INORGANIC AND ORGANIC SOIL AMENDMENTS USED FOR THE IMMOBILIZATION OF CADMIUM IN CONTAMINATED SOILS - Management of Hazardous Residues Containing Cd - page 112

55% of Cd total content. These results are at variance with some other
published papers where the application of compost significantly reduced the
concentration of EXCH-Cd in contaminated soils (Castaldi et al, 2005; Lin,
Zhou 2009; Tapia et al, 2010). Conversely, the application of L or C3+L
significantly reduced the concentrations of EXCH-Cd compared to control,
revealing that there was a net movement of Cd towards other soil fractions
following the addition of this amendment. These results are similar to
observations made by others for EXCH-Cd in the presence of lime (Brallier et
al. 1996; Fernandes et al. 1999; Hong et al. 2007, 2009).
Among soil factors controlling the adsorption of Cd, pH is probably the
most important (Christensenn, 1984). It has often been observed that the
adsorption of Cd 2+ increased with increasing pH, resulting in low Cd
phytoavailability (Naidu et al., 1994; Bolan et al., 1999; Hong et al. 2007).
The effect of pH is related to its great influence on the charge and structure of
the adsorbing surfaces and on the ionic composition of the soil solution
(Garcia-Miragaya and Page, 1978; Abd-Elfattah and Wada, 1981). An increase
in pH increases soil net negative charge, which is attributed to the dissociation
of H + from weakly acidic functional groups of organic matter or from some
clay minerals (Curtin et al. 1996).

Table 2. pH in the contaminated soils as a result of the addition
of amendments: SC: control, Ci: soil amended with compost i; L: soil
amended with lime. For each date, different letters indicate significant
differences according to Tuckey's test at 5% probability level (n = 3)

day 14 day 28 day 42

treatment pH

CS 5,72 ± 0,05 a 5,54 ± 0,01 a 5,54 ± 0,13 a

C1 5,66 ± 0,07 a 5,55 ± 0,10 a 5,47 ± 0,14 a

C2 5,83 ± 0,05 a 5,66 ± 0,06 a 5,48 ± 0,10 a

C3 6,00 ± 0,04 a 5,62 ± 0,13 a 5,54 ± 0,01 a

C3+L 7,75 ± 0,03 b 7,72 ± 0,13 b 7,74 ± 0,12 b

L 7,93 ± 0,01 b 7,98 ± 0,09 b 7,95 ± 0,31 b

Application of liming materials significantly increased soil pH compared
to the other treatments (Table 2). The increase in pH by lime can be explained
by the release of hydroxyl ion after hydrolysis of calcium carbonate. This
increase in pH resulted in enhanced Cd adsorption , as reported by other