TNT SORPTION AND BOUND RESIDUE FORMATION IN SOIL

L.S. Hundal, W.L. Powers, P.J. Shea, S.D. Comfort and D.L. McCallister

University of Nebraska, Lincoln, NE, 68583-0915, 402-472-6904


ABSTRACT

Environmental hazards are posed by the presence of 2,4,6-trinitrotoluene (TNT) and its degradates in munitions-contaminated soils. TNT sorption and bound residue formation must be characterized accurately to predict TNT transport and fate in soils. We found TNT sorption was concentration dependent and nonlinear for concentrations between 80 ÁM and 300 ÁM L-1. Sorption did not approach equilibrium even after 168 d. Consequently, predictions regarding transport and fate of TNT made on 24 h equilibration and linear adsorption may not be accurate. Particularly critical are TNT interactions with the top several centimeters of soil, which are highly contaminated at the sampling site. TNT sorption was determined in the presence and absence of solid phase TNT. We observed TNT adsorption continued to increase until the end of the experiment (168 d). Adsorption was rapid and 35 and 38% of the total 14C (added as 14C-TNT) was adsorbed within 0.5 h in both soils (with and without solid phase TNT). After 168 d, 79% of 14C was adsorbed by soils with solid phase TNT versus 93% for soils without solid phase TNT. The readily available (CaCl2-extractable) and potentially available (acetonitrile-extractable) pools of adsorbed TNT decreased rapidly with time. The 14C-activity continued to increase in the organic fractions (fulvic acid and humic acid) and a higher percentage of 14C was found in fulvic acid than in the humic acid fraction. Approximately one-half of the total 14C was irreversibly bound, and only a very small amount was released when treated with strong alkali (10% KOH in methanol) and strong acid (1N HCI in methanol). Our observations indicate that bound residue formation constitutes a significant route of detoxification in soil.

KEY WORDS

TNT, bound residue, sorption

This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.