25th International Meeting on Organic Geochemistry IMOG 2011

P-380
Distribution, fate and formation of non-extractable residues of a
nonylphenol isomer in soil derived organo-clay complexes and
first evidence for a stereoselective incorporation process
Jan Schwarzbauer, Patrick Riefer, Timm Klausmeyer, Andreas Schaeffer, Burkhardt
Schmidt
RWTH Aachen University, Aachen, Germany (corresponding author:schwarzbauer@lek.rwth-aachen.de)
Xenobiotics released to soil undergo complex processes
which lead to extractable but also non-extractable residues
(NER). The latter are characterized by interactions with
humic substances or mineral surfaces covering the range
from weak adsorptive to reversible or irreversible covalent
bonds. Generally,the formation of NER in soil have huge
implications in the fate of pollutants (e.g. bioavailability, plant
uptake, microbial degradation and toxicity).
Within soil, the clay fraction plays a major role in the
formation of non-extractable residues (NER) due to its
specific surface characteristics and the preferred association
of soil organic matter to the minerals.
4-Nonylphenols are of high environmental interest due to
their ubiquitous appearance and ability to disrupt the
endocrine system of higher organisms. Technical
nonylphenol is an isomer mixture used industrially to
produce nonlyphenol polyethoxylates (NPnEO) which act as
nonionic surfactants in many products. However, these
surfactants once released into the environment undergo
microbial degradation with release of nonylphenols as major
metabolites.
The aim of the presented study was to investigate the fate
and distribution of a specific NP isomer (353-NP) within soil
and soil derived organo-clay complexes. Therefore, 14 C- and
13 C-labeled 353-NP was added to soil samples and
incubated up to 180 days. Mineralization was measured and
soil samples were fractionated into sand, silt and clay. The
clay fraction was further separated in humic acids, fulvic
acids and humin. Lastly, the NER in the different humic
fractions were released by common organic-geochemical
approaches like alkaline hydrolyses, BBr3-treatment, RuO4oxidation
and TMAH-thermochemolysis.
After 180 days of incubation the predominate incorporation
sites of 353-NP were the organo-clay complexes (27% of
applied radioactivity), whereas only 22 % was mineralized.
The water extractable portion was low (9 % of applied 14 C)
and remained constant during the entire incubation period.
Separation of organo-clay complexes, after extraction with
solvents to release weakly incorporated, bioaccessible
portions, showed that non-extractable residues (NER) were
preferentially located in the humic acid fraction.
water solved
(15.11) 11.9%
CO 2 (1.62)
1.3%
loss (16.11)
12.7%
clay (55.32)
43.6%
sand (4.35)
3.4%
silt (34.45)
27.1%
Fig. 1: Distribution of NP radioactivity between individual soil
particle size fractions, water phase and CO2 as
mineralization indicator.
More detailed investigations by means of sequential
chemical degradation indicated a predominant incorporation
of non-extractable NP isomer residues via ester bonds as
released by alkaline hydrolysis. The amount of releasable
compounds decreased until day 180 indicating a change of
the incorporation behavior as a consequence of ageing
processes. BBr3-treatment, RuO4 oxidation and TMAHpyrolysis
released only low portions of non-extractable 14 C
giving evidence of minor influence of ether and C-C-linkages
in the incorporation processes.
Analysis of the diastereomeric composition of 353-NP in the
extractable and non-extractable fractions and comparison of
these ratios from biotic and abiotic experiments revealed
significant alterations. These systematic changes gave clear
evidence that the process of microbial assisted incorporation
of 353-NP into soil organic-clay complexes is a
stereoselective process. To our knowledge, this is the first
report on a stereoselective incorporation process of organic
substances forming non-extractable residues.
Fig. 2: Diastereomeric ratios of NP in soil derived organic-clay complexes. o =
extractable fraction,square = hydrolysable fraction from humic acids, triangle =
hydrolysable fraction from humins.
water solved
(434.26)
74.3%
509
loss (23.11)
3.9%
sand (15.49)
2.7% silt (43.01)
7.4%
clay (67.93)
11.6%
CO 2 (0.60)
0.1%