Suchergebnisse

Background, Aim and Scope. For decades, very large areas of former military sites have been contaminated diffusely with the persistent nitroaromatic explosive 2,4,6-trinitrotoluene (TNT). The recalcitrance of the environmental hazard TNT is to a great extent due to its particulate soil existence, which leads to slow but continuous leaching processes. Although improper handling during the manufacture of TNT seems to be a problem of the past in developed countries, environmental deposition of TNT and other explosives is still going on unfortunately, resulting from thousands of unexploded ordnance or low order explosions at munitions test areas and at current battlefields. Objective. Sustainable phytoremediation strategies for explosives in Germany, which intend to use trees to decontaminate soil and groundwater ('dendroremediation'), have to consider that most of the former German military sites are already covered with woodlands, mainly with conifer stands. Therefore, parallel investigation of the remediation potential is necessary for both of the selected hybrids of fast growing broadleaf trees, which are waiting for planting and forest conifers, which have already proven for decades that they are able to grow on explosive contaminated sites. Main Features. A short literature review is given regarding phytoremediation of TNT with herbaceous plants and some general aspects of dendroremediation are discussed. Furthermore, an overview of our TNT-dendroremediation research network is introduced, which has the strategic goal to make dendroremediation more calculable for a series of potent trees for site-adapted in situ application and for the assessment of tree remediation potentials in natural attenuation processes. Results and Discussion. Some of our methods, results and conclusions yet unpublished are presented. For a preliminary calculation of area-related annual TNT dendroremediation potential of five-year-old trees, the following values were assessed: Salix EW-13 6.0, Salix EW-20 8.5, Populus ZP-007 4.2, Betula pendula 5.2, Picea abies 1.9 and Pinus sylvestris 0.8 g m⁻² a⁻¹. For a 45-year-old spruce forest, an annual natural attenuation potential of 4.2 g TNT m⁻² a⁻¹ was found. Conclusion, Recommendations and Perspective. Our main results deliver quantitative proposals for dendroremediation strategies in situ and provide decision aids. Also aspects of growth of raw materials for energy production are considered. Our dendroremediation research concept for TNT and its congeners can be easily completed for other trees of interest and it can also be applied to herbaceous plants. Knowing the current bottlenecks of phytoremediation and considering the known environmental behaviour of other contaminants, elements of our methodological approach may be easily adapted to those pollutant groups, e.g. for pesticides, pharmaceuticals, PAHs, chlorinated recalcitrants and, with some restrictions, to inorganics and to multiple contaminations. Our dynamical dendrotolerance test systems will help to predict tree growth on polluted areas. To provide some light into the black box of TNT dendroremediation, experimental data regarding the uptake, distribution and degradation of [¹⁴C]-TNT in mature tree tissues will be reported in the second part of this publication.

For decades, the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) has been used for military and industrial applications. Residues of RDX pollute soils in large areas globally and the persistence and high soil mobility of these residues can lead to leaching into groundwater. Dendroremediation, i.e. the long-term use of trees to clean up polluted soils, is gaining acceptance as a green and sustainable strategy. Although the coniferous tree species Norway spruce and Scots pine cover large areas of military land in Central Europe, the potential of any coniferous tree for dendroremediation of RDX is still unknown. In this study, uptake experiments with a 14C-labelled RDX solution (30 mg L−1) revealed that RDX was predominantly retained in the roots of 6-year-old coniferous trees. Only 23 % (pine) to 34 % (spruce) of RDX equivalents (RDXeq) taken up by the roots were translocated to aboveground tree compartments. This finding contrasts with the high aerial accumulation of RDXeq (up to 95 %) in the mass balances of all other plant species. Belowground retention of RDXeq is relatively stable in fine root fractions, since water leaching from tissue homogenates was less than 5 %. However, remobilisation from milled coarse roots and tree stubs reached up to 53 %. Leaching from homogenised aerial tree material was found to reach 64 % for needles, 58 % for stems and twigs and 40 % for spring sprouts. Leaching of RDX by precipitation increases the risk for undesired re-entry into the soil. However, it also opens the opportunity for microbial mineralisation in the litter layer or in the rhizosphere of coniferous forests and offers a chance for repeated uptake of RDX by the tree roots.

Contamination of soils with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX, Research Department Explosive) as a result of military applications is a large-area problem globally. Since coniferous trees dominate the vegetation of large areas of military land in Central Europe, particularly in Germany, the long-term fate of 14C-RDX in the conifers Scots pine and Dwarf Alberta spruce was studied. Acetic acid was the most effective solvent for the removal of extractable RDX residues from homogenates of RDX-laden tree material (85%, 80–90% and 64–80% for roots, wood and needles, respectively). On average, only a fifth of RDX-derived 14C was bound in non-extractable residues (NER). Within the main cell wall compartments, lignin was the dominant binding site for NER (needles: 32–62%; roots: 38–42%). Hemicellulose (needles: 11–18%; roots: 6–11%) and cellulose (needles: 12–24%; roots: 1–2%) were less involved in binding and a considerable proportion of NER (needles: 15–24%; roots: 59–51%) was indigestible. After three-year incubation in rot chambers, mineralisation of tree-associated 14C-RDX to 14CO2 clearly dominated the mass balance in both tree species with 48–83%. 13–33% of 14C-RDX-derived radioactivity remained in an unleachable form and the remobilisation by water leaching was negligible (< 2%).