Location
On
the area of the former TNT
production plant "Werk Tanne", Clausthal-Zellerfeld, Germany), beside other plants, the following trees
were chosen for analysis to nitroaromatic compounds: willow,
birch, raspberry and spruce. In the forest covered area of "Werk Tanne",
Norway spruce (Picea
abies) is the predominant tree.
For
site information, see also: <http://www.uft.uni
bremen.de/tanne/tanne.htm>
Nitroaromatics in tree tissue
In woody
tree roots, whose surrounding soil
contains TNT, and the accompanying aminodinitrotoluenes
(ADNT),
both, TNT
and ADNT
were always
provable. A quantitative correlation of the extremely varying content of
nitroaromatics with the contamination degree of the surrounding soil, was not
useful, since the deviations of the soil sample contaminant concentrations
were reaching 1000% and more.
The bark
of adult trees is not suitable for exact GC-ECD analysis, because of its high matrix potential. Also needles of young spruces
(approx. 1-3 years old) are hardly analyzable because of the matrix potential and their
neighborhood to the highly polluted soil. Polluted soil dust could be deposited
on the resinous surface of spruce plants. The TNT/ADNT-containing dust is not
readily removable by cleaning procedures with organic solvents.
The bark-free wood (willow, birch, spruce)
, however can be analyzed at justifiable
expenditure by means of GC-ECD. The sampling from the inner tree stem region prevents
the measurement of tree surface contamination, which
is due to the rain splash-water or to TNT/ADNT-containing dust from the surrounding
high-contaminated soils.
In
aboveground ranges (stem height to 1 m) traces to maximally 0.4 mg/kg ADNT, but no
TNT
in provable in the wood of Salix. No nitroaromatics were found in the
1-m-stem wood of spruce and birch. In the spring
bleeding sap of birches from the former TNT-plant "Sythen" (North
Rhine-Westphalia, Germany) were no nitroaromatics provable as well.
Transpiration dependence
ADNT
detections obviously depend on the weather conditions. Sampling at the early midday hours of
hot summer days, when the trees are vigorously transpiring, gives the greatest
chance to detect the traces of nitroaromatics in the wood.
Conclusions
-
Since it was
meanwhile known from radiotracer
investigations with [14C]-TNT, that tissue of mature trees is
capable to the complete metabolisation of soil-derived TNT to still unknown
metabolites (20%) or to irreversible bound substances (80%), the negative
results in site tree analysis as well as missing evidences of nitroaromatics
in former pot
experiments become explainable.
The "cold"
GC-ECD analysis shows TNT/ADNT
in the tissue, only
when a steady TNT/ADNT
delivery into the plant is maintained
and when this delivery is higher than the metabolisation velocity of the
trees. Thus "snapshots" of the current pollutant concentrations in
tree tissues may not be used to assess the dendroremediation potential of
tree species.
-
A quantitative relationship between
nitroaromatic content within the trees and the soil sanitation
potential of these trees is impossible as long as the root-influenced
soil volume is can not be estimated and thus the respective initial TNT
mass in the
soil is unknown.
-
Moreover, tree
transpiration and lateral pollutant migrations
must be accurately quantifiable.
last update: 18.02.04 19:25
by Bernd
Schoenmuth 
Web date: June 2002
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