Lead Isotopes in Lichen Transplants around a Cu Smelter in Russia Determined by MC-ICP-MS Reveal Transient Records of Multiple Sources

Transplants of the lichen Hypogymnia physodes, which is
relatively tolerant to SO2 and heavy metals, were deployed
for 3 months over a 60 km long SW−NE transect centered
on a highly polluting Cu smelter and its adjoining town
of Karabash, southern Urals, Russia. The abundance of 206Pb,
207Pb, 208Pb, and 204Pb were determined by MC-ICP-MS.
The measurement of 204Pb revealed critical features, which
would otherwise remain concealed:  (i) The precise
isotope ratios referenced to 204Pb allowed several different
sources to be resolved even within the small area
covered:  (a) the obvious pollutant source of the Karabash
Cu smelter; (b) two dispersed sources, likely to include
soil with lower and different contributions of thorogenic and
uranogenic lead; and (c) one anthropogenic source with
higher contribution of 235U derived Pb. (ii) In part of the transect,
the Pb isotope composition changed while the Pb
concentrations remained the same. This indicates that the
Pb content of the transplantation material from the
background site was largely replaced and that the transplants
provide a transient record reflecting a continuous
accumulation and loss of environmental Pb, probably
mainly in the form of extracellular particles. Overall, the
method of lichen transplantation coupled with Pb isotope
ratio determinations proved effective in assessing the
usefulness of lichens in biomonitoring and in resolving
different sources of atmospheric deposition.