RDX loss in a surface soil under saturated and well drained conditions.

On military training ranges, low-order, incomplete detonations deposit RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) into surface soils. In this study, we evaluated RDX biodegradation in surface soils obtained from a military training range in Alaska. Two factors were compared: (i) soil water potential during the incubations; and (ii) the use of acetonitrile (ACN) as an RDX carrier to spike samples. Organic solvents have been used in laboratory studies to dissolve slightly water-soluble contaminants before addition to soil. We added ACN to obtain final soil ACN concentrations of 0 mg kg(-1) (0%), 1000 mg kg(-1) (0.1%) and 10 000 mg kg(-1) (1%). We then compared RDX attenuation in the soil under saturated and unsaturated conditions. RDX fell below the limit of detection within 3 wk of study initiation under the saturated condition. A maximum degradation rate of 0.15 mg RDX L(-1) d(-1) was measured. Under the unsaturated condition, 42% of the original RDX was still present at study termination (5 wk). The addition of acetonitrile at 0.1 or 1.0% had no affect on RDX loss in the saturated soil. In the unsaturated soil, however, ACN at 1.0% inhibited RDX loss by as much as 25%. These findings indicate that soil water potential and carrier solvent concentrations can impact the rate and extent to which RDX is attenuated in a surface soil.

Chemical signatures of TNT-filled land mines.

The equilibrium headspace above several military-grade explosives was sampled using solid phase microextraction fibers and the sorbed analytes determined using gas chromatography with an electron capture detector (GC-ECD). The 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 solid explosive, it was only a minor component of the equilibrium vapor. The flux of chemical signatures from intact land mines is thought to originate from surface contamination and evolution of vapors via cracks in the casing and permeation through polymeric materials. The levels of external contamination were determined on a series of four types of Yugoslavian land mines (PMA-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 measuring 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 flux 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 important land mine signature chemicals was determined as a function of temperature by fortifying soils with low aqueous concentrations of a suite of these compounds and analyzing the remaining concentrations after various exposure times. The kinetics of loss was not of first order in analyte concentration, 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 mg 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 established and a number of these same four mine types were buried. Soil samples were collected around several of these mines at several time periods after burial and the concentration of signature chemicals determined by acetonitrile extraction and GC-ECD analysis. Relatively high concentrations of 2,4,6-TNT 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 surface. 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 chemicals were generally below detection limits (<1 mug kg(-1)) near the TMM1 and PMA-2 mines, even 8 months after burial.

Comparison of environmental chemical results for split samples analyzed in different laboratories.

Data comparisons were made for split or co-located samples analyzed in contract laboratories and quality assurance (QA) laboratories during environmental studies directed by the U.S. Army Corps of Engineers. Archived results were analyzed statistically as concentration ratios (contract laboratory/QA laboratory). Concentration ratios were found to be lognormally distributed, and this was the model used for comparisons. For metals in soils and volatile organic compounds (VOCs) in groundwater, 10.2% of metal ratios in soils and 5.6% of VOC ratios in groundwater exceeded limits of 0.40-2.50. Considering that both methods are multianalyte, we find that only 4.0% of the metal samples and 2.0% of the VOC samples had more than one outlier ratio per sample. More recent data produced very similar results. For VOCs, total petroleum hydrocarbons (TPHs), and explosives in soils, limits of 0.25-4.00 are suggested with the understanding that large improvements are badly needed. Even with these wide limits, approximately 42% of VOCs, 14% of TPHs, and 11% of explosives contract laboratory/QA laboratory ratios were outside these limits. Here, too, the most recent data yielded very comparable results. Sampling and preparation procedures for VOCs in soils requires immediate attention, but all methods can and should be capable of producing improved agreement between laboratories.

Development of field screening methods for TNT, 2,4-DNT and RDX in soil.

Simple field-screening methods are presented for detecting 2,4,6-TNT, 2,4-DNT and RDX in soil. A 20-g portion of soil is extracted by manually shaking with 100 ml of acetone for three minutes. After the soil settles, the supernatant is filtered and divided into three aliquots. Two aliquots are reacted with potassium hydroxide and sodium sulfite to form the red-colored Janowsky complex when 2,4,6-TNT is present or the blue-purple complex when 2,4-DNT is present. The third aliquot of the extract is passed through a strong anion exchange resin to remove nitrate and nitrite. Then the extract is acidified and RDX is reduced with zinc to nitrous acid, which is reacted with a Griess reagent to produce a highly colored azo dye. Concentrations of TNT, 2,4-DNT and RDX are estimated from their absorbances at 540, 570 and 507 nm, respectively. Detection limits are about 1 microg/g for 2,4,6-TNT and RDX and about 2 microg/g for 2,4-DNT. Concentration estimates from field analyses correlate well with laboratory analyses.