pH and the presence of compounds have a great effect on the sorption of organic contaminants. In this study, batch equilibrium experiments were carried out to investigate the influence of pH on the sorption of p-nitrophenol (PNP) onto sediment in the presence of Pb(NO3)(2) and cetylpyridinium chloride (CPC) cationic surfactant. Results indicated that in the multi-solute system with PNP, Pb(NO3)(2) and CPC, the sorption of PNP increased with the increasing pH and the amount of sorbed PNP at equilibrium was much higher than in the single-solute system. This can be attributed to the presence of Pb(NO3)(2) and CPC. It is believed that the main reason for that was the larger sorption of CPC at higher pH allowing higher sorption of PNP. The results are believed to provide a useful insight into describing the transport and fate of PNP in natural environments. (C) 2007 Elsevier B.V. All rights reserved.