An Introduction to Environmental Chemistry

the particles: (i) a rapidly desorbable fraction; (ii) a slowly desorbable fraction;

(iii) a very slowly desorbable fraction; and (iv) non-extractable (bound) residues.

The non-extractable residue is the fraction of an organic compound (or its

metabolites) that persists in the matrix following an extraction process that has

124 Chapter Four

T O T T O T

Organic contaminant

Soil minerals Pore water Soil organic matter

H 2 O

Intraparticle diffusion Adsorption

Desorption

Biodegradation

Desorption

Entrapment

in humic

complexes

Adsorption

Fig. 4.28Interaction between organic contaminants and soil components. Of the inorganic

components, clay minerals have the most potential to react with organic contaminants. T,

tetrahedral sheet; O, octahedral sheet (see Fig. 4.12).

100

90

80

70

60

50

40

30

20

10

0

Time

Loss

Bioavailable

Non-bioavailable

Decreasing

bioavailable

fraction with

time

Increasing

non-bioavailable

fraction with

time

% component

Subsequent phase

of slow loss

Initial phase of rapid loss

Fig. 4.29Bioavailability of organic contaminants in soils as a function of time.