1 introduction to microbial degradation of xenobiotic compounds
TRANSCRIPT
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Introduction to microbial degradation of xenobiotic
compounds
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Photo degradation
Chemical degradation
MicrobialDegradation
Chemical compound
Leaching
Sorption
Fate of a chemical compound in the environment
Evaporation
Absorption
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The importance of microbiological degradation
Days
% herbicidestill left in the soil Sterilized soil
Non sterilized soil
From Helweg, 1988
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Who are involved in bio-degradation?
Fungi2-10 μm (diameter)
Bacteria0.5-1 μm
Protozoa3-100 μm
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Principle diagram for degradation of a xenobiotic compound
Xenobiotic compound
Microbial and chemicaldegradation
Metabolites
CO2
Micro-organisms
Humus
Salts
Water
Boundresidues
CO2
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Example of total mineralization of a xenobiotic compound
2,4-D is a herbicide
From Helweg, 1988
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Detoxication/Activation
An example of “activation” of a xenobiotic compound. One if the metabolites are far more persistent and toxicthan the original molecule
Presence of the insecticide aldrin and it´s main metaboliteDieldrin in soil:
From Alexander, 1999
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Environmental factors influencing microbial degradation of xenobiotic
compounds ?
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Biodegradation vs Chemical composition
• Water solubility?
• Sorption (Kd)?
• Molecule size?
• Aliphatic vs cyclic (aromatic)?
• Unsaturated (C=C ..) vs saturated?
• Cl, Br, I ?
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History – previous exposure
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Degradation of the herbicide MCPA in soil
Days
Concentrationof MCPA insoil water (mg/l)
1. addition 2. addition
From Helweg, 1988
Same substance – but what’s different?
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Variation in degradation rate caused by different soil types
Chemical compound
Days until 5% is mineralised
Topsoil Subsoil
(1 meter)
MCPA 11 100
TCA 16 300
2,4-D 9 100
Topsoil(approx 50 cm)
Subsoil
Typical soil profilein West Denmark:
sand, clayand organicmatter
mainly sand
OBS: nutrients (N & P) !!
(C/N/P : 100/10/1)
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Effect of temperature on the degradation rate
Temperature (°C) Days until 50%
is mineralized
23 29
8 120
3 245
From Helweg, 1988
Mineralization of the herbicidepropyzamid in soil at differenttemperatures:
Temperature variation over the year inDanish soil at different depths:
°C
Q10: 2 - 3
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Effect of water availability in top soil on the degradation rate
Water content (%) Days until 50% is mineralised
16 23
4 40
Degradation of the herbicide simazin in the same soil, at different water contents. From Walker 1978.
Normally: always enough water in the soil
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Electron acceptors…?
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Effect of O2 availability on the degradation
Topsoil
Subsoilunsaturated
Subsoilsaturated
Groundwater level
Level of microbial biomass: highO2 availability: high
Level of microbial biomass: lowerO2 availability: Primarily aerobic conditions
Level of microbial biomass: lowO2 availability: anaerobic conditions
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Aerobic >< Anaerobic degradation
• Generally, less activity is seen under anaerobic conditions
• Most compounds are degraded fastest under aerobic conditions. Exceptions are some chlorinated solvents, benzenes or alifatic componds