Soil:Organic interactions

Dr. Stephen Johnson

s.j.johnson@gre.ac.uk

n-Alkanes

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3 Dodecane

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

Tridecane

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

Undecane

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3 Decane

CH4Methane

CH3 CH3 Ethane

CH3

CH2

CH3

Propane

CH3

CH2

CH2

CH3 Butane

CH3

CH2

CH2

CH2

CH3Pentane

CH3

CH2

CH2

CH2

CH2

CH3Hexane

CH3

CH2

CH2

CH2

CH2

CH2

CH3Heptane

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH3 Octane

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3 Nonane

AromaticsEPA Priority PAHs

Naphthalene Acenaphthylene Acenaphthene

Phenanthrene Anthracene Fluoranthene Pyrene

Benzo[a]anthracene Chrysene

Benzo[k]fluoranthene Benzo[def]chrysene

= Benzo[a]pyrene Dibenzo[a,h]anthracene

Benzo[ghi]perylene Indeno[123cd]pyrene

Benzo[e]acephenanthrylene

= Benzo[b]fluoranthene

9H-Fluorene

Benzene Toluene Ethyl-benzene

o-Xylene m-Xylene

p-Xylene

Polar molecules

O

S

O

OO

Sulphuric acid mono-[4-(1-ethyl-decyl)-phenyl] esterLinear alkylbenzene sulphonate

O

S

O

OO

Sulfuric acid monododecyl esterSodium dodecyl sulphateSodium lauryl sulphate

Halogenated compounds

Cl

Cl

Cl

Cl

CH2Cl

Cl

CH

ClCl

Cl

CH3Cl

ClCl

1,1,2,2-Tetrachloroethene

1,1-Dichloroethene

1,1,2-Trichloroethene

1,1,1-Trichloroethane

Pesticides

O

PS

O

O

S

O

O

O

H

H

H

H

HH

H

H

HH

H

H

HH

H

H

H

H

H

Malathion

O

O

NCH3

Methyl-carbamic acid naphthalen-1-yl esterSevin(R)

0

2

4

6

8

10

12

0 2 4 6 8 10

Time

Co

nta

min

ant

con

cen

trat

ion

A

B

C

Contaminant loss in soil

?

Partitioning

Air

Sorbed to organicmatter and clays

Bioaccumulation etc.NAPL

Aqueoussolution

Partitioning

• Lipophilicity/hydrophobicity• Air:water partitioning• Solubility• Ionising potential

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

Soluble pollutant

Vadose Zone

Saturated Zone

Bedrock

Water table

LNAPL plume

Vadose Zone

Saturated Zone

Bedrock

Water table

DNAPL plume

Vadose Zone

Saturated Zone

Bedrock

Water table

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/pkatable/

Sorption

From http://www.ualberta.ca/~gray/Projects/Bioreactors.htm

Microorganisms

From http://cse.naro.affrc.go.jp/tomoki/bdcontents/microorganisms-e.html

Air/water partitioning

• Henry’s Law• Describes partitioning between air and aqueous

solution

• p = K'cc – p is the partial pressure of the gas– c is its molar concentration– K'c is the Henry's law constant on the molar

concentration scale.• Accurate when concentrations and partial

pressures are reasonably low.

“Aging”

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10

Time

Co

nta

min

an

t co

ncen

trati

on

Degradable

Readily available

Recalcitrant

Non-extractable

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”