PHOTOCATALYTIC DEGRADATION OF AROMATIC CHLORINATED COMPOUNDS USING TIO2 - TOXICITY OF INTERMEDIATES

The photocatalytic degradation of four chlorinated aromatic compounds, namely pentachlorophenol (PCP), 2,4,-dichlorophenol (2,4,-DCP), 3,5,- dichlorophenol (3,5,-DCP), and 2,3,5,-trichlorophenol (2,3,5,-TCP), wa s investigated in the presence of an aqueous suspension of TiO2 irradi ated with near-UV light. The toxicity of the transient species was com pared to that observed for the parent compound. The comparison was car ried out by monitoring the inhibition in bacterial respiration (Escher ichia coil) by measuring the CO2 in the aqueous culture medium using f low injection analysis (FIA). Only in the case of PCP and 2,3,5,-TCP w ere the intermediates. identified by HPLC and GC/MS, found to be more toxic than the parent compound. The principal intermediates observed d uring the photocatalytic oxidation process of PCP were 2,3,5,6,-tetrac hloro-1,4,-hydroquinone, 2,3,5,6,-tetrachloro-1,4,-benzoquinone and 2, 3,5,6,-tetrachlorophenol. In the case of 2,3,5,-TCP and 3,5,-DCP, the identified intermediates were 2,3,5,-trichloro-1,4,-hydroquinone and 2,5,dichloro-1,4,-hydroquinone, respectively. The intermediates of 2,4 ,-DCP were not identified. (C) 1997 Elsevier Science Ltd.