Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 377

9.3.5 Translocation from Roots into Stem and Leaves

Translocation of contaminants from roots into stems in the xylem is often described
by the transpiration stream concentration factor TSCF (Russell and Shorrocks
1959 ):

Concentration in xylem sap (mg mL − 1 )
Concentration in solution (mg mL − 1 )

TSCF = (9.12)

From experimental data, the concentration in xylem sap is found from the mass
of contaminant in shoots divided by the volume of transpired water. Briggs et al.
( 1982 ) fitted a Gaussian optimum curve to their data:

e − (log K OW − 1.78) 2

/

2.44

17, r 2 TSCF = 0.784 × ( n = = 0.73) (9.13)

Later experiments by other research groups yielded similar results (Burken and
Schnoor 1998 ; Hsu et al. 1990 ; Sicbaldi et al. 1997 ). However, recent research has
shown that these regressions might not be valid for the polar contaminants (log K OW
< 1) and a sigmoidal relationship between TSCF and log K OW has been established
(Dettenmaier et al. 2009 ):

11

118, r 2 TSCF = ( n = = 0.68) (9.14)

2.6 log K OW

11 −

9.4 Mechanistic Models for Estimating Uptake of Contaminants
into Plants

The first author met D. Mackay at his talk at the University of Bayreuth in 1986,
where he encouraged his audience to develop mechanistic models for the plant
uptake of organic contaminants. So we did (Trapp et al. 1990 ). D. Mackay and
his team also developed some of the early models for this purpose, formulated with
the fugacity approach (Paterson et al. 1994 ). These models were later simplified
by Hung and Mackay ( 1997 ) to three mass balance equations and solved numeri-
cally. At about the same time, the numerical model PlantX was developed (Trapp
et al. 1994 ). Later, crop-specific models were derived, i.e. specific models for roots
(Trapp 2002 ), potatoes (Trapp et al. 2007 a), leaves (Trapp and Matthies 1995 ) and
fruits (Trapp 2007 ). These models are all based on the same physico-chemical prin-
ciples and describe the same basic processes, such as advective uptake into plants,
diffusive uptake, chemical equilibrium, transport in xylem and phloem, dilution by
growth, and particle deposition from soil and air. The actually occurring processes
and their parameterization depend on the type of crop (Fig. 9.4 ). Plant models were
also developed by other groups, for example a partition-limited model by Chiou
et al. ( 2001 ) and the models for pesticide uptake by Fujisawa et al. ( 2002a , b ). For