Effect of nitrogen limitation on the biodegradability and toxicity of nitro- and aminophenol isomers to methanogenesis

Monosubstituted nitro- and aminophenol isomers exhibited limited biodegradability under methanogenic conditions when supplied as the sole source of carbon and energy. This was examined by supplying to the same sediment samples, each isomer of nitro- and aminophenol as a sole source of added carbon under either N-supplemented or N-deprived methanogenic conditions. The results demonstrated that under N-supplemented conditions, only 2-NP (NP=nitrophenol), 4-NP and 4-AP (AP=aminophenol) were stoichiometrically mineralized, 2-AP, 3-AP, and the 3-AP metabolite formed from 3-NP reduction were persistent over the 51-week incubation period. In addition, NP isomers inhibited initial rates of methanogenesis, while all AP amended cultures exhibited no significant inhibition in the rate of methanogenesis. Under N-deprived conditions, 2-NP, 2-AP and 4-AP were mineralized, while 3-NP, 4-NP and 3-AP were persistent over the 51-week incubation period. Although all NP isomers were still metabolized through the corresponding AP isomer, the deprivation of nitrogen significantly depressed both the rate and extent of methanogenesis. In general, nitrogen supplemented cultures produced 25% more methane than the nitrogen limited cultures, and the initial rates of methanogenesis were four times greater. While these data showed that under N-deprived conditions methanogenesis was inhibited to a greater extent by these compounds, it also suggests that N-deprived conditions may have facilitated the establishment of a 2-AP metabolizing consortium.