Folie 1

1
Effects of soil organic matter conformation and
of substrate additions on the formation and
release of bound residues
Bernd Marschner and Anastasia Shchegolikhina
Geographisches Institut, Ruhr-Universität Bochum
Hypotheses
Introduction
Bound residues of organic compounds develop
through interactions with soil organic matter,
either through sorption to specific sites (i.e.
hydrophobic cavities) or through slow diffusion
into less accessible domains (glassy vs.
rubbery). The relative density and flexibility of
SOM is affected by cations at the exchange sites.
Strongly hydrated monovalent cations (i.e. Na)
cause SOM to expand and thus make it more
accessible to xenobiotics (Fig. 1). Polyvalent
cations (i.e Ca2 or Al3) reduce the volume and
flexibility of SOM through cation bridging (Fig.
2), which can thus limit diffusion of xenobiotics
into the matrix and back out again.
1. The structural conformation of SOM affects
sorption and desorption kinetics of xenobiotics
and thus influences the formation of "bound
residues". 2. The addititon of substrates can
enhance the biodegradation of bound residues,
either through co-metabolism or through enhanced
degradation of the sorbent (priming effects).
glucose
Fig. 1 Expanded and flexible SOM structure
with monovalent cation
Fig. 2 Condensed and rigid SOM structure
with polyvalent cation
Methodological Approach
Preliminary results
In an incubation experiment with the steroid
hormone 17b-estradiol, its mineralization was
significantly stimulated by the addition of
glucose (Fig. 3). In the soil "Berlin ww-farm",
the glucose addition even had a long-lasting
effect.

• Preparation of soil samples with altered SOM
  conformation by varying the cation composition
  of the exchange sites (mono- vs. polyvalent,
  acidic vs. basic).
• Short-term sorption studies and long-term aging
  experiment with 14C-labelled phenanthrene and
  nonylphenol in the sterilized and non-sterilized
  soils from step 1.
• After 0, 3, 6 and 12 months of aging, analysis of
  SOM conformation (DSC and 1H-NMR) and of the
  following xenobiotic fractions - desorbable
  (batch water extract) - bioaccessible
  (extractable with cyclodextrine or surfactant) -
  biodegradable (14CO2 evolution from re-inoculated
  samples) - sequential extaction and structural
  analysis of NP-residues.
• Incubation of aged soil samples with substrates
  (i.e. glucose, alanine, catechol) to determine
  priming effects on xenobiotic mineralization.

Fig. 3 Effects of glucose additions on
mineralization rates of
14C-17b-estradiol in two soils. "HaMapil w/ glu"
also received the same glucose dose
at the beginning of the incubation
(Stumpe, unpublished).