The sorption of various antibiotics, pharmaceuticals, and personal care products in water onto didodecyldimethylammonium bromide (DDAB)-modified montmorillonite organoclay was studied. The extent of their sorption onto the organoclay was largely dependent on the DDAB content; the effect of DDAB modification on the sorption was also influenced by the hydrophobicity and/or net charge of the pharmaceutical. The binding constants of beta-lactam antibiotics were determined from their interaction with the DDAB molecules on the organoclay and were correlated with their aqueous-octanol distribution coefficients. Additionally, they were influenced by the net charge of the antibiotic. A wide range of beta-lactam antibiotics, including penicillin- and cephalosporin-type antibiotics, were sorbed on the organoclay and rapidly degraded under mild conditions (pH 7, 25 degrees C). The continuous sorption and degradation of penicillin G in a buffer solution and in synthesized hospital wastewater using an organoclay-packed column were demonstrated. The resulting effluent was free of penicillin, and contained only penicillin degradation products, suggesting the usefulness of DDAB-MT organoclay as a barrier material for controlling the diffusion of antibiotics.