In vitro toxicological evaluation of emissions from catalytic oxidation removal of industrial VOCs by air/liquid interface (ALI) exposure system in repeated mode.

Toxicity of toluene and by-products formed during its catalytic oxidative degradation was studied in human bronchial BEAS-2B cells repeatedly exposed. BEAS-2B cells were exposed using an Air-Liquid Interface (ALI) System (Vitrocell®) for 1 h per day during 1, 3 or 5 days to gaseous flows: toluene vapors (100 and 1000 ppm) and outflow after catalytic oxidation of toluene (10 and 100%). After exposure to gaseous flow, cytotoxicity, inflammatory response and Xenobiotic Metabolism Enzymes (XME) gene expression were investigated. No significant cytotoxicity was found after 5 days for every condition of exposure. After cells exposure to catalytic oxidation flow, IL-6 level increased no significantly in a time- and dose-dependent way, while an inverted U-shaped profile of IL-8 secretion was observed. XME genes induction, notably CYP2E1 and CYP2F1 results were in line with the presence of unconverted toluene and benzene formed as a by-product, detected by analytical methods. Exposure to pure toluene also demonstrated the activation of these XMEs involved in its metabolism. Repeated exposure permits to show CYP1A1, CYP1B1 and CY2S1 expression, probably related to the formation of other by-products, as PAHs, not detected by standard analytical methods used for the development of catalysts.

Usefulness of toxicological validation of VOCs catalytic degradation by air-liquid interface exposure system.

Toluene is one of the most used Volatile Organic Compounds (VOCs) in the industry despite its major health impacts. Catalytic oxidation represents an efficient remediation technique in order to reduce its emission directly at the source, but it can release by-products. To complete the classical performance assessment using dedicated analytical chemistry methods, we propose to perform an untargeted toxicological validation on two efficient catalysts. Using biological system allows integrating synergy and antagonism in toxic effects of emitted VOCs and by-products, often described in case of multi-exposure condition. Catalysts Pd/α-Al2O3 and Pd/γ-Al2O3 developed for the oxidation of toluene were both coupled to a Vitrocell® Air-Liquid Interface (ALI) system, for exposure of human A549 lung cells during 1h to toluene or to catalysts exhaust before quantification of xenobiotics metabolizing enzymes. This study validated initially the Vitrocell® as an innovative, direct and dynamic model of ALI exposure in the assessment of the performances of new catalysts, showing the presence of chemically undetected by-products. The comparison of the two catalysts showed then that fewer organic compounds metabolizing genes were induced by Pd/γ-Al2O3 in comparison to Pd/α-Al2O3, suggesting that Pd/γ-Al2O3 is more efficient for toluene total oxidation from a toxicological point of view.