UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

cadmium, indicating that cadmium and zinc compete for the same group of binding sites
(Benjamin and Leckie, 1981).
Although organic matter may influence adsorption of cadmium by soils (John, 1971; Levi-Minzi et
al., 1976), this effect is probably due to the CEC of the organic material rather than to
complexation by organic ligands (Singh and Sekhon, 1977). In fact, removal of organic material
from soils does not markedly reduce cadmium adsorption and may enhance adsorption (Petruzelli
et al., 1978). Clay minerals with adsorbed humic acids (organo-clay complexes) do not adsorb
cadmium in excess of that expected for clay minerals alone (Levy and Francis, 1976).
5.2.6 Partition Coefficient, K d , Values
5.2.6.1 General Availability of K d Data
A total of 174 cadmium K d values were found in the literature and included in the data base used
to create the look-up tables. 1 The cadmium K d values as well as the ancillary experimental data
are presented in Appendix C. Data included in this table were from studies that reported K d
values (not percent adsorption or Langmuir constants) and were conducted in systems consisting
of natural soils (as opposed to pure mineral phases), low ionic strength (< 0.1 M), pH values
between 4 and 10, low humic material concentrations (