An Introduction to Environmental Chemistry

The Chemistry of Continental Solids 123

pressure of water can be used as a ‘yardstick’
for comparison. At 25°C water has a vapour
pressure of 3.17 kPa. This means that liquid
water is at equilibrium with water vapour
at 25°C if the pressure is 3.17 kPa. As
temperature changes so too does the
equilibrium vapour pressure. At 100°C the
vapour pressure of water is 101.3 kPa, equal

to normal atmospheric pressure. At this

temperature the vapour pressure of water

molecules causes rapid formation of bubbles

(boiling). Boiling occurs when the vapour

pressure of the molecules in water equals (or

exceeds) local atmospheric pressure and

water vapour escapes to the atmosphere as

steam.

Fig. 2Schematic diagram illustrating experimental equilibration of compound X between water and octanol
and determination of the partition coefficient (KOW).

[octanol]

[water]

[12]

[3]

Octanol

(12 Xs)

X

X

X

X

X

X

X

X

X

X X X X X X

Water

(3 Xs)

KOW =

log KOW = log 4

=

= 0.60

= 4

X = Compound of interest

After equilibration

Deposition

Volatilization

S O I L B E D R O C K

Parent organic

contaminant

Leaching

Groundwater

Water table

Biodegradation

Abiotic degradation Metabolite

Volatilization Uptake in

plants

CO 2

CO 2

Fig. 4.27Schematic diagram showing the fate of organic contaminants in soils.