Hi Michael,

Some time ago, I was involved with a study on the Pb isotopic ratios in roof
dusts in the Wollongong area (an industrial city, approx. 90 kilometres south
of Sydney).  By measuring Pb isotope ratios in various samples of industrial
particulate matter, we were able to apportionate each industry's contribution
to any roof dust sample using triangulation (there were 3 known end members
contributing to the majority of the lead emissions).  Cored sediments from a
nearby estuarine lake system (Lake Illawarra) were treated in the same manner
and changes in industrial input, with time, could be plotted versus depth -
from these data, quite accurate sedimentation rates were calculated.  Please
refer to:

CHIARADIA, M., B.E. CHENHALL, A.M. DEPERS, B.L. GULSON & B.G. JONES (1997).
Identification of historical lead sources in roof dusts and recent lake
sediments from an industrialised area: indications from lead isotopes.  The
Science of the Total Environment, 205:107-28.

To your immediate problem - if you have accurate Pb isotopic signatures for
TEL and TML for different petroleum products of different "ages", then, yes,
in theory, a similar approach to the above could be applied.  As you are
dealing with fluids vs. solids (particulate material), you should be able to
apportionate contributions from different petroleum products.  Accurate
"dating" of a site will only occur if one petroleum product is present; if two
or more petroleum products have contaminated a site, then the "oldest" product
will date the first contamination period of the soil (data obtained from a
straight line correlation for two petroleum products or from triangulation for
three petroleum products (or 3D...3+D apportionation where petroleum products
are many).

I hope this all makes sense.

Regards,
Aivars Depers
School of Geosciences
University of Wollongong
Northfields Avenue
Wollongong, N.S.W. 2522
AUSTRALIA.

Michael Whiticar wrote:
>
> Dear Colleagues,
>
> My research group has been exploring the use of stable isotopes (C, H, S)
> in organic compounds (oils, lipids, gases, etc.) to fingerprint and track
> them (CSIC).
>
> Recently, we have turned our attention to the release of tetraethyl and
> tetramethyl lead from gasoline into soils. This topic certainly must sound
> very familiar to many of you. The twist, that we need your help with, is as
> follows.
>
> In our study area,  there may have been multiple release events that took
> place over decades. This can confuse the light element isotope fingerprint.
> Therefore I am interested in knowing if the isotope composition of lead
> could be a potential candidate to fingerprint. In order for this to work,
> there must be measurably different and diagnostic lead isotope compositions
> in the feedstock for TEL and TML.
>
> The best case scenario is if the source of lead for TEL and TML was
> different at different times, and that the lead isotope composition for the
> sources was different. If this is the case, then we could "date" the
> releases (obviously not radiogenically, but akin to Freon dating in the
> ocean).
>
> Questions:
>
> 1. Over the past decades, have there been numerous sources for the TEL and
> TML feedstock?
>
> 2. Was the lead for the TEL and TML feedstock generation a unique source?
>
> We would appreciate it if you can help, make suggestions or know of
> publications on this topic - even a response that refutes the idea would
> guide us.
>
> Thank you
>
> Michael Whiticar
> ([log in to unmask])
>
> __________________________________________________________
> Dr. Michael J. Whiticar
> Professor
> Biogeochemistry
> School of Earth and Ocean Sciences
> University of Victoria
>
> Email:                  [log in to unmask]
> Web Page:                       http://ceor.seos.uvic.ca/biogeochem/
>
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>
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>                                         250 721 6200 (Main Office)
>
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>
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