Hydroxylamines, produced as intermediates in the reductive metabolism of 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene between nitroaromatic parent compounds and corresponding amines, were unstable in aqueous solution in the presence of O-2. Reactions of hydroxylamines to compounds other than amines may be the major cause of poor mass balance observations in bioremediation systems where only aminated products are monitored. Results demonstrate the formation of azoxy compounds as products of abiotic aryl-hydroxylamine reactions.