25th International Meeting on Organic Geochemistry IMOG 2011

P-009
A new method for the combined detection of different faecal
biomarker classes and their binding types in soils using GC/MS
Michaela Dippold 1,2 , Jago Birk 1,3 , Guido Wiesenberg 2 , Bruno Glaser 3
1 Soil Physics Section, BAYCEER, University of Bayreuth, Bayreuth, Germany, 2 Department of
Agroecosystem Research, BAYCEER, University of Bayreuth, Bayreuth, Germany, 3 Soil Biogeochemistry,
Institute of Agricultural and Nutritional Science, Martin-Luther-University Halle-Wittenberg, Bayreuth,
Germany (corresponding author:midipp@gmx.de)
The detection of faeces in lacustrine, marine and
terrestrial ecosystems has already been established
based on quantification of several derivatives of the
∆ 5 -steroles, namely the stanoles, the stanones and
the bile acids. However, up to now, the combined
detection of these substance classes in soil was not
reliably possible so far. A joint quantification of these
substances would have the advantage to assess
robust and specific information about the faecal input
into soils. Thus, the objective of this work was the
development of a GC-MS-method for these faecal
biomarkers in soils, which accounts for the
methodological difficulties due to the high organic
matter contents of many Anthrosols and for the
different binding types of these biomarker classes.
For this purpose, a joint method was developed
based on existing methods for single biomarker
classes. After the weak alkaline saponification of the
total lipid extract separation of the neutral (∆ 5 -sterols,
stanoles and stanones) and the acidic lipid fraction
(bile acids) was performed by means of a sequential
liquid-liquid-extraction. The neutral fraction was
directly purified by deactivated silica whereas the
acidic lipids first had to be methylated before purifying
their methyl esters using activated silica. Finally both
fractions were derivatized by silylation. Evaluation of
this method was performed by standard addition to
lipid extracts from three Anthrosol-reference-profilepairs
with different soil properties and history: one
sandy and one clayey Amazonian Anthrosol under
pre-Columbian settlements, one loamy German
Anthrosol next to a Celtic settlement and reference
soils close to each Anthrosol. To get further
information about the content of faecal biomarkers in
differently bound lipid fractions saponified lipid
extracts were compared with not-saponified extracts
and direct saponification of soil samples.
The method evaluation by standard addition revealed
no significant differences between the recoveries of
the single substances and the applied first internal
standard. The precision and the high recoveries
(> 84%) of this method confirm its applicability in soils.
The different saponification treatments show that at
least 20% of the neutral biomarker classes were
bound to the soil matrix. For bile acids, which were
bound to about 50% to the soil matrix, this could be
explained by ester bondings via their carboxyl groups.
However, for less polar alcohol substance classes
(∆ 5 -steroles and stanoles) there are two potential
mechanisms for their stabilization. These include
covalent bonding of the hydroxyl group and a close
association of these hydrophobic molecules to the
organic substance of the soil, which could not be
distinguished by this method. The high content of
stanones in the bound lipid fraction can be attributed
to a very efficient association of this hydrophobic
substance class with the macromolecular network of
the organic substance. These stabilization processes
prevent the extraction of bound or encapsulated
molecules. Thus, a direct saponification of the soil is
necessary to make a high amount of faecal
biomarkers accessible for extraction.
The determination of the faecal biomarker fingerprint
in the Anthrosol-reference pairs revealed that input of
omnivorous faeces was only present in the
Amazonian Anthrosols but not in the reference
profiles. By means of bile acid fingerprint, these inputs
were identified as human faeces. The profiles
sampled in Germany showed a combined influence of
herbivorous and omnivorous faeces in both profiles,
which could be attributed to cattle, human, pig and
chicken.
Thus, this method copes with the often stipulated
multiproxy-approach for the quantification of faecal
biomarkers of different substance classes. The
additional consideration of the bound lipid pool in soil
enables the detection of a wide range of lipids
differing in age and origin in soil. Due to polygenetic
sources and the high recalcitrance of faecal
biomarkers, this is decisive for a correct and
comprehensive interpretation of ancient deposition of
faeces. Therefore this method is especially suitable
for the application in geoarcheological investigations
of Anthrosols.
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