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| Titel |
Contribution of microorganisms to non-extractable residue formation from biodegradable organic contaminants in soil |
| VerfasserIn |
K. M. Nowak, C. Girardi, A. Miltner, A. Schäffer, M. Kästner |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063137
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| Zusammenfassung |
| Biodegradation of organic contaminants in soil is actually understood as their transformation
into various primary metabolites, microbial biomass, mineralisation products and
non-extractable residues (NER). NER are generally considered to be composed of parent
compounds or primary metabolites with hazardous potential. Up to date, however, their
chemical composition remains still unclear. Studies on NER formation are limited to
quantitative analyses in soils or to simple humic acids-contaminant systems. However, in the
case of biodegradable organic compounds, NER may also contain microbial biomass
components, e.g. fatty acids (FA) and amino acids (AA). After cell death, these biomolecules
are incorporated into soil organic matter (SOM) and stabilised, ultimately forming biogenic
residues which are not any more extractable. We investigated the incorporation of the
13C-label into FA and AA and their fate during biodegradation experiments in soil with
isotope-labelled 2,4-dichlorophenoxyacetic acid (13C6-2,4-D) and ibuprofen (13C6-ibu) as
model organic contaminants. Our study proved for the first time that nearly all NER formed
from 13C6-2,4-D and 13C6-ibu in soil derived from harmless microbial biomass
components stabilised in SOM. 13C-FA and 13C-AA contents in the living microbial
biomass fraction decreased over time and these components were continuously
incorporated into the non-living SOM pool in biotic experiments with 13C6-2,4-D and
13C6-ibu. The 13C-AA in the non-living SOM were surprisingly stable from day 32
(13C6-2,4-D) and 58 (13C6-ibu) until the end of incubation. We also studied the
transformation of 13C6-2,4-D and 13C6-ibu into NER in the abiotic soil experiments. In these
experiments, the total NER contents were much lower than in the corresponding biotic
experiments. The absence of labelled biomolecules in the NER fraction in abiotic soils
demonstrated that they consist of the potentially hazardous parent compounds and / or their
metabolites.
Biogenic residue formation is relevant during biodegradation of organic contaminants,
whereas abiotic NER are formed from the non-biodegraded residual contaminants. Abiotic
NER and biogenic residue formation are competitive processes and do not occur in a similar
extent. In the biotic treatment, the rapid mineralisation of an organic compound reduces the
extent of abiotic NER formation via physico-chemical interactions between a parent
compound and / or its primary metabolites with SOM. Therefore, in order to properly assess
the potential risks of a target contaminant in soil to humans and the environment, it is
necessary to distinguish between abiotic NER and biogenic residue formation in the mass
balances of contaminants. |
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