Effect of dissolved organic compounds on the photodegradation of the herbicide MCPA in aqueous solution

Davide Vione (1) , Swapan Khanra (1) , Radharani Das (1) , Claudio Minero (1) , Valter Maurino (1) , Marcello Brigante (2, 3) , Gilles Mailhot (2, 3)

1 Dipartimento di Chimica IFM and NIS
2 ICCF - Institut de Chimie de Clermont-Ferrand
3 PMM - Photochimie moléculaire et macromoléculaire

This work shows that the addition of phenol and 2-propanol as model organic compounds significantly decreases the direct photolysis quantum yield of 4-chloro-2-methylphenoxyacetic acid (MCPA) upon UVB irradiation in aqueous solution. Laser flash photolysis data suggest that 2-propanol is able to decrease the formation of the MCPA excited states under irradiation. A decrease from 0.54 to 0.34 of the photolysis quantum yield of the anionic form of MCPA (which prevails over the undissociated one in surface waters) could have a considerable impact on the MCPA lifetime in ecosystems where the direct photolysis is the main phototransformation pathway. In surface water bodies where the direct photolysis has comparable kinetics as the reaction with OH, a decrease of the quantum yield would enhance the relative importance of the OH pathway, which yields considerably less toxic intermediates than the direct photolysis.

Domaines: Chimie théorique et/ou physique

Davide Vione, Swapan Khanra, Radharani Das, Claudio Minero, Valter Maurino, et al.. Effect of dissolved organic compounds on the photodegradation of the herbicide MCPA in aqueous solution. Water Research, 2010, 44 (20), pp.6053-6062. ⟨10.1016/j.watres.2010.07.079⟩. ⟨hal-00694930⟩