Agriculture Reference
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which was attributed to the interaction of P with Zn in soil (Grant and Bailey 1997;
McLaughlin et al. 1995). Cd availability in plants from PFs depends on many factors such as
soil texture, plant species, Cd concentration, and type of fertilizers used (Singh and Myhr
1997).
Trace Elements Transfer from Soil to Cichorium Intybus: Phosphogypsum
Accumulation ratio (element concentration in plant root to element concentration in soil)
and transfer coefficient (element concentration in aerial part/element concentration in root)
(Baker 1981; Kabata-Pendias and Pendias 2001; Madejon et al. 2002) were determined for
the different studied elements (Table 1) in order to provide a better understanding of the
relationship between TEs concentrations in soil and plants, and to investigate their potential
transfer into the food chain.
Cd showed a high accumulation ratio (3.2
‒
3.8) in all parcels with an increment of
approximately twenty five times (25x with relation to reference values (0.14). Previous
studies displayed that plants could accumulate high amounts of this element even when its
concentration in the soil was low (Ciura et al. 2005). However, in a balanced undisturbed soil,
Cd in the control plot must have been well retained by the soil particles compared with Cd
added with PG which seems to be more readily accessible to plants during its life cycle, and
transfer from fertilizer to soil solution, root and soil phase.
According to Ross criteria (Ross 1994), Cd concentration in roots was within the values
of contaminated plants (0.03- 3.8 mg kg
-1
).
Pb exhibited accumulation ratios greater than Zn in all parcels, with increments in parcels
P1 and P2 being approximately two times (2x higher than in control soil. This order disagrees
with previous studies showing Zn as the most and Pb the least readily accumulated TE in
vegetation (Chopin and Alloway 2007; Kabata-Pendias and Pendias 2001). This discrepancy
resulted from diversity of factors such as differences in TEs speciation and the consequent
variations in mobility and bioavailability, soil conditions, plants age and state of health, and
element concentrations (Batista et al. 2007; Kabata-Pendias and Pendias 2001; Ross 1994).
However, Pb and Zn concentrations (Figure 8) did not exceed the minimum levels of
contamination in plants reported by Ross (1994) (30 - 300 mg kg
-1
for Pb; 100-400 mg kg
-1
for Zn).
The accumulation ratio of Cu could be considered constant with time which probably is
related to the plants regulation of the uptake of this essential micronutrient. Copper
concentration (Figure 8) was not above the minimum values for plants contamination (20-100
mg kg
-1
) (Ross 1994).
As vegetation can only take up soluble TEs, these were absorbed by plants in mobile
forms (i.e., exchangeable, acid soluble). Chicory root exudates (i.e., H
+
, acetic acid, organic
acids, amino acid) could solubilize or mobilize TEs from the mineral and organic fractions in
soil (Carrillo-Gonzalez et al. 2006). Therefore, roots promoted mobilization and uptake of
exchangeable, acid soluble and oxidizable TEs (i.e., Pb in exchangeable fraction, Cu and Zn
in acid soluble and Zn in complexed form). According to Baker (1981), plants can be
classified according to their transfer coefficients as accumulators (TC > 1.5), indicators (TC
from 0.5 to 1.5), and excluders (TC < 0.1).
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