ADSORPTION AND DESORPTION OF 2,4,6-TRINITROTOLUENE BY SOILS

Potential environmental hazards are posed by the presence of 2,4,6-trinitrotoluene (TNT) in soils of U.S. Army Ammunition Plants (AAP). Especially important is TNT interaction with the top several centimeters of soil, where highest concentrations occur. The TNT adsorption and desorption studies were conducted using soil samples collected from 13 AAP. Steady state adsorption and desorption of TNT with test soils was reached within 2 h. Batch TNT adsorption isotherms were best fit by the Langmuir adsorption model and had an average adsorption coefficient (K(d)) of 4.0 for all soils. The TNT adsorption K(d)'s were most highly correlated with extractable Fe, cation exchange capacity, and clay content. Almost all of the adsorbed TNT was desorbed after three sequential desorption cycles. These results suggest that adsorption in surface soils will not greatly retard movement of TNT to lower soil horizons. The pH exerted little effect on adsorption and desorption, but oxidized conditions consistently decreased adsorption of TNT compared to reduced conditions. Two transformation products of TNT, 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene, were detected during the 24-h test period under both oxidized and reduced conditions.