Binding of RDX to Cell Wall Components of <i>Pinus sylvestris</i> and <i>Picea glauca</i> and Three-Year Mineralisation Study of Tissue-Associated RDX Residues

<div><p>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%).</p></div