Sorption and release of endocrine disruptor compounds onto/from surface and deep horizons of two sandy soils

Adsorption and desorption processes of environmental endocrine disruptor compounds (EDCs) bisphenol A (BPA), octylphenol (OP), 17-alpha-ethynilestradiol (EED) and 17-beta-estradiol (17ED) onto/from a surface and a deep horizon of two sandy soils have been investigated. Adsorption kinetics of EDCs onto soils are generally very fast, mainly occurring in the first few hours of contact. Experimental adsorption data were best fitted in a linear isotherm for BPA, in a nonlinear Freundlich isotherm for EED, either in a linear or a nonlinear Freundlich model for OP, and in a Langmuir isotherm for 17ED. The values of the Freundlich constant, K, and of the distribution coefficient, Kd, calculated from experimental isotherms showed that these parameters are positively correlated with the organic carbon (OC) content of the soils and that surface horizon soils exhibit a much higher adsorption capacity than deep horizon soils for any EDC. The small differences of the organic carbon partition coefficient (KOC) values measured among the various soils suggest that not only the content but also the nature and properties of OC affect the extent of adsorption, and that other soil components, e.g., clay minerals, might be involved in the adsorption process of EDCs. Among the various EDCs examined, OP appears to be the most adsorbed, and EED and 17ED show a similar extent of adsorption onto any soil. Adsorption of BPA is generally reversible and its desorption occurs quickly and is completed after few desorption steps. On the contrary, adsorption of OP and EED is mostly irreversible, partial desorption occurs slowly and most soil samples retain high amounts of adsorbate at the end of the experiment.