Effects of linear alkylbenzene sulfonate (LAS) on the adsorption behaviour of phenanthrene on soils

Experimental measurements of adsorption of phenanthrene were made at 25°C with and without the presence of linear alkylbenzene sulfonate (LAS) on two soils from Shenyang, P. R. China and LUFA, Speyer, Germany. Effects of LAS on the adsorption of phenanthrene were studied in LAS concentration range around its critical micelle concentration (cmc) with emphasis on low LAS levels which are relevant to the environment. Two methods were used to simulate different environmental conditions (contacting sequence of soils with test chemicals): “soil+phenanthrene+LAS” and “soil+LAS+phenanthrene”. The contacting sequences were found to have significant influence on phenanthrene adsorption at low LAS levels <50 μm ml−1. The combination of “soil+phenanthrene+LAS” resulted in an increase in phenanthrene adsorption probably due to partition of phenanthrene to LAS hemimicelles/admicelles formed on the soil surface, while the combination of “soil+LAS+ phenanthrene” decreased the adsorption because of occupation of active hydrophobic adsorption sites by LAS. In the presence of higher concentrations (>50 μm ml−1) of LAS, results obtained with both methods indicated that adsorption of phenanthrene decreased. The values of Kd decreased from 250.7 in the absence of LAS to 112.3 and 31.9 in the presence of 500 μg ml−1 and 1000 μg ml−1 LAS, respectively. Solubilization of phenanthrene by LAS may be the dominant effects that cause the decrease of phenanthrene adsorption at high LAS concentrations.