Geology Reference
In-Depth Information
air-water partitioning of a pesticide. Lindane is an organochlorine
insecticide that comprises of almost 100% g-hexachlorocyclohexane
(g-HCH). The chemical has been recently nominated as candidate
POP chemical and it is widely distributed in the global environment.
Indeed this chemical is routinely monitored in arctic air
29,30
and is
present in the polar environment largely through long-range atmos-
pheric transport. Let's assume that g-HCH has an air concentration
of 100 pg m
3
within an agricultural region during the summer, where
both air and surface water (lakes, rivers coastal seas) have a temper-
ature of 25
o
C. Using K
aw
we can estimate the water concentration
from the air concentration assuming equilibrium has been achieved.
In the Arctic, the air concentration of g-HCH is
B
10 pg m
3
(10-fold
lower), but the air and surface water temperatures in the high Arctic
during the summer are
B
1 1C. Again, the water concentration of
g-HCH can be estimated using K
aw
, but this time adjusted to 1 1C.
The surface water concentration in the temperate agricultural area is
calculated from the air concentrations as follows:
H for g-HCH has been measured as 0.24 Pa m
3
mol
1
at 298 K.
21
Whereby H
0
or K
aw
¼
H/RT (T is 25 1Cor
B
298 K)
Therefore, K
aw
¼
0.24/8.314
298
¼
9.69
10
5
or ln K
aw
¼
9.24
As K
aw
¼
C
a
/C
w
, then C
w
¼
C
a
/K
aw
¼
100/9.69
10
5
C
w
in the temperate agricultural region is 1.03
10
6
pg m
3
or
B
1000 ng m
3
or
B
1ngL
1
The water concentration in the Arctic is calculated in the same way
but using the C
a
for the Arctic. First, K
aw
has to be adjusted for 1 1C
(
B
274 K) using Equation 6.17, where:
lnK
aw
ð
274 K
Þ¼
lnK
aw
ð
298 K
Þ
DH
274
1
1
R
298
DH is 61400 J mol
1
determined from the slope, m, in Equation 6.16
by Sahsuvar et al.
21
Note that in this study, DH actually represented
the enthalpy of water to air volatilisation, rather than the enthalpy of
air to water dissolution, and we consider 61,400 as approximate only.
Therefore:
lnK
aw
ð
274 K
Þ¼
lnK
aw
ð
298 K
Þ
DH
R
274
1
1
298
The inverse of ln K
aw
11.4
¼
1.12
10
5
. Therefore, the surface
water concentration in the Arctic, attained through equilibrium par-
titioning with the air is
C
w
¼
C
a
/K
aw
¼
10 pg m
3
/1.12
10
5
¼
892,857 pg m
3
or
B
890 ng
m
3
or
E
lngL
1
