6.2.2 Mass
balance of
nitroaromatic compounds (NAC)
The
results and consequences resulting from the experiments can be summarized as
follows:
§
Quantitatively definable and temporally limitable additions of
bioavailable nitroaromatics permit balances of the pollutant fate.
§
Applied nitroaromatics (TNT,
the TNT-metabolites ADNT
and TNB,
and DNT) are subjected to
a considerable
(non-extractable) disappearance.
With
exception of 2,4-DNT
with a abnormal maximum recovery of approx. 10%,
more than the temporarily applied nitroaromatics disappear
in the system soil/plant,
despite the short soil recovery time of approx. two weeks.
§
T he absolute TNT
masses, which are disappearing
during the dendroremediation process, are in the range of 150-200 mg/kg,
(For Picea glauca even
230 mg TNT/kg dry
soil disappeared.)
§
High absolute degradation rates within the range of 200 mg/kg
dry soil give a possibility of the explanation for the 85%,
tree-independent balance lack, found in outdoor
investigations.
§
In contrast to measured soil pollutant concentrations, generally higher
concentration values of recovered nitroaromatics in roots represent
balance portions of beneath 1% because
of the low total mass of the roots.
§
The higher NAC concentrations in roots indicate that the
pollutants reached the plant indirectly by tree transpiration. But, due to the short recovery
phase of only two weeks, metabolisation of the nitroaromatics was not yet
complete at the time of soil analysis.
It is to be assumed that nitroaromatics found at or
in the roots can be further metabolized.
This is proven in the radiotracer
experiments both, with Picea and Salix respectively.
§
Tree planted soils showed no residual phytotoxicity in growth
and in transpiration of cress seedlings (Lepidium sativum).
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