environmental fate

• Environmental fate


  Can be studied at different scales: soil aggregate, through soil profile, catchment scale (water) and long range transport (POPs)
• Up scaling environmental fate is very challenging
• Fate of organic contaminants after emission

  1. Distribution between different phases

  2. Transformation/degradation by chemical/biological reactions

  3. Transport within and between compartment(s)
• Environmental compartment

  Made of 3 phases: gas-liquid-solid
• Partitioning coefficient


  K1,2 = C1/C2, Solid to liquid. The higher the K1,2 coefficient, the more chemical accumulates in phase 1 relative to phase 2
• Partitioning constant


  Henry constant, Koa, Kow
• Octanol/water partition coefficient (Kow)

  Measures hydrophobicity or water hating. If compound goes into lipid phase or water, indicates where it will be found in the environment. Higher Kow means higher water hating and more likely to partition into solid phases
• Solubility in water


  Inverse relationship with Kow: more hydrophobic, less soluble
• Distribution coefficients to environmental solids are proportional to Kow, so high Kow means high bioconcentration factor
• Transformation


  All reactions in which chemical bonds are broken/formed, ideally up to complete mineralisation (e.g. CO2, CH4, H2O, SO4)
• Transformation processes


  Abiotic: no direct participation of organisms (chemical reactions, photolysis)

  Biotic: biologically mediated, rate generally much higher, only process for complete mineralisation

  Redox: mediated by microorganisms gaining energy from degradation

  No e- transfer (e.g. hydrolysis)
• Requirements for biodegradation


  • Existence of organisms with degradation potential
  • Presence of specific degrader(s)
  • Accessibility of target pollutants
  • Induction of appropriate degradative enzymes
  • Availability of appropriate e- acceptors/donors
  • Availability of nutrients
  • Adequate pH and buffering capacity
  • Adequate temperature
  • Absence of toxic or inhibitory substances
• DT50 (half-life)


  Time required for 50% of a substance to degrade, used as an example of degradation in soil
• POPs have a DT50 > 2 months
• Fate of chemicals in soils and surface water

  High Kow means sticking to sediment, high Henry's constant means volatilisation, soluble means travelling with water