Geoscience Reference
In-Depth Information
mol
−1
] and
S
is the solubility,
in units of ppm, for organic compounds that are liquid in their pure state at 25
where MW is the molecular weight of the pollutant [g
⋅
°
C.
For organic chemicals that are solids in their pure state at 25
°
C:
log
S
=
−
1.08 log
K
ow
+
3.70
+
log MW - (
∆
S
f
/1360) (MP - 25)
(4.67)
where MP is the melting point of the pollutant [
°
C] and
∆
S
f
the entropy of fusion
of the pollutant [cal.mol
−1
deg
−1
].
Karickhoff et al.
146
have developed empirical expressions relating environmental
equilibrium partition coefficients to standard laboratory measurements, resulting in
fairly reliable estimations. The correlation is
⋅
K
ps()
=
f
ocs
⋅
K
oc
(4.68)
K
pB
=
1.0
K
oc
(4.69)
where
K
oc
=
organic carbon partition coefficient [l
w
/kg
oc
]
f
ocs
=
organic carbon fraction of the sediment
1.0
=
organic carbon fraction of DOC
Correlation of
K
oc
with the octanol/water partition coefficient of the chemical
(and through that to solubility) has yielded successful predictive tools for incorpo-
rating the hydrophobicity of a chemical in an estimate of its partitioning. If no log
K
oc
values are available, they can be generated internally using the following corre-
lation with the octanol/water partition coefficient
K
ow
(l
w
/
l
oct
):
log
K
oc
=
a
o
+
a
1
log
K
ow
(4.70)
where
a
o
and
a
1
are typically considered to be log 0.6 and 1.0, respectively. Once
the value of
K
oc
is determined, the computation of partition coefficient proceeds as
per Equation 4.68 and Equation 4.69.
The value of the partition coefficient is also dependent on other factors in addition
to the fraction of organic carbon of the sorbing particles. Of these, perhaps the most
potentially significant and the most controversial is the effect of particle concentra-
tion. Based on empirical evidence, the partition coefficient is inversely related to the
solids concentration. The equation defining partition coefficient is
K
MK
ps
0
K
=
(4.71)
ps
1
+
/
U
s
s
0
x
where
K
ps
0
=
limiting partition coefficient with no particle interaction (
f
ocs
K
oc
for neutral
organic chemicals)
M
s
=
solids concentration [kg l
−1
]
U
x
=
ratio of adsorption to particle-induced desorption rate
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