Kein Folientitel

1
Photodegradation of humic derived dissolved
organic matter Bleaching, production of
carboxylic acids, and influence of metal ions
Thomas Brinkmann, Philip Hörsch, Daniel
Sartorius, Fritz H. Frimmel
hn
DOM
dom CO2 RCO2H
µ-biology
CO2
2
Lake Hohloh water HO18b
pH ?(DOC) a254 nm a436 nm SUVA254 nm SUVA436
nm ? ?(NO3-) ?(SO42-) ?(Fe) ?(Cu)
4.3 (T 20 C) 20.6 ? 0.5 mg/L 111 m-1 7.55
m-1 5.4 L/(m mg) 0.37 L/(m mg) 31 µS/cm (T 19
C) 1.41 ? 0.01 mg/L 2.5 ? 0.1 mg/L 0.35 ? 0.03
mg/L (6.2 µmol/L) 16 ? 1 µg/L (0.25 µmol/L)
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Irradiation experiments
atmospheric attenuation filter
optical filter plate WG 295
xenon-lamp
cooling bath
samples
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Photon flux density of natural and simulated
sunlight
Frank and Klöpffer 1988, Schindelin 1998
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Photon flux density of natural and simulated UV
sunlight
Frank and Klöpffer 1988, Schindelin 1998
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Mineralization
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Photobleaching
?0(DOC) 18.7 mg/L, t 24 h
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Photobleaching
?0(DOC) 10.2 mg/L, pH0 4.0
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Size-exclusion chromatography
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Chromatographable fraction of DOC
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Size-exclusion chromatography
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Bioavailability
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Carboxylic acids
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Carboxylic acids
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Conclusion

• Increasing release of carboxylic acids from DOM
  with absorbed light energy, but
• Evidence for simultaneous degradation in the
  case of
• All these acids have a-C-O next to the
  carboxylic acid group
• Chelating properties

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Photocatalytic iron redox cycle
Voelker et al. 1997
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Influence of iron on photobleaching
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Suppression of iron photocatalysis by
desferriferrioxamine
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Influence of dissolved iron on photoformation of
carboxylic acids
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Influence of dissolved copper on photobleaching
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Influence of dissolved copper on photoformation
of carboxylic acids
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Summary

• Bleaching and mineralization of DOM is pH
  dependent
• Wavelengths of maximum bleaching and absorbance
  correspond
• Evidence for formation of more hydrophobic
  moieties
• Small aliphatic carboxylic acids are important
  photoproducts of DOM
• Simulated solar UV-light increased
  bioavailability of humic DOM
• - Carboxylic acids are important constituents of
  the biologically labile fraction
• Increasing concentrations of acids with
  increasing amounts of absorbed light
• Evidence for simultaneous photolysis of oxalic,
  pyruvic, and lactic acid presumably by iron
  catalysis
• Dissolved iron acts as photocatalyst for the
  degradation of DOM and the release of carboxylic
  acids
• Dissolved copper inhibits degradation of DOM and
  formation of carboxylic acids, but promotes
  oxalic acid production
• No influence of nitrate in highly colored waters

23
Many thanks to
DFG and DVGW for sponsoring Gabi Kolliopoulos
and Ulrich Reichert for performing the
SEC Reinhard Sembritzki for measuring metal
concentrations
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Effect of pH
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Size-exclusion chromatography
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Ion chromatogram before and after irradiation
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Electropherogram before and after irradiation
HO18b irradiated HO18b
Chloride
Sulfate
Formic acid
Malonic acid
Acetic acid
Pyruvic acid
Succinic acid
Lactic acid
relative absorbance
Oxalic acid
7.5
3.5
4
4.5
5
5.5
6
6.5
7
migration time in min
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Size-exclusion chromatography
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Influence of dissolved iron
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Desferriferrioxamine mesylate
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Influence of dissolved copper on mineralization
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Influence of dissolved copper on photoformation
of carboxylic acids
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Influence of nitrate
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Photolysis of nitrate?