The present paper deals with the photocatalytic transformation of HHCB (1,3.4.6,7,8-hexahydro-4,6,6,7.8,8-hexamethylcyclopent[gamma]+2-benzopyr an, trade name Galaxolide), under simulated solar irradiation using titanium dioxide as a photocatalyst. The investigation has involved a study of HHCB decomposition under a variety of experimental conditions, the identification of intermediate compounds, as well as the assessment of mineralization. A fully nested experimental design was applied to study the effect of various matrices (i.e. distilled water, surface water and wastewater) as well as the initial HHCB concentration on the variation of the photocatalytic efficiency. GC/MS and LC/MS were brought to bear in assessing the temporal course of the photocatalyzed process. A first pathway involves the hydroxylation, that is confined to the benzopyran moiety. Another route proceeds through the detachment of the hexamethylpentacycle moiety, with the formation of the ketoderivative. A parallel transformation involves benzopyran moiety with the ring cleavage. All the identified transformation products are degraded themselves until 2 h of irradiation, while complete mineralization is achieved until 8 h. (C) 2010 Elsevier B.V. All rights reserved.