Geology Reference
In-Depth Information
Figure 3 Schematic diagram of the gas-stripping apparatus used to measure temperature-
dependent Henry's Law constants (H) for semi-volatile organic compounds
(SVOCs)
From Bamford et al.
20
courtesy of SETAC press
higher temperatures), and accounting for the loss of water through
evaporation. Furthermore, the change in water volume in the reactor
vessel when extracting aliquots for chemical analysis should also be taken
into account
21
and efforts directed at shielding the apparatus from
laboratory light when determining H for light-sensitive chemicals.
6.4.1.3 Octanol-Air Partitioning Coefficient (K
oa
). Partitioning of a
chemical between some organic phase and air is often described using
K
oa
. Examples of terrestrial organic phases include organic carbon in soil,
the waxy cuticle and lipid portion of vegetation and the organic film that
coats atmospheric particle matter and partitioning between these phases
and air for a number of chemical groups have been successfully described
using K
oa
.
22-24
Laboratory-based measurements of temperature-dependent
K
oa
values have been derived for a number of semi-volatile chemical
groups, including PCBs
25,26
PAHs,
27
polychlorinated naphthalenes
(PCNs)
27
and organochlorine pesticides.
28
K
oa
can be described as the
ratio of the chemical (solute) concentration in octanol to the concentration
in air at equilibrium, represented as
K
oa
¼
C
o
C
a
ð
6
:
11
Þ
