Sorption Isotherms - Transport and Fate of Chemicals in Soils: Principles and Applications - page 17

and an estimated b value for any one of them could be estimated from soil
pH data using the regression equation for curve A in Figure 1.2. For many
purposes such an estimate would be useful, at least as a first approximation,
in describing the retention characteristics of a soil.

Curve A: b = 1.24 − 0.0831 pH ( r = 0.83) (1.17)

Curve B: b = −0.0846 + 0.116 pH ( r = 0.98) (1.18)

Sauvé, Hendershot, and Allen (2000) analyzed more than 70 studies of
various origins collected from the literature in an effort to correlate the
distribution coefficient K d with soil properties for five heavy metals, cad-
mium, copper, lead, nickel, and zinc. Specifically, the relationships between
the reported K d values were explored relative to variations in soil solution
pH, soil organic carbon (SOC), and total metal retained by the soil. Sauvé,
Hendershot, and Allen (2000) proposed two models to predict K d values for
several heavy metals based on chemical properties of the soil. These mod-
els were developed based on regression analysis of extensive K d values pub-
lished in the literature for a wide range of soils. The proposed models are

Model I log( K d ) = A + B pH (1.19)

Model II log( K d ) = A + B (pH) + C (SOC) (1.20)

where A, B, and C are fitting parameters. Sauvé, Hendershot, and Allen
(2000) proposed a third model, which incorporated retained heavy metals by
the soil prior to K d measurements. With the exception of contaminated sites,
the amounts of heavy metals retained are often extremely small, however. In
Figure 1.7, plots of K d values on a log scale versus soil pH are presented for all
five elements based on a compilation by Sauvé, Hendershot, and Allen (2000).
In 2013, Selim and coworkers (unpublished data) studied the retention of
five heavy elements by 10 soils from 10 soil orders to determine the effects
of element and soil properties on the magnitude of the Freundlich param-
eters K f and b . They measured adsorption after one and seven days, as well as
desorption following adsorption (based on successive dilution method; see
Chapter 2). The metals investigated were cadmium, copper, lead, nickel, and
zinc. These five metals are the same considered by Sauvé, Hendershot, and
Allen (2000) in their regression study. The names, taxonomic classifications,
and selected properties of the 10 soils used in this study are listed in Table 1.4.
The Ap horizons of all soils were used in this retention study. The only excep-
tion is that the sandy candor subsurface sample was sampled at a depth of
90 cm. Physical and chemical properties of the 10 soils were also quantified.
A comparison of K d parameter values for all 10 soils and five heavy metals is
provided in Table 1.5 for sorption at one and seven days. Freundlich model K f
and b parameter values for all 10 soils and five heavy metals are provided in