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

[Display omitted] •TiO2 based photo degradation of ethylbenzene, toluene, p,m-xylene and o-xylene (EXT).•By-products of EXT degradation are identified and quantified on GC–MS/GC.•Cancer risk and hazard index of by-products of EXT were assessed.•Degradation pathways for EXT were proposed based on identified by-products. 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 μg 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 220μg/m3 (ethylbenzene), 260μg/m3 (p,m-xylene), 260μg/m3 (o-xylene) and 320μg/m3 (toluene), at a flow rate of 7L/min for 12h in a laboratory of volume 195m3, the estimated cancer risks of by-products to the occupants were 1.51×10−6, 1.06×10−6, 4.69×10−7, and 1.58×10−9 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.