Quantification and human health risk assessment of by-products of photo catalytic oxidation of ethylbenzene, xylene and toluene in indoor air of analytical laboratories

The by-products of TiO2-based photocatalytic oxidation (PCO) of ethylbenze, p,m-xylene, o-xylene and toluene (EXT) in vapour phase and those adsorbed on the catalyst surface (solid phase) were identified and quantified on GC/GC-MS. A factor was developed in terms of mu g of by-product produced per mg of EXT removed per sq-meter surface area of catalyst for estimating the mass of by-products produced. The by-products quantified were: acetone, hexane, cyclohexane, benzene, crotonaldehyde, toulene, 1,4-benzoquinone, benzaldehyde, phenol, benzylalcohol, cresol, hydroquinone and benzoic acid. The by-products accounted for 2.3-4.2% of the total mass of EXT treated. For treating concentrations of 220 mu g/m(3) (ethylbenzene), 260 mu g/m(3) (p,m-xylene), 260 mu g/m(3) (o-xylene) and 320 mu g/m(3) (toluene), at a flow rate of 7 L/min for 12h in a laboratory of volume 195 m(3), the estimated cancer risks of by-products to the occupants were 1.51X10(-6), 1.06X10(-6), 4.69X10(-7), and 1.58X10(-9) respectively. The overall hazard index (HI) of the by-products for EXT was of the order 10(-4); which is much less than desired level of 1.0. The estimated risks were within the acceptable level. This study has also suggested the photocatalytic degradation pathways for EX which are through formation of toluene. (C) 2016 Elsevier B.V. All rights reserved.