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| Titel |
Formation of “bound” |
| VerfasserIn |
K. Nowak, M. Kästner, A. Miltner |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027003
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| Zusammenfassung |
| During degradation of organic pollutants in soil, metabolites, microbial biomass, CO2and
“bound” residues (“non-extractable” residues in soil organic matter) are formed. Enhanced
transformation of these contaminants into “bound” residues has been proposed as an
alternative remediation method for polluted soils. However, this kind of residues may pose a
potential risk for the environment due to their chemical structure and possible remobilization
under different conditions. Therefore particular attention is given actually to “bound”
residues. Part of these non-extractable residues may be “biogenic,” because microorganisms
use the carbon from the pollutant to form their biomass components (fatty acids, amino
acids, amino sugars), which subsequently may be incorporated into soil organic
matter. Furthermore, the CO2 originating from mineralization of xenobiotics, can be
re-assimilated by microorganisms and also incorporated into “biogenic residue”. The
hazard posed by "bound" residues may be overestimated because they are “biogenic”
(contain microbial fatty acids and amino acids). The knowledge about the pathways of
“biogenic residue” formation is necessary for a proper assessment of the fate of
tested pollutants and their turnover in the soil environment. Moreover, these data are
needed to establish the realistic degradation rates of the contaminants in soil. The
main objectives of this study are: to quantify the extent of “biogenic residue” (fatty
acids, amino acids, amino sugars) formation during the degradation of a model
pollutant (2,4-dichlorophenoxyacetic acid = 2,4-D) and during CO2 assimilation by
microorganisms and to evaluate which components are mainly incorporated into “bound”
residues. To investigate the extent of “biogenic residue” formation in soil during the
degradation of 2,4-D, experiments with either 14C-U-ring and 13C6-2,4-D or carboxyl-14C
2,4-D were performed. The incubation experiments were performed according to
OECD test guideline 307, in the dark, at constant temp 20Ë C (+/-2Ë C) and with
intermittent aeration. During incubation, the mineralization was quantified and soil
samples were analyzed for the presence of both “biogenic residues” and remaining
2,4-D. Mineralization of 2,4-D in both experiments was very high. However, the
14CO2 evolution was higher from carboxyl-14C 2,4-D than from 14C-ring 2,4-D.
After 7 days of incubation, 30% of initial amount of 14C in soil contaminated with
14C-ring 2,4-D was mineralized, whereas 40% of total radioactivity was evolved
as CO2after 4 days from soil incubated with 14C-carboxyl 2,4-D. The amount of
extractable 2,4-D residues was very low in both experiments (14C-ring 2,4-D: 2%
and 14C-carboxyl 2,4-D: 1%). The soil incubated with 14C-ring 2,4-D contained
60% of “non-extractable” residues of 2,4-D after 7 days, while the amount of these
residues in soil contaminated with 14C-carboxyl 2,4-D reached 50% of the initial
radioactivity in the tested system 4 days after application. More ”biogenic residues”
were formed in soil spiked with 14C-U-ring 2,4-D (10%) than in soil with carboxyl
14C 2,4-D (7%). Both 2,4-D and CO2-derived C were incorporated mainly into
microbial amino acids (9.5% at day 7 and 7.0% at day 4, respectively). After 7
days of incubation, 0.5% of initial applied radioactivity in system was found in
microbial lipids in the soil contaminated with 14C-ring 2,4-D. Only 0.1% of the total
radioactivity was incorporated into lipids in soil treated with 14C-carboxyl 2,4-D on day
4 after application. Thin Layer Chromatography identified the microbial lipids
containing the radioactivity as phosphatidylethanolamine, a phospholipid typical for
microorganisms. The amount of microbial lipids (which corresponds to phospholipids) in
both cases decreased with time; this can be explained by the death of the microbial
biomass. To the best of our knowledge, this is the first report on the formation of
“bound” residues from biomass during the biotic degradation of herbicide in soil. |
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