Nonylphenol (NP), the metabolite of non-ionic surfactant nonylphenol ethoxylates, is a well-known environmental endocrine disruptor. Nonylphenol is frequently detected in treated wastewater effluent, impacted surface water and even in drinking water due to its heavy use. Nonylphenol has been treated as a single compound in most studies to date, but in reality it is a mixture of numerous isomers. Recent studies showed that different NP isomers displayed different estrogenicity and biodegradability in the environment. In this study, we examined, for the first time, the potential isomeric selectivity in the oxidation of NP. The reaction kinetics of 19 NP isomers, including 6 diastereoisomers, with potassium permanganate was measured at pH 5, 7 and 9. At pH 7 with 10 mg L-1 of KMnO4 and 50 mu g L-1 technical mixture of NP, the half-lives of 19 isomers varied from 4.8 to 6.3 min. In general, the reaction followed the order: alpha-dimethyl > alpha-ethylmethyl approximate to alpha-methylpropyl approximate to alpha-iso-propylmethyl. The oxidation rate of NP isomers with KMnO4 increased with increasing pH and a greater dependence on pH was observed for isomers with alpha-dimethyl substituents. This study suggested that alpha-substituents may be the dominant factor regulating the reactivity and persistence of NP isomers during advanced oxidation processes. (C) 2014 Elsevier B.V. All rights reserved.