Bisphenol A in the Yellow River: Sorption characteristics and influential factors

Sorption is an important means for pollutant migration in aquatic environments and an important mechanism of pollutant transfer and transformation. Thus, understanding the sorption/desorption of organic pollutants in an aquatic environment is vital to predicting pollutant fate. In this study, Bisphenol A (BPA) was selected as the target pollutant for an investigation of sorption characteristics on three sediments in the Lanzhou section of the Yellow River, with examination of sorption thermodynamic parameters and the effects of temperature, pH, and sediment particle size. Sorption is described well by the pseudo-second-order kinetic model, occurring at two stages, fast (0-6 h) and slow (6-16 h), with equilibrium reached within 16 h. The results suggested that the intraparticle diffusion was dominant in the sorption process. Sorption thermodynamics was nonlinear, fitting well with the Freundlich isotherm model. Physical sorption is the likely mechanism, combining the contributions of π-π interaction and hydrophobic interaction. Thermodynamic parameter analysis showed that Gibbs free energy, enthalpy, and entropy were less than zero, showing that it is spontaneous, exothermic, and chaos-decreasing. Among tested influence parameters, pH values, ionic strengths, temperatures, and particle sizes were found to considerably influence the sorption of BPA. Sorption capacity decreased as sediment particle size increased and as pH increased. Sorption capacity increased with increasing Ca2+ and decreased with increasing Na+. The results have important implications regarding the impact of sorption/desorption at different environmental factors and fate of BPA in Yellow River.