Ageing behavior of phenanthrene and pyrene in soils: a study using sodium dodecylbenzenesulfonate extraction

The surfactant SDBS has potential to be used as an extractant in advanced extraction methods. It was investigated if SDBS in concentrations of 10,000 mg L(-1) can be used to study the ageing behaviors of phenanthrene and pyrene in two soils. Compared to dichloromethane extraction, extraction with 10,000 mg L(-1) SDBS can improve the precision of the determination due to the low volatility of surfactant solution. In all cases tested, the amount of sorbed phenanthrene and pyrene in soils increased with contact time from 1 to 120 days, and can be applied well to both the three-domain model and the dual mode model. Redundancy analysis showed that time, organic carbon content and logK(ow) are major factors affecting the fitted Freundlich parameters and the sorption kinetics of phenanthrene and pyrene. The amount of sorbed phenanthrene and pyrene in low-concentrations samples varied more with time than the one in high concentrations, indicating that the sorption on soils is concentration-dependent. Also, the isotherms were operationally separated into a "fast" fraction and a "slow" fraction. The results imply that the adsorption sites are internal to the SOM matrix and unevenly distributed.