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Title: Effects of wet and dry cycles on TNT losses from soils
Authors: Pennington, Judith C.
Price, Cynthia B.
McCormick, Erica.
Hayes, Charolett A.
Keywords: Soil pollution
Nitroaromatic compounds--Biogradation
Decomposition (Chemistry)
Publisher: Environmental Laboratory (U.S.)
U.S. Army Engineer Waterways Experiment Station.
Series/Report no.: Technical Report;EL-92-37
Abstract: Although 2,4,6-trinitrotoluene (TNT) is not remarkably volatile from the crystalline solid, TNT losses from amended soils were significant during plant uptake studies. The losses exceeded the amount of TNT or transformation products found in the plants. This study postulated that TNT may be lost from soils through volatilization of the parent compound or its microbial or photochemical transformation products as the soil undergoes wetting and drying cycles. Specific objectives of the study were to quantify and characterize any volatile losses and to determine the effects of light on volatility of TNT from soils. Two soils, a silt and a clay, amended with radiolabeled TNT were taken through 13 wet/dry cycles in chambers allowing 1 cu ft (0.03 cu m) of air per minute to pass over the soil surface. Soils were tested under abiotic and biotic conditions and with and without light. Air exiting test chambers passed through XAD resin to trap volatile organic compounds followed by four sodium hydroxide traps in series to collect radiolabeled carbon dioxide. Carbon dioxide traps were analyzed after each cycle. At the end of the test, XAD traps were extracted and analyzed by liquid scintillation counting. Soils were extracted and analyzed by high performance liquid chromatography (HPLC) with both ultraviolet and radiation detectors. Soils were also combusted in a sample oxidizer, and the radiolabeled carbon dioxide was trapped and counted by liquid scintillation. Radiolabeled carbon dioxide accounted for less than 1 percent of the tracer initially added to each test. Recovery of volatile organic carbon was 1 percent or less in all treatments. Therefore, volatile losses were minimal. Biotic treatments lost significantly more radiolabel than abiotic treatments. Results of HPLC analysis revealed more 4-amino-2,6-dinitrotoluene, a transformation product of TNT, than TNT in the soils. Complete combustion of the soils resulted in recovery of virtually all of the radiolabel. However, significantly greater recoveries from combustion data than from HPLC data revealed an average of 70 percent unextracted radiolabeled material in the soil. An unextractable residual in soils after prolonged contact with TNT has been reported previously. The existence of a residual is a potential source of error in current evaluations of TNT concentrations at contaminated sites and may result in significant underestimation of contamination hazard. The long-term stability of the residual and its ultimate contribution to environmental hazard is unknown. Volatile losses of TNT or its decomposition products from soils were limited. Light exerted no effect on the limited losses observed. An average of 70 percent of the initial TNT treatment was unextractable by the standard method for analyzing TNT in soils. This large unextractable residual has important implications for assessing environmental contamination with TNT.
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