Modeling Phototransformation Reactions in Surface Water Bodies: 2,4-Dichloro-6-Nitrophenol As a Case Study

The anionic form of 2,4-dichloro-6-nitrophenol (DCNP), which prevails in surface waters over the undissociated one, has a direct photolysis quantum yield of (4.53 +/- 0.78) x 10(-6) under UVA irradiation and second-order reaction rate constants of (2.8 +/- 0.3) x 10(9) M-1 s(-1) with center dot OH, (3.7 +/- 1.4) x 10(9) M-1 s(-1) with O-1(2), and (1.36 +/- 0.09) x 10(8) M-1 s(-1) with the excited triplet state of anthraquinone-2-sulfonate, adopted as a proxy for the photoactive dissolved organic compounds in surface waters. DCNP also shows negligible reactivity with the carbonate radical. Insertion of the data into a model of surface water photochemistry indicates that the direct photolysis and the reactions with center dot OH and O-1(2) would be the main phototransformation processes of DCNP, with center dot OH prevailing in organic-poor and O-1(2) in organic-rich waters. The model results compare well with the field data of DCNP in the Rhone river delta (Southern France), where O-1(2) would be the main reactive species for the phototransformation of the substrate.