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| Titel |
Influence of alternating soil drying and wetting on the desorption and distribution of aged 14C-labeled pesticide residues in soil organic fractions |
| VerfasserIn |
N. D. Jablonowski, M. Mucha, B. Thiele, D. Hofmann, P. Burauel |
| 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 |
250067352
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| Zusammenfassung |
| A laboratory experiment was conducted to evaluate the effect of alternating soil drying and
wetting on the release of aged 14C-labeled pesticide residues and their distribution in soil
organic fractions (humic acids, fulvic acids, and humin substances). The used soils (gleyic
cambisol; Corg 1.2%, pH 7.2) were obtained from the upper soil layer of two individual
outdoor lysimeter studies containing either environmentally long-term aged 14C
residues of the herbicide ethidimuron (ETD; 0-10 cm depth; time of aging: 9 years) or
methabenzthiazuron (MBT; 0-30 cm depth; time of aging: 17 years). Triplicate soil samples
(10 g dry soil equivalents) were (A=dry/wet) previously dried (45Ë C) or (B=wet/wet)
directly mixed with pure water (1+2, w:w), shaken (150 rpm, 1 h), and centrifuged (~2000
g). The resulting supernatant was removed, filtered (0.45 μm) and subjected to 14C activity
analysis via liquid scintillation counter (LSC), dissolved organic carbon (DOC) analysis,
and LC-MS-MS analysis. This extraction procedure was repeated 15 individual
times, for both setups (A) and (B). To determine the distribution of the aged 14C
labelled pesticide residues in the soil organic matter fractions, the soil samples
were subject to humic and fulvic acids fractionations at cycles 0, 4, 10, and 15.
The residual pesticide 14C activity associated with the humic, fulvic, and humin
substances (organic fraction remaining in the soil) fractions was determined via
LSC.
The water-extracted residual 14C activity was significantly higher in the extracts of the
dry/wet, compared to the wet/wet soil samples for both pesticides. The total extracted 14C
activity in the dry/wet soil extracts accounted for 51.0% (ETD) and 15.4% (MBT) in contrast
to 19.0% (ETD) and 4.7% (MBT) in the wet/wet extracts after 15 water extractions.
LC-MS-MS analysis revealed the parent compound ETD 27.9 μg kg-1 soil (dry/wet) and
10.7 μg kg-1 soil (wet/wet), accounting for 3.45 and 1.35% of total parent compound
initially applied after a total of 10 water extractions, respectively. MBT was detected but not
quantified, whereas its metabolite MABT (2-methylamino-benzothiazole) was detected (0.8
vs 0.3 μg kg-1, in dry/wet vs wet/wet soil water extracts, respectively) after 10 water
extractions. These results demonstrate the long-term persistence of ETD and MBT
and metabolites and their remobilization potential facilitated by soil drying and
rewetting.
For all samples, the DOC content was significantly higher for the water extracts
obtained after dry/wet cycles compared to values obtained from the constantly
moistened soil samples. The DOC and water extracted residual 14C activity correlated
positively. This result indicates that pesticide residues are associated with DOC
which might function as a shuttle for the distribution of pesticide residues. This
molecular association can be released into solution where it might be degraded
co-metabolically.
Overall, the results suggest that intermittent soil drying and rewetting alters the
disaggregation of soil aggregates, resulting in a release of entrapped organic carbon and
pesticide molecules.
Furthermore, analysis of the organic fractions obtained from the 14C pesticide residues
containing soil revealed that 14C residues were mainly associated with the humin
fraction.
The analysis of the organic fractions revealed that extractable residual 14C activity of
ETD was more associated with the fulvic acid fraction compared to the residual pesticide 14C
activity of MBT, being more associated with the humic acid fraction.
For 14C MBT residues, the distribution of the 14C residues in the organic fractions
remained rather equal throughout the water extraction cycles. This observation
can be supported by the non-mobile character of MBT in soil and its higher KOC
value of 247–587 compared to the rather mobile pesticide ETD with a KOC value
of 37.1–149. However, for both pesticides a decrease of residual 14C activity in
the humic and fulvic acid fractions throughout the water extractions cycles was
observed. This observation was more pronounced in the samples of the dry/wet setup. |
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