Page 137 - Partition & Adsorption of Organic Contaminants in Environmental Systems

128 CONTAMINANT SORPTION TO SOILS AND NATURAL SOLIDS

TABLE 7.3. Continued
SA
2
No. Source (m /g) % OC K oc,CT K oc, DCB
36. Niyanghe River, 3.12 0.54 93 487
Gongbujiangda Co.,
Tibet, China

Suspended Solids
1. Mississippi River, Thebes, 1.82 60 296
Illinois
2. Mississippi River, St. Louis, 1.78 58 283
Missouri
3. Illinois River, Hardin, Illinois 2.60 89 423
4. Missouri River, Herman, 2.87 49 231
Missouri
5. Yellow River, Zhengzhou, 0.38 63 300
Henan, China
Source: Data from Kile et al. (1995).

of CT and DCB on representative soils and bed sediments are presented in
Figures 7.8 and 7.9. The virtual linearity of the isotherms is typical of the solute
partition in SOM, as expected. With the reported uncertainty of K oc values
being about ±8% and that of the organic-carbon mass fraction in soil/
sediment (f oc ) being ±5%, the observed differences between soil K oc values (or
between sediment K oc values) for both CT and DCB are relatively small. The
mean K oc value for CT on 32 normal soils is 60 (SD =±7) and the mean K oc
value for DCB is 290 (SD =±42). The K oc values for both CT and DCB on 36
normal bed sediments are generally higher and show about the same varia-
tion as the K oc values on soils. The mean K oc value on bed sediments for CT
is 102 (SD =±11) and for DCB is 502 (SD =±66); they are greater by a factor
of 1.7 than the mean K oc values for CT and DCB on soils. This difference
is more than the standard deviation (SD) of the means and is illustrated
graphically in Figure 7.10 for CT and in Figure 7.11 for DCB. The finding
that the K oc values for DCB are a factor of 4 to 6 greater than respective K oc
values for CT on all soils and sediments is essentially what Eq. (3.15) would
predict, based on the different water solubilities of CT (800mg/L) and DCB
(154mg/L) and the comparable solubilities of low-polarity liquids in SOM
(Rutherford et al., 1992), as shown in Table 7.2.
The high degree of invariance of the CT and DCB K oc values between most
soils or between most bed sediments is phenomenal. The normalized sorption
coefficients (K oc values) for both solutes show little dependence on soil or sed-
iment OC contents (e.g., 0.16 to 6.09% for soils) and on (dry) soil or sediment
2
surface areas (e.g.,1.07 to 54.0m /g for soils),as shown in Table 7.3.This finding
reveals the similarity in SOM polarity/composition between soils and between