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| Titel |
The fate of organic pollutants in soil - Emerging views on the environmental relevance of non-extractable residues |
| VerfasserIn |
Anja Miltner, Karolina Nowak, Cristobal Girardi, Andreas Schäffer, Matthias Kästner |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048323
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| Zusammenfassung |
| The fate of organic chemicals in soils is determined by both physicochemical (e.g. sorption
and sequestration) and biological processes (microbial degradation). As a result, C from
the pollutants entering the soil partitions into the parent compound, metabolites,
non-extractable residues (NER), CO2 and microbial biomass. This distribution has to be
considered for proper risk assessment. The majority of biodegradability tests have been
conducted in aqueous systems (e.g. OECD 301 tests). For approval of chemicals in the
new EU legislation (REACH), however, information about the fate of the tested
compound in soil is required. As the necessary simulation tests in soils (e.g. OECD
307) are rather expensive and complex, it would be advantageous to use the data
from aqueous systems to predict the fate of a chemical in soils. This, however, is
difficult because not all processes occurring in soil are reflected in these data. In
particular, NER formation cannot be simulated by tests in aqueous systems, but this is
important for adequate risk assessment. The chemical nature of NER, which has not
yet been sufficiently elucidated, determines the potential hazard associated with
them.
In general, it is assumed that NER are mainly composed of adsorbed and sequestered
parent compound or metabolites. In contrast, we could show that part of the NER is derived
from the biomass of bacteria using the pollutant as carbon source. The biogenic residues are
completely harmless in contrast to NER derived from the pollutant or toxic metabolites,
which might be remobilized under certain conditions and thus have to considered hazardous.
We therefore compared the biodegradation of isotope labeled 2,4-D, ibuprofen
and ciprofloxacin in aqueous systems and in soil. In the soil experiment, we also
quantified the contribution of microbial residues to NER formation. The results
revealed the processes responsible for NER formation and allowed establishing a
quantitative relationship between the degradation in the two systems. Both 2,4-D and
ibuprofen were mineralized fast in the aqueous system, although ibuprofen narrowly
failed to meet the criteria for ready bioavailability. In soil, mineralization was lower
than in the aqueous system, and significant amounts of NER were formed. High
label incorporation into fatty acid and amino acids indicated that virtually all of
the NER derived from microbial biomass. In contrast, ciprofloxacin was not at
all mineralized in aqueous systems. In soil, we detected a small but significant
mineralization of this compound but no metabolites. NER formation from ciprofloxacin was
fast and independent of the microbial activity showing that NER formation from
sequestration of parent compounds and from biogenic residues are competitive
processes in soil. As ciprofloxacin is a potent antibiotic, it reduced the activity of both
sewage sludge and soil microorganisms. This effect was weaker in soil than in the
aqueous system, because sorption and spatial inaccessibility reduced the toxic effect in
soil.
In conclusion, for readily degradable compounds, mineralization is lower in soil than in
water. A significant part of the carbon will be incorporated into microbial biomass, which
may later be stabilized in soil organic matter, resulting in biogenic residues. These may
account for a large portion or even all of the NER detected by isotope mass balance. In
contrast, toxic compounds are mineralized more easily in soil than in water, because NER
formation and the spatial heterogeneity of soil together with the vast microbial biodiversity
result in lower toxicity of the compounds. NER formation which is not accompanied by
corresponding mineralization indicates formation of potentially hazardous NER derived from
the parent compounds or (toxic) metabolites. In contrast, NER formation associated with
significant mineralization indicates biogenic residue formation and thus a low hazard. |
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