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Figure 6.
Time-variation of TEs geochemical fractions concentrations in the soil profile - Reference
parcel R (T=0); PF-amended parcels P1 (T1 = 4 months); P2 (T2 = 11 months); and P3 (T3 = 15
months). F1-Exchangeable; F2-Acid Soluble; F3-Reducible; F4-Oxidizable; and F5-Residual
fraction.
Cd Speciation
When PG was amended, Cd solubilization was increased at the depth 0-20 cm (from 46
to 61%, respectively at reference and PG1 parcels) as Cd was found associated to the mobile
fractions (exchangeable and acid-soluble fraction F1 and F2) in the parcel PG1, 5 months
following PG amendment (Figure 5); this behavior was due to pH decrease (from 8.24 ± 0.13
to 7.73
± 0.08). This increase was in the detriment of Fe and Mn oxides (F3) (53 to 34% in R
and PG1, respectively). In addition, 12 months following PG amendment and after a period of
precipitations (winter season), Cd was related to the exchangeable fraction F1 at the depth 35-
55 cm. Cd transferred from acid soluble phase of PG (54%), was dissolved in soil profile, and
migrated to a depth of 55 cm, which explained the increment of 20% of Cd in the mobile
phase when comparing to PG1. The exchangeable fraction was predominated at the end of the
study in the PG3 (16 months following PG amendment) in soil profile
(
87, 90 and 77% in 0-
15 cm, 15-35 cm and 35-55 cm, respectively). In soils and sediments polluted with metal
wastes, the greatest percentage of the total Cd was
associated with the exchangeable fraction
(Kuo et al. 1983; Tessier et al. 1980).
On the other hand, a different behavior for Cd was observed in PF application (Figure 6).
Cd concentrations increased in the top layer (0-20 cm) in the mobile fractions (F2 and F1 in
parcels PF1 and PF2, respectively). Furthermore, Cd related to the oxidizable fraction (F4)
appeared in all depths of the soil profile of parcel PF1 (4 months following PF application)
and increased at depth 20-55 cm of parcel PF2 (11 months following PF application).
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