Environmental photochemistry research at the department of analytical chemistry, University of Torino, Italy Davide Vione

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1 Environmental photochemistry research at the department of analytical chemistry, University of Torino, Italy Davide Vione The group of Environmental Chemistry at the Department of Analytical Chemistry, University of Torino, carries out research in the fields of environmental analytical chemistry, heterogeneous photocatalysis, and environmental process understanding. Here a brief outline will be given of recent studies in the field of environmental photochemistry, related to both atmospheric aerosols and surface waters. Environmental photochemical processes are induced by sunlight irradiation of various matrices and, following absorption of solar radiation, photoactive compounds can undergo different transformation reactions. Accordingly, direct and organic matter-sensitised photolysis processes and the photogeneration of reactive transient species can take place and be involved into the transformation of natural and xenobiotic compounds, including organic pollutants, in the environment. In some cases pollutant phototransformation reduces the toxic and/or mutagenic effect of harmful compounds, but in other instances more harmful compounds than the parent ones can be formed. It is therefore very interesting to study the phototransformation processes of model molecules under environmentally relevant conditions, with the purposes of better understanding the photochemical behaviour of the natural environments and of identifying possible harmful compounds that can be formed by photoinduced processes. The cited studies are often carried out in collaboration with other institutions with the aim of producing joint research articles, exchanging personnel, and possibly collaborating in joint research projects. Extension of the collaboration network is one of our topical aims, and proposals in this sense by research groups or people interested in collaboration are therefore strongly encouraged. Present collaboration is being carried out with the following foreign institutions: Laboratoire Chimie et Environnement, Université de Provence, Marseille, France. Departement de Chimie, Université de Bretagne Occidentale, Brest, France. Laboratoire de Photochimie Moleculaire et Macromoleculaire, Université Blaise Pascal, Clermont- Ferrand, France. Department of Inorganic and Analytical Chemistry, Al. I. Cuza University of Iasi, Iasi, Romania. Hadley Centre, Met Office, Exeter, United Kingdom. Department of Chemical Engineering, University of Calcutta, Calcutta, India. Department of Genetics, Development and Molecular Biology, Aristotle university of Thessaloniki, Greece. Institute for the Environment at the Brunel University, United Kingdom. Institute of earth Sciences Jaume Almera, Barcelona, Spain. ETHZ (Swiss Federal Institute of Technology), Zurich, Switzerland. Two pictures of Lake Rouen (2391 m a.s.l., NW Italy), one of the lakes that have been the object of investigation concerning photochemical processes in surface waters. 43

2 Photochemical processes in natural waters Various studies have been focused on the production and reactivity of OH radicals in surface waters, mainly lakewater, using the reaction transforming benzene into phenol as a probe for OH quantification. In this way the relative roles of dissolved organic matter (DOM), nitrate and nitrite as OH sources under sunlight, and of DOM, carbonate and bicarbonate as sinks have been assessed (1). It has thus been possible to develop a model, based on water composition data and irradiation kinetics, to quantify the steady-state [ OH] under sunlight irradiation, and therefore to foresee the degradation kinetics, upon reaction with OH, of any dissolved compound for which the rate constant for reaction with the hydroxyl radical is known (2). Seasonal and water-column effects could be taken into account in the model as far as the photochemistry of nitrate and nitrite is concerned (3). From the cited model it has also been possible to estimate the steady-state [ NO2] that can be observed in surface waters because of nitrate photolysis and nitrite photooxidation (4,5). This allows the assessment of the potentiality for aromatic photonitration processes in surface waters, leading to toxic and mutagenic nitroaromatic compounds. It has for instance been possible to conclude that photonitration induced by nitrate and nitrite is compatible with the observed summertime transformation of 2,4-dichlorophenol into 2,4-dichloro-6-nitrophenol in a couple of weeks in shallow paddy fields in the Rhône delta (Southern France). Note that 2,4-dichlorophenol is an environmental transformation intermediate of the herbicide dichlorprop, heavily used in flooded rice farming (6). The pathways leading to the photonitration of aromatic compounds upon nitrate photolysis have also been studied (7,8). Interest has also been focused on the role of radical species such as Cl2 as photogenerated co-oxidants in the degradation of organic compounds (9-11). The dichlorine radical can be formed on chloride photooxidation by Fe(III) oxide colloids and it enhances, as an oxidising and chlorinating agent, the degradation of organic compounds in brackish waters. In the case of the anti-epileptic drug carbamazepine it has been demonstrated that chloride-enhanced photodegradation by Fe(III) colloids is much faster than direct and DOM-sensitised photolysis (12). 1. D. Vione, G. Falletti, V. Maurino, C. Minero, E. Pelizzetti, M. Malandrino, R. Ajassa, R.I. Olariu, C. Arsene. Sources and Sinks of Hydroxyl Radicals upon Irradiation of Natural Water Samples. Environ. Sci. Technol. 2006, 40, C. Minero, V. Lauri, V. Maurino, E. Pelizzetti, D. Vione. A Model to Predict the Steady-State Concentration of Hydroxyl Radicals in the Surface Layer of Natural Waters. Ann. Chim. (Rome), in press. 3. D. Vione, C. Minero, V. Maurino, E. Pelizzetti. Seasonal and Water Column Trends of the Relative Role of Nitrate and Nitrite as OH Sources in Surface Waters. Ann. Chim. (Rome), in press. 4. C. Minero, S. Chiron, G. Falletti, V. Maurino, E. Pelizzetti, R. Ajassa, M. E. Carlotti, D. Vione. Photochemical Processes Involving Nitrite in Surface Water Samples. Aquat. Sci., 2007, 69, C. Minero, V, Maurino, E. Pelizzetti, D. Vione. Assessing the Steady-State [ NO2] in Environmental Samples. Implications for Aromatic Photonitration Processes Induced by Nitrate and Nitrite. Env. Sci. Pollut. Res., 2007, in press. 6. S. Chiron, C. Minero, D. Vione. Occurrence of 2,4-Dichlorophenol and of 2,4-Dichloro-6- nitrophenol in the Rhône River Delta (Southern France). Environ. Sci. Technol., 2007, 41, C. Minero, F. Bono, F. Rubertelli, D. Pavino, V. Maurino, E. Pelizzetti, D. Vione. On the effect of ph in aromatic photonitration upon nitrate photolysis. Chemosphere, 2007, 66, D. Vione, C. Minero, F. Housari, S. Chiron. Photoinduced transformation processes of 2,4- dichlorophenol and 2,6-dichlorophenol on nitrate irradiation. Chemosphere, accepted. 9. C. Minero, V. Maurino, E. Pelizzetti, D. Vione. An Empirical, Quantitative Approach to Predict the Reactivity of Some Substituted Aromatic Compounds towards Reactive Radical Species (Cl2, Br2, NO2, SO3, SO4 ) in Aqueous Solution. Env. Sci. Pollut. Res. 2006, 13, D. Vione, V. Maurino, C. Minero, P. Calza, E. Pelizzetti. Phenol Chlorination and Photochlorination in the Presence of Chloride Ions in Homogeneous Aqueous Solution. Environ. Sci. Technol. 2005, 39, S. Khanra, C. Minero, V. Maurino, E. Pelizzetti, B. K. Dutta, D. Vione. Phenol transformation insuced by UVA photolysis of the complex FeCl2+. Environ. Chem. Lett., in press. 12. S. Chiron, C. Minero, D. Vione. Photodegradation Processes of the Antiepileptic Drug Carbamazepine, Relevant to Estuarine Waters. Environ. Sci. Technol. 2006, 40,

3 A predictive model to foresee the steady-state concentration of hydroxyl radicals, [OH], under 22 W m 2 sunlight UV irradiation in the surface layer of natural waters as a function of nitrate concentration, Non-Purgeable Organic Carbon (NPOC), and Inorganic Carbon (IC) (2). Half-life times (in summer sunny days equivalent to 15 July at 45 N latitude) of hypothetical compounds, due to reaction with OH, as a function of the steady-state [OH] (22 W m 2 sunlight UV irradiation) and of the second-order rate constant koh, the units of which are M 1 s 1 (2). 45

4 A multi-wavelength calculation of the sunlight intensity at different water column depths in Lake Piccolo in Avigliana (NW Italy) and of the potential for OH photoproduction by nitrite, present in lakewater at μm levels (3). Photochemical processes in atmospheric aerosols Various studies have been devoted to the elucidation of aromatic photonitration processes induced by nitrate and nitrite photolysis in atmospheric water droplets and on the surface of airborne particulate matter (13). It has been possible to identify the different nitration pathways that phenolic and non-phenolic aromatic compounds undergo under otherwise identical conditions (14), and the gas-phase reactivity of solid nitrate in the presence of airborne particulate matter components (15). The results of these studies give insight into the environmental secondary formation of harmful nitroaromatic compounds, including the powerful phytotoxic agent 2,4-dinitrophenol (16). It has also been assessed the role of organic compounds present in snow and cloud into the enhancement of the photochemical production of nitrite upon nitrate photolysis (17). The studied process can be relevant to the photogeneration of HNO2 on irradiated snow layers in the polar regions and the photochemical formation of nitrite inside cloud droplets and on particles. Further studies have been focused on the assessment of the role of coadsorption of organic and inorganic species in the photochemical processes that occur on the surface of atmospheric water droplets. It was shown that up to 15% of the total photochemical reactivity in a 1 μm droplet takes place in a surface layer that weights only 0.1% of the volume (18). 13. D. Vione, V. Maurino, C. Minero, E. Pelizzetti, M. A. J. Harrison, R. I. Olariu, C. Arsene. Photochemical Reactions in the Tropospheric Aqueous Phase and on Particulate Matter. Chem. Soc. Rev. 2006, 35, D. Vione, V. Maurino, C. Minero, E. Pelizzetti. Nitration and Photonitration of Naphthalene in Aqueous Systems. Environ. Sci. Technol. 2005, 39, D. Borghesi, D. Vione, V. Maurino, C. Minero. Transformations of Benzene Photoinduced by Nitrate Salts and Iron Oxide. J. Atmos. Chem. 2005, 52, D. Vione, V. Maurino, C. Minero, E. Pelizzetti. Aqueous Atmospheric Chemistry: Formation of 2,4- Dinitrophenol upon Nitration of 2-Nitrophenol and 4-Nitrophenol in Solution. Environ. Sci. Technol. 2005, 39, C. Minero, V. Maurino, F. Bono, E. Pelizzetti, A. Marinoni, G. Mailhot, M. E. Carlotti, D. Vione. Effect of Selected Organic and Inorganic Snow and Cloud Components on the Photochemical Generation of Nitrate by Nitrite Irradiation. Chemosphere, in press. 18. D. Vione, C. Minero, A. Hamraoui, M. Privat. Modelling Photochemical Reactions in Atmospheric Water Droplets: An Assessment of the Importance of Surface Processes. Atmos. Environ., 2007, 41, Dr. Davide Vione was born in Moncalieri (Turin, Italy) on 14 October He received his Laurea degree in Chemistry at the University of Torino (Italy) in 1998 with full honours, and PhD in Chemistry in Since 2002 he has been a University lecturer in Torino. His research interests focus on environmental photochemistry applied to 46

5 surface waters and atmospheric aerosols, and on Advanced Oxidation Processes (heterogeneous photocatalysis, Fenton reaction, sonochemistry) for water and wastewater decontamination. He has authored to date 52 scientific articles on ISI journals (accepted, in press or published) and 5 book chapters. Received a Young Researcher s Award in 2003 from the Italian Chemical Society Analytical Chemistry Division and was awarded as European Young Researcher of the Year 2003 by the European Association of Chemistry and the Environment. Davide Vione Dipartimento di Chimica Analitica, Università di Torino, Via Pietro Giuria 5, Torino, Italia. Tel ; Fax