Chemical signatures of TNT-filled land mines

The equilibrium headspace above several military-grade explosives was sampl ed using solid phase microextraction fibers and the sorbed analytes determi ned using gas chromatography with an electron capture detector (GC-ECD). Th e major vapors detected were the various isomers of dinitrotoluene (DNTs), dinitrobenzene (DNBs), and trinitrotoluene (TNTs), with 2,4-DNT and 1,3-DNB often predominating. Although 2,4,6-TNT made up from 50 to 99% of the soli d explosive, it was only a minor component of the equilibrium vapor. The fl ux of chemical signatures from intact land mines is thought to originate fr om surface contamination and evolution of vapors via cracks in the casing a nd permeation through polymeric materials. The levels of external contamina tion were determined on a series of four types of Yugoslavian land mines (P MA-1A, PMA2, TMA5 and TMM1). The flux into air as a function of temperature was determined by placing several of these mines in Tedlar bags and measur ing the mass accumulation on the walls of the bags after equilibrating the mine at one of five temperatures. TNT was a major component of the surface contamination on these mines, yet it accounted for less than 10% of the flu x for the three plastic-cased mines, and about 33% from the metal antitank mine (TMM1). Either 2,4-DNT or 1,3-DNB produced the largest vapor flux from : these four types of land mines. The environmental stability of the most i mportant land mine signature chemicals was determined as a function of temp erature by fortifying soils with low aqueous concentrations of a suite of t hese compounds and analyzing the remaining concentrations after various exp osure times. The kinetics of loss was not of first order in analyte concent ration, indicating that half-life is concentration dependent. At 23 degrees C, the half life of 2,4,6-TNT, with an initial concentration of about 0.5 m g kg(-1), was found to be only about 1 day. Under identical conditions, the half-life of 2,4-DNT was about 25 days. A research minefield was establish ed and a number of these same four mine types were buried. Soil samples wer e collected around several of these mines at several time periods after bur ial and the concentration of signature chemicals determined by acetonitrile extraction and GC-ECD analysis. Relatively high concentrations of 2,4,6-TN T and 2,4-DNT were found to have accumulated beneath a TMA5 antitank mine, with lower concentrations in the soil layers between the mine and the surfa ce. Signatures were distributed very heterogeneously in surface soils, and concentrations were very low (low mug kg(-1) range). Lower, but detectable, concentrations of signatures were detectable irregularly in soils near the PMA-1A mines in contrast to the TMA5 mines. Concentrations of signature ch emicals were generally below detection limits (<1 <mu>g kg(-1)) near the TM M1 and PMA-2 mines, even 8 months after burial. (C) 2001 Elsevier Science B .V. All rights reserved.