Adsorption of the quinolone antibiotic nalidixic acid onto anion-exchange and neutral polymers

Pharmaceutical products are being found in surface and ground waters around the world. While the consequences to human health are unknown, it is suspected that these contaminants adversely alter aquatic ecosystems. This study presents adsorption results for one pharmaceutical product, nalidixic acid (NA), on neutral and anion-exchange polymers at three pH values. The adsorption of NA below and above its pKa of ∼6 on polymers with different matrices, forms, and degrees of polarity were evaluated. By comparing the Freundlich constants KF and n, the results show that the neutral form of NA adsorbs to a greater extent on neutral polymers, and that the anionic form of NA adsorbs more to anion-exchange polymers. Also, results of the adsorption experiments suggest that aromatic ring interactions between NA and the surface of both neutral and anion-exchange polymers are important in the adsorption process. These results have important implications for the treatment of pharmaceutical-contaminated water, as many pharmaceutical contaminants are ionizable and have aromatic rings in their structure. This study illustrates the importance of pH and sorbate and sorbent structure in considering polymer sorption for treatment of pharmaceutical-contaminated aqueous systems.