CLEAN-UP OF WATER POLLUTED WITH SULFONAMIDE ANTIBIOTICS: STRUCTURAL MODIFICATIONS INDUCED BY ADSORPTION INTO ORGANOPHYLIC H-Y ZEOLITE

An actual and underestimated problem is the environmental pollution due to drug release by humans and feedstocks. Generally, after administration, drugs, (i.e. antibiotics, hormones, antiepileptics, pain-killers) are excreted from the organism, for the most part, unchanged. Drug residues are detected in the outlets of waste water treatment plants or in the agricultural wastes, as a consequence of manure spreading. Whether drugs are not adsorbed by soils, they move along the soil profile towards the groundwaters. Antibiotics, used in the treatment of diseases or as growth-promoting additives in animal feeds (banned from European Community on 2006 but still permitted in USA), are the most diffuse classes of veterinary drugs. Among these, sulfonamides are the fifth most widely used group of veterinary antibiotics within the EU and are considered ubiquitarious pollutants [1,2,3]. Because of their unique adsorption and ion-exchange properties, zeolites are versatile materials, commonly applied as adsorbent, molecular sieves or catalysts [4,5]. Sulfadiazine [4-amino-N-(4-methyl-2-pyrimidinyl)benzenesulfonamide], sulfamethazine [4-amino-N-(4,6-dimethyl-2-pyrimidinyl)benzenesulfonamide], and sulfachloropyridazine [4-amino-N-(6-Cl-3-pyridazinyl)benzenesulfonamide] were purchased as certified standards. The organophylic faujasite (Y) zeolite with channel size comparable to sulfadrugs dimension was supplied by Tosoh Corporation (Japan) in H+-form (H-Y). With the aim to perform a cheap and environmentally friend clean-up system of waters contaminated by antibiotics, in this study we have investigated the adsorption of sulfonamides into H-Y zeolite. Sulfonamides were completely and quickly (t < 1 min) removed from water on H-Y zeolite. After 10 adsorption cycles, the maximal amounts of antibiotics adsorbed on zeolite ranged beetween 18-26% of zeolite dry weight as evidenced by thermogravimetric analyses. The adsorbed amount accounts for about one antibiotic molecule per zeolitic cage. Despite of the large amount of antibiotics adsorbed, the adsorption was not reversible in water. X-ray structure analyses were carried out by Rietveld method on zeolite before and after adsorption. Unit cell parameter variations and structural deformations after adsorption revealed the presence of sulfonamide molecules inside zeolitic cage. The most evident deformation effect was the lowering of Fd-3m real symmetry of the parent H-Y to Fd-3 after the adsorption of sulfadiazine or sulfachloropyridazine. As a consequence, remarkable deformations occur in the 12-membered ring channel system as reported in the table below. The deformation of H-Y after sulfamethazine adsorption caused a lowering of symmetry up to the monoclinic P2/m space group, as shown by the diffraction pattern here reported, preventing the Rietveld structure refinement. The arrows reported in the patter indicate the reflections forbidden in the cubic system.