Usefulness of Toxicological Validation of Vocs Catalytic Degradation by Air- Liquid Interface Exposure System Crossmark

Environmental Research 152 (2017) 328–335 Contents lists available at ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres Usefulness of toxicological validation of VOCs catalytic degradation by air- liquid interface exposure system crossmark Margueritta Al Zallouha, Yann Landkocz, Julien Brunet, Renaud Cousin, Eric Genty, ⁎ Dominique Courcot, Stéphane Siffert, Pirouz Shirali, Sylvain Billet Unité de Chimie Environnementale et Interactions sur le Vivant EA4492, Université du Littoral Côte d′Opale, 189 A Avenue Maurice Schumann, 59140 Dunkerque, France ARTICLE INFO ABSTRACT Keywords: Toluene is one of the most used Volatile Organic Compounds (VOCs) in the industry despite its major health Catalytic oxidation impacts. Catalytic oxidation represents an efficient remediation technique in order to reduce its emission Air-liquid interface exposure directly at the source, but it can release by-products. To complete the classical performance assessment using Toluene dedicated analytical chemistry methods, we propose to perform an untargeted toxicological validation on two Toxicological validation efficient catalysts. Using biological system allows integrating synergy and antagonism in toxic effects of emitted By-products identification 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 1 h 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. 1. Introduction where 80% of the absorbed dose undergoes a chain of oxidation reactions by the intervention of different enzymes which make the Volatile Organic Compounds (VOCs) represent a variety of sub- molecule more hydrophilic and allow urine excretion of metabolites. stances belonging to different chemical families (aromatic hydrocar- Between 10% and 20% of inhaled toluene are excreted in the expired bons, ketones, alcohols, alkanes, aldehydes, etc.) and known for being air with a half-life of about 25 min (Benoit et al., 1985). Toluene is important contributors to air pollution (Khan and Ghoshal, 2000). known for both acute and chronic toxic effects (Tormoehlen et al., Among the major VOCs, Benzene, Toluene, Ethylbenzene and Xylenes 2014). It is classified as a Carcinogenic, Mutagenic and Reprotoxic (BTEX) have major and direct impact on human health. Toluene is (CMR) category 3 due to its toxicity for reproduction. widely used in many industrial sectors where 32% of commercial Because of toluene toxicity, it is necessary to reduce emissions toluene enter in the process of benzene synthesis and 19% is used as directly at source. When substitution is not possible, catalytic oxidation solvents with almost 90 kt/year as paint solvents in European Union represents an economical and environmental alternative to the thermal (Hansen et al., 2002). Toluene has a relatively well known toxicity with oxidation of VOCs. The choice of suitable catalysts for the total the respiratory tract as major route of absorption. Limit values for oxidation of toluene should usually take into account the activity, occupational exposure to toluene were established in France, in 2012, stability, cost and feasibility of large scaling-up of laboratory systems. with an exposure limit value of 20 ppm equivalent to 76.8 mg/m3 for A catalyst is generally formed by a support and an active surface. 3 8 h and 100 ppm (384 mg/m ) on a short-term (under 15 min). The Aluminium oxides, especially α-Al2O3 and γ-Al2O3, present good same values were set for the 8 h exposure in the USA since 2007 (INRS, performances as supports for active phases for BTEX oxidation. 2012). Aluminas have some interesting properties like a high thermal stability After absorption, toluene is primarily metabolized in the liver, for α-Al2O3 or a high specific surface area with acidic properties for γ- ⁎ Corresponding author. E-mail address: [email protected] (S. Billet). http://dx.doi.org/10.1016/j.envres.2016.10.027 Received 22 July 2016; Received in revised form 24 October 2016; Accepted 27 October 2016 0013-9351/ © 2016 Published by Elsevier Inc. M. Al Zallouha et al. Environmental Research 152 (2017) 328–335 Al2O3 (Burgos et al., 2002; Kim and Shim, 2009; Ordóñez et al., 2002; 2.2.1. Palladium impregnation of support Papaefthimiou et al., 1997). In order to increase the activity of these Palladium was deposed on α-Al2O3 by an aqueous impregnation oxides, palladium and platinum can be used as actives phases since method with a content of 0.5 wt%. Alpha alumina was suspended in an they showed very good performances although palladium constitutes a appropriate volume of a palladium nitrate solution (0.25 g/L). The good compromise between performance and cost (Papaefthimiou et al., suspension was maintained for 18 h at 60°C. Then, water was removed 1998; Rusu and Dumitriu, 2003). by rotary evaporator. The solid was dried one night at 100°C before to Total oxidation of VOCs should produce only water and carbon be calcined 4 h at 400°C (1°C/min) under air flow (2 L/h) (Brunet dioxide. However, during operation, the catalytic process can lead to et al., 2015). the release of by-products, sometimes more toxic than the original VOCs. In order to ensure an evaluation procedure of catalyst perfor- 2.2.2. Characterization of catalysts mances from an environmental and health-safety approach, here we Specific surface areas (SBET) were measured by the Brunauer- propose to perform an untargeted toxicological validation of two Emmet-Teller method with a “ThermoElectron Qsurf series Surface catalysts preliminary selected on chemical criteria. The validation we Area Analyzer” apparatus. Prior to measurement, calcined catalyst propose corresponds to the evaluation the response of biological samples were heated at 130°C for 1 h under a helium flow. Adsorption system exposed to catalytic exhaust. This method integrates potential was made with a N2/He mixture (30/70) at -196°C. Desorption of synergy and antagonism existing in toxic effects of emitted VOCs and gaseous N2 was quantized with a thermal conductivity detector. by-products, often described in case of multi-exposure condition. Elementary analysis was performed with an ICP-OES (Thermo, model In case of gaseous or very volatile compounds, exposure of in vitro ICAP 6300 Duo) after acidic dissolution of 50 mg of catalyst sample. systems becomes a challenge. According to Rasmussen, in vitro methods of exposure to gaseous mixtures have to follow some funda- 2.2.3. Catalytic test mental requirements: (i) the contact between the cells and the test Total oxidation of toluene was studied in a conventional fixed bed compounds should be as close as possible to avoid interactions, and to reactor loaded with 100 mg of catalyst. A Toluene/Air mixture was realize direct contact of cells and gas phase components and (ii) generated with a saturator CAL-PC-5 from Calibrage in order to obtain methods have to be developed to maintain a humidified atmosphere 1000 ppm in a flow of 100 mL/min. The tests were made between 50 in order to avoid cells drying (Rasmussen, 1984). Recent methodolo- and 400°C with a temperature ramp of 1.5°C/min. The catalysts were gical and technical breakthroughs of in vitro methods have the pre-treated 2 h at 200°C (1°C/min) under air flow (2 L/h−1) and then, potential to fulfill these essential requirements. This pattern of cell for impregnated catalysts, were reduced 2 h at 200°C (1°C/min) under exposure was initially performed culturing cells on collagen-coated H2 (5.0) flow (2 L/h). The organic compounds were analysed by gas membranes located on special platforms (Chen et al., 1993) and more chromatography with a CP-4900 microGC (Agilent) coupled to a recently on porous membranes located in Transwell® inserts Pfeiffer-Vacuum Omnistar Quadrupole Mass Spectrometer (QMS- ® (Aufderheide et al., 2003). Cells culture exposed on Transwell inserts 200). CO and CO2 were analysed with an infrared analyzer (ADEV indeed provides a perfect system to study the cellular responses caused 4410 IR). by very close exposure to airborne chemical, avoiding the possible Toluene conversion was calculated considering products, by-pro- interference of culture medium. The dynamic direct exposure of human ducts and carbon number for each compound: cells to chemicals in the atmosphere can be achieved using the ⎛ ⎞ ® [CO2T ] + [CO] T + [C 6 H 6T ] *6 Vitrocell model. This system provides the ability to grow cells on X=T ⎜ ⎟*100 ⎝ [CO ] + [CO] + [C H ] *6 + [C H ] *7 ⎠ permeable membranes in the presence of culture medium and to 2T T 6 6T 7 8T expose them directly to a continuous and dynamic gas flow at the Air- Where: Liquid Interface (ALI) (Aufderheide and Mohr, 1999). Target cells can thus be continuously exposed to airborne chemicals on their apical – XT was the toluene conversion at the T temperature (%); side, while being nourished and hydrated with culture medium from – [I]T was the concentration of the compounds I at the T temperature their basolateral side. (ppm); In this study, two catalysts Pd/α-Al2O3 and Pd/γ-Al2O3 were both chemically and toxicologically tested in order to determine the most Catalytic intrinsic activity was calculated at a toluene conversion of efficient one for toluene oxidation.

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