Metabolism of Nitrophenols in Flooded Soils

Nitrophenols (p‐,o‐, and m‐isomers and 2,4‐dinitrophenol) disappeared fairly rapidly from flooded alluvial and organic matter‐rich acid sulfate (pokkali) soils inoculated with parathion (O,O‐diethyl O,p‐nitrophenyl phosphorothioate)‐enrichment cultures from the respective soils. Nitrite, one of the reported end‐products of nitrophenol (O,O‐dimethyl O,p‐nitrophenyl phosphorothioate) metabolism, accumulated only in inoculated alluvial soil, irrespective of the type of nitrophenol added. In an isotope study, ring cleavage of p‐nitrophenol leading to carbon dioxide was demonstrated in flooded soils inoculated with parathion‐enrichment culture, particularly under stirred conditions. Nitrophenols decomposed also in uninoculated samples of both soil types, though slowly as compared to inoculated soils; but nitrite and carbon dioxide were not formed. Resting cells of a bacterium, Pseudomonas sp. ATCC 29353, readily hydrolyzed parathion and then liberated nitrite from p‐nitrophenol. In cell‐free suspension, the reaction ceased at the p‐nitrophenol stage. In bacterial cultures, parathion was hydrolyzed without proliferation while subsequent degradation of p‐nitrophenol involved metabolism leading to bacterial enrichment.