In principle, stable isotope methodology can be
diagnostic in such studies. Problems arise in that multiple sources often exist
for a given element. Also isotopic fractionation might
occur during and post deposition. Competent interpretation of the data
would probably require isotopic data from other relevant samples.
Interestingly, I have been involved with a
colleague in a European city studying erosion of sections of walls of
older buildings at an elevation range from ground level up to about
one meter. It seems unlikely that industrial pollutants in the air would
have such localized effects . Organic-N was present in the eroded
areas. One possible scenario is centuries of urination against
the walls by males particularly after they had consumed beer in nearby
taverns. (Although dogs might be a minor source close at ground level,
they would not be effective contributors at the higher elevations!).
My colleague and I have
been pondering some isotope ( N,S) data for about a
decade. They can best be described as consistent with the human
urination scenario but to say that they definitely prove it would be a leap of
Isotope methodology is more definitive when many
elements are studied particularly where different sources and biological
conversions are involved. It often becomes a question of deciding the importance
of the answer in relation to the costs in time and materials required
to acquire it. To this end it is appropriate to better "define" your
sample before proceeding with isotope measurements as suggested by Kurt
One possibility might be to examine the
oxygen isotope composition of sulfate. The sulfate concentration of urine
exceeds that ingested by a few orders of magnitude. Most of the sulfate in urine
arises from oxidation of dietary
organic-S. During oxidation, some of the
oxygen in the sulfate is derived from body water. The latter in turn is close to
but not identical isotopically to meteoric water. Consequently we have shown
that the O-isotopic composition of sulfate in urine varies geographically
dependent upon the isotope composition of consumed water. We have
also verified the latter with O-isotope labeling studies in the laboratory.
With our study of the old city walls and possibly with your deposit,
there is possibly a post depositional complication. About half of
the sulfur in urine is organic-S and some would probably be oxidized to
sulfate after voiding. The oxygen isotope composition of this sulfate
might not differ radically from that produced in the animal but that assumption
Along the lines of Kurt Kyser's comments, have you
looked for evidence of bio-organic material such as hair which is remarkably
resistant to weathering?
At 06:26 PM 7/23/2004, you wrote:Hi,
We were referred to this list server by Prof. Robert
Clayton (Univ. of Chicago), since this is not our field.
We wonder if we can trouble you with a question on a rock specimen we
have analyzed recently. that urine samples of
mammals contain (C, N, O, Ca, Cl, Na, K, Si and S, among other cations).
The reason that we are e-mailing you is to ask if
isotopic abundance measurements which is your specialty might be of some value
in approaching this problem. Previous studies on chlorine-36 in fossil rat
urine(1) has shown that 36-Cl/Cl ratio could be used to track temporal patterns
dating back ~ 38,000 years before the present (as measured by 14-C).
According to ref. 1, the 36-Cl/Cl ratio shows a discontinuity around 12,000
years before the present with a ratio between 125 %- 200% of modern pre-bomb
values whereas during the past 10ky the ratio ranged from 50-100% of modern
Since we appreciate this is a
difficult matter and the cementum could have abiogenic origins, we wonder if
isotopic abundance can be employed to ascertain if this rock specimen cementum
is abiogenic or biogenic in origin in general. We have ample specimens of
the rock for analysis, if there is any interest.
helpful comments and/or offers of assistance would be greatly appreciated by
us. Please reply off list. Sincerely
Gerry Zajac BP research
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