Enhancing the attenuation of explosives in surface soils at military facilities: sorption-desorption isotherms

The primary objective of the present study was to develop inexpensive soil amendments that can be applied to enhance the adsorption of energetic compounds on military training ranges, thus limiting the potential for these compounds to migrate to groundwater. Adsorption and desorption isotherms were determined for 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine with a wide variety of natural and man-made adsorbents, including wheat straw, sawdust, peat moss, ground rubber tires, and clays. Among the various adsorbents tested, peat moss proved to be the most effective sorbent for the three explosives. The adsorption coefficients (Kd(s)) for TNT and RDX with peat (310 and 87 L/kg, respectively) were at least two orders of magnitude higher than that determined for adsorption of these energetics with two surface soils. The adsorption-desorption isotherms for the explosives showed considerable hysteresis (Kd(s) < Kd(d)) with some of the solid adsorbents, suggesting that the sorption process is not readily reversible but, rather, that some fraction of the adsorbed contaminant is either irreversibly bound or present as a slowly desorbed fraction. The data indicate that the application of specific adsorbents to soils at military impact ranges may significantly improve the protection of local groundwater resources.