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Soil:Organic Interactions

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Guest lecture given to the University of Greenwich MSc in Environmental Science class on 9 February 2004.

N.B. Contact details are out of date.

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Soil:Organic Interactions

  1. 1. Soil:Organic interactions Dr. Stephen Johnson s.j.johnson@gre.ac.uk
  2. 2. n-Alkanes H2 H2 H2 CH4 Methane C C C CH3 H3C C C C Octane H2 H2 H2 H3C CH3 Ethane H2 H2 H2 H2 C C C C H2 H3C C C C CH3 Nonane Propane H2 H2 H2 C H3C CH3 H2 H2 H2 H2 H2 C CH3 C C C C CH3 Decane H3C C Butane H3C C C C C H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 C C C C C C C Undecane H3C C CH3 Pentane H3C C C C C CH3 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 C C CH3 C C C C C CH3 H3C C C Hexane H3C C C C C C Dodecane H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 H2 C C C C C C Tridecane C C C Heptane H3C C C C C C CH3H3C C C CH3 H2 H2 H2 H2 H2 H2 H2
  3. 3. Aromatics EPA Priority PAHs Naphthalene 9H-Fluorene Acenaphthylene Acenaphthene Phenanthrene Anthracene Fluoranthene PyreneBenzene Toluene Ethyl-benzene Benzo[a]anthracene Benzo[e]acephenanthrylene Chrysene = Benzo[b]fluoranthene o-Xylene m-Xylene Benzo[k]fluoranthene Benzo[def]chrysene = Benzo[a]pyrene p-Xylene Dibenzo[a,h]anthracene Benzo[ghi]perylene Indeno[123cd]pyrene
  4. 4. Polar molecules O O S O O O O S O O Sulphuric acid mono-[4-(1-ethyl-decyl)-phenyl] ester Linear alkylbenzene sulphonateSulfuric acid monododecyl esterSodium dodecyl sulphateSodium lauryl sulphate
  5. 5. Halogenated compounds Cl CH3 Cl CH2 Cl Cl Cl 1,1,1-Trichloroethane 1,1-Dichloroethene Cl H Cl C Cl Cl Cl Cl Cl 1,1,2-Trichloroethene 1,1,2,2-Tetrachloroethene
  6. 6. Pesticides H H H O H O H H P S H CH3 H SO O N H H O O H H H H O H H O H H H MalathionMethyl-carbamic acid naphthalen-1-yl esterSevin(R)
  7. 7. Contaminant loss in soil 12Contaminant concentration 10 8 A 6 B C 4 2 ? 0 0 2 4 6 8 10 Time
  8. 8. Partitioning AirAqueous Sorbed to organicsolution matter and clays NAPL Bioaccumulation etc.
  9. 9. Partitioning• Lipophilicity/hydrophobicity• Air:water partitioning• Solubility• Ionising potential
  10. 10. Lipophilicity/hydrophobicity• Octanol-water partition coefficient (Kow) is a measure of the equilibrium concentration of a compound between octanol and water that indicates the potential for partitioning into soil organic matter (i.e., a high Kow indicates a compound which will preferentially partition into soil organic matter rather than water)• Kow is inversely related to the solubility of a compound in water.• Log Kow is used in models to estimate plant and soil invertebrate bioaccumulation factors• Sorption to soil – Log Koc = (0.52 x Log Kow + 0.62) x 1.72• Uptake by plants – Log (Root concentration factor – 0.82) = 0.77 x log Kow -1.52• Bioconcentration factor (earthworms) – Log BCF = 0.48 log Kow + 1.04
  11. 11. Soluble pollutant Vadose Zone Water table Saturated Zone Bedrock
  12. 12. LNAPL plume Vadose Zone Water table Saturated Zone Bedrock
  13. 13. DNAPL plume Vadose Zone Water table Saturated Zone Bedrock
  14. 14. pKa• pH at which 50% is ionised• Soil usually has a net –ve charge• Low pKa → ↑ sorption• High pKa → ↓ sorption• http://www.chem.wisc.edu/areas/reich/pka table/
  15. 15. SorptionFrom http://www.ualberta.ca/~gray/Projects/Bioreactors.htm
  16. 16. MicroorganismsFrom http://cse.naro.affrc.go.jp/tomoki/bdcontents/microorganisms-e.html
  17. 17. Air/water partitioning• Henry’s Law• Describes partitioning between air and aqueous solution• p = K c c – p is the partial pressure of the gas – c is its molar concentration – Kc is the Henrys law constant on the molar concentration scale.• Accurate when concentrations and partial pressures are reasonably low.
  18. 18. “Aging” 100 90Contaminant concentration 80 70 Degradable 60 50 40 Readily available 30 20 Recalcitrant 10 Non-extractable 0 0 2 4 6 8 10 Time
  19. 19. Summary• Hydrophobic effects depend on solubility and log Kow• Electrostatic effects (e.g. sorption) depend on pKa• Volatilisation depends on Henry’s Law constant• All these factor influence “Bioavailability”

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