Degradation kinetics and estrogenic activity of 17β-estradiol removal by aqueous manganese dioxide

Abstract

Natural and synthetic hormones have emerged as a new group of contaminants in soil and water systems. To better understand the processes affecting these compounds in soils and sediments, the kinetics of 17β-estradiol (E2) transformation by hydrous manganese oxide (δ-MnO2 were investigated as a function of reactant concentration, MnO2 concentration, pH and the presence of co-solutes. The reaction of E2 degradation by δ-MnO2 did not exhibit simple pseudo–first-order kinetics, although a good linear fit (R2 = 0.97) was obtained during the first 30 min, which was indicative of pseudo–first-order reaction kinetics in the first stage. The initial reaction rate (rinit) values of E2 degradation were enhanced with increasing E2, MnO2 and H+ concentration. The reaction orders for E2, MnO2 and H+ concentrations were 0.80, 0.72 and 0.07, respectively. The presence of metal ions and carboxylic acids had an inhibitory effect on rinit as a result of the decreased number of active surface sites in the presence of co-solutes. The same inhibitory effect on rinit was also observed in wastewater. Furthermore, the results showed that δ-MnO2 not only degraded E2 but also removed 62% and 48% of the estrogenic activity originating from E2 in ultrapure water and wastewater, respectively. This study demonstrated that natural manganese oxides in soils and sediments are likely to promote appreciable degradation of E2, and that reaction rates are strongly dependent on solution conditions. However, a combination of methods should be adopted in order to completely remove the estrogenic activity of E2.