Environmental Engineering Reference
In-Depth Information
Often, the results were ambiguous, because the influence of concentrations in air
could not be quantified (compare Section
9.3.1
), but also due to large uncertainties
in measured as well as predicted concentrations in plants (McKone and Maddalena
2007
). The primary role of models is to indicate relevant processes and the potential
for accumulation of contaminants in plants. Good decision making needs to consider
both model predictions and experimental data.
In a critical review of uncertainties related to soil-to-plant bioconcentration
factors by McKone and Maddalena (
2007
),
BCF
-values for the explosive RDX
(hexahydro-1,3,5-trinitro-1,3,5-triazine) are listed. RDX is a quite persistent, rel-
atively polar (log
K
OW
: 0.87) and non-volatile contaminant (
K
AW
:6.3
10
−
8
atm
m
3
mol
−
1
).
BCF
-values range from 0.06 (mg kg
ww plant
−
1
:mgkg
dw soil
−
1
) in bean
pods and 0.07 (mg kg
ww plant
−
1
:mgLwater
−
1
) in bean fruits at the lower end to
19.2 (mg kg
ww plant
−
1
:mgL
water
−
1
) in bean leaves and 28.6 (mg kg
dw plant
−
1
:mg
kg
dw soil
−
1
) in carrot shoots at the upper end. Overall, fruits tend to have lower
BCF
values than roots, and leaves have the highest accumulation, but there is a very large
variation in the data. The
BCF
values for fruits range from 0.07 to 5.50, for roots
from 0.08 to 4.50 and for leaves from 0.30 to 28.6, i.e. the maximum
BCF
is 79
fold, 56 fold or 93 fold larger than the minimum
BCF
. Even though the units are not
uniform (i.e. a mix of wet weight and dry weight, soil and water), this variation is
quite impressive for one single contaminant and similar crop type.
×
9.8 Uptake Potential of Specific Substance Classes
This section gives a short classification of several frequently found soil and ground-
water contaminants with respect to their uptake into plants. It is based on the model
simulations, measured data and the process review above, but also on the experience
of the authors.
9.8.1 Chlorinated Solvents (PCE, TCE and Others)
Chlorinated solvents such as perchloroethene (PCE) and trichloroethene (TCE) are
probably the most frequently found groundwater contaminants world-wide. They
are water-soluble, relatively persistent and very volatile. Uptake of chlorinated sol-
vents into tree trunks has been reported frequently (Chard et al.
2006
; Larsen et al.
2008
; Sorek et al.
2008
; Vroblesky et al.
1999
). However, these contaminants are
highly volatile and escape rapidly from branches, small stems and leaves into the air
(Baduru et al.
2008
). Thus, in fruits, only metabolites of chlorinated solvents could
be detected (Chard et al.
2006
). Accumulation in root crops and potatoes is likely,
though not described yet. During storage and cooking, chlorinated solvents could
be eliminated from food stuff, due to their high volatility. Moreover, these contam-
inants are not expected to be present in high concentrations in top soil, i.e. the root
zone, due to volatilization to the air and leaching to the groundwater.
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