25th International Meeting on Organic Geochemistry IMOG 2011

P-399
Resolving sources and preservation mechanism of
ahthropogenic and natural organic matter in sediment of Beijing-
Hangzhou Great Canal, China with usage of Hydropyrolysis
(HyPy)
Xiaoyu Zhang, William Meredity, Colin Snape, Yongge Sun, Xin Chen, Yang Xu
Earth Science, Zhejiang University, Hangzhou, China (corresponding author:zhang_xiaoyu@zju.edu.cn)
Traditionally, most investigations of sources of
organic materials in sediments regarded the
extraction fraction exclusively. Actually, low molecular
weight organic compounds can be affected by
intermolecular interactions with geomacro-molecules,
preventing their extraction. The major quantities of
bound residues in sediments (soils) are thought to be
incorporated reversibly, implying the classification of
the phenomenon as a temporary sink for
contaminants on the one hand. On the other hand,
bound residues recover an additional contamination
potential, which is not concerned by conventional
analyzes, considering extractable compounds only.
HydroPyrolysis at high hydrogen pressures (>10 MPa)
in the presence of a dispersed sulphided molybdenum
catalyst has demonstrated the unique ability of
maximizing yields of aliphatic skeletons with
minimizing the structural rearrangement of
stereochemistry, releasing incorporated bound lower
molecular aromatic hydrocarbon through degrading
geo-macromolecules whilst keeping the low molecular
stable. Furthermore, Staged HydroPyrolysis has
confirmed that molecular biomarkers release at higher
temperatures through cleaving relatively strong bonds
are quantitatively more significant than those released
at lower temperatures for immature source rock. Thus,
HydroPyrolysis is considered to be an attractive route
to provide better insight into the preservation of
covalently-bound biomarker and useful especially for
assisting organic compounds source correlations.
In this study, comparisions of covalently-bound
aliphatic and aromatic hydrocarbon and aliphatic
biomarkers released via Single and Staged HyPy with
their solvent-extractable counterparts for the sediment
collected at Beidaqiao Bridge, Jing-Hang Great Canal,
Hangzhou, China have been carefully analyzed to
illustrate the main sources and preservation
mechanism of anthropogenic and natural organic
matter in this highly polluted river sediment.
The results from solvent-extractable aliphatic and
aromatic both strongly suggest that the organic
materials in the Canal sediment are the admixture of
sources from uncombusted fossil fuel residues and
land derived higher plant waxes inputs and also from
combustion/pyrolysis of fossil fuels, although the
evidence of combustion/pyrolysis of fossil fuels are
relatively weak.
The comparison of yields from Single and Staged
HyPy indicate that most n-alkanes (>80%) are
generated at stage ~350°C, with decreasing yield of
n-alkane under higher temperatures, only 5% of nalkanes
are genereated under 400~450°C. Both
Single HyPy and Staged HyPy at lower temperature
demonstrate the prevalence distribution of precursers
of fatty acid derived from land higher plants in this
case. The distribution pattern of n-alkanes at
400~450°C Staged HyPy suggest that small amount
of petroleum residue combined in the sediment.
Meanwhile the 20S/(S+R) ratio of C29 sterane
increases obviously with increasing temperature,
which indicate the capability of Staged HyPy to
release the biomarker species for tracing the source
of oil pollutant in environmental samples. On the
contrary, yields of PAHs increase with temperature
which need further research especially from evidence
of δ13C information to illustrate the possible sources
correlations of PAHs.
The research indicates that major quantity of
anthropogenic organic matter in the sediment are
extractable, while very few amount of them exist with
covalently bound. Further research need to carry out
especially for the PAHs in the sediments.
This work was financially supported by ZJNSF(No.
Y5100117), Education of Zhejiang Provence (No.
Y200907741) and The State Key Laboratory of
Organic Geochemistry, China (No. OGL-200810).
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