Daniel C. Leggett

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.

Organic compounds in volcanic gas from Santiaguito Volcano, Guatemala

Gas samples collected at Sapper fumarole, Santiaguito, Guatemala, on December 5, 1969, were analyzed by gas chromatography-mass spectrometry. A number of compounds were found, including saturated and unsaturated hydrocarbons, aldehydes, ketones, alcohols, aromatics, halogenated hydrocarbons, and inorganic sulfur compounds. The compounds are probably produced by heating of fossil soil or sedimentary layers by the magma.

Surface Contamination by TNT

We have performed experiments that indicate TNT contamination is present on surfaces exposed to TNT vapor, and that TNT contamination is transferred rapidly between proximate surfaces. Contaminated surfaces continue to be nearly constant sources of TNT vapor for some time after removal of the primary source.

Solvent/water partitioning of dimethylmethylphosphonate (DMMP) as a probe of solvent acidity

Experimentally determined partition coefficients for DMMP between NaCl-saturated water and 20 solvents were correlated using the solvatochromic parameters α, β, and π*. An inverted LSER was then used to predict α for 7 additional solvents. The new cohesion parameters αβ and π*2 were found to be more representative of cavity formation than δH2. Most importantly, it was essential to include either αβ or δH2 in the LSER. The partition method appears to be a useful adjunct to solvatochromic techniques in refining and extending the α scale of solvent acidity and could be used to rationalize solvent selection in extraction processes.

Modeling the equilibrium partitioning of organic contaminants between PTFE, PVC, and groundwater

Sorption of contaminants by organic polymers used in well casings and sampling devices has the potential to bias the results of groundwater analysis. Until now, no attempt has been made to explain quantitatively the results of sorption eXperiments. Here a multiparameter linear solvation energy relationship (LSER) was developed to describe the squilibrium partitioning between water, PVC, and PTFE of a group of organic compounds selected for their interest to environmental agencies as potential groundwater contaminants. Partitioning of these solutes was related to their basicity (β), acidity, polarity/polarizability, and molecular volume. These models proved more accurate than octanol/water partition coefficients in correlating the experimental partitioning data

Toxic organics removal kinetics in overland flow land treatment

Abstract The efficiency in removing 13 trace organics from wastewater was studied on an outdoor, prototype overland flow land treatment system. More than 94% of each substance was removed at an application rate of 0.4 cm h−1 (0.12 m3 h−1 m−1 of width). The % removals declined as application rates were increased. Removal from solution was described by first-order kinetics. A model based on the two-film theory was developed using three properties of each substance (the Henrys constant, the octanol-water partition coefficient and the molecular weight) and two system parameters (average water depth and residence time). The dependence of the removal process on temperature was consistent with the known dependence of Henrys constant and diffusivity on temperature. The model was tested on a second overland flow system.

H-bond acidity of solvents: II. Transformation of the Snyder chi proton donor scale to the Taft-Kamlet alpha scale

AbstractBy including a solvent cohesion term it was possible to transform Snyders χd scale into the Taft-Kamlet α scale for aliphatic H-bonding solvents. The transforming equation was:

Removal of volatile trace organics from wastewater by overland flow land treatment

\alpha = 2.386_{\chi d} + 1.27\alpha \beta - 0.482