Geology Reference
In-Depth Information
A concentration of 10 ppb in air
¼
1.013
10
5
10
8
Pa
¼
1.013
10
3
Pa
C
octanol
¼
1
:
013
10
5
10
8
Pa
¼
1
:
013
10
3
Pa
¼
1
:
013
10
3
K
oa
¼
1
:
013
10
3
7
:
00
10
3
¼
7
:
09 gm
3
and
C
soil
¼
0
:
2
C
octanol
¼
0
:
2
7
:
09
¼
1
:
42 gm
3
In order to calculate the equilibrium partitioning of a substance within
the model world, a mass balance exercise is conducted. Thus, for a
system comprising simply air, water, and soil, the mass balance equation
would be
M
¼
V
1
C
1
þ
V
2
C
2
þ
V
3
C
3
¼
V
1
C
1
þ
V
2
C
1
K
21
þ
V
3
C
1
K
31
¼
C
1
ð
V
1
þ
V
2
K
21
þ
V
3
K
31
Þ
where M is the total mass of substance and V
i
and C
i
represent,
respectively the volumes and concentrations of each medium, i.
It may be seen that by rearranging this equation, the concentration C
1
in one of the media can be estimated from knowledge of the total mass
of compound in the system, the volume of each of the three media and
the equilibrium partition coefficients between them.
It may also be seen that if the various partition coefficients are known,
then concentrations in all three compartments, C
1
, C
2
,andC
3
can be
calculated and therefore the overall distribution of the chemical within the
environment inferred. For partitioning, for example, into soil, it is assumed
that the substance partitions solely into the organic carbon fraction of the
soil solids, and since this is a relatively small percentage of the total soil, the
mass fraction of organic matter has to be included in the calculation.
