Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 380

where A L is leaf area (m 2 ), K LA is the partition coefficient between leaves and air
(L kg − 1 ), C A is the total concentration in air (mg m − 3 ) and f P (

) is the fraction
of the total concentration in air that is adsorbed on particles. Uptake from air can
either be by diffusive exchange in the gas phase with conductance g L (m d − 1 ), or
by deposition of particles on the surface of the leaves ( A L /2) with velocity v dep
(m d − 1 ). The concentration in leaves is as follows:

−

dC L
dt

Q
M L ×

A L × g A L × v dep

=

K RW ×

C R + × (1 − f P ) × C A + × f P × C A

M L 2 × M L

1000 Lm − 3
K LA ×

A L × g L ×

− × C L − k L × C L

M L

(9.20)
where k L (d − 1 ) again is the first-order rate that includes growth dilution and biotic
and abiotic (photolysis) degradation processes. The first term of the equation quan-
tifies translocation from roots to leaves and replaces the TSCF in earlier model
versions (Trapp and Matthies 1995 ). The advantages of this new formulation are
as follows:

• There is a relation between concentrations in roots and in leaves. This allows, for

example, calculation of the fate of metabolites formed in roots.

• The TSCF is related to plant physiological parameters, such as transpiration Q ,

growth rate k and partitioning between root tissue and xylem, K RW (Eq. 9.10 ).

The calculated concentration ratio between the xylem and the external solution is
close to the calculated concentration resulting from the empirical TSCF -regression
by Dettenmaier et al. ( 2009 ) for all contaminants, and to the TSCF -regressions fol-
lowing a Gaussian curve for contaminants with log K OW > 2 (Trapp 2007 ). Trapp
( 2007 ) speculates, based on this equation, that plants growing in soil outdoors would
have a different TSCF -curve than plants grown in hydroponic solutions. This is due
to the formation of root hairs in soil, which leads to better diffusive uptake of polar
contaminants and subsequently higher TSCF -values (the TSCF remains high (i.e.
near 1) for contaminants with a log K OW < 1). Dettenmaier et al. ( 2009 ) suggests
that differences in experimental methods and plant growth conditions cause the
disparity.
An additional process not considered in Eq. 9.20 is the contamination of leaves
with attached soil, R (kg soil kg plant − 1 (wet weight)). A convenient way of cal-
culation is to add the concentration due to attachment of particles from soil with
subsequent deposition on leaves to the calculated C L , as follows:

C L ,Final = C L ,Calc + R × C Soil (9.21)

Default values for R range from 0.001 kg kg − 1 to 0.01 kg kg − 1 (see

Section 9.6.3 ).