Direct UV photolysis of cloperastine in aqueous solution: Kinetic model and degradation pathway

The increasing production and release of synthetic organic chemicals, including pharmaceuticals, into our environment has allowed these substances to accumulate in our surface water systems. Current purification technologies have been unable to eliminate these pollutants, resulting in their ongoing release into aquatic ecosystems. This study focuses on cloperastine (CPS), a cough suppressant and antihistamine medication. The environmental impact of CPS usage has become a concern, mainly due to its increased detection during the COVID-19 pandemic. CPS has been found in wastewater treatment facilities, effluents from senior living residences, river waters, and sewage sludge. However, the photosensitivity of CPS and its photodegradation profile remain largely unknown. This study investigates the photodegradation process of CPS under simulated tertiary treatment conditions using UV photolysis, a method commonly applied in some wastewater treatment plants. Several transformation products were identified, evaluating their kinetic profiles using chemometric approaches (i.e., curve fitting and the hard-soft multivariate curve resolution-alternating least squares (HS-MCR-ALS) algorithm) and calculating the reaction quantum yield. As a result, three different transformation products have been detected and correctly identified. In addition, a comprehensive description of the kinetic pathway involved in the photodegradation process of the CPS drug has been provided, including observed kinetic rate constants.