Page 144 - Partition & Adsorption of Organic Contaminants in Environmental Systems

SORPTION FROM WATER SOLUTION 135

1985). As an approximation, we assume that log (K° om /K om) c H/2.203 in the
present analysis.
Comparison of the magnitude of -logS w V with that of log (K° om/K om) indi-
cates that -logS w V is the major determinant of logK om for the organic com-
pounds, which results in a highly linear correlation of logK om with logS w V as
shown in Figure 7.13. For the 12 compounds (mainly chlorinated benzenes and
PCBs) on Woodburn soil, the regression equations gives
logK om =- 0 .813 logS V - 0 .993 (7.12)
w
2
with r = 0.995, where the S w values (mol/L) for solid solutes are their esti-
mated supercooled liquid solubilities [see Eq. (3.9)]. Here one sees a good
correspondence between the correlation of logK om versus logS w V in Eq.
(7.12) and the correlation of logK ow versus logS w in Eq. (5.3) for substituted
aromatic solutes. The increased deviation between logK° om and logK om
relative to that between logK° ow and logK ow is ascribed to the increased incom-
patibility of these low-polarity solutes with relatively polar SOM over that
with the less-polar octanol. For more-polar solutes, the differences between
logK° om and logK om should be less because of their enhanced partition in SOM,
and the relation of logK om to logS w V (or a related property) may change
accordingly.
Since the variation of V among solutes is quite small compared to that of
S w, a linear relation should also exist between logK om and logS w, as has been
widely recognized (Chiou et al., 1979, 1983; Karickhoff et al., 1979; Kenaga and
Goring, 1980; Means et al., 1980; Briggs, 1981; Hassett et al., 1981; Karickhoff,
1984). Using the data in Table 7.4, one finds a correlation equation of
logK om =-0.729logS w + 0.001 (7.13)

2
with n = 12 and r = 0.996. Here the predominant effect of S w on K om is much
anticipated for the partition equilibria of organic solutes in a partially misci-
ble mixture of an organic phase and water, despite the fact that SOM is not
nearly as good a solvent for nonpolar solutes as normal organic solvents such
as octanol. For this reason, the logK om is largely linearly related to logK ow,
as illustrated for a wide variety of organic contaminants on various soils and
sediments, as stated earlier. From the data in Table 7.4 one finds that

logK om = 0.904logK ow - 0.779 (7.14)

2
with n = 12 and r = 0.989. For compounds with logK ow in the range 2 to 5, the
K om values are roughly one order of magnitude smaller than the correspon-
ding K ow values. If the sorption coefficient is expressed in terms of soil organic
carbon (K oc ), equivalent correlation equations may be established through
K oc 1.72K om . The conversion factor of 1.72 is derived with the assumption
that SOM is about 58% in carbon (Hamaker and Thompson, 1972). (Based
on the mean K oc of CT on soils and the relation of K oc to the organic matter