Chemical degradation of substituted aromatic hydrocarbon compounds in soil/sediment systems: Progress report. [Nitrogen-containing aromatics and alkyl substituted aromatics]

This study investigated the role of manganese oxide as an oxidant for substituted aromatic organic solutes. Manganese oxide may be the most reactive oxidizing agent in soils and sediments in the absence of molecular oxygen and nitrate. The study provides data on chemical mechanisms for abiotic degradation of anthropogenic organic solutes in soilsediment and groundwater systems. The dissolution of MnOOH and deltaMnO/sub 2/ was studied with five nitrogen-containing aromatic compounds and seven alkyl-substituted aromatics under anoxic conditions. Screening tests were performed at several values of pH and initial organic and oxide concentrations, and the rates of dissolution were evaluated. Quinoline, methylimidazole and 5.5-dimethyl hydantoin did not exhibit a significant dissolution rate at pH values around 6.0. Aniline dissolved deltaMnO/sub 2/ readily at a pH value of 4.4 but not at pH = 6.5 in tests with comparatively high initial concentrations (5 /times/ 10/sup -3/M) of organic and oxide. A methoxy substituent of aniline, p-anisidine, dissolved deltaMnO/sub 2/ very rapidly at low pH (4.4) with comparatively low concentrations of organic (6.25 /times/ 10/sup -5/M) and oxide (3.25 /times/ 10/sup -4/M). Hydroquinone, catechol and their alkyl substituents dissolved appreciable amounts of deltaMnO/sub 2/ at pH 6.5, with initial organic concentrations in themore » range of 5 /times/ 10/sup -4/M to 5 /times/ 10/sup -3/M and initial oxide concentrations around 2 /times/ 10/sup -3/M. An equation is presented which describes dissolution rate (up to about 15% manganese dissolution) for low initial organic concentrations (5 /times/ 10/sup -4/M and 1.5 /times/ 10/sup -3/M) with the assumption that the organic soluted are two equivalent reductants. In general, alkyl substitution increased the reaction rate except for trimethyl hydroquinone. Reactivity also increased with the size of the alkyl substituent. 29 refs., 46 figs., 17 tabs.« less