Environmental Engineering Reference
In-Depth Information
such as the effect of H
+
and Zn
2+
on Cd
2+
uptake by plants, similar to BLMs
(Ingwersen and Streck
2006
).
8.5.1.6 Barber-Cushman Mechanistic Model
A commonly-used model to predict the uptake of nutrients by plants is the
Barber-
Cushman model
(Barber
1995
). This model has also been used to describe the uptake
of heavy metals, including uptake of zinc by rice (Adhikari and Rattan
2000
), cad-
mium by maize and
Thlaspi
(Sterckeman et al.
2004
) and zinc by
Thlaspi
(Whiting
et al.
2003
). The Barber-Cushman model includes plant and soil parameters, such
as root geometry, growth and kinetic parameters for the uptake of ions, parame-
ters which can only be determined in detailed, small scale experiments. In general,
application of this kind of model helps to identify which factors determine metal
uptake by plants from a research perspective, but is less useful for generic predictive
modelling.
8.5.2 Application of Models
In most Risk Assessment studies, soil-plant transfer models have been used. Also
the physiological model of Ingwersen and Streck (
2006
) has been applied in a small
region. Human exposure due to vegetable consumption has been described in Elert
et al. (
Chapter 11
of this topic). Soil-plant transfer models have been used in:
•
large-scale Risk Assessment on the basis of national soil data (Brus and Jansen
2004
;Brusetal.
2002
; De Vries et al.
2008
);
•
derivation of critical soil concentrations (Brus et al.
2005
; De Vries et al.
2007
)
on the basis of limit values for crops and fodder;
•
local and regional Risk Assessment on the basis of standard soil analysis in CLEA
or CSOIL (Römkens et al.
2005
); and
•
local and regional Risk Assessment on the basis of soil analysis and soil maps
(Hough et al.
2004
).
Soil-to-plant transfer models for metals can be applied in Risk Assessment stud-
ies on a regional and local scale, either as such or in combination with additional
sampling of soil and vegetables. However, parameters of current models very much
depend on soil and plant data on which they are based which renders most models
suitable for local applications only. The applicability of generic soil-to-plant transfer
models to predict heavy metal contents in local circumstances should be checked.
Ideally the models are verified with measurements on soil and plants. A practical
use of the models in Risk Assessment of vegetable gardens is, for example, to cal-
ibrate the models for the crops which have the highest contribution to metal intake
by humans (e.g. potato, leafy vegetables) and to use generic models for all other
crops. In the next chapters it will be shown that the use of the model also depends
on the questions asked.
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