Distribution Coefficient and Adsorption–desorption Rates of di (2-ethylhexyl) Phthalate (DEHP) onto and from the Surface of Suspended Particles in Fresh Water

The commonly used plastic softener, di (2-ethylhexyl) phthalate (DEHP), also a known Endocrine Disrupting Compound, was found contaminated in various aquatic environments, including river water in Thailand. The data of adsorption kinetics from this study indicated that DEHP can adsorb onto pure bentonite and natural suspended sediment with average adsorption rate constants of 0.0056 and 0.0039 min^?1 respectively. The average distribution coefficients between suspended particles and water found in this study for pure bentonite and natural suspended sediment were 0.045 and 0.043 l g^?1 respectively. Although the studies were carried out in pH 4.0, 7.0 and 10.0, there were no obvious influences of pH on adsorption rates and distribution coefficients of DEHP onto both pure bentonite and natural suspended particles. The desorption rate was very small and was estimated to be less than 0.03 μg min^?1. The results indicated that suspended sediment could become a long term release of DEHP and facilitate the transport of DEHP mainly due to fast adsorption rate and relatively high adsorption capacity.