Fate of anthropogenic organic pollutants in soils with emphasis on adsorption/desorption processes of endocrine disruptor compounds*
Elisabetta Loffredo and Nicola Senesi
Dipartimento di Biologia e Chimica Agroforestale e Ambientale, University of Bari, Via Amendola 165/A, 70126-Bari, Italy
Abstract: After providing a brief overview of the various phenomena that anthropogenic organic pollutants (AOPs) of various nature and origin are subjected to in soil, the paper focuses on an important class of these, the endocrine disruptor compounds (EDCs), which are hormone-like substances able to alter (i.e.) disrupt, the normal endocrine functions in animals and humans. EDCs may enter the soil through current agricultural practices andor disposal of urban and industrial effluents, sludges, and wastes. The estrogenic risk of EDCs is generally related to their distribution and speciation in the various soil phases, in which adsorption/desorption processes play a very important role. Adsorption kinetics and adsorption/desorption isotherms of the EDCs: bisphenol A (BPA), octylphenol (OP), 17-α-ethynilestradiol (EED), and 17-β-estradiol (17ED), onto four samples collected from the surface (depth 0-30 cm) and deep (depth 30-90 cm) horizons of two acidic sandy soils in Portugal (P) and Germany (G) (P30 and G30, and P90 and G90, respectively) were determined using a batch equilibrium method and the high-performance liquid chromatography (HPLC) technique. Adsorption of EDCs onto all soils examined occurs in two phases, a rapid one in less than 10 h of contact, and corresponding to more than 90 % of total adsorption, and a slow one that may need several hours until attainment of equilibrium. Experimental adsorption data fit best in a linear isotherm for BPA, in a nonlinear, L-shaped Freundlich isotherm for EED, in either a linear or a nonlinear Freundlich isotherm for OP, and in a Langmuir isotherm for 17ED. Thus, no limiting adsorption is observed for soils examined over the concentration range tested for BPA, OP, and EED, whereas a maximum adsorption (i.e., saturation) is reached only by 17ED. In general, the values of the Freundlich constant, K, and of the distribution coefficient, Kd, calculated from the experimental isotherms of the four EDCs onto soils examined follow the same trend, that is: G30 > P30 > P90 > G90. Further, the K and Kd values of any EDC are positively correlated with the soil organic carbon (OC) content, which is larger for surface horizon soils than deep horizon soils. Adsorption of BPA is generally reversible, and its desorption occurs quickly and completely, thus, it is expected to move down the soil profile, and possibly contaminate the groundwater. On the contrary, OP and EED are adsorbed almost irreversibly, and are slowly and only limitedly desorbed, thus are expected to accumulate, especially in the top soil layer, and cause soil contamination.
Keywords: anthropogenic organic pollutants; soil; endocrine disruptor compounds; adsorption kinetics; adsorption/desorption isotherms.
*Paper presented at the 40th IUPAC Congress, Beijing, China, 14-19 August 2005. Other presentations are published in this issue, pp. 889-1090.