Destruction of 2,4,6-Trinitrotoluene by Fenton Oxidation Z.M. Li, S.D. Comfort,* and P.J. Shea ABSTRACT Past disposal practices at munitionsproduction facilities have gener- ated numerous acres of 2,4,6-trinitrotoluene (TNT)-contaminated soil. Wedetermined the potential of the Fenton reagent (Fe z+ and H2Oz) to remediate TNT contamination in water, aqueous extracts of contami- nated soil, and soil-water slurries. The effects of HzOz and Fez + concentrations, solution pH, temperature, and initial TNT concentra- tion on transformation and mineralization rates were evaluated. Treat- ing an aqueous TNT solution (70 mg TNT L-~) with Fenton reagent (1% HzO2,80 mgFe z+ L- ~) in the dark resulted in 100% destruction of TNT within 24 h. This coincided with 40% mineralization. Subsequent exposure to light resulted in >90% mineralization. We observed genera- tion of 2,4,6-trinitrobenzoic acid and 1,3,5-trinitrobenzene within 15 min following Fenton oxidation of TNT. This indicates that initial TNT destruction likely occurs by methyl group oxidation and decarbox- ylation. Subsequent transformations involve nitro moiety removal with ring hydroxylation and cleavage, as evidenced by the stoichiometric recovery of TNT-nitrogen as NOr and production of oxalic acid as the primary C-containing end product. Uponexposure to light, Fe(ID was regenerated and the oxalate produced from ~4C-TNT oxidation disappeared; this coincided with a decrease in solution ~4C activity. Similar observations were made when ~4C-oxalic acid was the starting substrate. Fenton oxidation was also effective in destroying TNT in aqueous extracts of contaminated soil and soil-water slurries. Experi- mental data provide evidence that the Fenton reagent can effectively remediate TNT-contaminated water and soil. A SE~,IOUS ~’ROBLEM facing the Department of Defense is the presence of TNT-contaminated soils at facili- ties where munitions were formerly manufactured, loaded, or demilitarized (Jenkins and Walsh, 1992). Past disposal practices conducted at the former Nebraska Ordnance Plant (Mead, NE) have left the state with approximately 6400 m 3 of contaminated soil. This is a concern for state and local officials since several muni- tions compounds and, in some cases, their reduction products have been found in surface and groundwater in the vicinity of munitions plants (Jerger et al., 1976; Periera et al., 1976). Some of these nitroaromatics and nitramines are known to be mutagenic (Won et al., 1974, 1976), carcinogenic, or otherwise toxic to aquatic and terrestrial organisms (McCormick et al., 1976; Smock et al., 1976; Kaplan and Kaplan, 1982; Wellington and Mitchell, 1991). Human health concerns regarding ex- posure to TNT primarily arise from evidence linking occupational contact with liver damage, aplastic anemia, dermatitis, ocular disorders (Sittig, 1985), and gastro- intestinal distress (Stewart et al., 1945). Remediation of TNT-contaminatedsites is needed to ensure environmental quality and safety. To date, the most demonstrated remediation technology for explosive- containing soils is incineration. This technology was recently recommended for remediating the 6400 m 3 of contaminated soil at the former Nebraska OrdnancePlant (NOP) at an estimated cost of more than 14 million dollars. Although incineration is effective, it is expensive, produces an unusable by-product, and [tas poor public acceptance due to safety concerns :regarding air emis- sions. The high costs and associated dJisadvantages of incineration have motivated researchers to seek alterna- tive treatment technologies. Aerobic and anaerobic biodegradation of TNT have been investigated (McCormick et al., 1976; Osmon and Klausmeier, 1972; Boopathy and Kulpa, 1992), and oxi- dative and reductive pathways for TNT transformation have been proposed (McCormick et al.,. 1976; Kaplan, 1990; Walker and Kaplan, 1992). However,the literature indicates microbial mineralization of TNT is generally slow and limited (<5 %) (Boopathy et al., 1994) because of the electron-withdrawing nitro groups that impede electrophilic attack by oxygenases of aerobic bacteria (Bruhn et al., 1987; Thiele et al., 1988; Rieger and Knackmuss, 1995). TNT resistance to biological oxida- tion indicates that effective destruction through an oxida- tive pathway will likely require an advanced oxidative process. The Fenton reaction (Fenton, 1894) is recognized one of the oldest and most powerful oxidizing reactions available. This reaction has been used to decompose a wide range of refractory synthesized or natural organic compounds (Sedlak and Andren, 1991; Watts et al., 1991). The Fenton reagent is a mixture of hydrogen peroxide (H202) and ferrous iron (Fe2+),. which produces OH radicals. Although several propagating reactions can occur (Walling, 1975), Tomita et al. (1994) provided strong experimental evidence supporting the hypothesis that the ¯ OH is the primary oxidizing species formed by Fe(II)-catalyzed decomposition of H2O2 in the absence of a ferrous chelator. The hydroxyl radical is second only to fluorine as an oxidizing agent (.OH, ° = -2.8 V vs. fluorine, E ° = -3.0 V) and is capable of nonspecific oxidation of manyorganic compounds. If a sufficient concentration of OH and other radicals are generated, the reactions can continue to completion, ultimately oxidizing organic compounds to CO2, H20, and low molecular weight organic acids. Our objectives were to determine the potential of the Fenton reagent to remediate TNT contamination in water, aqueous extracts of contaminated soil (soil washings), and contaminated soil-water slurries, and assess the effects of reaction variables and light on the efficiency of TNT destruction. TNT-contaminated soil was obtained from the former NOP and treated by Fenton oxidation. Institute of Agriculture and Natural Resources, Univ. of Nebraska, Lin- coln, NE 68583-0915. No. 11001, Agric. Res. Div., Univ. of Nebraska- Lincoln. Received 21 Feb. 1996. *Corresponding author (agrol30@ unlvm.unl.edu). Published in J. Environ. Qual. 26:480-487 (1997). Abbreviations: NOP,Nebraska Ordnance Plant; TNT, 2,4,6-trinitro- toluene; TNBA, 2,4,6-trinitrobenzoic acid; TNB, 1,3,5-trinitrobenzene; HPLC, high performance liquid chromatography; LC/MS/MS, liquid chro- matography tandem mass spectrometry; SIM, selective ion monitoring; QI, first quadrupole; USEPA, United States Environmental Protection Agency;API, atmospheric pressure ionization. 480 Published March, 1997