Drugs as new environmental contaminants: photocatalytic degradation process as a tool to study biological/environmental fate of salbutamol and atenolol

Introduction The presence of drug residues in the environment, therapeutic, veterinary and illicit drugs, has recently become quite alarming and monitoring of pharmacologically active compounds is more and more necessary. The purpose of this study is to artificially produce degradation compounds similar to those formed in oxido/reductive metabolic and environmental pathways by adopting a photocatalytic process as a model-system and, afterwards, to identify them in urine/water samples, beside parent compounds. We chose salbutamol and atenolol, due to popular use of these drugs. Liquid chromatography appears the best technique for direct analysis of these samples (neither derivatization nor complex extraction procedure for polar compounds), together with an high resolution MSn detection that empowers diagnostic identification and metabolites characterization. Methods Heterogeneous photocatalysis experiments were performed under simulated solar light adopting TiO2 as photocatalyst. Solar light simulation was obtained using a 1500 W xenon lamp, in a device equipped with a 360 nm cut-off filter, for 24 hours at room temperature. LC-MS analysis were accomplished on a LTQ-Orbitrap instrument, with an electrospray interface. Chromatographic separation were achieved on C18 reversed phase columns. Degradation products identification has been performed acquiring MSn spectra at 100,000 resolution, with internal standards, in order to have elemental composition confirmation. Under these conditions experimental uncertainity was < 5 mmass units. Photodegradation model was applied to salbutamol and atenolol. Studied substances and metabolites were quantified in environmental and in human urine samples coming from treated patients. Preliminary data In beta-blocker drugs photocatalytic degradation, many oxidative potential metabolites were formed in the simulation model, beside some hydrolysis and molecule breakdown sub-products. Main degradation products induced by photocalysis were hydroxyl- (on aromatic ring and aliphatic chain) and de-methyl derivatives, while foremost breakdown products contains the aliphatic lateral chain. High resolution MSn spectra were used to identify and confirm the proposed structures. Kinetics of formation of the main degradation products have been studied by LC-MS. An highly sensitive method has been developed to measure the degradation products in different matrices that allows detection of parent drugs at the ng/L level. Future studies will be focused to the identification and measurement both of parent drugs and their metabolic degradation products in biological samples (human urine) and in water samples (urban drains, sewage treatment plants, freshwaters). Findings will be compared to the proposed degradation mechanisms. Novel aspects Identification and measurements of new drug-derived environmental contaminants and their photodegradation products in surface water samples