Oxidation of nonylphenol and octylphenol by manganese dioxide: Kinetics and pathways

Due to their potent estrogenicity and ubiquitous occurrence, non-ionic surfactant metabolites nonylphenol (NP) and octylphenol (OP) are of significant concern. Abiotic chemical oxidation by naturally abundant metal oxides may be an important route of their environmental attenuation, but is poorly understood. We investigated the reaction kinetics and pathways of NP and OP with MnO2. At pH 5.5 and 100 mg/L δ-MnO2, 92, 84 and 76% of 4-n-NP, 4-tert-OP and technical nonylphenol (tNP) was transformed in 90 min, respectively. A further experiment using a Mn-containing soil and Mn-removed soil confirmed that soil MnO2 caused NP removal. Multiple reaction products, including hydroquinone, hydroxylated products, dimers and trimers were identified through fragmentation analysis by GC–MS/MS and UPLC–MS/MS, allowing the construction of tentative pathways. This study suggested that abiotic oxidation by MnO2 may contribute to the dissipation of tNP, 4-n-NP, 4-tert-OP and their analogues in the natural environment. Highlights: •The oxidation of nonylphenol and octylphenol by manganese dioxide was efficient and pH dependent. •The importance of soil MnO2 was further confirmed by experiment using Mn-containing soil. •The reaction in environment is substantially slower than with synthetic MnO2. •The oxidation was inhibited by metal ions and enhanced by humic acids. •Reaction pathway is proposed based on reaction intermediates identified. -- Naturally occurring MnO2 may contribute significantly to the attenuation of nonylphenol and octylphenol in soil, water and sediment