engleski

Sorption behaviour of munitions constituents in natural soils

The environmental fate of organic micropollutants is strongly influenced by their sorption in natural sorbents. Understanding their sorption behaviour could help us predict their transport in the environmental compartments. In this study the sorption and desorption behaviour of high explosives hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX), 1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetraazacyclooctane (HMX), and 2, 4, 6-trinitrotoluene (TNT) as well as propellants 2, 4-dinitrotoluene (2, 4-DNT), 2, 6-dinitrotoluene (2, 6-DNT), and trinitroglycerin (TNG) was analysed in two natural uncontaminated surface soils and two contaminated soils collected at a military training ground. Batch experiments were carried out in a wide range of initial mass concentrations of single compounds and their mixtures in aqueous solutions of different ionic strength. After achieving sorption/desorption equilibrium, mass concentrations of non-sorbed compounds were determined in aqueous phase using high-performance liquid chromatography with a UV diode-array detector. Corresponding mass fractions in soil were calculated as the difference between the initial and equilibrium mass concentrations in the aqueous phase. Experimental data sets were fitted to the Freundlich sorption/desorption isotherm curve. No competitive effects between multiple solutes were observed by comparison of Freundlich sorption/desorption coefficients calculated in experiments with single sorbates and with the sorbate mixtures. The results of batch experiments with sorbates dissolved in aqueous solution of calcium chloride or of a mixture of calcium chloride and sodium azide showed that ionic strength affected sorption/desorption intensity. Sodium azide should be added to all solutions to prevent biodegradation of sorbates. To see how sorbate and sorbent chemical-physical characteristics affect sorption/desorption intensities, the Freundlich sorption coefficients were correlated with hydrophobicity and water solubility of sorbates and organic matter content and pH values of sorbents. Desorption experiments showed apparent sorption-desorption hysteresis for most sorbate/sorbent pairs, which indicates a highly reversible sorption of compounds in both contaminated and uncontaminated soils. Easy desorption could facilitate the transport of investigated munitions constituents from contaminated soils to surface and ground waters used as public water supplies.

high explosives; munition constituents; sorption/desorption; soil

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