Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 385

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Fig. 9.5 Concentration in
root (fresh weight) with
varying log K OW , predicted
with the regression of Travis
and Arms (T&A), the root
concentration factor (RCF),
the root model and the potato
model. Concentration in soil
is equal to 1 mg kg − 1 (wet
weight)

1

0.1

0.01

0.001

0.0001

0 2 4 6 8

log Kow

T&A RCF

root model potato model

root and the potato model include growth dilution, and the effect of this growth
dilution increases with increasing log K OW .The BCF predicted by the root model
at log K OW 7 is more than a factor 1000 below chemical equilibrium. Chemical
equilibrium may be found in the peel or close to the peel. But the inner substance of
roots and potatoes will have much lower concentrations (Trapp 2002 , 2007 ).
Interestingly, the T&A regression was originally established for above-ground
crops. But Fig. 9.5 shows that the predicted bioconcentration in plants is very
close to that predicted by the root model (advective uptake) and the potato model
(diffusive uptake).
In current chemical Risk Assessment (EC 2003 ) and in some Risk Assessment
tools for contaminated soils, predictions of concentrations in root vegetables are
based on the equilibrium approach. This will lead to an overestimation of the
concentration in roots and, hence, of human exposure (Legind and Trapp 2009 ).
Recent studies showed that uptake into root vegetables (radishes) may also be
from air (Mikes et al. 2009 ). This has not yet been considered in any available root
uptake model.

9.5.2 K OW and K AW on Accumulation of Contaminants in Leaves

Simulations were done with the leaf model described in Section 9.4.3 (Eq. 9.23 ). A
value of 0.1% attached soil was chosen as default. This gives a minimum BCF of
0.001 kg kg − 1 (wet weight) for all contaminants.
Figure 9.6 a shows the calculated concentration in leaves for a concentration in
soil of 1 mg kg − 1 , and in air of 0 mg m − 3 .Log K OW ( x -axis) is varied for volatile
( K AW :0.2LL − 1 ), semi-volatile ( K AW : 0.001 L L − 1 ) and non-volatile contaminants
( K AW :is10 − 6 LL − 1 ). For all volatile contaminants, the concentration in leaves
is low (0.001 mg kg − 1 ) over the whole range of log K OW . This means that their
accumulation due to translocation to leaves is low; the plotted concentration is due
to attachment of soil particles only (default 0.1%).
The semi-volatile contaminants show some accumulation, up to a BCF of 0.01
kg kg − 1 for the most polar contaminants. With increasing lipophilicity of the