Sorption of Amphiphile Pharmaceutical Compounds onto Polar and Nonpolar Adsorbents

Abstract

Pharmaceuticals play a vital role in human and animal daily life, and as a result have been detected in groundwater and surface water in many countries. Although these compounds are detected at low concentrations in the environment, the long-term effect of such exposures is not yet known, and information on their fate and transport is still limited. Sorption of two pharmaceuticals, acetaminophen, and nalidixic acid, onto polar and nonpolar adsorbents was investigated in batch experiments. Nonionic polymeric resins (Amberlite XAD2, XAD7, and XAD761) and activated carbon were used as polar and nonpolar adsorbents, respectively. Nalidixic acid shows greater sorption than acetaminophen onto all adsorbents. Sorption of acetaminophen and nalidixic acid onto polymeric resins is well fitted with the Langmuir isotherm, while sorption onto activated carbon follows the Freundlich isotherm. For sorption of pharmaceuticals onto polymeric resins, interaction of both polar and hydrophobic moieties of pharmaceutical compounds played a role in sorption onto the adsorbents. Activated carbon shows greater sorption capacity than the polymeric resins for the two pharmaceuticals. Our results thus demonstrate that these pharmaceuticals can adsorb on both polar and nonpolar surfaces due to their amphiphilic characteristic, and that the sorption behavior strongly depends on the molecular structure of pharmaceuticals and the surface properties of adsorbents.