Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 392

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Fig. 9.9 Simulation of the
concentration of carbofuran
in plants as a function of
time, with low transpiration
( Q is 1 L d − 1 ) and high
transpiration ( Q is 5 L d − 1 ).
Dynamic model version, data
Tabl e 9.1

10

8

6

4

2

0

0 5 10 15 20

Time (d)

root low Q leaf low Q

root high Q

leaf high Q

availability of water. Students in a field course at the Technical University of
Denmark noticed that concentrations of chlorinated solvents (PCE and TCE) mea-
sured in wood cores taken from trees growing at the Glostrup site (Denmark) were
much lower in the very dry June 2008 than in the very wet June 2007 (Mette
Broholm, personal communication). A plausible explanation is a reduced transpi-
ration due to water stress in 2008. Transpiration in field settings can be estimated
using the Penman-Monteith model by Penman ( 1948 ) and Monteith (1964) (cited in
(Monteith 1995 )).
Leaves grow and contaminants entering the leaf with the transpiration stream are
not uniformly distributed in the leaf, but tend to accumulate in the leaf tip (Doucette
et al. 2005 ).

9.6.3 Plant Morphology and Collection Efficiency for Particles

The resuspension of contaminated soil particles from soil to plant surfaces is an
important transport mechanism for lipophilic contaminants. This transfer pathway
was well studied using insoluble radionuclides, and large variations were found in
soil attachment among plant species. Soil particles may reach leaf surfaces mainly
by three mechanisms, namely rain splash, wind erosion and erosion due to agricul-
tural practice (ploughing, harvesting et cetera). Table 9.2 shows measured values
for the transfer of radionuclides (Li et al. 1994 ). The transfer range varies from
1.1 to 260 mg soil g plant − 1 (dry weight), depending on the species. But also, the
intraspecies variation was considerable, as can be seen from the standard devia-
tions given in Table 9.2 . The highest value was found for lettuce, with 260 mg soil
g plant − 1 (dry weight), probably due to the small size of the plant (< 40 cm), the leaf
morphology where leaves are collecting particles to the interior of the plant, and
the surface structure. It was also demonstrated that particle-bound organic contami-
nants migrate from the leaf surface to the interior of the leaf (i.e. are overgrown by
surface waxes), from where they can not be washed off (Kaupp 1996 ). A BCF for
radish leaves to soil of 0.08 kg kg dw − 1 was recently measured at a Czech site for