Photodegradation of single and mixture of parabens – Kinetic, by-products identification and cost-efficiency analysis

Abstract

Esters of p-hydroxybenzoic acid, commonly known as parabens are preservatives used in a variety of personal care products, cosmetics, pharmaceutical and food products.This paper presents the results of studies on photochemical degradation of hazardous water contaminants – methyl- (MP), ethyl- (EP), propyl- (PP), butyl- (BuP), benzylparaben (BeP) and p-hydroxybenzoic acid (p-HBA) (individually or in mixture) using ultraviolet C lamps in the presence and absence of hydrogen peroxide. Both systems were very efficient on the degradation of the single parent compounds. Total removal of individual pollutant was achieved after 2h or 6min for UVC and UVC/H2O2, respectively. The kinetic constants of hydroxyl radicals reaction and the photolysis quantum yields were obtained for each pollutant. The decomposition of the mixture of the six compounds with the H2O2/UVC system ensures a complete degradation after 30min with a degree of mineralization of 25%. Whereas only 10% of mineralization was observed after the same time for photolysis. The pseudo-first-order fluence-based rate constants (for UVC and H2O2/UVC) for each paraben in the mixture reaction were calculated for the first time. The analysis using UHPLC/MS/MS technique shows that hydroxylation is the main pathway of the reaction with hydroxyl radicals. In fact, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid were identified as a major transformation products. Moreover the mono, di and tri derivatives of parabens were detected as the main intermediates formed during oxidation. The fluence-based experimental data and cost analysis showed that the H2O2/UVC treatment was effective in mineralizing of the parabens mixture.