly however, Pb
concentrations were found to be similarly low (0.0028 ppm). The Pb appears to
have come predominantly from Australian sources. Pb isotopic compositions of
older sewage works deposits (#7, 8 and 9) allow for the conclusion that this older
'sewage' Pb was derived from more local sources. Sewage deposits (#15) from the
year 1976 show a Pb isotopic signature which can not relate to any lead ore
deposit. Not even by mixing various ore bodies can such Pb isotope compositions
be reached. The only known ore body on Earth which has a similar isotopic
composition can be found in the Altay mountains (Russia). Was lead illegally
imported into Germany and used in the Munich area up to 1976'?
As we have seen, heavy metals are so much more enriched in an
anthropogenically influenced environment than in nature. This makes it possible
to use their concentrations and isotopic ratios in tracing both the source and extent
of anthropogenic contamination. Lead is the prime example but is not always the
only or the best possibility as seen in a recent multi-isotope (Pb, Sr, Nd) and REE
study of a heavy metal contaminated soil (Steinmann and Stille 1997).
One of the most sensitive indicators of the influence of sewage particles on the
marine environment is silver (Ag) content. Silver concentrations are
characteristically enhanced by up to 200 fold in sewage sludge relative to pristine
marine sediments. Why sludge should be so enriched in silver must have
something to do with its specialist uses in photography and electronics, on top of
the fact that it is such as a rare element in nature: background Ag concentrations
in marine sediments are only on the order of tens of ppb.
In some marine and aquatic environments, the concentrations of rare metals
may be naturally enhanced as in the Black Sea, for example. Therefore, for a more
definitive measure of contamination, we need to look at the isotopic ratios of rare
metals as their high masses make kinetic isotopic fractionation of negligible
importance. Anomalous isotopic ratios are most likely to occur due to the mixing
of two end members, as with Pb, one anthropogenic and the other natural. The
established use of Ag as a tracer for contamination enabled, first Esser and
Turekian (1993), and then Ravizza and Bothner (1996) to test the potential of an
even rarer element Osmium (Os) and its isotopic ratio Is'7Os/l~SOs for the same
purpose, im Re decays to m'r Os as a result of beta decay with a half-life of 45.6 Ga.
More details about the systematics of this decay can be found in Sect. 6.4. The
system is essentially analogous to the Rb-Sr isotopic system in that crustal rocks
Peter Stille and Graham Shields
consider that the lead concentrations in cereal crops and beer are very low, around
0.04 his 0.08 ppm. Tap water also lies on the mixing line but below that value
which is characteristic for natural lead from the area around Munich and in the
drainage area for the Munich water. This allows us to surmise that a part of the
lead in tap water comes from anthropogenic sources. As the lead concentrations in
tap water are extremely low, around 0.002 ppm, even the tiniest traces of
anthropogenic lead are likely to have an influence and cause a shift in the lead
isotopic composition.
Lead in the sewage from a sewage works in Munich (#1) shows a completely
different isotopic composition than tap water (#6). Astoundingly however, Pb
concentrations were found to be similarly low (0.0028 ppm). The Pb appears to
have come predominantly from Australian sources. Pb isotopic compositions of
older sewage works deposits (#7, 8 and 9) allow for the conclusion that this older
'sewage' Pb was derived from more local sources. Sewage deposits (#15) from the
year 1976 show a Pb isotopic signature which can not relate to any lead ore
deposit. Not even by mixing various ore bodies can such Pb isotope compositions
be reached. The only known ore body on Earth which has a similar isotopic
composition can be found in the Altay mountains (Russia). Was lead illegally
imported into Germany and used in the Munich area up to 1976'?
As we have seen, heavy metals are so much more enriched in an
anthropogenically influenced environment than in nature. This makes it possible
to use their concentrations and isotopic ratios in tracing both the source and extent
of anthropogenic contamination. Lead is the prime example but is not always the
only or the best possibility as seen in a recent multi-isotope (Pb, Sr, Nd) and REE
study of a heavy metal contaminated soil (Steinmann and Stille 1997).
One of the most sensitive indicators of the influence of sewage particles on the
marine environment is silver (Ag) content. Silver concentrations are
characteristically enhanced by up to 200 fold in sewage sludge relative to pristine
marine sediments. Why sludge should be so enriched in silver must have
something to do with its specialist uses in photography and electronics, on top of
the fact that it is such as a rare element in nature: background Ag concentrations
in marine sediments are only on the order of tens of ppb.
In some marine and aquatic environments, the concentrations of rare metals
may be naturally enhanced as in the Black Sea, for example. Therefore, for a more
definitive measure of contamination, we need to look at the isotopic ratios of rare
metals as their high masses make kinetic isotopic fractionation of negligible
importance. Anomalous isotopic ratios are most likely to occur due to the mixing
of two end members, as with Pb, one anthropogenic and the other natural. The
established use of Ag as a tracer for contamination enabled, first Esser and
Turekian (1993), and then Ravizza and Bothner (1996) to test the potential of an
even rarer element Osmium (Os) and its isotopic ratio Is'7Os/l~SOs for the same
purpose, im Re decays to m'r Os as a result of beta decay with a half-life of 45.6 Ga.
More details about the systematics of this decay can be found in Sect. 6.4. The
system is essentially analogous to the Rb-Sr isotopic system in that crustal rocks