Environmental Engineering Reference
In-Depth Information
1000
10000
1.2
1000
root
shoot
Yie
ld
1.0
100
1000
0.8
100
10
100
0.6
0.4
10
10
1
0.2
1
0.1
1
0.0
0.1
1
10
100 1000
0.1
1
10
100 1000
0.01 0.1
1
10
100 1000
Cd (µg/l)
Cd (µg/l)
Zn (µg/l)
Fig. 8.5
Typical relationships between metal concentrations in the exposure solution and concen-
trations in shoot and root tissue for (
a
) a non-shoot cadmium excluder and (
b
) a shoot cadmium
excluder (graphs based on results from Florijn and Van Beusichem,
1993b
), and (
c
) for uptake of
the essential element Zn. Panel (
c
) also shows the yield response (based on results of Degryse et al.
2006b
)
('non-shoot excluder'; Florijn and Van Beusichem
1993a
). In contrast, 'excluders'
species retain most of the metals in the root, though the ability to retain the element
in the root may strongly diminish beyond a threshold concentration (Fig.
8.5b
).
Figure
8.5c
illustrates the partitioning of essential elements such as zinc. In the
lower concentration range, the shoot concentrations are strongly regulated, and do
not fall beneath a critical concentration. At low supply, the growth rate rather than
the plant concentration decreases with decreasing metal supply.
Since the translocation to the shoot depends strongly on the genotype and exter-
nal conditions - such as the availability of the metal - the translocation factor
(usually defined as the ratio of shoot to root concentration) is not constant for a
given element and plant species (Fig.
8.6
). As a result, BCF values for vegetables
expressed between shoot and soil reflect the combined impact of bioavailability of
the contaminant in soil and the effect of soil conditions on the internal translo-
cation. Table
8.5
gives a non-exhaustive overview of metal distribution in plants.
This table illustrates the dependence of translocation on the metal, plant species and
R/S 1
R/S 10
1000
Zn
R/S 100
Cu
100
Fig. 8.6
Typical
relationships between
concentration in shoots and in
roots for a non-shoot
cadmium excluder, a shoot
cadmium excluder, and for
the essential elements zinc
and copper (
full lines
)The
dotted lines
give the relations
for the given ratios of root to
shoot concentration (R/S)
10
Cd non-
excluder
1
Cd excluder
0.1
0.1
100
Root concentration (mg/kg DW)
1
10
1000
10000
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