EFFECT OF NITROGEN LIMITATION ON THE BIODEGRADABILITY AND TOXICITY OFNITROPHENOL AND AMINOPHENOL ISOMERS TO METHANOGENESIS

Monosubstituted nitro- and aminophenol isomers exhibited limited biode gradability under methanogenic conditions when supplied as the sole so urce of carbon and energy. This was examined by supplying to the same sediment samples, each isomer of nitro- and aminophenol as a sole sour ce of added carbon under either N-supplemented or N-deprived methanoge nic conditions. The results demonstrated that under N-supplemented con ditions, only 2-NP (NP = nitrophenol), 4-NP and 4-AP (AP = aminophenol ) were stoichiometrically mineralized, 2-AP, 3-AP, and the 3-AP metabo lite formed from 3-NP reduction were persistent over the 51-week incub ation period. In addition, NP isomers inhibited initial rates of metha nogenesis, while all AP amended cultures exhibited no significant inhi bition in the rate of methanogenesis. Under N-deprived conditions, 2-N P, 2-AP and 4-AP were mineralized, while 3-NP, 4-NP and 3-AP were pers istent over the 51-week incubation period. Although all NP isomers wer e still metabolized through the corresponding AP isomer, the deprivati on of nitrogen significantly depressed both the rate and extent of met hanogenesis. In general, nitrogen supplemented cultures produced 25% m ore methane than the nitrogen limited cultures, and the initial rates of methanogenesis were four times greater. While these data showed tha t under N-deprived conditions methanogenesis was inhibited to a greate r extent by these compounds, it also suggests that N-deprived conditio ns may have facilitated the establishment of a 2-AP metabolizing conso rtium.