Evidence of 2,7/2,8-dibenzodichloro-p-dioxin as a photodegradation product of triclosan in water and wastewater samples

A photodegradation study of triclosan, a commonly used antimicrobial agent, was carried out in order to investigate the formation of dibenzodichlorodioxin as a by-product of photodegradation in various environmental matrices and under different conditions. Deionized water and wastewater samples, spiked at 8 mug/mL with triclosan, were irradiated with natural sunlight. Aliquots of the spiked water samples were taken at different times of irradiation and compounds were isolated from the water samples by solid-phase extraction. Separation and detection of the compounds and degradation products was accomplished by gas chromatography-mass spectrometry. A major photolysis degradation product of triclosan, 2,7/2,8-dibenzodichloro-p-dioxin, was identified in wastewater samples. The photolysis experiment showed the simultaneous disappearance of triclosan and the appearance of the dioxin dependent on the pH and the organic matter content. Furthermore, a pilot survey monitoring for influent and effluent waters from a wastewater treatment plant was carried out. The presence of triclosan in all wastewater samples analyzed was revealed and dioxin was found in 80% of the cases, in influents and effluents, thus indicating its input and persistence through the wastewater treatment process. This represents a major finding since dioxins are more toxic than triclosan. Moreover, the presence of such compounds in wastewaters revealed the immediate need to improve the "classical" water treatment techniques, as well as considering limitation in water re-use. (C) 2004 Elsevier B.V. All rights reserved.